Ablation: Ablation is a surgical procedure that removes or destroys tissue, or a specific part of an organ.

Accelerometer: An accelerometer is a device used to measure change in speed or rate of increasing speed. In medicine, it can be used to measure the change in speed of a tremor.

Acetylcholine (ACh): Acetylcholine is a type of neurotransmitter. It is a chemical that is used by neurons to communicate with other neurons and with parts of the body. It is also used by the part of the nervous system that is responsible for resting and digesting. It lowers blood pressure and slows down heart rate and breathing rate.

Action tremor: An action tremor is a tremor that happens when a person moves, or begins a movement.

Activities of daily living (ADL): ADLs are basic activities that a person does on a daily routine. These include dressing, bathing, eating, and using the bathroom.

Acute: Acute is a word that describes symptoms that come on quickly, and are extremely severe or intense.

Adenosine triphosphate (ATP): ATP is the molecule that provides the energy in the cells of all living things.

Adverse event: According to the United States Food and Drug Administration (FDA), an adverse event is any undesirable experience associated with the use of a medical product in a patient. The event is serious and should be reported to the FDA when the patient outcome is death or is life-threatening; results in hospitalization, disability, or defects in developing fetuses; or requires intervention to prevent permanent impairment or damage.

Agonist: An agonist describes a group of muscles. When any movement occurs, there are two sets of muscles working around a joint. The muscles on one side of the joint must relax so that the muscles on the other side can contract. Agonist refers to the group of muscles that contract. For example, when a person bends his arm at the elbow, the biceps and triceps are working in this way. The biceps are the agonists.

Akathisia: Akathisia is a neurologic condition where the person has restlessness in their muscles. There are a number of different ways that people experience akathisia. In some people, it feels as though their muscles are quivering. In others, they feel the urge to constantly move around and cannot sit still.

Akinesia: Akinesia is an absence of movement. It comes from two Greek words—a and kinçsis—a means without, and kinçsis means movement.

Akinetic: Akinetic is an absence of movement. It comes from two Greek words—a and kinçsis—a means without, and kinçsis means movement. This can mean loss of movement in part of or all of the body.

Alpha 2-adrenergic agonist: An alpha 2 adrenergic agonist is a drug that has an effect within the central nervous system (CNS). There are two systems within the CNS that have the opposite effects. One system acts to speed up the heart rate, breathing, and increase blood pressure during times of stress. This system is controlled by a neurotransmitter called norepinephrine. An Alpha 2-adrenergic agonist decreases the activity of norepinephrine. They therefore may cause a slower heart rate and lower blood pressure.

Alpha synuclein: Alpha synuclein is a protein found in the brain. Nobody knows what the function of this protein is. In some diseases, it is found in large quantities clumped together. It is found in the brains of people with Parkinson’s disease, and other diseases like Lewy Body Dementia and multiple system atrophy.

Alzheimer disease: Alzheimer disease is a disease of the nervous system in which abnormal proteins (tangles and plaques) develop in the brain, and brain tissue shrinks. Over time, the accumulation of these proteins leads to problems with normal thought processes and the ability to make decisions (abstract thinking and judgment) impaired abstract thinking and judgment, personality changes, abnormal behavior, and memory problems. Alzheimer disease is one of the leading causes of dementia.

Ambulant (ambulatory): To be ambulant means a person is able to walk. This term may be used to describe patients who do not need a wheelchair or are not confined to bed.

Ambulation: Ambulation is the act of walking without any devices such as canes or walkers.

Amino acid: An amino acid is the basic building block of life. In the body, proteins are made up of amino acids. There are 20 different amino acids that are used in different combinations to make up all the proteins in the body. Some amino acids, called essential amino acids, cannot be made by the body. A person has to get these amino acids from food in their diet. Other amino acids, called nonessential amino acids, can be made by the body.

Amniocentesis: Amniocentesis is a procedure performed on some pregnant women. It is used to screen for or diagnose different conditions of the fetus. A doctor will use a needle guided by ultrasound to take a sample of the fluid that surrounds the fetus within the uterus. This fluid, called amniotic fluid may be used to detect certain genetic disorders, metabolic diseases, chromosomal abnormalities, or developmental defects. Amniocentesis is usually performed between the 14th and 18th week of pregnancy.

Amplitude: The amplitude is the "size" or "height" of a tremor.

Analog (Analogue): Analog has two different definitions. (1) As a chemical compound, an analog is a man-made chemical substance that is similar in structure to a chemical found naturally in the body. The analog can have either the same or a different action within the body. (2) As a tissue, organ, or other bodily structure, an analog has the same function or organization as another. The only difference in this case is that the two come from different evolutionary origins.

Animal model: An animal model is a laboratory animal that is used in research. Scientists can create an animal with specific characteristics or the animal may naturally have specific characteristics that resemble a human disease or condition.

Anosmia: Anosmia is a lack of sense of smell. People who have complete anosmia are not able to detect any odors. People who have partial anosmia are not able to detect one or more odors.

Antagonist: Antagonist has two definitions. (1) As a drug, an antagonist blocks a receptor, which doesn’t allow a normal body function (biological process) to occur. (2) In a group of muscles, an antagonist refers to the muscles that relax. When any movement occurs, there are two sets of muscles working around a joint. An antagonist describes a group of muscles on one side of a joint must relax so that the muscles on the other side can contract. For example, when a person bends his arm at the elbow, the biceps and triceps are working in this way. The triceps are the antagonists.

Antibodies: Antibodies are a key part of the immune system. They are specialized proteins that fight things in the body that aren’t supposed to be there. By doing this, antibodies destroy anything in the body shouldn’t be there. Any foreign substance such as a bacteria, virus, or foreign tissue is destroyed.

Anticholinergic agents: Anticholinergic medications are drugs that block the action of acetylcholine. Acetylcholine is a neurotransmitter that has an effect opposite to that of dopamine. By blocking the action of acetylcholine, these drugs increase the ability of dopamine to control movement. Examples of anticholinergic drugs used in the treatment of Parkinson disease include trihexyphenidyl, benztropine, and ethopropazine.

Anticholinesterase: Anticholinesterase is an agent that blocks the action of acetylcholinesterase (AChE). AChE is an enzyme that breaks down acetylcholine, a neurotransmitter. By blocking the activity of AChE, acetylcholine levels increase.

Anticonvulsant medication: Anticonvulsant medications prevent or stop seizures from occurring.

Antiemetic: An antiemetic is a drug that reduces nausea or vomiting.

Antigen: An antigen is any substance that may cause the body’s immune system to act (an immune response). Antigens may be microorganisms (e.g., viruses, bacteria), toxins, or foreign tissue cells (e.g., used in transplantation).

Antihistamine: Antihistamine is a drug that is commonly taken during allergic reactions. The drug opens airways and narrows blood vessels to return breathing and blood pressure to normal.

Antioxidants: Antioxidants are agents that prevent molecules called free radicals from destroying nerves and other cells in the body.

Aorta: The aorta is the main artery of the body. The aorta receives blood filled with oxygen (oxygenated) from the heart and delivers it to the rest of the body.

Apomorphine: Apomorphine is a type of drug that is being studied to treat severe Parkinson’s disease. It is made from morphine but does not actually contain morphine. It increases the levels of dopamine available in the brain.

Apoptosis: Apoptosis is the process a cell in the body goes through when it dies. Apoptosis is a scheduled process, controlled by the body.

Apraxia: Apraxia is a condition where a person can no longer do movements when asked to do so. There is nothing wrong with the muscles themselves. The person understands the command, and wants to make the movement, but cannot physically do it. Usually there is a problem in the brain. Apraxia can affect almost any movement, including those required for eye movement, walking, speaking, or writing.

Archimedes spirals: Archimedes spirals is a simple test used to determine how severe a tremor is. During this test, the patient is asked to draw increasingly wider circles on a piece of paper.

Asterixis: Asterixis is a type of tremor where the hands make jerking or flapping movements, like a bird flapping its wings. When the person’s hand is bent backwards at the wrist, the tremor starts. It usually happens in people who have severe liver disease.

Astrocyte: An astrocyte is a type of cell found in the central nervous system. It holds together and protects nerves. Astrocytes also form the blood brain barrier that keeps chemicals from entering into the brain.

Ataxia: Ataxia is caused by damage to a part of the brain called the cerebellum that is responsible for movement and balance. Therefore, the symptoms of the disease are problems with these things. A person with Ataxia will have difficulty with balance and holding their posture. Also, a person’s manner or way of walking is damaged, causing them to stagger and lurch around. He will also have problems with speech and focusing his eyes on what he wants to look at.

Ataxia-telangiectasia (AT): AT is a disease that first shows up in childhood and becomes worse over time. AT is caused by damage to a part of the brain called the cerebellum that is responsible for movement and balance. Therefore, the symptoms of the disease are problems with these things. A person with AT will have difficulty with balance and holding their posture. Also, a person’s manner or way of walking is damaged causing them to stagger and lurch around. He will also have problems with speech and focusing his eyes on what he wants to look at. This disease also causes permanent widening of groups of blood vessels, especially on the skin that receives a lot of sunlight. AT is a disease that is passed down from one generation to the next, as an autosomal recessive trait.

Athetosis: Athetosis is a slow, writing movement that a person cannot control. These movements flow into one another, so it looks almost like a dance. A person usually has athetosis in the head, neck, tongue, or hands, but any part of the body can be affected.

Atrophy: Atrophy is when a tissue or organ slowly wastes away. It can be caused by a number of things such as disease, malnutrition, damage to the nerves, or not enough blood flow.

Attention-deficit/hyperactivity disorder: ADHD is a disease that affects both children and adults. A person with ADHD has a certain set of symptoms and behaviors that develop as the person ages. These behaviors fall into three different: inattention, hyperactivity, and impulsivity.

Atypical: Atypical means something that is irregular or not ordinary.

Atypical neuroleptics: Atypical neuroleptics are a group of antipsychotic drugs. They are newer drugs used to treat psychosis that do not have as many side effects as the older drugs. The main benefit for the atypical neuroleptics is that they do not have parkinsonian side effects.

Auditory: The word auditory refers to the sense of hearing.

Augmentation: Augmentation is something that happens after taking certain medications. After using these medications, including levodopa, a person will have worsening symptoms earlier in the day. This usually happens in people who have severe symptoms or who take high doses of the medication.

Autoimmune: Autoimmune refers to the body reacting against its own tissue or organs. Usually the body fights infections (e.g., bacteria and viruses) that invade it. This is called an immune response. In an autoimmune response, the body reacts against itself, fighting or attacking its own tissues or organs and causing damage. There are many different types of autoimmune diseases.

Automatic behavior: Automatic behaviors are behaviors that a person does without being aware of it, such as mirroring someone else speech or movements.

Autonomic dysregulation: Autonomic dysregulation is condition where there is a problem with the autonomic nervous system (ANS). The ANS is responsible for functions in the body that are not under conscious control, such as the heart beating, breathing, and digestion.

Autonomic nervous system: The autonomic nervous system controls most of the involuntary reflexive activities of the human body such as the rate of breathing and movements of the intestines as food moves through the colon. The system is constantly working to regulate the glands and many of the muscles of the body. The autonomic nervous system is made up of two primary parts: the sympathetic and parasympathetic systems. The sympathetic nervous system prepares the body for emergencies or times of stress and is responsible for the body's "fight or flight" response when faced with a dangerous situation. During this response, the heart rate and blood pressure increase, the pupils of the eye dilate, and the digestive system slows down. The parasympathetic system helps the body's functions return to normal after they have been stimulated by the sympathetic nervous system and also has some responsibility for keeping the body's immune system properly functioning.

Autonomic testing: Your autonomic nervous system controls a variety of functions in your body, including blood pressure, heart and breathing rates, and sweating. Autonomic testing is used to see of your autonomic nervous system is working as it should be or if you have had damage to nerves in this system. Testing usually involves measuring your blood pressure, blood flow, heart rate, the amount of sweat you produce, and your skin temperature.

Autosomal dominant: Human traits, including eye color, hair color, and disorders, are passed down from one generation to the next through genes. A person has two genes for each trait—one from the father and one from the mother. For a disorder that is autosomal dominant, one disease gene is needed to have the trait of the disorder appear in their children. If an individual has an autosomal dominant disorder, there is a 50% chance that their child will inherit the abnormal (mutated) disease gene.

Autosomal recessive trait: Human traits, including eye color, hair color, and disorders, are passed down from one generation to the next through genes. A person has two genes for each trait—one from the father and one from the mother. For a disorder that is autosomal recessive, both disease genes are needed to have the trait of the disorder appear in their children. When only one of their genes carries the disease, the person will usually not be affected by the disorder. If an individual has an autosomal recessive disease, each of his or her children has a 25% chance of inheriting the abnormal (mutated) disease gene.

Axons: An axon is a part of a neuron. A neuron is made up of three parts: a dendrite, cell body and axon. An axon takes information from the cell body and carries it to the other end of the neuron in order to share the information with other neurons.

Baclofen: Baclofen is a drug used to treat spasticity by inhibiting or slowing down muscle activity.

Ballismus: Ballismus is a condition where the arm and leg muscles jerk violently around, making what looks like flinging or throwing movements. The person cannot control these movements. Sometimes it only affects one side of the body (hemiballismus).

Basal ganglia: The basal ganglia are structures located deep inside the brain. They are responsible for normal movements, such as walking. The basal ganglia comprise three parts—the caudate nucleus, putamen, and globus pallidus.

Behavior therapy: Behavior therapy is a method of treating psychiatric disorders. It focuses on getting rid of unusual, unwanted or abnormal behaviors. This form of therapy reinforces desired behaviors and loss of unwanted behaviors.

Benign myoclonus of infancy: Benign myoclonus of infancy is a neurologic condition that starts showing up in infants around four months old. Babies will have muscle spasms that look like a shock. These usually affect the muscles of the head, neck, trunk and arms. By two or three years old, the muscle spasms typically disappear.

Benzodiazepines: Benzodiazepines are a class of medications that lower the activity in the brain. They are used for a number of different reasons, including reducing anxiety or stress, promoting sleep, relaxing muscles and reducing restlessness.

Beta-adrenergic receptor: A receptor is the part of a neuron that receives information from other neurons in the form of neurotransmitters. A beta-adrenergic receptor receives only norepinephrine, a specific type of neurotransmitter. When a receptor receives norepinephrine it can cause that neuron to send signals of its own to other neurons.

Bilateral: Bilateral refers to something that has or affects two sides. In the body, the word bilateral means that both sides of the body are affected.

Biosynthesize: Biosynthesize means that the body is able to make or produce something itself.

Biphasic: Biphasic refers to a process that has two separate stages or phases.

Bipolar disorder: Bipolar disorder is a psychiatric disease characterized by mood swings. The moods include mania, during which the person has lots of energy or is excessively irritable, and depression, during which the person feels sad and hopeless. The person with bipolor disorder can also have normal moods between the swings but may also switch quickly or slowly between the highs and lows.

Blood-brain barrier: The brain is a very important and delicate organ in the body. The blood-brain barrier protects the brain from being damaged by anything that can get into the blood system. The barrier keeps chemicals and toxins out. Many drugs that people take get into the blood system but cannot reach the brain unless they are specifically designed to do so.

Body mass index: The body mass index is a measure of body fat and is based on a person’s height and weight.

Botulinum toxin (BTX): Botulinum neurotoxin or BoNT any one of seven toxins, designated A through G, which produced by Clostridium botulinum bacteria. Injections of very small amounts of commercially prepared BoNT may help to relax an overactive muscle. BoNT acts by blocking the release of acetylcholine, a neurotransmitter responsible for the activation of muscle contractions.

Bowel: The bowel is the last part of the digestive tract. It is also called the intestines. There is a large and a small bowel. Nutrients and water are absorbed from the small bowel into the body. The left over waste moves through to the large bowel. It is stored here until the waste is emptied from the body by a bowel movement in to form of stool or feces.

Bradykinesia: Bradykinesia simply means abnormally slow movement. It comes from two Greek words—bradys and kinçsis—bradys means slow or slowly, and kinçsis means movement.

Brainstem: The brain stem is a part of the brain that controls basic actions in the body such as breathing, regulating the heart beat and swallowing. It also serves as the connection to send signals between the spinal cord and other parts of the brain.

Branched-chain amino acids: Branched-chain amino acids are a specific type of amino acid found in the body. These amino acids have a structure that branches, like a tree. (Amino acids are the building blocks of proteins.)

Bruxism: Bruxism is present when people grind or clench their teeth without even realizing it. This usually happens when a person is sleeping or stressed. If a person does not use a protective device, like a mouth guard to wear at night, the teeth can become worn down and damaged. Bruxism is also associated with certain medical conditions.

Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS): The BFMDRS is a physician evaluation tool that measures the severity and provoking factors for dystonia in nine body areas, including the eyes, mouth, speech or swallowing, neck, right and left arms, trunk and right and left legs.

Cabergoline: Cabergoline is an ergotamine-based dopamine-receptor agonist. In the United States, it is marketed as Dostinex for the treatment of the rare disorder hyperprolactinaemia, or high levels of the hormone prolactin.

Carbidopa: Carbidopa is a drug that, when combined with levodopa, slows the breakdown of the levodopa in the body, thereby allowing more of the levodopa to enter the brain and thus providing more effective relief of symptoms.

Carbonic anhydrase inhibitors: Carbonic anhydrase inhibitors are a class of medications used to treat a variety of conditions. These drugs work in the kidney to increase the amount of certain substances excreted in the urine. Carbonic anhydrase inhibitors are used to increase urine production, lower fluid pressure in the eyes of people who have glaucoma and treat epilepsy.

Carnitine: Carnitine is a natural substance found in muscle, the heart and liver. Carnitine is important for energy production and the breakdown of fatty acids.

Cataplexy: Cataplexy is a sudden loss of voluntary muscle control, usually triggered by emotions such as laughter, surprise, fear or anger. Cataplexy occurs most often during times of stress or tiredness. The loss of muscle control may vary from a feeling of weakness to total body collapse. Although people having a cataplectic attack may appear to be asleep, they are actually awake, just unable to move.

Catecholamine: Catecholamine refers to a group of hormones made from a similar substance called catechol. Adrenaline and noradrenaline are two types of catecholamines.

Caudate: The caudate is a part of a structure in the brain known as the basal ganglia. The caudate receives information from the brain and sends it to other areas responsible for controlling complicated motor functions such as walking or voluntary arm movements.

Caudate nuclei: Caudate nuclei are specialized nerve cells found within the caudate. The caudate is a part of a structure in the brain known as the basal ganglia. The caudate receives information from the brain and sends it to other areas responsible for controlling complicated motor functions such as walking or voluntary arm movements.

Central nervous system (CNS): The central nervous system (CNS) is made up of the brain and spinal cord. It coordinates and controls activities and functions of the entire body. It does this by sending signals to the body to move and receives signals from the body about the surrounding environment.

Central oscillators: Central oscillators are nerve cells that send signals along tracts in the central nervous system. When these nerves fire their signals, it causes changes (fluctuations) in the electricity down the tracts.

Cerebellum: The cerebellum is a two-part region of the brain located behind the brainstem. The cerebellum receives messages about balance, posture, muscle tone and muscle contraction or extension. It also sends messages from the brain to the muscles.

Cerebral cortex: The cerebral cortex is the outer layer of the brain. It is made up of four different lobes, or parts: the frontal, temporal, occipital and parietal lobes. It is responsible for integrating higher mental processes (such as decision-making and judgment), conscious thoughts, sensations and movements.

Cerebrospinal fluid (CSF): CSF flows through and around the brain and spinal cord. It provides a cushion to the brain and spinal cord to protect it from injury. A lumbar puncture is a procedure that removes a small amount of CSF for laboratory examination. The fluid is removed by a physician from the area around the spinal cord in the lower back.

Chemodenervation: Chemodenervation is the chemical “silencing or interruption” of a nerve or group of nerves. A nerve sends a signal down a pathway. Chemodenervation happens when this pathway is “interrupted” after injecting a chemical, such as botulinum neurotoxin (BoNT). For example, when BoNT is injected into a muscle, the muscle relaxes because the BoNT slows the release of a certain chemical that allows communication between nerve cells—telling them to move or contract.

Chorea: Chorea is a jerky, rapid and irregular movement of the face, arms, or legs. People with chorea cannot control these movements. Choreic movements can be relatively simple or highly complex in nature. Several different choreic movements can be present at the same time, so the movement looks slow and writhing, like another movement called athetosis. Chorea can be present in neurodegenerative diseases or as a result of certain medications.

Chorionic villus sampling (CVS): CVS is a screening and diagnostic procedure performed where a needle is used to take tissue from the placenta of a pregnant woman. The placenta is a blood-rich organ attached to the lining of the uterus and links the blood supplies of the developing fetus and the mother. Tissue samples obtained during chorionic villus sampling are analyzed to detect certain genetic or chromosomal abnormalities.

Chromosome: A chromosome is a thread-like structure made up of DNA and proteins. Each chromosome is like a string of beads, where each bead represents a different gene. There are normally 46 chromosomes or 23 pairs in the nucleus of human cells.

Circadian: Circadian is a rhythm or repeated pattern of biological functions, occurring in a 24-hour periodic cycle (e.g., sleeping, eating, etc.).

Clinical Global Impression (CGI): The CGI is a tool used by a physician to evaluate a patient’s response to treatment. The first time the CGI is usedthe doctor rates how much the disease or illness impacts a patient’s life; this is called the “baseline.” The patient then receives treatment or, in some cases, a certain amount of time passes, and the doctor again rates the impact of the disease or illness while noting the changes such as very much improved, much improved, minimally improved, no change, minimally worse, much worse, or very much worse.

Clinical trial: A clinical trial is a research study that tests how safe or how well a drug or treatment works in humans.

Clonus: Clonus is a movement characterized by rapid, alternate contractions and relaxations of a muscle. Clonus is frequently observed in conditions such as spasticity and certain seizure disorders.

Co-contraction: When any movement occurs, there are two sets of muscles working around a joint. Normally, the muscles on one side of the joint must relax so that the muscles on the other side can contract. In co-contraction both sets of muscles contract.

Cognition: Cognition involves thinking skills such as perception, memory, awareness, reasoning, judgment, intellect and imagination.

Cognitive impairment: Cognitive impairment is a decrease in the ability to process, learn and remember information.

Cognitive therapy: Cognitive therapy is a method of treating psychiatric disorders that focuses on revising a person's thinking, perceptions, attitudes and beliefs.

Cogwheel rigidity: Cogwheel rigidity is stiffness of muscles around a joint. If a person has cogwheel rigidity of the elbow, and another person tries to bend and straighten his elbow, it will not move smoothly. It will be a jerky movement. Imagine the wheels of a clock moving against each other. They don’t glide past each other. Instead they move one notch at a time, and then stop. This is what cogwheel rigidity looks like. It is a motor symptom of Parkinson’s disease.

Complementary and alternative medicine: Complementary and alternative medicine, as defined by National Institutes of Health, is a group of diverse medical and health care systems, practices and products that are not presently considered to be part of conventional clinical medicine.

Composite Autonomic Scoring Scale: The Composite Autonomic Scoring Scale is a group of validated, sensitive and specific tests to meaure the various functions of the autonomic nervous system.

Computerized tomography (CT) imaging or scanning: CT scanning is an advanced diagnostic scanning technique. X-rays are taken of the body in cross sections at different angles. In some cases, a contrast medium (e.g., a dye) may be injected into the veins to produce enhanced images of certain tissues, organs or blood vessels.

COMT inhibitors: COMT inhibitors are drugs that block catechol-O-methyltransferase, an enzyme that breaks down dopamine. COMT inhibitors include entacapone and tolcapone and are used to treat Parkinson’s disease.

Congenital: The word congenital means that something existed or was present at birth.

Constipation: Constipation is a change in bowel movements from normal. Bowel movements are infrequent and the stool may become hard and dry. Bowel movements become difficult for people with contipation. Constipation may occur as a side effect of medications or because of a condition such as Parkinson’s disease.

Contractures: Contractures are “frozen joints,” and occur when a limb or body part cannot be stretched or moved (when another person tries to moves it about its joint). Contractures may develop because the muscles were shortened or wasted away (atrophy), or from the development of scar tissue (fibrosis) formed over the joints.

Contralateral: Contralateral means the opposite side. For example, during brain surgery for essential tremor, if the surgery is performed on the right side of the brain, the left side of the body will be affected.

Controlled-release formulation: Controlled-release formulations are forms of a drug (e.g., L-dopa) that are absorbed slowly by the digestive system. This means that the beneficial effects and side effects of the drug last longer.

Conversion disorder: A conversion disorder is a condition in which people have neurologic symptoms such as numbness, paralysis or seizures, but no neurologic cause of the symptoms can be found. These symptoms typically begin in response to difficulties in the person's life. A conversion disorder is considered to be a psychiatric disorder.

Corticobasal degeneration (CBD): CBD is a neurologic movement disorder that becomes worse over time. Certain parts of the brain are damaged and loss their ability to function, leading to the symptoms seen in affected people. Symptoms can include stiffness, slow movements and loss of the ability to coordinate movements. People can also experience sensory problems such as the feeling that a limb is not their own. As the disease progresses, people can develop slurred speech, dystonia, and "shock-like" contractions of certain muscle groups, particularly of the hands and forearms.

Corticospinal: Corticospinal refers to the connection between the outer region of the brain (cerebral cortex) and the spinal cord.

Corticosteroid agents: Corticosteroid agents are man made medications similar to corticosteroid hormones, which are naturally made in the body. Corticosteroid agents may be prescribed to: treat inflammatory conditions; as long-term therapy to suppress the immune system (immunosuppressive therapy) in order to prevent rejection of a transplanted organ; as hormone replacement therapy for those with insufficient levels of natural corticosteroid hormones; or as therapy for other conditions. High-dose, long-term corticosteroid therapy can result in various adverse effects, including an increased susceptibility to infection; progressive loss of bone mass (osteoporosis); high blood pressure (hypertension); tissue swelling (edema); or retarded bone growth in children.

Cranial: Cranial refers to the cranium or skull.

Cranial nerve nuclei: Nerve nuclei are specialized groups of nerve cells (nuclei). In the brain, there are 12 pairs of cranial nerves that send and receive information. The nerves are responsible for sensing taste, smell, hearing, and vision. They also send messages to muscles to control eye movements, chewing, swallowing, and facial expressions.

Cranial neuropathy: Cranial neuropathy is disease or damage of a cranial nerve or nerves. In the brain, there are 12 pairs of cranial nerves that send and receive information. The nerves are responsible for sensing taste, smell, hearing and vision. They also send messages to muscles to control eye movements, chewing, swallowing and facial expressions. Cranial neuropathy may result in muscle weakness, abnormal sensations, such as numbness, tingling, or pain, or other findings. Specific symptoms depend upon the specific nerve(s) affected.

Creutzfeldt-Jakob disease (CJD): A rare, degenerative, life-threatening brain disorder, CJD is characterized by severe, progressive dementia; visual disturbances; muscle weakness; and abnormal involuntary movements, such as sudden, brief, "shock-like" muscle spasms (myoclonus), tremor, and relatively slow writhing motions that appear to flow into one another (athetosis). Although CJD usually appears to occur sporadically, about 10 percent of cases are familial, potentially suggesting a hereditary predisposition to the disease. In rare cases, CJD can also result from exposure to contaminated surgical instruments during brain surgery and was reported in the past due to therapy with pituitary-derived human growth hormone. In addition, a variant form of CJD (V-CJD) has been reported primarily in the United Kingdom; V-CJD has been potentially linked to consumption of beef from cows with bovine spongiform encephalopathy or BSE (so-called "mad cow disease"). Evidence suggests that CJD may be caused by abnormal changes (mutations) in the human prion* protein gene or contamination with abnormal prion protein. (*The term "prion" was named for "protein infectious agent.") Changes in the prion protein appear to lead to distinctive neurodegenerative abnormalities, i.e., relatively small, round, "sponge-like" (spongiform) cavities or gaps in certain brain regions. CJD and bovine spongiform encephalopathy or BSE belong to a group of related neurodegenerative disorders categorized as "transmissible spongiform encephalopathies."

Crossreact: When the body encounters a foreign substance (antigen), such as bacteria or virus, it produces an antibody to fight that antigen. Crossreact refers to when an antibody reacts with an antigen that did not specifically or originally trigger its production.

Cytokine: Cytokines are small proteins that regulate the body’s immunity, inflammation and blood-cell production responses.

Cytoplasm: The cytoplasm is the part of the cell that surrounds the nucleus.

DC inhibitors: DC inhibitors are drugs that block decarboxylase, one type of enzyme that breaks down dopamine. Also called AADC inhibitors, they include carbidopa and benserazide.

Decarboxylase: Decarboxylase is a type of enzyme that breaks down or removes a part of another chemical substance. This stops the substance from working in the body. Decarboxylase breaks down levodopa in the body, keeping it from working in the brain. Carbidopa stops the decarboxylase from working. This allows levodopa to get to the brain without being broken down.

Deep brain stimulation: Deep brain stimulation (DBS) involves an operation during which a neurosurgeon (a medical doctor who specializes in surgery on the brain, spine, and other parts of the nervous system) places very thin wires through tiny holes in the skull. These wires, called leads or electrodes, go into the area of the brain that controls movements. The leads arre then connected to an insulated wire (extension) that is tunneled under the skin and connected to a battery-operated device called a neurostimulator. The surgeon sews the neurostimulator, which is about the size of a stopwatch, under the skin of the chest or abdomen. The device sends electrical pulses or signals through the wires to targeted areas deep within the brain. These signals block the abnormal nerve signals causing the symptoms of Parkinson disease, essential tremor, or dystonia. A physician or nurse uses a remote controller to transmit radio signals that can adjust the electrical pulses generated by the neurostimulator.

Degenerative: Degenerative refers to loss of function or form (deterioration). It usually refers to the slow loss of function or structure of tissues.

Delirium: Delirium is a abnormal mental state of frenzied excitement or wild enthusiasm.

Delusion: A delusion is a false belief that a person has about himself or the world. The key to a delusion is that the person believes it no matter what. Even when someone shows evidence that the belief is not true, this does not change the person’s belief.

Dementia: Dementia is not a disease in and of itself; rather, it is a term used to describe a group of symptoms. It is a loss of mental processes such as memory, language, or the ability to think. The loss is significant enough to cause problems with daily functions, and becomes worse over time. Dementia is also characterized by personality changes.

Dendrites: A dendrite is a part of a nerve cell (neuron). A neuron is made up of three parts: a dendrite, cell body and axon. A dendrite is like a tree branch or long rod—a projection from the cell body. It receives information from other neurons and sends the information to the cell body.

Dentatorubropallidoluysian atrophy: Dentatorubropallidoluysian is a rare genetic disorder that is most commonly described in Japan. Associated symptoms may become apparent in adolescence or adulthood. Early-onset disease is characterized by rapidly progressive neurodegenerative changes, including seizures, cognitive impairment and brief, "shock-like" muscle spasms of certain muscles or muscle groups (myoclonus). Late-onset disease is associated with progressively impaired control of voluntary movement (ataxia) and symptoms often seen in Huntington's disease (HD), including chorea (jerky, rapid, irregular movements) and gradual loss of thought processing and acquired intellectual abilities (dementia). Brain imaging studies typically reveal degenerative changes of the globus pallidus and specialized nerve cell clusters within the cerebellum (dentate nucleus). Similar to HD, the disorder may result from abnormally long "repeats" of particular coded instructions within a gene (located on chromosome 12).

Depression: Depression is a disease. A person with depression cannot talk themselves out of the disease. Depression is characterized by many symptoms including either a depressed mood or loss of interest in things that normally give pleasure. A person with depression also experiences weight loss or gain, fatigue, and feelings of worthlessness or guilt. Depression also causes a person to sleep and move around either too much or not at all.

Detoxification: Detoxification is the process of removing toxins or making them harmless in the body

Diaphragm: The diaphragm is a large dome-shaped muscle that separates the chest and abdomen. The diaphragm plays an essential role in breathing, contracting when air is drawn into the lungs and relaxing upon exhalation.

Differential diagnosis: A differential diagnosis is a list of two or more diseases and conditions with similar symptoms. Doctors compare and order certain tests to determine the correct diagnosis for their patients. The physician will use physical signs and symptoms as well as laboratory tests or imaging studies (e.g., x-ray, MRI, etc.) to help make a diagnosis.

Diuretics: Diuretics are medications that encourage the elimination of urine from the body (urination). These medications are often prescribed to help reduce abnormally high fluid levels in the body. Heart failure, high blood pressure (hypertension), kidney or liver diseases can cause excess fluid in the body.

DNA: DNA stands for deoxyribonucleic acid. DNA is a spiraling, ladder-like molecule that contains the body’s genetic code. DNA is the main “ingredient” of the chromosomes within the core or nucleus of the body’s cells. DNA is also found in mitochondria; these are rod-like structures outside the nucleus of a cell that function as a main supplier of cellular energy.

Dopamine: Dopamine is a chemical neurotransmitter. Neurotransmitters help relay messages from one nerve cell to another. Dopamine is especially important in relaying messages about the body’s movement.

Dopamine agonist (DA): A dopamine agonist is a chemical substance that behaves or acts like dopamine. When used in medications, DAs produce the same effects in the brain as naturally occuring dopamine.

Dopamine autoreceptor: A dopamine autoreceptor is a type of dopamine receptor that acts like a thermostat. It prevents dopamine from being released when there are already high levels of dopamine present.

Dopamine receptor: A dopamine receptor is a molecule on a nerve cell (neuron). When dopamine or a medication containing a dopamine agonist interacts with this receptor, the nerve cell responds in a particular way. There are at least five types of dopamine receptors including D1, D2, D3 receptors and the dopamine autoreceptor.

Dopamine receptor antagonist: A dopamine receptor anatagonist is a medication that works together with dopamine receptors. When the antagonist interacts with the receptor, the antagonist blocks dopamine from connecting with its receptor. When this happens, the nerve cell cannot send or respond to its messages, even if dopamine is present.

Dopamine transporter: Dopamine is a chemical in the body that allows one nerve cell to send a message or signal to another nerve cell and helps to control movement. After dopamine finishes sending its message, a substance called a dopamine transporter carries the dopamine back from the nerve ending to the cell that produced it so that the dopamine can be reused. The number of dopamine transporters is a sign of the number of nerve endings that produce or release dopamine.

Dopaminergic: Dopaminergic is a word used to describe a chemical or a drug that either acts like or involves dopamine.

Dopaminergic drug: A dopaminergic drug is any drug that acts like dopamine in the brain, having the same effects as dopamine. Levodopa is converted in the body to dopamine, and dopamine agonists mimic the effects of dopamine at the receptors.

Dopaminergic dysfunction: Dopaminergic dysfunction occurs when there is a problem with the dopamine receptors.

Double-blind trial: A double-blind trial is a clinical experiment in which neither the patients nor the researchers are aware of which patients are receiving the active treatment (the drug or device that is being tested) and which are receiving inactive treatment (placebo), like a “sugar pill.”

Duodenum: The duodenum is the upper part of the small intestine. It is connected to the stomach.

Dysarthria: Dysarthria is difficulty forming words or speaking them. It can be caused by problems in the brain or with the muscles used for speech. As a result, speech can be slurred or slowed and difficult to understand.

Dysesthesias: Dysesthesias are unpleasant sensations that are produced in response to normal stimuli such as intense pain when the skin is lightly touched.

Dyskinesias: Dyskinesia is difficulty with movement. It comes from two Greek words—dys and kinçsis—dys means difficulty, and kinçsis means movement.

Dyskinesias while awake (DWA): DWA are uncontrolled, unexpected movements of the legs and sometimes the arms. These movements can be very rapid or explosive (myoclonic) or they can be quite slow and prolonged (dystonic). Dyskinesia can disappear when a person goes to perform a voluntary action. Some researchers suspect that DWAs may be a wakeful form of periodic limb movements in sleep (PLMS).

Dysphagia: Dysphagia means difficulty in swallowing. Dysphagia may be associated with blockage of the esophageal or with certain neurodegenerative or motor disorders involving the esophagus.

Dyspraxia: Dyspraxia means the loss or partial loss of the ability to coordinate and perform certain purposeful movements such as driving, grooming, etc. The key in dyspraxia is that there is no motor or sensory impairment.

Dystonia: Dystonia is a neurologic movement disorder characterized by lasting muscle tightening or contractions. The contractions result in repeated twisting or writhing movements and unusual postures or positioning that the person with dystonia cannot control. Dystonia may be limited to specific muscle groups (focal dystonia), such as dystonia affecting muscles of the neck (cervical dystonia or spasmodic torticollis) or the eyes, resulting in closure of the eyelids (blepharospasm). Dystonia is associated with certain underlying genetic disorders, such as dystonia musculorum deformans, dopa-responsive dystonia, and paroxysmal kinesigenic and paroxysmal non-kinesigenic dystonic choreoathetosis. The condition may result from the use of certain medications, lack of oxygen during or immediately after birth, or other causes of brain trauma.

Dystonic: Dystonic refers to dystonia.

DYT-1 dystonia: The DYT-1 gene regulates or "encodes" production of a protein called torsinA. Although its specific function is not known, torrsinA appears to be related to a class of proteins that enable cells to recover from injury or stress. The change or mutation that causes DYT-1 dystonia involves one of a pair of three basic chemical "building blocks" of DNA. These are called guanine, adenine, and guanine, or "GAG" trinucleotides and are part of the genetic code within the DYT-1 gene. The specific mutation that occurs in DYT-1 dystonia is an absence, or deletion, of GAG. This relatively tiny change in the blueprint for torsinA apparently causes critical changes in the function of the protein and may lead to the symptoms of dystonia.

Echocardiogram: An echocardiogram is a medical test that is used to study the structure and function of the heart. A computer captures echoes that are created from sound waves, which are bounced off of the heart.

Economic burden: Economic burden involves both direct medical costs such as money paid for drugs and doctor’s appointments as well as indirect costs due to lost wages from illness, premature death and disability.

Edema: Edema is fluid accumulation in the tissues of the body, which causes swelling.

Edentulousness: Edentulousness is the lack of permanent teeth.

Effector organs: Effector organs cause something to happen. They produce an effect after the nerve has been stimulated, such as a muscle contracting or a gland secreting a substance.

Electrical stimulation (ES): ES is a test in which a small electrical charge is applied to a muscle via a needle. This determines the level of muscle responsiveness by looking at what happens when the electricity is delivered to the muscle.

Electrocardiogram (ECG, EKG): An EKG is a non-surgical, diagnostic test that looks at the electrical activity of the heart muscle (myocardium). The test may be administered while a patient is at rest or while performing certain designated exercises. ECGs may help to detect or characterize cardiac conduction defects (the movments of the electrical signals within the heart), abnormal heart rhythms (arrhythmias), enlargement (cardiac hypertrophy), or localized damage in heart muscle.

Electroencephalography (EEG): An EEG is a non-surgical, diagnostic technique that records the electrical impulses produced by the brain. An EEG reveals typical brain wave patterns that may assist in the diagnosis of particular neurologic conditions, such as seizure disorders, impaired consciousness and brain lesions or tumors.

Electromyography (EMG): An EMG is a diagnostic test that records the electrical responses of skeletal muscles while at rest and during voluntary action and electrical stimulation. During this test, a small needle is inserted into a muscle to record the level of activity.

Electron microscopy: An electron microscope beams electrons, instead of light beams, to magnify an object, providing very detailed images that are approximately 1,000 times the magnification of a typical light-beam microscope.

Electrophysiologic recording : Electrophysiologic recordings include the study of the electrical activity associated with a specific body function, such as muscle function during an electromyogram or brain waves during an electroencephalogram.

Electrophysiologic studies: An electrophysiologic study is the study of the electrical activity associated with a specific body function (e.g., EMG, EEG, etc.).

Encephalitis: Encephalitis is inflammation of the brain. It is most commonly caused by viral infections. Usually, symptoms include fever, headache, irritability, listlessness (lethargy), and weakness. Some affected individuals may also develop confusion, disturbances of speech and memory, abnormal involuntary movements, paralysis of one side of the body, seizures and/or coma.

Encephalopathies: Encephalopathies are any abnormal conditions or diseases of the structure or function of the brain, particularly disorders involving ongoing loss of brain structure and function (chronic, degenerative conditions).

Endogenous opiate system: Endogenous means produced in the body. Endogenous opiate is a morphine-like substance that is produced within the body.

Endoplasmic reticulum (ER): The ER is a system of membranes within a cell.

Endoscopy: Endoscopy is an in-office procedure during which the doctor looks inside the stomach or intestine using a hollow, thin, flexible tube. The tube has a lens or miniature camera on the end of it.

Endotoxin: An endotoxin is a poisonous substance that is released from bacteria after the bacteria die or break apart.

Enzyme: An enzyme is a protein made by the body’s cells. There are chemical reactions that occur all the time in the body. Enzymes either speed up or slow down these reactions. Enzymes are not used up or permanently changed during the process.

Epidemiological study: An epidemiological study is a study that looks at the patterns and causes of disease in a group of people. This type of study will try to determine factors that relate to a specific disease or to identify health problems in a specific population.

Epidemiology : Epidemiology is the study of the patterns and causes of disease in groups of people.

Epworth Sleepiness Scale (ESS): The ESS is a paper-and-pencil test. In this test, patients record how likely they are to fall asleep during seven different situations: sitting and reading, watching TV, sitting inactive in a public place (such as at a theater or in a meeting), as a passenger in a car for an hour without a break, lying down to rest in the afternoon when circumstances permit, sitting and talking with someone, sitting quietly after a lunch without alcohol, while driving a car that is stopped for a few minutes in traffic.

Eradication: Eradication is the process of permanently eliminating something.

Ergot: Ergot is a plant substance that contains nitrogen. The pH of an alkaloid is basic, or non-acidic. Ergots are produced by a certain type of fungus.

Ergot-derived medication: Ergot-derived medications have a chemical structure similar to an on ergot, a plant substance that contains nitrogen and produced by a certain fungus. Pergolide and bromocriptine are examples of ergot-derived medications that may be used to treat certain neurologic movement disorders. Ergot medications have been associated with a risk for the development of heart value defects.

Esophageal atony: Esophageal atony is a lack of normal muscle tone within the esophagus, the muscular tube that transports food from the throat to the stomach.

Essential tremor (ET): ET is a common neurologic movement disorder that becomes worse over time. It is characterized by a rhythmic back and forth movement of a body part of parts that a person cannot control. A tremor can either be postural or kinetic, or both. Postural means that when people try to hold one position, such as sitting or standing, they will have a tremor. A kinetic tremor is when a person tries to do a specific action, such as reaching a hand out towards an object, they will experience the tremor. ET can affect the hands or head commonly, less commonly, the voice, tongue or roof of mouth. The cause of ET is not known, and it can either occur randomly or be passed down from one generation to the next as an autosomal dominant trait.

Estrogen: (1) Estrogen is a female sex hormone that promotes female development and the proper functioning of the reproductive system; (2) Estrogen is also a compound chemically produced to treat a variety of conditions. It is found in birth control pills and medication to treat the symptoms of menopause. It also is used to reduce bone mass loss in osteoporosis and to treat breast and prostate cancer.

Eukaryotic: Meaning literally "true nucleus," eukaryotic organisms include microorganisms, plants, animals and fungi, all of which have separate membrane-bound nuclei that contain genetic material (mDNA).

Excessive Daytime Sleepiness (EDS): EDS is more than the normal amount of sleepiness during the day along with a lack of energy, even after a normal night's rest. EDS may be measured using the Epworth Sleepiness Scale.

Executive function: Executive function refers to a person’s ability to establish a goal and then make decisions and put into action activities to meet that goal.

Exon: An exon is a region of a gene that contains part of the code for producing the gene's protein. Each exon codes for a specific portion of the complete protein. Exons are separated by long regions of DNA (called introns or sometimes "junk DNA") that have no apparent function.

Extrapyramidal system: Extrapyramidal system refers to central nervous system structures that control motor functions. Extrapyramidal disturbances may result in problems maintaining posture and muscle tone. It can also lead to involuntary movements.

Fatigue: Fatigue is a feeling of tiredness or a sense of having low energy that may lead to a decrease in a person's ability to perform work or daily activities.

Feldenkrais: Feldenkrais is a method of improving the body’s ability to function, learn, and change by increasing awareness of movement, posture, and breathing.

Ferritin: Ferritin is a protein that stores iron inside your cells so that your body can use the iron when it is needed. A serum ferritin level is a blood test that measures the amount of ferritin in the cells. The amount of ferritin stored, or the serum ferritin level, reflects the amount of iron that is stored in the body. Symptoms of RLS have been shown to be increased in people who have low ferritin levels.

Festinating Gait: People with a festinating gate will take very small steps. Their feet never come all the way off the floor, so it looks like the person is shuffling along. People cannot control the shuffling or take bigger steps.

Fibrosis: Fibrosis is the build up of fibrous tissue in an abnormal place in the body. One example is scar tissue.

First-, second- and third-degree relatives: First-degree relatives include a person’s mother, father, brothers, sisters, sons, and daughters who are related by blood and not through adoption or marriage. Second-degree relatives include aunts, grandmothers, uncles, and grandfathers. Third-degree relatives include great-grandmothers, great-aunts, great-uncles, and first cousins.

Flexion: Flexion is the act of bending (as opposed to extending) a joint.

Focal dystonia: Focal dystonia is a type of dystonia that is limited to a specific group of muscles. Some types of focal dystonia involve muscles that control movement of the neck (cervical dystonia), eyes (blepharospasm), hand (writer’s cramp or musician’s dystonia), or vocal cords (spasmodic dysphonia).

Food and Drug Administration (FDA): The FDA is a federal agency charged with ensuring that the food supply in the United States is safe and wholesome, that cosmetics are not harmful, and that medicines, medical devices, and radiation-emitting consumer products are safe and effective.

Free radicals: Free radicals are unstable molecules that can damage cells.

Freezing: Freezing is when motion is halted. It looks like the person is nailed to the floor and cannot move forward.

Frequency: Frequency is the number of cycles or repetitions within a fixed unit of time such as the number of cycles per second (Hertz or Hz). For example, essential tremor is typically 4 to 12 Hz.

Friedreich's ataxia: Friedreich's ataxia is the most common autosomal recessively inherited type of ataxia. The main symptoms are loss of coordination and unsteadiness of gait. Other systems may also be affected and people with Friedreich's ataxia should be monitored for heart disease and diabetes. The affected protein is called frataxin, and is thought to be involved in iron metabolism.

Froment's sign: Froment’s sign is a maneuver that a physician can perform to check for muscle resistance. Here is an example of a positive Froment’s sign. A person is told to move one part of the body, for example the leg. While he or she does this, the doctor moves another part, the arm. If the arm is stiff and resists movement, this is Froment’s sign.

Functional Magnetic Resonance Imaging (fMRI): An fMRI is a non-surgical, diagnostic scanning procedure that produces detailed, computerized images. The use of a "contrast agent" or dye enhances the detail of the images. Watching the images in the order in which they were taken can help physicians visualize the body's functioning, thus aiding differential diagnosis.

Gait: Gait is a manner or way of walking. Gait disturbances are associated with certain neurologic or neuromuscular disorders, orthopedic conditions, inflammatory conditions of the joints such as arthritis and other abnormalities.

Gait apraxia: Gait apraxia is the loss of ability to coordinate and execute walking. Gait apraxia may result in unsteady walking patterns, toe-walking, a widely based, jerky gait and balance difficulties.

Gamma knife radiosurgery: Gamma knife radiosurgery is a highly specialized technique to produce an area of damage known as a lesion. This procedure uses a device that focuses a beam of high intensity irradiation to a targeted area. It is used as localized therapy to treat individuals with certain brain diseases such as brain tumors, certain movement disorders, etc.

Gamma-aminobutyric acid (GABA): GABA is an amino acid neurotransmitter that inhibits or decreases the electrical activities of nerve cells. GABA is the primary neurotransmitter in the brain that decreases electrical activity.

Gastroesophageal reflux: Gastroesophageal reflux occurs when the stomach contents flow backwards into the esophagus. Another name for this is acid reflux or heartburn. It can be a chronic condition caused by weakness in the muscle that is supposed to keep the contents in the stomach.

Gastrointestinal: Gastrointestinal refers to the stomach and small and large intestines as well as to the mouth, esophagus, anus and related organs.

Gastrostomy tube: A plastic tube inserted into the stomach through a surgical incision in the abdomen. A gastrostomy tube is used to deliver liquified food to the digestive system when swallowing becomes dangerous or difficult.

Gene: Genes, or units of heredity, are found in all cells of the body. The information from all the genes together makes up the blueprint or plan for the human body and its functions. A gene is a short segment of DNA, which is interpreted by the body as a plan or template for building a specific protein.

Generic drug: A generic drug is a medication that has the same active ingredients as its comparable brand-name drug. It works the same way a brand-name drug works, but is usually less expensive. Generic drugs meet the same FDA standards as brand-name drugs.

Genetic anticipation: Genetic anticipation refers to the appearance of the symptoms of a hereditary disease at an earlier age in each generation. In some hereditary disorders, such as Huntington’s disease, genetic anticipation has been identified.

Genetic heterogeneity: Genetic heterogeneity means that damage to different genes can produce the same characteristic or trait.

Germline mosaicism: Germline mosaicism is an abnormal change in a gene (mutation) in some but not all of a person’s reproductive cells (i.e., egg cells in the ovaries or sperm cells testes. This gene mutation is passed down to the children, but the parent doesn’t have the condition.

Gland: A gland is a structure or organ in the body that makes a substance, such as a hormone or chemical, which is used elsewhere in the body. Some hormones include insulin, bile, growth hormone, estrogen and testosterone.

Gliosis: Gliosis is an abundance of certain cells (astrocytes) in damaged areas of the central nervous system (CNS). Astrocytes are relatively large glial cells, which are the connective tissue cells of the CNS. Gliosis and neuronal loss in certain brain regions are findings seen in various neurodegenerative disorders.

Globus pallidus: The globus pallidus is a part of a structure in the brain known as the basal ganglia. The globus pallidus receives information from the brain and sends it to other areas responsible for controlling complex motor functions.

Glottis: The glottis is the slit-like opening between the vocal cords.

Glutamate: Glutamate is a chemical messenger (neurotransmitter) that “excites” other nerve cells in the central nervous system.

Gram staining: Gram staining is a method used to classify bacteria. In the first step of the process, bacteria are stained with gentian violet and then treated with Gram solution (named after Dr. Gram, the inventor of the technique). After the bacteria are treated with alcohol to remove the stain and then treated with a red organic dye called safranine, they are washed in water. Those bacteria that keep the gentian violet are gram-positive and those that do not are gram-negative.

Gray matter: Neurons are made up of three parts: the cell bodes, dendrites and axons. Axons can be covered in a sheath of fat called myelin to help the signals travel faster. Some neurons are covered in myelin and others are not, called unmyelinated axons. Gray matter is the portion of the nervous system that is made up of the cell bodies, dendrites and unmyelinated axons. White matter, on the other hand, is made up of axons that are coated in myelin.

Half life: The half life of a drug is the time it takes for the blood level to decrease by half after a drug is stopped.

Hallervorden-Spatz disease: Hallervorden-Spatz disease is a rare hereditary disorder where large amounts of iron gather in certain regions of the brain (i.e., basal ganglia). This autosomal recessive disorder typically becomes apparent during late childhood or adolescence. People with this disease experience rigidity, dystonia, choreoathetosis and other problems. The symptoms become gradually worse with time (progressive).

Hallucination: An hallucination is something that a person sees, smells, touches, hears or tastes but it is not really there. The hallucination is only present in the mind of the person. No one else experiences a hallucination because it is not a part of the environment.

Heat pain: Heat pain arises from warm or hot temperatures.

Hemichorea: Chorea is a jerky, rapid, irregular movement that a person cannot control in the face or arms and legs. Choreic movements can be relatively simple or highly complex in nature. Hemichorea are movements that involve only one side of the body or muscle groups that are only on one side of the body.

Hemidystonia: Hemidystonia is a form of dystonia that affects one side of the body or is characterized by one-sided involvement of the upper and lower limbs.

Hemizygote: Normally in humans, every cell has two pairs of genes. A hemizygote refers to a cell, organism or individual with only one of a pair of genes for a specific trait. This term is often used to describe males who inherit one copy of an X-linked disease trait.

Hereditary: Hereditary means inherited. A genetic trait, condition or disorder that is hereditary means that it is passed down from one generation to the next through the genes.

Heredodegenerative: Heredodegenerative is a term used to describe disorders that are passed down from one generation to the next. These disorders, which become gradually worse with time (progressive), affect the nervous system (neurodegenerative disorders).

Hertz (Hz): Hertz is the number of cycles per second.

Heterogeneity: Heterogeneity means that something has different forms or variations. For example, in the United States there is a heterogeneous population because there are people here from all over the world.

Heterozygous carriers: Every person has two copies of every gene. These copies can be the same, homozygous, or different, heterozygous. A heterozygous carrier has two different copies at a specific gene. This gene is responsible for a disease trait. Because the person has one good copy and one bad copy, usually he or she will not have the disease. They pass the gene to their offspring, however, and their child could have the disease.

Hoehn and Yahr Scale: The Hoehn and Yahr Scale is a commonly used physician-administered rating of the severity of the motor symptoms of Parkinson's disease. Scores range from 0, no signs of disease, to 5, wheelchair bound or bedridden without assistance.

Homeopathy: Homeopathy is a system of medicine that is based on the Law of Similars. According to this law, substances that cause healthy people to have certain symptoms can also be used to restore the body to health.

Homeostasis: Homeostasis exists when an organism’s internal state is in balance, even when the outside environment is changing.

Homocystinuria: Homocystinuria is a rare metabolic condition where an amino acid, called homocystine, is found in abnormally high levels in the urine. It is an autosomal recessive trait. People with homocystinuria experience developmental delays and worsening mental retardation. They may have dislocated eye lens, weak muscles and skeletal defects and blood clots in the blood vessels.

Huntington disease: Huntington disease (HD) is a rare disorder that causes a specific type of nerve cell in the brain to stop functioning and die off. In the early stages of the disease, symptoms can include slight personality changes, forgetfulness, clumsiness and fidgeting movements of the fingers, eyes or toes. As HD becomes worse, it can cause memory, thinking, behavior and planning problems, as well trouble talking, swallowing and walking. HD is an autosomal dominant, heriditary disoder. This means that if one parent has HD, a child will have a 50-50 chance of developing HD. A genetic blood test can determine if the child has the HD gene and will eventually develop the disease. Genetic counseling can help people to decide if they want to be tested for HD, weighing the risks and benefits of taking the test. There is no cure for HD, but some medicines can help with the symptoms.

Huntington’s Disease-like 2 (HDL2): This rare disease strongly resembles Huntington’s disease in its inheritance and symptoms, which include abnormal movements, personality changes, and changes in the ability to think and process information. HDL2 is due to damage to the same parts of the brain as in HD; however, HDL2 is caused by a change (mutation) of a different gene.

Hyperglycemia: Hyperglycemia is an abnormally high level of glucose in the blood.

Hyperkalemic: Hyperkalemia is an abnormally high level of potassium in the blood. Potassium is important in contolling fluid balance in the body, contracting muscles and sending messages along nerves. Hyperkalemia can lead to various signs and symptoms, such as diarrhea, nausea, abdominal cramps, weakness and, with increasing severity, abnormal heart rhythms and muscle paralysis.

Hyperkinetic: Hyperkinetic means excessive movement. Usually it is caused by a problem in motor activity or function. Certain movement disorders are termed "hyperkinetic" such as tics or essential tremor.

Hypertension: Hypertension, also referred to as high blood pressure, is an abnormal increase in the pressure of blood against the walls of the arteries. Hypertension can be essential, meaning that it has no known cause, or can be related to another disease such as kidney disease or diabetes.

Hyperthyroidism: Hyperthyroidism is a condition caused by the effects of too much thyroid hormone in the body.

Hyperventilation: Hyperventilation is when a person breathes very rapidly. When a person hyperventilates, it can cause changes in the body’s oxygen and carbon dioxide balance. Sometimes, a person can hyperventilate so strongly that they lose consciousness.

Hypnagogic hallucinations: Hypnagogic hallucinations are vivid, realistic, often frightening dreams that occur while the person is falling asleep or immediately upon awakening.

Hypocretin: Hypocretin (also known as orexin) 1 and 2 are protein-like molecules (neuropeptides) found in the brain that act like hormones or neurotransmitters. They are involved in the regulation of sleep and wakefulness.

Hypokalemic: Hypokalemia is abnormally low level of potassium in the blood. Potassium is important in regulating fluid balance, contracting muscles and sending messages along nerves. Hypokalemia may result in confusion, fatigue, weakness and, in severe cases, paralysis and heart rhythm abnormalities.

Hypokinesia: Hypokinesia is abnormally decreased movements. It comes from two Greek words—hypo and kinçsis—hypo means decreased, and kinçsis means movement.

Hypomimia: Hypomimia is reduced facial expressions. This can be caused by weakness or paralysis of facial muscles.

Hypoparathyroidism: Hypoparathyroidism is a condition associated with low levels of a hormone produced by the parathyroid glands. Parathyroid hormone regulates calcium levels in the body. With hypoparathyroidism, there are low levels of calcium in the body that causes symptoms. It can cause tetany, which results in uncontrollable, painful muscle spasms and cramps. It can also cause chorea, spasms of the larynx, and seizures. Calcium can also be deposited in areas where it is not supposed to be including the basal ganglia in the brain or the lens of the eye. The skin can become dry and scaly and the teeth enamel can become weakened.

Hyposmia: Hyposmia refers to a decreased sense of smell.

Hypotension: Hypotension is low blood pressure. It comes from two Greek words—hypo and tension—hypo means low and tension means pressure.

hypoxia: Hypoxia is an abnormally low level of oxygen.

Iatrogenic: Iatrogenic is a disease or disorder that is caused not deliberately by a physician or surgeon, or by medical treatment or diagnostic procedures.

Idiopathic: Idiopathic is a disorder or condition of that occurs on its own, for no apparent cause. The term comes from the prefix "idio-" meaning one's own and "pathos" indicating disease.

Idiopathic epilepsy: Idiopathic epilepsy is a disease with repeated seizures of unknown origin or cause. There is no detectable area of damage in the brain, but the person keeps having seizures. Another name for this is essential or primary epilepsy. These conditions are often thought to have a genetic component.

Illusions: Illusions occur when a person sees something that is real but misinterprets what it is. For examples, heat waves on the desert floor can look like waves of water.

Immunofluorescence: Immunoflorescence is a laboratory technique that uses antibodies linked to a light-emitting or fluorescent dye in order to study foreign substances in a tissue sample.

Immunogenicity: When the body detects a foreign substance such as a virus or bacteria, it begins an immune response. Immunogenicity is the ability or strength to which this substance launches the immune response.

Implantable Pulse Generator (IPG): IPG is a device that is placed under the skin, usually near the collarbone, as part of a surgical procedure known as deep brain stimulation. Wire leads from electrodes implanted in the brain are connected to the pulse generator, which then delivers continuous high frequency electrical stimulation to the thalamus via the implanted electrodes. This form of stimulation probably "jams" the nucleus, changing the electrical messages in the movement control centers of the brain. These changed message help to control or suppress tremor.

Incontinent: Incontinent usually means that people have lost control over their bladder. People can urinate or “dribble” urine while not using the toilet. Some people can lose control of their bowels (fecal incontinence).

Inflammation: Inflammation is the body’s response to injury or irritation. The classic signs of inflammation are pain, heat, redness, swelling and loss of function.

Inheritance patterns: Inheritance patterns are the different ways that a person inherits genes from their parents. For example, autosomal dominance is a specific pattern of inheritance. Each person inherits two copies of almost every gene, one from the mother and one from the father. Some diseases develop when only one copy of a gene is changed or mutated, even if the other copy is completely normal. Such a gene is passed from parent to child in an autosomal dominant inheritance pattern. A parent who has the abnormal, “disease” gene (mutation) may be affected by the disease. Each child of that parent has a 50% chance of inheriting the mutation and likely developing the disease. Other diseases develop only when both copies of a gene are mutated. In this case, the mutated gene is passed from both parents in an autosomal recessive inheritance pattern. Parents carrying one copy of the mutated gene are typically unaffected by the disease. Each parent must contribute one disease gene to a child for that child to develop the disease. Each child has a 25% chance of inheriting both mutations and developing the disease.

Inhibition: Inhibition is when a process or action in a cell or organ is stopped or restrained. It can also be slowing down or stopping of a chemical reaction. The term "reciprocal inhibition" refers to the restraint or "checking" of one group of muscles upon stimulation (excitation) and contraction of their opposing (antagonist) muscles.

Inhibitor: An inhibitor is a substance that blocks, restricts or interferes with a particular chemical reaction or other biologic activity.

Innervate: To innervate is to supply a body part, tissue, or organ with nerves or nervous stimulation.

Insidious: Insidious means that something develops slowly or gradually. If a disorder is insidious, this means that the symptoms develop so slowly that the people may not that they have a disorder until it is full blown.

Insomnia: Insomnia is not being able to fall asleep or stay asleep for the night.

Intestine: The intestine is sometimes called the bowel or the gut. It is the part of the digestive system that extends from the stomach to the rectum. It is made up of the small and large intestines and serves to absorb water and nutrients from the food and liquids that we drink and eat. The small intestine extends from the stomach to the large intestine and is made up of three segments: the duodenum, the jejunum and the ileum.

Intravenous: Intravenous means within a vein or veins. Substances such as fluids, nutrients, or medications, can be given intravenously, meaning directly into a vein.

Involuntary: Involuntary means that a person does not have control over something. In the body, it means the things that a person does not have conscious control over.

Ion: An ion is an electrically charged atom or group of atoms. Positively charged ions, known as cations, include potassium, calcium, sodium, hydrogen, ammonium, and magnesium. Negatively charged ions, called anions, include chloride, phosphate, and bicarbonate.

Ischemia: Ischemia occurs when the flow of oxygen-rich blood to tissue in the body is reduced or stopped.

Isoleucine: Isoleucine is an essential amino acid, meaning that the body does not make this amino acid, so it must be obtained through diet.

Jejunostomy tube: The jejunostomy tube is similar to a gastrostomy tube, although this tube is longer and inserted through the abdominal wall into the jejunum, the middle section of the small intestine.

Joint contractures: The abnormal and mostly permanent shortening of a muscle resulting in the loss of normal joint movement. When muscle fibers are shortened (due to injury, scar tissue or muscle overactivity), the nearby joint can remain fixed in one position.

Juvenile myoclonic epilepsy: Juvenile myoclonic epilepsy is a form of idiopathic epilepsy or recurrent seizures of unknown origin. Symptoms usually first appear around 12 to 16 years of age. The condition is characterized by sudden, involuntary, "shock-like" muscle jerks (myoclonus) that primarily occur during the morning or with stress, fatigue or alcohol consumption. Patients can eventually develop generalized seizures that are associated with loss of consciousness and rhythmic contractions and relaxations of all muscle groups (tonic-clonic).

Kinesigenic: Kinesigenic means something is caused by movement. This term is often used to describe abrupt episodes of uncontrolled and unintended movement that are provoked by sudden motions or unexpected stimuli. For example, exercise can cause abnormal movements in some people who have paroxysmal kinesigenic dykinesia (PKD).

Lafora's disease: A progressive myoclonic encephalopathy (PME) that is inherited as an autosomal recessive trait. Symptoms begin in childhood or early adolescence. These symptoms include frequent seizures characterized by loss of consciousness and rhythmic contraction and relaxation of all muscle groups (generalized tonic-clonic seizures); sudden, involuntary, "shock-like" muscle jerks (myoclonus); and rapidly progressive deterioration of thought processing and acquired intellectual abilities (dementia). When tissue is examined with a microscope, there are abnormal clumps of proteins and carbohydrates within the fluid part of the cells. These are called Lafora bodies.

Lance-Adams syndrome: Lance-Adams syndrome is a rare condition characterized by the development of chronic action myoclonus due to lack of oxygen to the brain. This is called posthypoxic or postanoxic action myoclonus. Patients with action myoclonus experience sudden, involuntary, "shock-like" muscle contractions that may be triggered or aggravated by voluntary movement. Lance-Adams syndrome is also often associated with cerebellar ataxia or lack of coordination and balance.

Laryngoscope: A laryngoscope is a long, thin, flexible tube that has a light and a small camera attached to the end. A doctor uses a laryngoscope to look at the larynx or voice box.

Lateral: Lateral means sideways or towards the side.

Leigh disease: Leigh disease is a rare disorder of infancy that is caused by abnormal function of mitochondria. Mitochondria are special parts of the cell that act like tiny power plants, providing energy to the rest of the cell. Affected infants have problems with feeding and swallowing, vomiting, muscle weakness, low muscle tone and delayed muscle and language skills. Infants and children can also have seizures, ataxia, abnormal eye movements (nystagmus), tremor, and dystonia. There are specific areas in the brain that lose tissue as well.

Leucine: Leucine is an essential amino acid. Essential means that the body does not make this amino acid, so it must be obtained through diet. Amino acids are the building blocks of proteins.

Levodopa: Levodopa is a drug used to treat Parkinson's disease and other movement disorder. It is also called L-dopa; in the United States, it is sold as Sinemet. Levodopa crosses the blood-brain barrier and is converted by the body into dopamine.

Lewy body: A Lewy body is a mass of protein found in dying nerve cells in the brain.

Lewy Body Disease: Lewy body disease (LBD), also called diffuse Lewy body disease or Lewy body dementia, is a common cause of dementia. LBD accounts for approximately 15-20% of all cases of dementia. The age of onset is typically in the late 50s through the 70s. It is more common in men than women. Lewy body disease is characterized by more daily changes in symptoms than Alzheimer's disease, as well as more prominent severe psychiatric problems (e.g., psychosis). People with LBD frequently experience troublesome side effects to drugs used to treat psychosis. Patients also have parkinsonian features early in the disease, including slowed movements and rigidity. Tremor is usually absent. The Lewy body is a protein clump found in dying neurons of the brain. In Lewy body disease, the Lewy bodies are most prominently found in the cortex or surface of the brain. In people with Parkinson’s disease, Lewy bodies are typically found in the midbrain, not the cortex.

Lipopolysaccharide: A lipopolysaccharide is a molecule made up of a fat with a complex sugar. In most circumstances, the terms lipopolysaccharide and endotoxin can be used interchangeably.

LRKK2: LRRK2 is an abbreviation that stands for “leucine-rich repeat kinase 2.” It is the name of a gene that is responsible for providing instructions for making a protein called dardarin. The gene is thought to be active in the brain. Although little is known about the LRRK2 gene or dardarin protein, researchers do know that part of the LRRK2 gene provides instructions to make a protein segment that is rich in a protein building block (amino acid) called leucine. Proteins with leucine-rich regions appear to play a role in activities that require protein-protein interactions, such as transmitting signals from nerve cell to nerve cell or helping to assemble the cell's structural framework (cytoskeleton).Researchers also suspect that the dardarin protein has an enzyme activity known as kinase, which may help to turn many cell activities on and off.

Lumbar puncture: Lumbar puncture is a procedure during which some cerebrospinal fluid (CSF) is removed from around the spinal cord. A needle is used to take the CSF from the fluid-filled space around the spinal cord in the lower back. The fluid can be sent to a laboratory for testing about infections, tumors and other neurologic disorders. Sometimes, a lumbar puncture is used to inject medication, such as anticancer drugs or pain medications into the CSF.

Lysosomal: Lysosomal refers to lysosomes. Lysosomes are small structures within cells that contain chemicals (enzymes) that aid in digestion with the cell.

Lysosomal storage diseases: In normal cells, lysosomes break down certain substances using enzymes. Enzymes speed up chemical reactions in the body. In lysosomal storage diseases, there are either not enough enzymes or the enzymes don’t work. This leads to a build up of that substance. This can affect various tissues and organs in the body. Most lysosomal storage disorders are thought to be inherited as a recessive genetic trait.

Machado-Joseph disease: Machado-Joseph disease, also known as spinocerebellar ataxia (SCA) type III, is a rare disorder but probably the most common dominant form of SCA. In addition to unsteadiness of walking (ataxia), symptoms can involve parkinsonism, dystonia and chorea. The abnormal protein that causes Machado-Joseph disease is called ataxin-3; however, its function is not yet known.

Magnetic resonance imaging (MRI): An MRI is a non-surgical diagnostic scanning or imaging study. The scans create detailed images in cross section of the body. MRI is a valuable tool for the neurologist to examine the brain and spinal cord; it can scan images from various angles. Sometimes a dye may be used to improve the images, providing strong contrast between healthy and abnormal tissues.

MAO inhibitors: MAO inhibitors are a group of medications that prevent the action of an enzyme called monoamine oxidase (MAO). This enzyme helps to break down dopamine. When MAO is inhibited, dopamine acts in the brain for a longer period of time. Examples of MAO inhibitors that are used in the treatment of Parkinson disease include rasagiline and selegiline.

MAO-B inhibitors: MAO-B inhibitors are medications that prevent the action of an enzyme called monoamine oxidase B (MAO-B). This enzyme helps to break down dopamine. When MAO is inhibited, dopamine acts in the brain for a longer period of time. MAO-B is a specific type of MAO inhibitor.

Matched control subjects : Matched control subjects are people in a study group or clinical trial who have similar characteristics, such as age, height, weight, education, sex or other characteristics, as the patients being studied, but they do not have the disease. An example would be control subjects that were matched with regard to age and sex to each person who had PD, but the control subjects did not have PD, parkinsonism or any other form of tremor.

Mean: The mean is the average of a set of numbers.

Mechanical pain: Mechanical pain arises from pressure or touch.

Media impression: A media impression is the interaction between a web site, radio spot, television program, or newspaper or magazine article and a single member of the audience who is exposed to that medium.

Medially: Medially means towards the middle or midline. The "median plane" refers to the imaginary line that divides a body into two identical halves.

Medication: Medication is a drug that has an effect on the body. It is usually used to treat a certain illness or condition.

Melanoma: Melanoma is a serious and potentially life-threatening type of skin cancer. The tumor cells develop in the melanocytes, the cells that give skin its color.

Membrane: A membrane is a thin wall or film that allows only some substances to pass through it or that prevents the mixing of two substances.

Membrane lipid peroxidation: Membrane lipid peroxidation is the breakdown of certain fatty acids into another form of fatty molecules.

Memory: Memory is how information is processed. It requires that a person is able to gather information. That information is then stored and held onto for a period of time. The final step is to recall the information when the person wants it.

Meningitis: Meningitis is an infection of the meninges, the thin three-layer membranes that cover and protect the brain and spinal cord.

MERFF syndrome (myoclonus epilepsy with ragged-red fibers): MERFF is a rare disorder passed down from one generation to the next. In MERFF, mitochondria that provide the energy to cells have defective genetic material. This causes neurologic and muscle problems. When the muscle fibers are examined using a microscope, the mitochondria are abnormal and look like “ragged-red fibers.” People with MERFF experience muscle weakness, myoclonus, seizures, ataxia, and dementia. Some people may also have hearing loss, breakdown of the nerves that send information from the retina of the eye to the brain, short stature and heart muscle disease.

Metabolism: Metabolism is a group of activities in the cells that use food to make energy or other compounds that are essential to life. There are two types of metabolism, catabolism and anabolism. Catabolism is when chemicals are broken down into simpler substances. This process gives off energy. Anabolism is when chemical compounds are build up into more complex substances. This process requires energy.

Methylphenidate: Methylphenidate is a drug that is used to speed up the functions of the central nervous system (a stimulant). This drug is usually used to treat symptoms of attention-deficit/ hyperactivity disorder or narcolepsy. It acts like caffeine but has a more powerful effect; however, it is not as potent as amphetamines.

Metoclopramide: Metoclopramide is a medication used to treat nausea and vomiting or migraine headaches and to help with emptying the stomach for people with specific medical conditions. It works by blocking dopamine receptors.

Micrographia: Micrographia is unusually small writing. It comes from two Greek words—micro and graph—micro means small, graph means to write.

Mini-Mental State Examination : This short, doctor-administered test measures the ability to think, calculate and reason (cognition). This test is used to measure the presence of impaired cognition or a change in cognition over time.

Mitochondrial: Mitochondria are structures found in cells that produce and regulate energy. They are the main energy source of cells. Mitochondria convert nutrients into energy and also perform many other specialized tasks.

Mitochondrial dysfunction: Dysfunction means that something is not working or functioning in the correct way. Mitochondrial dysfunction refers to a situation in which the mitochondria are not working properly.

Monoamine: A monoamine is a molecule that contains one amine group. An amine is an organic compound containing nitrogen. Monoamines that are found naturally in the body are called biogenic monoamines. The body uses these as neurotransmitters. They include dopamine, serotonin, noradrenaline and epinephrine.

Monotherapy: Monotherapy refers to the use of a single drug to treat a disease. The opposite of this is combination therapy, where more than one medication is used.

Motor fluctuations: Motor fluctuations occur when levodopa is used to treat Parkinson’s disease. As the disease becomes worse, the number of cells in the brain that store dopamine decreases, the symptoms of Parkinson’s disease worsen, and levodopa is not as effective in controlling the symptoms. When this happens, a person is said to have “on” and “off” episodes.

Motor symptoms: The motor symptoms of Parkinson's disease include tremor, stiffness (called rigidity), slowness or absence of movement (called bradykinesia or akinesia, respectively), and difficulty maintaining balance or unstable posture.

Multiple sclerosis (MS): MS is a disease of the central nervious system that becomes worse over time (progressive). In people with MS, the fatty coating that insulates nerves is destroyed. Myelin is a fatty substance that wraps around axons, which are the part of the nerve cell that carries information from one nerve cell to another neuron. The loss of myelin decreases the speed with which neurons can send information to other nerves. People with MS may develop paresthesias, such as numbness or tingling; muscle weakness and stiffness; impaired coordination; abnormal reflexes; an inability to control urination (urinary incontinence); slurred speech; and visual disturbances.

Multiple Sleep Latency Test (MSLT): The MSLT is used to measure how likely a person is to fall asleep. The test takes place over a seven-hour period during the day. Every two hours, for 20 minutes, the patient lies in a quiet dark room and is hooked up to a machine that measures brain waves, heart rate, muscle activity, and eye movements. This recording allows the doctor to see how quickly the patient falls asleep in this situation or if the patient falls asleep at all.

Multiple System Atrophy: MSA is a rare, neurodegenerative movement disorder. The main symptoms include ataxia, and problems with the autonomic nervous system.

Muscle tone: The low level of contraction in a muscle not being intentionally contracted.

Mutated: Changed

Mutation: A mutation is a change in a gene, such as loss, gain, or substitution of genetic material. This change alters the gene’s function or expression. This change is passed along with subsequent divisions of the affected cell. Gene mutations may occur randomly for unknown reasons or may be inherited.

Myelin: Myelin is a fatty substance that wraps around axons. Myelin insulates the axons which allow nerve signals to be sent more rapidly.

Myelinated: Myelinated means that an axon or long nerve fiber is covered in myelin, which is a fatty insulator. Myelin insulates the axons, helping them to send rapid nerve signals.

Myoclonic: Myoclonic refers to myoclonus or irregular, involuntary, shock-like contractions or spasms of a muscle or muscle group.

Myoclonus: Myoclonus is a neurologic movement disorder characterized by brief, involuntary, twitching or "shock-like" contractions of a muscle or muscle group. Myoclonus can be found along with other neurologic disorders or it can be present by itself. Depending on its cause, the muscle jerks can occur repeatedly or infrequently. They also may tend to occur only during specific circumstances. The muscle jerks can affect any body region or regions.

Narcolepsy: Narcolepsy is a sleep disorder marked by sudden, uncontrollable urges to sleep that cause a person to fall asleep at inappropriate times.

Nasoduodenal tube: A nasoduodenal tube is a flexible rubber tube that is inserted through the nose and into the section of the small intestine closest to the stomach (duodenum) via the esophagus and stomach. It can be used to remove the contents of the small intestine or to provide nutrition support or medication.

Nasolaryngoscopy: Nasolaryngoscopy is an in-office procedure during which the doctor looks at the larynx or voice box. During this procedure, the doctor inserts a laryngoscope through the patient’s nose into the throat.

National Institutes of Health (NIH): The NIH is one of the world’s foremost medical research centers and the federal focal point for medical research in the United States. The NIH, comprising 27 separate Institutes and Centers, is one of eight health agencies of the Public Health Service, part of the U.S. Department of Health and Human Services.

Nausea: Nausea is a feeling of discomfort in the stomach that people feel before they vomit. A person does not have to vomit though in order to have nausea.

Necrosis: Necrosis means cell death. Necrosis may result from a loss of blood supply (ischemia), infection, excessive exposure to harmful radiation, certain chemicals, or extreme temperatures.

Neoplastic: Neoplastic refers to the formation of a neoplasm, which is another word for a tumor. A neoplasm is simply uncontrolled growth of cells. Neoplasms may be benign (non-cancerous) or malignant (cancerous).

Nerve conduction velocity (NCV) test: A NCV test is a diagnostic study during which both sensory and motor nerves are repeatedly stimulated with electricity. This measures the speed at which nerve impulses are conducted. Unusually slow speeds or conduction velocities suggest damage to nerve fibers.

Nervous system: The nervous system of the human body is divided into two interconnected systems: the central nervous system, which is made up of the brain and spinal cord, and the peripheral nervous system. The peripheral nervous system is further divided into the somatic nervous system (made up of peripheral nerve fibers that send sensory information to the central nervous system and motor nerve fibers that connect to skeletal muscle) and the autonomic nervous system.

Neuroacanthocytosis: Neuroacanthocytosis, also known as choreoacanthocytosis, is a rare, genetic disorder that most often becomes apparent between the ages of 25 to 45 years. The disorder is usually transmitted as a recessive trait. Symptoms include chorea; dystonia affecting muscles of the mouth and tongue; potentially mutilating lip- and tongue-biting; and sudden, involuntary, repetitive muscle movements (motor tics) and vocalizations (vocal tics). Patients may also develop personality changes and declines in the ability to think and reason, seizures, parkinsonism, loss or wasting (atrophy) of muscle tissue (amyotrophy), and difficulties speaking and swallowing.

Neurochemical: Neurochemical refers to the chemical and its biochemical processes of the nervous system. This includes activities that involve neurotransmitters, which are chemical messenger made by the body. Neurotransmitters enable nerve cells (neurons) to communicate.

Neurodegenerative: Neurodegenerative is a term that means neurologic degeneration. Neurologic degeneration is when the tissue in the nervous system is destroyed.

Neuroimaging: Neuroimaging is any technique that produces images of the brain and spinal cord. These images can be used to do research or help make a diagnosis or a treatment decision. Neuroimaging includes CT scanning, MRI, and PET scanning.

Neuroleptic: A neuroleptic is a drug used to treat psychiatric disorders, especially psychotic behavior.

Neuroleptic malignant syndrome: Neuroleptic malignant syndrome is a life-threatening neurologic disorder. It is usually caused by a reaction to neuroleptic drugs. Symptoms include high fever, sweating, unstable blood pressure, coma-like state, muscular rigidity, and problems with the autonomic nervous system. In most people, the disorder develops within the first two weeks of treatment with the drug; however, the disorder may develop any time during the therapy period.

Neurologic: Neurologic refers to the nervous system. The nervous system is made up of the brain, spinal cord and nerves throughout the body. It can also refer to neurology. This is the medical specialty that deals with disorders of the nervous system.

Neurologist: A neurologist is a doctor who diagnoses and treats diseases of the nervous system. The nervous system is made up of the brain, spinal cord and all the nerves in the body.

Neuron: A neuron is a nerve cell. It is the smallest unit within the nervous system, which is made up of the brain, spinal cord and all the nerves in the body. A neuron can send and receive information by using either electrical or chemical signals. This information is passed from one neuron to another neuron or to a body part using these signals.

Neuronal: Neuronal is a term that means something involves a neuron or neurons.

Neuropathology: Neuropathology is the study of diseases in the nervous system. The nervous system is made up of the brain, spinal cord and all of the nerves in the body.

Neuroprotection: A neuroprotective effect means that something has the ability to prevent or slow down the death of neurons—thus protecting the nervous system.

Neuroreceptor: A neuroreceptor is a specific place on a neuron. This is where neurotransmitters attach themselves or bind. After the neurotransmitters bind, they cause signals to be sent to other neurons.

Neurotoxin: A neurotoxin is a substance that interferes with the electrical activity or functioning of nerve cells (neurons). This prevents them from communicating with each other.

Neurotransmitter: A neurotransmitter is a chemical substance that is made in the body, allowing for nerve cells to communicate. It is the chemical messenger sent from one nerve cell to another.

Nigrostriatal system: Nigrostriatal system refers to a system that connects two areas in the brain. These two areas are called the substantia nigra and the striatum.

Nocardia asteroides: Nocardia asteroides are gram-positive bacteria that are found in soil throughout the world. Infections usually occur in the skin following contamination of a scrape or scratch; the infection can spread when a person with a compromised immune system inhales the bacteria. The primary site of infection is typically the lungs, where abscesses form. The infection may spread to other parts of the body, including the brain, liver and kidneys.

Nocturnal Sleep Dysfunction: Nocturnal means at night. Sleep dysfunction refers to basically anything that affects or interrupts sleep. Nocturnal sleep dysfunction can be caused by Parkinson disease, for example. It can also be caused by sleep disorders such as insomnia, restless legs syndrome, rapid eye movement sleep behavior disorder or sleep apnea.

Nomenclature: Nomenclature is a system of names used in a particular scientific field. This allows scientists to order or classify the things in their field. By using nomenclature, people can avoid confusion and misunderstandings.

Non-ergotoline medication: A non-ergotoline medication is a dopamine agonist that acts like a drug made from an ergot, although it is not an ergot. They are used to treat neurologic movement disorders.

Non-kinesigenic: Non-kinesigenic means that movement does not cause something. This term often refers to abrupt episodes of involuntary movement that occur spontaneously or may be worsened by fatigue, stress, alcohol or caffeine intake, heat or cold, fasting or other factors.

Nonmotor symptoms: Non-motor signs and symptoms of Parkinson disease include general lack of interest (apathy), anxiety, bladder problems, constipation, dementia, depression, fatigue, excessive sweating, numbness, pain, psychosis, sexual dysfunction, excessive drooling and sleep disorders.

Noradrenaline (norepinephrine): Noradrenaline is a hormone and neurotransmitter made in the body. When it is released noradrenaline acts in the sympathetic nervous system. The release of noradrenaline causes breathing to deepen, and blood pressure and heart rate to rise. It also plays a role in regulating mood.

NREM sleep: Non-REM (non-rapid eye movement) sleep is one phase of the sleep cycle. NREM sleep is a lighter sleep where there are no dreams. The majority of sleep is spent in NREM sleep.

Nuclear envelope: The nuclear envelope is a membrane that surrounds the nucleus in cells, separating the DNA in the nucleus from the rest of the cell.

Nucleic acids: Nucleic acids are molecules that carry human genetic information. The most common nucleic acids are DNA and RNA. These molecules were named nucleic because scientists first found them in the nucleus of the cell. More recently, however, scientists have also found these molecules outside the nucleus of cells.

Nucleus: The nucleus is the part of the cell that contains the genetic material; it is surrounded by the nuclear envelope.

Obsessive-compulsive behaviors: The performance of certain repetitive actions or rituals in response to persistent thoughts or impulses. For example, obsessions may consist of repeated doubts, such as wondering whether the stove was left on; a need for routine; or impulses to perform certain inappropriate actions. Compulsions frequently include repeated checking and rechecking, such as ensuring that the stove is indeed off; touching particular objects in a specific pattern or sequence; repetitive hand washing; or other repetitious behavior performed in an attempt to prevent or relieve anxiety, distress, or a feeling of dread.

Obstructive sleep apnea: A sleep disorder characterized by episodes of temporary cessation of breathing due to obstruction of the airway.

Oculomotor: Relating to or causing movement of the eyes.

Off episodes: This term refers to the times when people with Parkinson's disease have a decrease in the ability to move (hypomobility) and other symptoms that cause difficulty rising from a chair, speaking, walking, or performing their usual activities. Off episodes occur because the person's dose of levodopa has worn off too soon or has suddenly and unexpectedly stopped providing benefit.

Off time: This term refers to the times when people with Parkinson's disease have a decrease in the ability to move (hypomobility) and other symptoms that cause difficulty rising from a chair, speaking, walking, or performing their usual activities. Off episodes occur because the person's dose of levodopa has worn off too soon or has suddenly and unexpectedly stopped providing benefit.

Olivopontocerebellar atrophy (OPCA): A group of rare hereditary disorders characterized by neurodegenerative changes of certain brain regions, including the cerebellum and specialized groups of nerve cells (nuclei) in the brainstem (e.g., olivary and pontine nuclei). With most forms of the disorder, initial symptoms become apparent from adolescence to mid-adulthood; however, a rare form has been identified that may be evident at birth. Depending upon the type of OPCA, symptoms may include progressively impaired coordination, postural instability, slurred speech (dysarthria), and other associated findings (i.e., cerebellar ataxia); parkinsonism; rapid, involuntary, rhythmic eye movements (nystagmus); and/or retinal degeneration. Some affected individuals may also have additional symptoms and findings, such as involuntary, rapid, jerky movements (chorea); relatively slow, writhing motions that appear to "flow" into one another (athetosis); increased muscle stiffness (rigidity) with associated twisting or distorted posturing of affected muscles (dystonia); and/or other abnormalities. Most forms of OPCA are inherited as autosomal dominant traits; however, autosomal recessive forms have also been identified.

On time: Motor fluctuations occur when levodopa is used to treat Parkinson’s disease. As the disease becomes worse, the number of cells in the brain that store dopamine decreases, the symptoms of Parkinson’s disease worsen, and levodopa is not as effective in controlling the symptoms. When this happens, a person is said to have “off” episodes. The times in which the levodopa is effective and the person with Parkinson’s disease is able to function normally is called “on time.”

On-off phenomenon: ON-OFF phenomenon or effects refer to the unpredictable response to levodopa medication for the treatment of Parkinson disease. A sudden change can occur in a person’s ability to move around, with the person being able to move with ease (that is, ON) and then, for no apparent reason, having difficulty with movement (OFF).

Opiate: Any preparation or derivative of opium.

Opioids: Means "like or similar to opium" and refers to medications with opium-like effects. This term is used to describe any synthetic drug that possesses the characteristic properties of opiate narcotics but is not derived from opium.

Organic: An organic disease or disorder is caused by a problem with the function or structure of tissue or one or more organs of the body.

Orthostatic hypotension: Orthostatic hypotension is a particular kind of blood pressure drop. It happens when a person is lying or sitting down. When the person stands up then, the blood pressure drops a lot. This can cause dizziness or even fainting.

Otolaryngology: Otolaryngology is a medical specialty that studies and treats diseases of the ear, nose, and throat.

Oxidative stress: Oxidative stress is a process in which substances called free radicals build up in the cells as the cells convert nutrients into energy. The free radicals damage different parts of the cells in a process that is similar to the way in which rust builds up on metal. The free radicals can be counteracted by antioxidants, but if your cells do not have enough antioxidants, the free radicals accumulate and cause damage. Coenzyme Q10 acts as a scavenger of free radicals.

Palate: The bony and muscular structure that forms the roof of the mouth and separates the oral and nasal cavities.

Pallidotomy: A pallidotomy is a surgical procedure that destroys the globus pallidus, a structure in the brain. The thalamus is found deep inside the brain. Pallidotomy can be used to treat tremor and rigidity in Parkinson’s disease. It is rarely recommended anymore, and has been replaced by deep brain stimulation.

Parallel-group study: In a parallel-group study, each participant is assigned to receive a single treatment. This is opposed to a cross-over study, in which participants receive some or all of the treatments.

Paranoia: Elaborate and overly suspicious thoughts and feelings of persecution

Parasympathetic nervous system: Part of the nervous system that, together with the sympathetic nervous system, forms the autonomic nervous system (ANS). The ANS controls the functioning of involuntary structures, including the heart, glands, and smooth muscle. The parasympathetic nervous system regulates nerve transmissions to certain effector organs under normal conditions, as opposed to times of stress. It serves to "steady" involuntary activities and conserve or restore energy. Parasympathetic responses may include slowing of the heart and breathing rates, contraction of the pupils, an increase in glandular activity, and an acceleration in the rate of peristalsis.

Parathyroid glands: Two pairs of endocrine glands located in the neck at the back of the thyroid gland. The parathyroid glands produce parathyroid hormone, which increases blood calcium levels by causing bones to release calcium into the blood, the kidneys to conserve calcium, and the intestines to increase calcium absorption from food. When blood calcium levels are high, the parathyroid glands reduce their production of parathyroid hormone, essentially reversing the process.

Paresthesias: Abnormal sensations occurring spontaneously or in response to stimulation. Paresthesias may include prickling, tingling, burning, or tickling feelings; numbness; "pins and needles"; or cramp-like sensations. Various neurologic movement disorders may be characterized by paresthesias, including restless legs syndrome (RLS), paroxysmal kinesigenic dyskinesia (PKD), and paroxysmal non-kinesigenic dyskinesia (PNKD).

Parkinson's disease (PD): PD is a disorder of the central nervous system characterized by slowness of movement (bradykinesia), rigidity, difficulty with balance and a tendency to fall, and tremor primarily while at rest. Additional characteristic findings include a shuffling, unbalanced manner of walking; forward bending or flexion of the trunk; a fixed or "mask-like" facial expression; weakness of the voice; abnormally small, cramped handwriting (micrographia); depression; anxiety; musculoskeletal pain; or other symptoms and findings. PD is a progressive disease, meaning it gets worse over time. Loss of nerve cells (called neurodegeneration) in a part of the brain called the substantia nigra is thought to cause most of these abnormalities. Because of the damage to the substantia nigra, there is a decrease in the amount of dopamine, a neurotransmitter, available in the brain. Other parts of the brain may also be affected in later stages of the disease, including those responsible for thinking and planning. Loss of nerve cells in these areas may lead to dementia.

Parkinsonism: Parkinsonism is a term that refers to a group of symptoms: tremor, rigidity, bradykinesia, and postural instability. These are usually seen in Parkinson’s disease, but there are other diseases that cause parkinsonism. Certain drugs can also cause this, and are usually reversible once the drug is stopped.

Paroxysmal: Pertaining to or occurring in paroxysms or sudden, recurrent episodes. The term paroxysms often describes transient episodes of abnormal involuntary movements (e.g., chorea, athetosis, dystonia, and/or ballismus) or ataxia, which is characterized by an impaired ability to coordinate voluntary movements.

Paroxysmal movement disorders: Certain neurologic movement disorders characterized by abrupt, transient episodes of abnormal involuntary movement, such as chorea, athetosis, dystonia, and/or ballismus (i.e., the paroxysmal dyskinesias) or impaired coordination of voluntary actions and other associated findings (i.e., paroxysmal ataxias). Depending upon the specific disorder present, episodes may be precipitated or worsened by different factors. As examples, in those with paroxysmal kinesigenic dyskinesia (PKD), episodes may be triggered by sudden voluntary movements. In non-kinesigenic dyskinesia (PNKD), episodes occur spontaneously and may be worsened by caffeine or alcohol consumption, stress, fatigue, or other factors. In patients with paroxysmal kinesigenic ataxias, episodes may be triggered by sudden voluntary movements or postural changes. These disorders may be familial, appear to occur randomly for unknown reasons (sporadically), or occur secondary to other underlying conditions or disorders (symptomatic).

Pathogenesis: the origination and development of a disease.

Pathophysiology: The effects of disease on body functions; the physiology of altered function seen in disease. ("Patho-" is a combining form denoting any disease state, and "physiology" refers to the study of the processes and functioning of the human body.)

Patient registry: A patient registry is a list of people who have a specific disease. This list allows researchers and doctors to contact people who have an illness or disease to see if they want to participate in clinical studies. The information on a patient registry is not available to anyone other than the researchers, and patient privacy is always protected.

Penetrance: The regularity or frequency with which a specific gene yields its effect or "is expressed." For example, if a specific gene produces a disease in all individuals who carry the gene, it is termed 100% penetrant. If a gene produces the disease less than 100% of the time, it is not fully penetrant.

Peptide: Peptides are short chains of amino acids.

Pericardium: The pericardium is the two-layered sac that surrounds and protect the heart. If the pericardium becomes fibrotic or filled with fluid, it limits the motion of the heart and, therefore, the ability of the heart to pump efficiently.

Periodic apnea: Episodes of the temporary cessation of spontaneous breathing. Periodic apnea may be characterized by absence of airflow, absence of chest wall movements, or airway obstruction that may result from poor control of tongue movements, impaired coordination of upper airway muscles, or other abnormalities.

Periodic limb movements in sleep (PLMS): Periodic limb movements of sleep are regular rhythmic twitches of the limbs that occur during sleep. The twitches usually affect the legs but they also sometimes affect the arms. The twitches usually last between half a second and five seconds and usually occur every five to 90 seconds. The diagnosis of periodic limb movement disorder is based on the results of an overnight sleep study. If the person has five or more series of limb movements per hour of sleep, a diagnosis of periodic limb movement disorder is made.

Perioperative setting: The perioperative setting is the time before, during, and after an operation.

Peripheral edema: unusual fluid accumulation, resulting in swelling of the arms or legs.

Peripheral nervous system: The peripheral nervous system is that portion of the nervious system outside of the brain and spinal cord (central nervous system)

Peripheral neuropathy: Inflammation, degeneration, or damage of nerves of the peripheral nervous system (PNS). The PNS includes nerves that extend from the brain and spinal cord (central nervous system) to various parts of the body. Peripheral neuropathy may involve motor nerves, causing muscle weakness, and/or sensory nerves, resulting in pain, abnormal sensations, such as numbness or tingling, or other findings.

Peristalsis: Rhythmic, wave-like contractions of smooth or involuntary muscle fibers that propel food through the digestive tract.

Phenomenology: classification based on a scientific explanation.

Phenylalanine: an essential amino acid that is converted in the body to tyrosine.

Phenylketonuria: an inherited disorder that, if untreated, causes profound mental retardation as well as other medical problems.

Phonation: The production of speech; utterance of sounds through use of the vocal cords.

Physiatrist: a physician specializing in physical medicine and rehabilitation.

Physiologic tremor: A form of rapid tremor that may occasionally occur in any individual. Physiologic tremor is typically the result of fear, anxiety, or excitement. Physiologic tremor may affect the arms, legs, and, in some patients, the face or neck.

Pill-rolling tremor: To understand what a pill-rolling tremor looks like, imagine a person holding a pill between her first finger and thumb. You can get an idea by extending your first finger and your thumb and holding them together at the first joint of each. Slide the finger away from your hand and your thumb toward your hand—in opposition. Now reverse the movement, sliding your finger toward your hand and your thumb away from your hand. Slowly repeat these movements and you will have an idea of what the pill-rolling tremor looks like. People with Parkinson disease have this type of tremor when their hands are at rest. At first, it may affect only one hand, but over time, it may affect both hands or may alternate, at times affecting one and then the other hand.

Pittsburgh Sleep Quality Index: This 24-item self-administered questionnaire is designed to provide a brief clinically useful assessment of a variety of sleep disturbances that might affect sleep quality.

Placebo: A placebo is a substance that appears to be identical to the treatment under study but that has no effects on the test subject. The placebo is given to members of the control group during experimental trials that test the effects of a drug or other substance.

Placebo-controlled trial: A placebo-controlled trial is a clinical experiment in which patients have been randomly assigned to receive either the treatment under study or placebo, an alternative that has no effects.

Pleura: The pleura are the two-layer membranes that cover the outside of the lungs and line the chest cavity.

Polymerase chain reaction (PCR): A highly sophisticated technique during which a known sequence of DNA is copied rapidly over a short period, such as millions of copies over a few hours. PCR testing assists in diagnosing certain genetic disorders, helps identify individuals through analysis of a single cell or so-called "DNA fingerprinting," or characterizes certain strains of infectious microorganisms.

Positron emission tomography (PET): An advanced, computerized imaging technique that uses radioactively-labels substances (e.g., glucose) to demonstrate chemical and metabolic activities in the brain as well as track other brain functions. Brain structures are also visualized on PET scans.

Positron emission tomography (PET) scanning: A noninvasive, diagnostic procedure used to record the uptake and distribution of certain substances in the tissues and organs of the body. Thus, PET assists in evaluating various metabolic and physiological activities in the body. During this procedure, three-dimensional, color-coded images are created based upon the detection of positively charged particles (positrons). The positrons are produced by certain biochemicals (e.g., glucose) carrying radioactive substances that have been introduced into the body (via intravenous injection). PET scanning may help to detect abnormal biochemical patterns associated with certain neurologic conditions, such as Parkinson’s disease, brain tumors, seizure disorders, and psychiatric abnormalities.

Postural instability: Postural instability is a difficulty with balance.

Postural tremor: Any tremor that is present while an individual voluntarily maintains a position against gravity, such as holding the arms outstretched.

Precursor: Literally a "forerunner," such as a substance that precedes another in a biochemical reaction.

Prenatally: Before birth.

Prevalence: Prevalence refers to the number of people in a given group or population who have a disease.

Probe: A genetic probe is a single strand of DNA or RNA with a specific base sequence used to detect the corresponding base sequence by hybridization—which is the process of joining two complementary strands of DNA or one each of DNA and RNA to form a double-stranded molecule. The single strand is either radioactively or immunologically labeled.

Progressive supranuclear palsy (PSP): A progressive neurological disorder characterized by neurodegenerative changes of certain brain regions, including particular areas of the basal ganglia and the brainstem. Symptom onset most often occurs in the sixth decade of life. Associated findings may include balance difficulties, sudden falls, stiffness (rigidity), slowness of movement (bradykinesia), an impaired ability to perform certain voluntary eye movements, and visual disturbances. Affected individuals may also develop slurred speech; swallowing difficulties; personality changes; dystonia; sudden, involuntary, "shock-like" muscle contractions (myoclonus); or other abnormalities. The disorder usually appears to occur randomly for unknown reasons (sporadically); however, there are some reports of families with multiple affected members, suggesting a possible hereditary component to the disease.

Prophylactic: Referring to preventive treatment (i.e., prophylaxis); a medication, procedure, or device that serves as a preventive against disease.

Prophylaxis: Protection from or the prevention of disease; preventive (i.e., prophylactic) therapy; often refers to the use of a drug, mechanical agent, or procedure to prevent infection with certain microorganisms (e.g. bacteria).

Proteasome inhibitor: A proteasome inhibitor is a chemical that interferes with, or inhibits, the action of proteasomes—the recyclers of proteins in the cells.

Protein: Proteins are large complex molecules made up of amino acids. Each protein starts out as a chain of amino acids. Determined by the sequence of the base pairs in the gene that encodes it, the protein then folds itself into its unique shape. Proteins serve many different roles within the body, including providing structure (collagen), allowing movement (actin and myosin), increasing the rate of a chemical reaction (enzymes), transporting substances (hemoglobin); regulating processes within the cells (insulin); and responding to the stimuli (receptor proteins on surface of all cells).

Proxy: A proxy is someone who is authorized to act on behalf of another person. This person may be a relative or friend, for example.

Psychogenic: A psychogenic disorder has a mental or emotional origin. Psychogenic also refers to a symptom, condition, or disorder that is caused by mental, psychological, or emotional factors rather than physical illness.

Psychosis: Psychosis is a psychiatric disorder characterized by impaired ability to distinguish reality from fantasy, personality changes and deterioration of normal social functioning. People with psychosis may experience hallucinations, illusions, or delusions, or they may be paranoid or have distorted thinking.

Pulmonary: Referring to the lungs.

Pulmonary fibrosis: Pulmonary fibrosis is a condition in which excessive scar tissue forms in the lungs, making them stiff, decreasing the amount of surface area that is available to provide gas exchange, and interfering with their function.

Putamen: One of the 3 major brain regions that, together with the caudate nuclei and the globus pallidus, comprise the basal ganglia. Relatively similar in function and structure, the putamen and the caudate nuclei are collectively referred to as the striatum. Specialized groups of nerve cells within the putamen receive input from various regions of the cerebral cortex. The messages are processed and relayed by way of the thalamus to the motor cortex, influencing voluntary movement.

Randomized controlled : In a randomized controlled trial or study, participants are randomly assigned to different treatments or conditions to study the effectiveness of the treatment or condition.

Range of motion (ROM): The extent of a joint's free movement. The normal ROM of the elbow, for instance, carries the forearm through a half-circle. Passive ROM is tested while the limb is relaxed. Active ROM is movement controlled by the patient.

Receptor: A receptor is one end of the nerve cell that receives messages from other nerve cells. These messages are usually neurotransmitters sent by other nerve cells. Drugs, however, can affect receptors directly without using neurotransmitters.

Reduced penetrance: Reduced expression of a genetic disorder. The term penetrance refers to the frequency with which a specific genetic mutation produces its typical effect in those with the genetic abnormality. For example, if fewer than 100 percent of individuals who inherit a gene mutation for an autosomal dominant disorder develop the disease, the specific trait is said to have "reduced penetrance."

Reflex: Involuntary, predictable response to a particular stimulus.

Refractory: Resistant to or not readily yielding to treatment.

Regurgitation: In reference to the heart, regurgitation is the backward flow of blood through a defective valve.

REM sleep: Rapid Eye Movement (REM) sleep is one part of a sleep cycle. The eyes move around quickly, hence the name. This is the phase where dreaming occurs. During this phase, the body is paralyzed so that a person does not act out his dreams. Adults spend about 20% of their time in this phase.

REM sleep behavior disorder (RBD): During REM sleep, a person is normally paralyzed while dreaming. In RBD, a person is not paralyzed so he acts out his dreams. This can put the person or bed partner in danger of injury.

Restless legs syndrome (RLS): A neurologic movement disorder characterized by unusual, uncomfortable sensations (paresthesias/dysesthesias) deep within the calves and/or thighs, resulting in an irresistible urge to move the legs, and motor restlessness in response to or in an effort to alleviate discomfort. In some patients, the arms may also be affected. Symptoms become obvious or worse during periods of relaxation or inactivity; occur most frequently during the evening or the early part of the night; and may be temporarily relieved by voluntary movements of the affected area. Most patients experience associated sleep disturbances, including difficulties drifting off to and remaining asleep. RLS is also often associated with periodic limb movements of sleep (PLMS) or repeated, stereotypic, upward extension of the great toe and foot, potentially followed by flexion of the knee, hip, or ankle. Episodes of PLMS typically occur during periods of lighter (i.e., non-REM) sleep.

Restorative sleep: A refreshing sleep, i.e., receiving a sufficient amount of rest to feel refreshed and to engage in the activities of daily living without experiencing excessive daytime sleepiness (EDS).

Retina: The nerve-rich membrane that forms the innermost region of the eye. As light passes through other areas of the eye (including the cornea, pupil, and lens), it is bent or refracted to focus on the retina, which contains nerve cells that respond to light (photoreceptors). Images formed on the retina are converted into nerve impulses that are transmitted to the brain via the optic nerve (second cranial nerve).

Retinal: Referring to the retina, which is the nerve-rich membrane forming the innermost region of the eye. As light passes through the eye, it is bent (refracted) to focus on the retina, which contains photoreceptors or specialized nerve cells that respond to light. Images formed on the retina are converted into nerve impulses, which are then transmitted to the brain by the optic nerve (also known as the second cranial nerve).

Retrocollis: spasmodic torticollis in which the head is drawn directly backward.

Retroperitoneum: The retroperitoneal area is the area behind peritoneum, the covering of the intestines. The kidneys and the adrenal glands lie in the retroperitoneal area.

Reye syndrome: A potentially life-threatening disease characterized by sudden inflammation and swelling of the brain (acute encephalopathy) and rapid fat accumulation within certain internal organs (viscera), particularly the liver, occurring subsequent to certain viral infections, such as chickenpox or upper respiratory tract infections (e.g., influenza B). Reye syndrome primarily occurs in children and adolescents, although it has sometimes been reported during infancy or young adulthood. About a week after the onset of a viral infection, patients may develop uncontrollable vomiting, followed by a rapid onset of listlessness, confusion, and memory loss, a state of unconsciousness (coma), seizures, and/or other findings, potentially leading to life-threatening complications. Evidence suggests that the use of aspirin-containing preparations (salicylates) as a treatment for particular viral infections plays a role in the development of Reye syndrome. Therefore, experts advise that such medications be avoided for the treatment of viral infections during infancy, childhood, adolescence, and young adulthood.

Rhythmical myoclonus: Involuntary, shock-like contractions or spasms of a muscle or muscle group that occur in a rhythmical pattern. This usually occurs as a result of a lesion in the central nervous system.

Ribonucleic acid (RNA): RNA is a chemical that is found in the nucleus and cytoplasm of cells; it plays an important role in protein synthesis and other chemical activities of the cell.

Ribosomes: Ribosomes are small structures within a cell that are the site of protein synthesis.

Rigidity: Rigidity is stiffness or resistance to movement. It is one of several motor symptoms in Parkinson’s disease.

Rush Hallucination Inventory: This standardized clinician-administered questionnaire assesses the presence or absence of false visual (see), auditory (hear), tactile (touch), or gustatory (taste) experiences in the setting of a clear sensorium.

Sandhoff's disease: A neurodegenerative metabolic disorder that is characterized by symptoms and findings similar to those associated with Tay-Sachs disease as well as possible, moderate enlargement of the liver and spleen (hepatosplenomegaly). Sandhoff's disease is a lysosomal storage disease in which deficiency of the enzymes hexosaminidase A and B results in an abnormal accumulation of certain fats (i.e., gangliosides) in particular tissues of the body. The disorder is transmitted as an autosomal recessive trait and affects only non-Jewish individuals (as opposed to Tay-Sachs disease, which primarily occurs in individuals of Ashkenazi Jewish ancestry).

Schizophrenia: a psychiatric disorder characterized by hallucinations, delusions, disordered thinking, unusual speech or behavior and social withdrawal that impair the affected person’s ability to interact with others.

Scoliosis: Lateral or "sideways" curvature of the normally vertical line of the spine. Progressive spinal deformity may be associated with numerous neuromuscular and neurodevelopmental disorders (neurogenic scoliosis), such as cerebral palsy, spinal muscular atrophy, and Rett syndrome. The severity of the deformity varies, depending upon the degree of weakness, the nature and progression of the underlying disorder, or other factors.

Seborrhea: Seborrhea is an increased amount of the oily substance that is produced in the sweat glands of the skin. It causes the skin to glisten or appear shiny.

Sedation: An induced state of quiet or sleep

Seizures: Episodes of uncontrolled electrical activity in the brain. These abnormal electrical disturbances may lead to involuntary jerking, spasms, or rhythmic contraction and relaxation of certain muscle groups and impaired control of involuntary functions such as breathing or bladder or bowel control. There may also be loss of consciousness or sensory or behavioral abnormalities.

Sensorimotor: Pertaining to both the sensory and motor aspects of a bodily function.

Sequelae: Plural of sequela, which is any abnormal condition that occurs subsequent to and/or is caused by disease, injury, or treatment.

Sequence: As a noun, a sequence is a series of chemical bases—adenine (A), thymine (T), cytosine (C) and guanine (G)—in DNA or a string of amino acids in a protein. As a verb, sequence refers to the process of determining the order of the bases or amino acids.

Serotonin (3-[2-aminoethyl]-5-indolol): A vasoconstrictor found in many tissues of the body that is present in relatively high concentrations in portions of the central nervous system (e.g., hypothalamus, basal ganglia, etc.). Serotonin functions as a neurotransmitter, regulating the delivery of messages between nerve cells (neurons). This neurotransmitter is thought to play some role in regulating consciousness and mood states. Serotonin is also present in other tissues of the body such as the intestines and blood platelets.

Sexual dysfunction: Sexual dysfunction is any problem with sexual activity. It could be a problem with desire, arousal, or orgasm. In men, it usually means having problems with erections.

Sialidosis: A lysosomal storage disease in which deficiency of the enzyme neuraminidase leads to abnormal accumulation of certain complex carbohydrates (sialyloligosaccharides) in particular tissues and organs. There are different variants of the disorder, based upon age of onset, severity, and other factors. Sialidosis type I, also known as "cherry-red-spot myoclonus syndrome," usually becomes apparent during the second decade of life. Associated symptoms include the development of characteristic, cherry-red circular areas within the middle layers of the eyes; gradual loss of visual clarity; and sudden, involuntary, "shock-like" contractions (myoclonus) of muscles of the arms and legs. The myoclonus is progressive in nature and may be triggered by voluntary movements (action myoclonus) or certain external stimuli, such as sound (reflex myoclonus). Sialidosis is inherited as an autosomal recessive trait.

Sialorrhea: Sialorrhea means having too much saliva. It causes a person to drool. It could be because a person makes too much saliva. It could also be because a person has problems swallowing, and the saliva stays in the mouth.

Side effect: An effect of a drug that is not the main or intended effect. Side effects may be of no concern, or they may be bothersome or even dangerous, in which case they may limit the upper dose a patient can tolerate. Side effects are also called adverse effects.

Single photon emission computed tomography (SPECT): SPECT is a noninvasive scanning procedure during which a radioactive substance known as a radionuclide is introduced into the body to help evaluate the function and structure of certain organs or tissues. The amount of the substance taken up by particular tissues may depend upon the amount of blood flow within such regions. For example, absence of radionuclide uptake in a targeted region may indicate a lack of blood flow in certain areas. Following intravenous administration of the radioactive compound, a specialized rotating camera detects the radiation emanating from the radionuclides in the form of particles known as protons. The recorded images may produce colorized, horizontal and vertical cross-sections and may be reconstructed by computer to create three-dimensional images. By evaluating the blood supply to particular tissues, SPECT may be particularly helpful in detecting certain changes within the brain, spinal cord, or heart.

Sinus bradycardia: an abnormally slow heart rate (i.e., of less than 60 beats per minute).

Sleep fragmentation: Sleep fragmentation is a continual disruption of sleep, which often leads to excessive daytime sleepiness. This disruption can occur as the result of a variety of factors, including sleep disorders, the need to get up to use the bathroom, pain, and a noisy or uncomfortable sleeping environment.

Sleep latency: The interval of time between "settling in" to go to sleep and the onset of sleep.

Sleep maintenance: Once asleep, the ability to remain asleep.

Sleep paralysis: Sleep paralysis is a total inability to move that occurs while the person is falling asleep or immediately upon awakening.

Sodium Oxybate: Sodium oxybate is also known as gamma hydroxybutyrate or GHB. This clear odorless liquid was approved by the US Food and Drug Administration in 2002 for the small number of people who have narcolepsy with cataplexy. Because of the high potential for abuse and misuse, the drug is only available from a single central pharmacy and its distribution is tightly controlled.

Somatization disorder: A person with a somatization disorder has symptoms that mimic or look like those of a disease or injury but for which there is no physical cause. Although somatization disorders are likely caused by a psychological factor, they are not the result of the person deliberately producing or exaggerating symptoms.

Spasm: A spasm is an uncontrollable sudden tightening of a muscle or group of muscles.

Spasmodic dysphonia (SD): A manifestation of dystonia. SD involves the muscles of the larynx and surrounding muscles and therefore involves speech. In individuals with SD, speech in blocked by intermittent spasms of the voice box (larynx).

Spasmodic torticollis (ST): A form of dystonia involving the muscles of the neck, and therefore called "cervical dystonia." As a result of the abnormal involuntary contractions of the neck muscles, the head may be rotated, tilted, flexed, extended, or any combination of these postures. The movements may be quick, sustained, or patterned and, therefore, may be associated with tremor.

Spasmolytic: Antispasmodic; referring to agents that may eliminate or relieve spasms, typically of involuntary (i.e., smooth) muscle, such as within the arteries, the intestine, the ring-shaped muscles around certain natural openings or passages (sphincters), the bladder, the muscular tubes that carry urine from the kidneys to the bladder (ureters), etc.

Spasticity: An abnormal increase in muscle tone that may be caused by certain types of damage to the nerve pathways regulating muscles. Spasticity is a common complication of cerebral palsy, brain injuries, spinal cord injuries, multiple sclerosis, and stroke. Spasticity can lead to incoordination, loss of function, pain, and permanent muscle shortening, or contracture.

Speech pathologist: A speech pathologist is a person who diagnoses and treats problems with speech and language. This could be a problem with the voice, swallowing, or communication.

Speech therapist: A speech therapist is a professionally trained person. The speech therapist helps people with speech, language, communication, and swallowing problems.

Spinal cord: The cylindrical structure of nerve tissue that, together with the brain, comprises the central nervous system. The spinal cord is an extension of the medulla oblongata--which is part of the lowest region of the brain (brainstem)--and is contained within a central canal in the spinal column. The spinal cord and the brain are surrounded by a protective, 3-layered membrane (meninges). Cerebrospinal fluid (CSF) flows through the cavities (ventricles) of the brain, the spinal cord's central canal, and the space between the middle and inner layers of the meninges (subarachnoid space). The spinal cord consists of an inner core of gray matter and surrounding areas of white matter, composed of bundles of myelinated nerve fibers (axons) known as spinal tracts. These include ascending tracts that carry sensory impulses up the spinal cord to the brain and descending tracts that transmit motor impulses from the brain down the spinal cord. Nerves emerge from both sides of the spinal cord (i.e., spinal nerves) through the narrow gaps (foramina) between bones of the spinal column (vertebrae). The spinal nerves, which are attached to the spinal cord by specialized nerve bundles (spinal nerve roots), contain both motor and sensory neurons.

Spinocerebellar ataxias (SCA): This group of disorders, of which there are now 17 genetically identified types, are inherited as an autosomal dominant genetic trait and appear to be mostly due to increased numbers of repeats in the various genes involved (as in HD). All types of SCA involve degeneration of the cerebellum, causing impaired balance, walking, and coordination. Each type of SCA has its own typical pattern of symptoms; however, these may vary greatly from person to person. Some forms of SCA affect eye movements, swallowing, thinking, reflexes, or cause parkinsonism, chorea, or dystonia. In most types of SCA, the onset of symptoms occurs during adulthood; symptoms slowly become worse over the years.

Sporadically: Occurring intermittently, randomly, or in isolation.

SSRIs: Selective serotonin reuptake inhibitors. Drugs belonging to this class are antidepressant agents that selectively inhibit the absorption of serotonin at certain nerve membranes (e.g., presynaptic neuronal membranes). These drugs increase the concentration of serotonin within the central nervous system and enhance serotonin's neurotransmission activities.

Statistician: A statistician is a mathematician who studies data, analyzes it, and interprets it. This allows people to make sense of information collected.

Stereotactic: refers to use of precise coordinates to identify deep structures of the brain. The coordinates may be obtained by fitting a patient's head with a special frame and taking a CT or MRI scan. The position of the brain structures relative to the frame permits fine localization of the deep brain structures. Stereotactic methods are used during brain surgery for tremor, Parkinson's disease, and dystonia. These brain structures are located with precise, three-dimensional coordinates.

Stereotypic: Inappropriate, persistent repetition of particular bodily postures, actions, or speech patterns. These are typically involuntary, rhythmic, coordinated, and purposeless movements, postures, or vocalizations that may appear ritualistic or purposeful in nature. Stereotypies may be associated with a variety of neurologic and behavioral disorders, such as Tourette syndrome, obsessive-compulsive disorders, Rett syndrome, restless legs syndrome, schizophrenia, and autism.

Stereotypical: Conforming to a repetitive pattern as in repetition of particular movements or gestures.

Stimulus: A stimulus is something that creates a response in a muscle, nerve, gland or other excitable tissue or organ of the body. The plural is stimuli.

Stretch reflex: Contraction of a muscle stimulated by rapid stretching.

Stretch-loop circuits: Pathways of electrical impulses along specific nerve fibers (alpha motoneurons) that result in a "stretch" reflex in a muscle.

Striatum: An area of the brain that controls movement and balance. It is connected to and receives signals from the substantia nigra.

Study group: A study group can also be called a working group. The members of the study group meet regularly to discuss a specific topic--in this case, spasmodic dysphonia. They also work together to design research studies.

Substantia nigra: A dark band of gray matter deep within the brain where cells manufacture the neurotransmitter dopamine for movement control. Degeneration of cells in this region may lead to a neurologic movement disorder such as Parkinson's disease.

Substrate: A chemical substance that is acted upon by an enzyme is called a substrate.

Subthalamic nucleus: The subthalamic nucleus is an oval mass of gray matter located beneath the thalamus.

Sydenham's chorea: A usually self-limited condition in which chorea develops in association with an inflammatory disease caused by certain strains of streptococci bacteria. This disease, known as rheumatic fever, is characterized by the sudden onset of fever and joint pain, with subsequent inflammation of the heart (carditis), chest pain, skin rash, and other symptoms. If rheumatic fever involves the nervous system, Sydenham’s chorea may develop. This condition commonly affects children aged 5 to 15 or women during pregnancy. Sydenham's chorea involves involuntary, uncontrollable, jerky movements that gradually worsen in severity, potentially affecting arm movements, the manner of walking (gait), and speech. In most patients, the condition spontaneously resolves in weeks or months.

Sympathetic nervous system: Part of the nervous system that along with the parasympathetic nervous system forms the autonomic nervous system (ANS). The ANS regulates the functioning of involuntary structures, such as the glands, smooth muscle, and heart. The sympathetic nervous system regulates certain involuntary responses during times of strong emotion, such as fear or anger; exercise; or other forms of stress. These responses, sometimes referred to as the "fright-or-flight response," include widening of the pupils; increased heart and breathing rates; constriction of most blood vessels, raising blood pressure; widening of those blood vessels that supply skeletal muscles; and reduction in the rate of peristalsis.

Synapse: The junction between two neurons or between a neuron and an effector organ. As a nerve impulse reaches a synapse, the terminal or end of the "presynaptic" neuron's axon releases neurotransmitters, which diffuse across the gap and bind to receptors of the "postsynaptic" neuron or the effector organ (i.e., muscle or gland). As the electrical impulse is conducted across the gap, electrical changes are triggered that serve to continue or hinder transmission of the impulse.

Synthesis: The formation of a complex chemical compound through the union of simpler substances.

Systemic lupus erythematosus: an autoimmune disease involving multiple organ systems that is defined clinically and associated with antibodies directed against cell nuclei.

Tardive dyskinesia: A movement disorder that may result from extended therapy with certain antipsychotic medications such as haloperidol. The condition is characterized by involuntary, rhythmic movements of the face, jaw, mouth, and tongue, such as lip pursing, chewing movements, or protrusion of the tongue. Facial movements are sometimes accompanied by involuntary, jerky or writhing motions (choreoathetoid movements) of the trunk, arms, and legs. In some patients, symptoms discontinue months or years after withdrawal of antipsychotic therapy. However, in others, the condition may not be reversible.

Tardive dystonia: A form of tardive dyskinesia characterized by chronic dystonia due to administration of medications that block dopamine D2 receptors (dopamine receptor antagonists), such as certain antipsychotic agents. (Dopamine receptors are molecules on the surfaces of receiving nerve cells that are sensitive to stimulation by dopamine, a neurotransmitter that controls movement and balance. Several types of dopamine receptors have been identified, including D1, D2, and D3.) Dystonia is a neurologic movement disorder characterized by sustained muscle contractions that often result in repetitive twisting motions or unusual postures or positions. Tardive dystonia is the most common form of secondary dystonia--i.e., dystonia that results from certain environmental factors or "insults" that affect the brain. In adults, tardive dystonia often initially affects facial or neck muscles. Dystonia may remain limited to such regions or extend to affect adjacent muscles of the trunk and arms. Children are more likely to be affected by generalized dystonia that involves muscles of the trunk and legs.

Tauopathy: Tauopathy refers to any group of diseases that cause dementia related to a problem with tau, a protein that is important in maintaining the structure of brain cells.

Tay-Sachs disease: A progressive neurodegenerative metabolic disorder that belongs to a group of diseases called lysosomal storage diseases. Also known as GM2 gangliosidosis type I or infantile type, Tay-Sachs disease results from deficiency of the enzyme hexosaminidase A, which leads to an abnormal accumulation of certain fats (i.e., gangliosides) in particular tissues, particularly nerve cells of the brain. An autosomal recessive disorder, Tay-Sachs disease primarily affects individuals of northeastern European Jewish (Ashkenazi Jewish) ancestry. Symptom onset typically begins from about 3 to 6 months of age. Associated symptoms may include an exaggerated startle response, increasing listlessness, loss of previously acquired skills (psychomotor regression), severely diminished muscle tone (hypotonia), and the development of characteristic, cherry-red circular areas within the middle layers of the eyes (Tay's sign). With disease progression, affected infants and children may develop increasing muscle stiffness or rigidity; seizures; sudden, involuntary, "shock-like" contractions of multiple muscle groups in response to certain stimuli (generalized, stimuli-sensitive myoclonus); enlargement of the brain (metabolic megalencephaly); deafness; blindness; and dementia. Life-threatening complications may develop between 2 to 5 years of age.

Tendon: A tough fibrous cord of tissue that attaches muscle to bone (or other structures of the body).

Teratogenic: Possessing the ability to disrupt normal fetal development and causing fetal abnormalities.

Thalamotomy: A thalamotomy is a surgical procedure that destroys the thalamus, a structure in the brain. The thalamus is found deep inside the brain. Thalamotomy can be used to treat tremor and rigidity in Parkinson’s disease. It is rarely recommended anymore, and has been replaced by deep brain stimulation.

Thalamus: An area of the brain consisting of 2 relatively large masses of gray matter. The thalamus relays information from most sensory organs to the outer region of the cerebrum or cerebral cortex; receives and processes messages from the body concerning heat, cold, pain, pressure, and touch; and influences motor activity of the cerebral cortex.

Threshold: A pain threshold is the point at which a feeling or sensation becomes painful.

Tics: Involuntary, compulsive, stereotypic muscle movements or vocalizations that abruptly interrupt normal motor activities. These repetitive, purposeless motions (motor tics) or utterances (vocal tics) may be simple or complex in nature; may be temporarily suppressed; and are often preceded by a "foreboding" sensation or urge that is temporarily relieved following their execution. Simple tics include abrupt, isolated movements, such as repeated facial twitching, blinking, or shoulder shrugging, and simple sounds, including grunting, throat clearing, or sighing. Complex tics may involve more sustained, complex movements, such as deep knee bending or leg kicking, or complex vocalizations, including repeating another person's words or phrases (echolalia) or, rarely, explosive cursing (coprolalia). Tourette syndrome is defined as the presence of multiple motor and vocal tics for at least one year, changes in the nature of the tics (e.g., complexity, severity, anatomical location) during the course of the disorder, and symptom onset before age 21.

Tone: Resistance or tension in a muscle when a limb or other body part is moved passively and in a relaxed state about a joint. A state of muscle tension balanced by partial contraction or alternate contraction and relaxation.

TorsinA: TorsinA is a protein that, when defective, may cause DYT-1 dystonia. Although its exact function is not known, TorsinA is believed to be related to a series of compounds that enable cells to recover from stress and injury.

Total Functional Capacity: The Total Functional Capacity Scale is a tool that clinicians use to assess the function of people with Huntington disease. The scale includes five domains: workplace, finances, domestic chores, activities of daily living, and the need for skilled or unskilled care.

Toxic metabolites: Potentially harmful substances formed as the result of normal body functions.

Toxin: A toxin is a poisonous substance that is produced by a plant or animal

Transdermal: Transdermal means, literally, through the skin.

Transient: Temporary; transitory; not lasting or enduring.

Tremor: A tremor is a rhythmic motion involving a specific part of the body--the hands, arms, neck, head, vocal cords, trunk or legs. The motion involves the muscles going back and forth, like a rocking chair. A person with a tremor cannot control it.

Tropical spastic paraparesis (HTLV-1-associated myelopathy): A rare disorder characterized by slowly progressive weakness (paraparesis), stiffness (rigidity), and spasticity of the leg muscles due to infection with the human T-cell lymphotropic virus-1 (HTLV-1). Modes of transmission include sexual contact, mother-to-child transmission (e.g., via breastfeeding), and blood transfusion.

Tryptophan: an essential amino acid.

Tyrosine: an aromatic nonessential amino acid that is a metabolic precursor of thyroxine, the pigment melanin, and other biologically important compounds.

Unified Parkinson Disease Rating Scale (UPDRS): The UPDRS is the most commonly used to tool to rate the symptoms of Parkinson disease. This scale is intended to be used to follow the course of Parkinson disease in patients over a period of time. It is made up of four parts: (1) mentation (the process of thinking), behavior, and mood; (2) activities of daily living; (3) motor symptoms, and (4) complications of therapy.

Unilateral: Affecting, pertaining to, or confined to one side only.

Unverricht-Lundborg's disease (Baltic myoclonic epilepsy): A form of progressive myoclonic encephalopathy (PME) characterized by the development of repeated seizures or episodes of uncontrolled electrical activity of the brain (epilepsy); sudden, "shock-like" muscle contractions that may be induced by voluntary movements or in response to certain external stimuli (action or reflex myoclonus); and eventual impairment of coordination, postural instability, and other associated findings (i.e., cerebellar ataxia). Although mental deterioration may also be associated with the disorder, it is typically milder than that seen with Lafora's disease (another form of PME). Unverricht-Lundborg's disease is thought to be inherited as an autosomal recessive trait. Symptom onset typically begins from about age 6 to 13. The disorder is slowly progressive; however, the degree of disease progression and disability may be extremely variable among affected family members.

Upper motor neurons: Nerve cells extending from the brain to the spinal cord that control movement.

Vaginosis: Bacterial vaginosis involves the abnormal increased growth of certain bacteria in the vagina.

Valine: an essential amino acid.

Variable expressivity: Varying manifestation of a genetic trait. The term "expressivity" refers to the degree to which a hereditary trait appears in an individual. Thus, in individuals with a gene mutation for an autosomal dominant disorder that has variable expressivity, the specific characteristics that are manifested may vary in range and degree from mild to severe.

Vascular: Pertaining to or containing blood vessels.

Vasoconstrictor: A chemical substance whose actions result in the narrowing of blood vessels.

Vasodilator: A chemical substance whose actions cause an increase in the diameter of blood vessels.

Vasomotor: Pertaining to the muscles and nerves that control blood vessel diameter, thereby regulating or modulating blood pressure.

Ventral intermediate (VIM) nucleus: A specific region of the thalamus. This area of the brain is involved in the control of movement and is the "target" area for thalamotomy and deep brain stimulation when treating patients with tremor.

Ventriculography: Brain imaging method that uses an injected dye and X-rays to visualize the brain's ventricles (cavities)

Virulent: Referring to or characterized by virulence or the degree to which an invading microorganism, such as a bacterium or virus, is able to produce disease. Measures of virulence may be based upon the microorganism's ability to invade bodily tissues and the severity of the disease produced.

Visual-analog scale: This linear scale allows responses on a continuum.

Wearing off: The wearing-off phenomenon is a decrease in how long levodopa works. Over time, the ON state (the time in which the levodopa is effective) becomes shorter. The person returns to the OFF state (when the drug is not effective) more quickly after having taken levodopa. Wearing off is usually related to how long a person has been taking levodopa.

Wearing-off phenomenon: Wearing-off phenomenon is a decrease in how long Levodopa works. Over time, the ON state is shortened. The OFF state comes back quicker the more time a person takes the drug.

White matter: Bundles of myelinated nerve fibers or axons. These nerve fibers have a creamy white appearance due to myelin, a whitish substance that primarily contains fats and proteins. Myelin forms a protective, insulating sheath around certain axons, functioning as an electrical insulator and ensuring efficient nerve conduction. The breakdown, destruction, or loss of myelin from a nerve or nerves (demyelination), such as seen in certain neurodegenerative diseases, results in impaired nerve impulse transmission.

Wilson disease: A rare genetic disorder of copper metabolism, leading to an excessive accumulation of copper in certain tissues and organs, including the liver, brain, kidneys, or corneas of the eyes. Without prompt, appropriate treatment, the disorder may result in progressive liver disease, degenerative changes of the brain, psychiatric abnormalities, and other symptoms. Neurologic findings may include tremor; involuntary, rapid, jerky movements combined with relatively slow, writhing movements (choreoathetosis); impaired muscle tone and sustained muscle contractions, producing repetitive movements and abnormal posturing; increasingly slurred speech; and difficulties swallowing. Some patients may also experience increasing irritability, anxiety, severe depression, unusual behaviors, or other psychiatric problems.

X-linked dominant trait: Human traits, such as an individual's specific blood group, eye color, or expression of certain diseases, result from the interaction of one gene inherited from the mother and one from the father. In X-linked dominant disorders, the gene mutation for the disease trait is transmitted as a dominant gene on the X chromosome and therefore may "override" the instructions of the normal gene on the other chromosome, resulting in expression of the disease. Because females have two X chromosomes yet only one functioning copy is necessary, a percentage of X chromosomes with the mutated gene may not be expressed (random X chromosome inactivation). As a result, females often have less severe symptoms than affected males. In contrast, because males have one X chromosome from the mother and one Y chromosome from the father, those who inherit an X-linked dominant disease trait typically fully express the mutated gene on the X chromosome, causing a more severe form of the disorder that may result in lethality before or shortly after birth. Fathers with an X-linked dominant trait transmit the gene to their daughters but not to their sons. Mothers with a single copy of an X-linked dominant gene have a 50 percent risk of transmitting the gene to their daughters as well as to their sons.

X-linked recessive trait: Human traits, such as a person's eye color, specific blood group, or expression of certain diseases, result from the interaction of one gene inherited from the mother and one from the father. In X-linked recessive disorders, the gene mutation for the disease trait is located on the X chromosome. Because females have two X chromosomes yet only one functioning copy is necessary, a percentage of X chromosomes with the mutated gene may not be expressed (random X chromosome inactivation). However, because males have one X chromosome from the mother and one Y chromosome from the father, those who inherit an X-linked recessive disease trait typically fully express the mutated gene on the X chromosome. Some females who carry a single copy of the disease gene (heterozygous carriers) may have certain symptoms associated with the disorder; however, such findings are usually more variable and less severe than those seen in affected males. Fathers with an X-linked recessive trait may transmit the gene to their daughters but not to their sons. Mothers with an X-linked recessive gene have a 50 percent risk of transmitting the gene to their daughters and their sons.

Zydis: Unlike drugs that are incorporated into pills or capsules that must be swallowed, Zydis drugs are incorporated into fast-dissolving freeze-dried wafers that "melt" on the tongue. The term Zydis refers to the vehicle that is used for drug delivery and not to the drug itself.