Here’s a list of common terms that you might come across when reading about the brain or about the diseases and disorders that can affect it. The definitions have been compiled using a number of sources, including medical dictionaries, governmental agencies, and advocacy groups for various medical conditions. A complete list of sources is provided at the end of this glossary.


Acquired Immunodeficiency Syndrome (AIDS) - A disease caused by the human immunodeficiency virus (HIV) and marked by loss of immune function and subsequent susceptibility to disease and infection.

ADHD - Abbreviation for Attention Deficit Hyperactivity Disorder.

AIDS - Abbreviation for Acquired Immunodeficiency Syndrome.

Alcoholism - The addiction to alcohol that results in physical withdrawal symptoms when alcohol use is stopped.

Alzheimer’s disease - A progressive disease of the brain that results in impaired cognitive functions such as memory, reasoning, and perception.

Amygdala - See Amygdaloid nucleus.

Amygdaloid nucleus - The oval-shaped area of the brain that contributes to sense of smell, as well as to motivational and emotional responses.

Amyotrophic lateral sclerosis (ALS) - Also called Lou Gehrig’s disease, ALS is a disease of the motor neurons that causes weakness and muscle atrophy, ultimately causing paralysis and death.

Aneurysm - An abnormal widening in a localized area of a blood vessel, which can weaken the structure of the blood vessel and lead to rupture.

Anorexia nervosa - A disorder characterized by a pathological fear of being fat and a distorted perception of body shape resulting in obsessive weight-loss efforts that often lead to emaciation and associated health complications.

Anxiety disorders - A set of disorders, including generalized anxiety disorder (GAD), obsessive-compulsive disorder (OCD), panic disorder, posttraumatic stress disorder (PTSD), and social anxiety disorder (SAD), marked by irrational and debilitating fear of everyday occurrences.

Aphasia - A speech disorder marked by the loss of ability to express or comprehend spoken or written language.

Arteriovenous malformation - A genetic disorder that causes the growth of abnormal bundles of blood vessels in the brain.

Attention deficit hyperactivity disorder (ADHD) - A neurobehavioral disorder that results in an inability to maintain attention and in impulsive behavior.

Asperger syndrome - A developmental disorder that causes a varying degree of impaired communication skills and is often marked by an obsessive focus on a particular topic of interest. One of the autism spectrum disorders.

Ataxia - The loss of coordination or muscular stability, usually resulting from a disease affecting the cerebellum.

Autism - The primary developmental disorder of the autism spectrum disorders characterized by impaired social interaction abilities, verbal and nonverbal communication skills, and cognitive functioning.

Autism spectrum disorders - A spectrum of psychological disorders, including Autism and Asperger syndrome, primarily marked by impaired social and communicative abilities.

Autonomic nervous system - The portion of the nervous system that facilitates several critical body functions, such as heart-muscle activity.

Axon - The fibrous portion of a neuron that sends signals to target cells via electrical impulse.

Basal ganglia - The set of nerve clusters located at the base of the brain that facilitate involuntary body functions.

Batten disease - A genetic disease that causes progressive loss of motor function, vision, and cognitive function.

Bell’s palsy - A condition in which the nerve responsible for muscle movement on either side of the face becomes paralyzed, resulting in muscle paralysis on the corresponding side of the face.

Bipolar disorder - A psychological disorder marked by a vacillating pattern of extreme mood changes—from manic happiness to severe depression.

Brain - The primary organ of the central nervous system responsible for receiving, processing, and relaying information to all areas of the body.

Brain injury - Any damage to the brain resulting from trauma, disease, stroke, etc.

Brain tumor - A benign or malignant cell formation in the brain tissue.

Brain stem - The portion of the central nervous system that connects the brain with the spinal column. The brain stem conducts messages from the brain to the rest of the body and also plays a role in maintaining key functions such as breathing, swallowing, and heart rate.

Broca’s area - The portion of the brain located in the cerebral motor cortex that facilitates speech development.

Bulimia - An eating disorder characterized by obsession with body weight and image and an alternating cycle of extreme overeating (binging) and self-induced vomiting (purging).

Cell body - The primary area of a nerve cell, excluding the axon and dendrites.

Central nervous system (CNS) - The portion of the nervous system consisting of the brain and spinal cord.

Central sulcus - The deep groove on the surface of the brain occurring between the right and left hemispheres.

Cerebellum - The portion of the brain that controls complex motor functions and regulates balance.

Cerebral hemisphere - Each of the two halves of the brain, referred to as the right and left hemispheres.

Cerebral palsy - A disability in which brain damage incurred at or shortly after birth results in a varying degree of impaired movement, as well as other symptoms, such as poor coordination and speech problems.

Cerebrum - The largest portion of the brain, consisting of both the right and left cerebral hemispheres, that facilitates voluntary movement and intellectual functions, such as conscious thought, emotion, and reasoning.

Charcot-Marie-Tooth disease - A hereditary neurological disorder affecting the nerves of the extremities, causing progressive weakening of the muscles in the hands, feet, arms, and legs.

Cognitive disability - See mental retardation.

Conduct disorder - A set of emotional and behavioral disorders in children marked by inability to adhere to rules and poor social interaction that can last into adulthood.

Corpus callosum - The portion of the brain that connects the right and left cerebral hemispheres.

Creutzfeldt-Jakob disease - A fatal prion disease of the brain that causes progressive dementia and loss of muscle control.

Dandy-Walker syndrome - A developmental disorder characterized by malformation of the brain, including the absence of the corpus callosum, which causes a variety of symptoms, such as delayed motor development and cognitive impairment, and their associated prognoses.

Dementia - The loss of cognitive functioning, such as memory, motor skills, language use, and attention.

Dendrite - An extended outcropping of a nerve cell that receives impulses from other cells.

Depression/depressive disorder - Chronic feelings of sadness or despondence that interfere with daily functioning and require treatment to be resolved.

Diencephalon - The rear portion of the forebrain.

Dorsal - A term used to describe the rear or upper portion of an organ.

Down syndrome - An inherited condition marked by the presence of an extra chromosome in an individual’s genetic composition. Results in cognitive delays, distinctive physical traits (such as a characteristic upward slant to the eyes), and increased susceptibility to specific diseases and medical conditions.

Drug abuse - The habitual use of mind, mood, or consciousness-altering substances, which can lead to dependence.

Eating disorders - A set of psychological disorders that lead to pathological eating patterns, including bulimia, anorexia nervosa, and binge eating disorder.

Encephalitis - Any inflammation of the brain.

Encephalization quotient - The approximate measure of an animal’s capacity for intelligence, based on a ratio of brain weight to body weight.

Epilepsy - A disorder marked by a recurring pattern of seizures caused by abnormal neurological activity.

Glial cell - A cell that provides structural support and insulation for nerve cells located in the central nervous system.

Gray matter - Brain tissue comprised primarily of nerve cell bodies.

Guillain-Barré syndrome - A condition marked by temporary inflammation of nerve cells in the extremities, such as the hands, which results in muscle weakness, pain, and in some cases, paralysis of  the affected muscles.

Gyrencephalic - The physical characteristic of the outer surface of the brain marked by a twisting series of distinct ridges formed by gyri and sulci.

Gyri - The plural form of gyrus.

Gyrus - One of a winding pattern of raised brain tissue that, with the sulci they are surround by, forms distinct ridges located on the outer surface of the brain.

Hemifacial spasm - A neuromuscular disorder that causes involuntary movements in the muscles on either side of the face.

Hindbrain - The portion of the brain comprised of the cerebellum, pons, and medulla oblongata.

Hippocampus - The portion of the brain that plays a role in the processing of memory and emotion.

HIV - Abbreviation for Human Immunodeficiency Virus.

Human immunodeficiency virus - A virus that destroys cells of the immune system and causes Acquired Immunodeficiency Syndrome (AIDS).

Huntington’s disease - A hereditary disease that causes gradual loss of nerve cells in the brain, leading to loss of muscle control and impaired cognition; also called Huntington’s chorea.

Hypothalamus - The portion of the brain responsible for regulating body temperature as well as thirst and hunger.

Lateral - A term that describes either the far left or far right of the brain in relation to the center.

Learning disability - A disorder, affecting children of normal to above-normal intelligence, in which the ability to interpret written or spoken information or to connect various pieces of information is impaired.

Limbic system - The set of structures in the center of the brain that play a role in memory, emotion, and homeostasis.

Lissencephalic - The physical characteristic of the outer surface of the brain of certain animals that lacks the twisting series of distinct ridges as found on the human gyrencephalic brain.

Lou Gehrig’s disease - See amyotrophic lateral sclerosis.

Magnetic resonance imaging (MRI) - A diagnostic procedure that produces detailed electronic images of specific body structures.

Medulla oblongata - The portion of the brain, located at the base, which governs essential body functions such as breathing and blood circulation.

Meningitis - Inflammation of the membranes covering the brain and spinal cord, often as a result of infection.

Mental retardation - A condition in which cognitive function is impaired due to abnormal brain development or brain damage.

Mesencephalon - See Midbrain.

Metencephalon - The rear portion of the hindbrain, consisting of the cerebellum and pons.

Midbrain - The portion of the brain that connects the forebrain and hindbrain.

Migraine headache - A set of neurologic symptoms, often severe, including intense pain on one or both sides of the head, dizziness, extreme sensitivity to sensory stimuli (such as light), and nausea.

Motor cortex - The portion of the brain that sends messages to voluntary muscles throughout the body.

Motor neuron disease - Any disease affecting nerve cells associated with muscle movement, called motor neurons.

MRI - Abbreviation for Magnetic Resonance Imaging.

Multiple sclerosis - A disease in which inflammation destroys the myelin that insulates nerve fibers, causing symptoms of varying severity such as impaired movement, speech problems, numbness, and cognitive disturbances.

Muscular dystrophy - A set of genetic diseases marked by degeneration of muscles and impaired movement ability of varying severity.

Myasthenia gravis - An autoimmune disorder in which the body’s immune system erroneously attacks neurotransmitter receptors on muscle cells, impeding their ability to receive signals from the brain and resulting in symptoms such as chronic muscle weakness, breathing difficulty, slurred speech, and vision problems.

Myelencephalon - See Medulla oblongata.

Myelin - The white-colored tissue that surrounds myelinated nerve fibers to serve as an insulator.

Narcolepsy - A chronic disorder marked by sudden episodes of uncontrollable compulsion to sleep.

Neocortex - The layers of tissue located in the brain that process most higher cognitive functions.

Nerve cell - See Neuron.

Nervous System - The system of cells and tissues that regulate internal functions and enable response to external stimuli. The nervous system comprises the central, peripheral, and autonomic nervous systems.

Neural connectivity - The interconnection of various components of the nervous system.

Neuroanatomy - A term referring to the physical structure of the nervous system.

Neurodegeneration - An attribute of several neurological conditions in which nerve cells are negatively affected.

Neuron - A cell of the central nervous system that sends and receives messages, via electrical impulses, to other cells throughout the body.

Neuroscience - A term referring to several scientific disciplines focused on the nervous system.

Neurotransmitter - A chemical that conducts impulses across a synapse from a nerve cell to another cell.

Neurotoxicity - The property of being poisonous to nerve tissue.

Nicotine addiction - The habitual physiological dependence on nicotine in which cessation of use results in withdrawal symptoms.

Obsessive-compulsive disorder (OCD) - A disorder marked by obsessive focus on certain thoughts and compulsive behaviors, such as repetitive, unnecessary washing.

Occipital lobe - The rear portion of both right and left cerebral hemispheres of the brain that is involved with optical information.

Olfactory bulb - The portion of the brain in which the olfactory nerve terminates.

Panic disorder - A disorder marked by sudden, irrational bouts of extreme fear and panic, often accompanied by symptoms such as rapid heartbeat, lightheadedness, and hyperventilation.

Parietal lobe - The portion of the brain that processes complex sensory input and speech comprehension.

Parkinson’s disease - A neurodegenerative disorder in which brain cells responsible for producing a neurotransmitter called dopamine die off, resulting in loss of muscular control. Symptoms include muscle tremors (shaking), impaired speech, balance difficulties, and facial stiffness.

Peripheral nervous system (PNS) - The portion of the nervous system outside the central nervous system (brain and spinal cord).

Peripheral neuropathy - A result of certain diseases and disorders that affect areas of the peripheral nervous system, marked by numbness, tingling, and muscle weakness.

Pervasive developmental disorders - A set of childhood disorders marked by delayed development of social and communication abilities, including the autism spectrum disorders and Rett syndrome.

Pick’s disease - A condition marked by the progressive loss of intellectual abilities, such as memory and social skills.

Pituitary gland - The gland near the base of the brain that regulates hormone production and distribution throughout the body.

Pons - The compilation of nerves connecting the midbrain, medulla oblongata, and cerebrum.

Prefrontal cortex - The portion of the brain that governs behavior and enables the acquisition of certain kinds of knowledge.

Presynaptic - An area located in front of a synapse. Also, an occurrence that precedes synaptic activation.

Primary motor cortex - The portion of the brain responsible for coordinating voluntary muscle movement.

Primary somatosensory cortex - The portion of the brain responsible for processing the sense of touch.

Primary visual cortex - The portion of the brain responsible for processing visual identification of objects and coordinating movement in relation to visual input.

Prion disease - One of a group of usually fatal brain diseases caused by an infectious particle known as a prion, which, unlike a virus, bacteria, or fungus, contains no genetic material.

Prosencephalon - See Forebrain.

Putamen - The membrane that covers the central portion of each cerebral hemisphere of the brain.

Restless legs syndrome - A disorder marked by an irresistible urge to move the legs, often disturbing sleep.

Rett syndrome - A developmental disorder in girls in which normal physiological development slows down at 6 to 18 months of age, eventually leading to progressive loss of motor and language abilities.

Rhombencephalon - See Hindbrain.

Sagittal - The vertical plane that separates the right and left cerebral hemispheres of the brain.

Schizophrenia - A neurological disorder marked by hallucinations, delusion, paranoia, depression, poor coordination, and other cognitive disruptions.

Seizure - An instance of abnormal electrical activity in the brain that can result in convulsions and thought disruptions.

Sleep apnea - A condition characterized by intermittent, temporary breathing interruptions during sleep, either due to airway obstruction (obstructive sleep apnea) or to abnormal neurological functioning (central sleep apnea); the condition often results in excessive daytime sleepiness.

Spinal cord injury - Any damage to the spinal cord resulting from trauma, disease, or infection.

Spinal muscular atrophy (SMA) - A hereditary condition that causes the loss of motor neurons in the spinal cord and subsequently results in progressive muscle atrophy.

Stroke - A condition in which brain damage is caused by lack of oxygen due to a rupture or blockage of blood vessels in the brain that interrupts blood supply.

Substance abuse disorders - A set of disorders marked by pathological behavior due to chronic use of drugs or alcohol.

Suicide - The deliberate ending of one’s own life.

Sulci - Plural form of sulcus.

Sulcus - One of a winding series of grooves that, with the gyri they surround, forms the distinct ridges located on the outer surface of the brain.

Sympathetic nervous system - The portion of the nervous system that regulates blood pressure and heart rate.

Synapse - An interface point between a nerve cell and a target cell that enables the sending of messages via the expression of neurotransmitters.

Tay-Sachs disease - A fatal genetic disorder, particularly prevalent in those of Eastern European Jewish descent, in which abnormal lipid metabolism results in the accumulation of a neurotoxic substance in the nervous system, resulting in severe impairment of cognitive and motor function.

Tectum - The upper portion of the midbrain.

Tegmentum - A series of vertically aligned fibers found through the length of the midbrain.

Telencephalon - The front portion of the forebrain.

Temporal lobe - The portion of the brain containing the auditory cortex, which facilitates hearing.

Thalamus - The portion of the brain that relays sensory information to facilitate sight, hearing, touch, and taste.

Torsion dystonia - A movement disorder, marked by sustained, involuntary muscle contraction that results in deformity; it begins in children at an average of 12 years of age and is also known as early onset dystonia.

Tourette syndrome - A neurological disorder marked by involuntary motor or verbal convulsions, or tics, that may manifest as twitching or vocalizations, including grunting and shouting.

Transient ischemic attack (TIA) - A temporary interruption of blood flow to the brain due to blockage of a blood vessel—characterized by symptoms such as blurred vision, dizziness, numbness, and slurred speech.

Trigeminal neuralgia - A condition in which nerve inflammation causes episodes of intense, often debilitating facial pain.

Tuberous sclerosis - A genetic disorder that causes the growth of nonmalignant tumors in many of the major organs in the body and can result in developmental delay and mental retardation.

Visual cortex - The area of the brain responsible for sight by processing impulses sent by the optic nerve.

White matter - Brain tissue comprised primarily of nerve fibers, which are each encased in myelin for insulation.


The terms in this glossary were compiled based on educational information provided by the following:

MedTerms™ Medical Dictionary
Dorland’s Illustrated Medical Dictionary, 28th Edition
The Alzheimer’s Association
The Autism Society of America
The Muscular Dystrophy Association—ALS Division
Mayo Clinic
The National Institute of Mental Health
The National Institute of Neurological Disorders and Stroke
The National Autism Association
The Batten Disease Support and Research Association
The Charcot-Marie-Tooth Association
The American Academy of Child and Adolescent Psychiatry
The Creutzfeldt-Jacob Disease Foundation
The Dandy-Walker Alliance
The National Down Syndrome Society
The National Eating Disorders Association
The National Fragile X Foundation
The Centers for Disease Control and Prevention
The Migraine Research Foundation
The Multiple Sclerosis Association of America
The Myasthenia Gravis Association of America
The Obsessive-Compulsive Foundation
The National Parkinson Foundation
The Restless Legs Syndrome Foundation
The National Tourette Syndrome Association