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Brain Health Glossary

Focus on dementia, depression and anxiety, Parkinson’s disease, stroke and traumatic brain injury

Terms and Definitions

Dementia is an umbrella term for conditions caused by damaged brain cells that progressively impair a person’s ability to think, reason and remember. The impairment is extensive enough to interfere with daily life.

 

acetylcholine

The neurotransmitter that supports normal brain and nerve function and behaviors including memory and learning. Imbalances in the level of acetylcholine play a role in some neurological disorders, including Alzheimer’s and Parkinson’s. 

 

Aduhelm (aducanumab)

A medication that received approval on an accelerated basis by the U.S. Food and Drug Administration in 2021 to slow cognitive decline in patients with early-stage Alzheimer’s. One of the first medications intended to treat a cause, not just the symptoms, by clearing amyloid plaques from the brain. It has seen limited use after questions were raised about its safety and effectiveness. See also Leqembi (lecanemab). 

 

Alzheimer’s disease

The most common form of dementia, Alzheimer’s is progressive — it gets worse over time — and affects memory, thinking and the ability to carry out daily tasks. It is characterized by the abnormal buildup of amyloid plaques and tau tangles in the brain, which are considered the hallmarks of Alzheimer’s.

 

amyloid plaques

The result of large accumulations of a naturally occurring protein, beta-amyloid, that form clusters. See also entry for tau. Alzheimer’s is believed to be caused by a buildup of plaques and tau tangles in the brain, which damage and destroy brain cells, disrupting normal communication among cells.

 

aphasia

A disorder resulting from damage to parts of the brain involved in language. Stroke or neurological diseases such as Alzheimer’s or frontotemporal dementia are among possible causes. There are several types of aphasia, depending on what part of the brain is affected. For example, people with damage in the temporal lobe — behind the ears — might speak in long but meaningless sentences and cannot understand the meaning of what others say. Those with damage to the frontal lobe — behind the forehead — may be able to understand others but cannot say more than a few words at a time.

 

delirium

Not a form of dementia, but sometimes mistaken for that condition, delirium is one of several treatable conditions with symptoms that resemble those of dementia, so they can be misdiagnosed. Delirium comes on quickly, while dementia usually occurs over the course of years. 

 

dementia

An overall term used to refer to a number of conditions caused by damaged brain cells. The main types of dementia are Alzheimer’s, frontotemporal, Lewy body and vascular. “Mixed dementia” describes having more than one of these disorders. These conditions impair a person’s ability to think, reason and remember, enough to interfere with daily life.

 

early-onset dementia

A form of dementia diagnosed in a person younger than 65. Like other forms of dementia, it can lead to loss of memory and personality changes. 

 

frontotemporal dementia

Frontotemporal dementia (FTD), results from damaged neurons in the area of the brain behind the forehead (the frontal lobes) or behind the ears (the temporal lobes). This form of dementia, also called frontotemporal disorders, gets worse over time and often occurs at younger ages than other dementias. FTD falls into three categories. Behavioral variant FTD, the most common form, involves changes in personality, judgment and ability to plan. Primary progressive aphasia affects a person’s ability to use language and communicate. The rarest form, movement disturbances includes muscle weakness or stiffness or problems with balance or walking.

 

Leqembi (lecanemab)

A medication approved by the Food and Drug Administration in July 2023 to slow cognitive decline in patients with early-stage Alzheimer’s. One of the first medications to treat the cause, not just the symptoms, by clearing amyloid plaques from the brain. See also Aduhelm (aducanumab). 

 

Lewy body dementia

An umbrella term for a group of disorders associated with the presence of abnormal protein deposits called Lewy bodies in the brain. Symptoms get worse over time and include problems with thinking — including visual hallucinations — movement, sleep disorders and mood. Named after Friedrich Lewy, the neurologist who discovered them. Parkinson’s disease is included in this broad category of dementia.

 

mild cognitive impairment

Lapses in memory or the inability to find words, problems that are noticeable to friends and seem worse in degree than seen in other people of the same age. The symptoms of MCI are not as severe as dementia. Not everyone who has MCI will develop dementia.

 

mixed dementia

A condition that gets worse over time as more than one form of dementia occurs simultaneously. The most common form of mixed dementia involves both the abnormal protein buildup associated with Alzheimer’s disease and blood vessel problems of vascular dementia.  

 

posterior cortical atrophy

A rare form of Alzheimer’s disease that gets gradually worse and affects the part of the brain responsible for spatial perception, complex visual processing, spelling and calculation. Those with PCA might have trouble reading a sentence, judging distances and using common tools.

 

tau

A naturally occurring protein that is thought to be part of the cause of Alzheimer’s disease when it becomes tangled inside nerve cells in the brain. See also entry for amyloid plaques. Alzheimer’s is believed to be caused by a buildup of plaques and tangles in the brain that damage and destroy brain cells, disrupting normal communication among cells.

 

vascular dementia

Occurs because of damage to or blockage of blood vessels in the brain. Symptoms, which get worse over time, include changes to memory, thinking and behavior.

 

For more on Alzheimer's and other dementias, click here.

Anxiety disorders differ from normal occasional feelings of nervousness and involve fear or unrealistic worry that triggers emotional agitation and sometimes physical symptoms that will not go away. 

 

Depression is a mood disorder that affects how a person thinks, feels and behaves. Sadness, an inability to feel pleasure or other symptoms persist, lasting two weeks or more. It is one of the most common mental disorders in the United States.

 

agoraphobia

An anxiety disorder that involves intense fear of being in a place or situation in which escape seems difficult.

 

anxiety

Feelings of dread or worry. Though anxiety is a normal behavioral response meant to help humans detect and handle possible threats, these feelings become a problem when they are persistent and interfere with daily life. 

 

depression

Referred to also as major depression, major depressive disorder or clinical depression, a serious mood disorder that is diagnosed as such if it lasts for at least two weeks. Symptoms differ, depending on age and background, but might include feelings of hopelessness, emptiness and anxiety, as well as difficulty sleeping and concentrating.  

 

depressive disorder due to another medical condition

A type of depression that is a consequence of a separate illness, such as heart disease or multiple sclerosis.

 

generalized anxiety disorder

Excessive and persistent worry — often out of proportion to a real threat — that lasts for at least six months and is often targeted at everyday things such as family, health, finances or job responsibilities. Physical symptoms, which can interfere with day-to-day activities, include restlessness, fatigue, difficulty concentrating, irritability, muscle tension or sleep disturbance.

 

major depressive disorder

A type of depression that includes symptoms lasting at least two weeks that interferes with a person’s ability to perform daily tasks. 

 

panic disorder

An anxiety disorder that brings on frequent and unexpected panic attacks — racing heart, sweating, feeling of impending doom — even when there is no clear reason or danger.

 

persistent depressive disorder (dysthymia)

A depressed mood that lasts more than two years, but during which the person may still be able to perform daily tasks. 

 

seasonal affective disorder

A form of depression that lasts over certain seasons, typically during winter so it’s also known as winter depression. Less common is summer depression, when feelings of depression last over the warmer months. These mood changes can affect how a person feels, thinks and behaves.

 

social anxiety disorder

A feeling of self-consciousness or persistent fear of being watched and judged negatively by others. The disorder can keep people from daily activities such as going to work or school or socializing.

 

substance/medication-induced depressive disorder

A type of clinical depression related to the use of substances, such as alcohol or pain medication.

 

For more on anxiety and depression, click here.

Parkinson’s disease occurs when nerve cells in the part of the brain that controls movement become damaged or begin to die. Researchers believe that Parkinson’s results from a combination of genetic and environmental factors, such as exposure to toxins.

 

acetylcholine

A neurotransmitter that supports normal brain and nerve function involved in memory and learning. Imbalances in the level of acetylcholine play a role in some neurological disorders, including Parkinson’s, and some dementias, including Alzheimer’s. 

 

anticholinergics

Medications that can affect the activity of the neurotransmitter acetylcholine.

 

bradykinesia

Slowness of movement, one of the main symptoms of Parkinson’s disease. 

 

dyskinesia

Involuntary movements of face, arms, legs or trunk that can be caused by medications used to treat Parkinson’s. Also called levodopa-induced dyskinesia, as it typically occurs after a few years of use of the medication levodopa. 

 

dystonia

Involuntary and sustained muscle contractions causing abnormal posture or movement of limbs. One possible symptom of Parkinson’s, it can appear at any age — although not everyone who shows symptoms of this separate neurological disorder has Parkinson’s disease. See tremor. 

 

levodopa

The main medication used to treat Parkinson’s disease. Levodopa helps to replenish the brain’s supply of dopamine, a chemical produced by the nerve cells in the brain that control movement. Parkinson’s occurs when those nerve cells — or neurons — start to die.

 

Parkinson’s disease

Called a movement disorder because symptoms include muscle stiffness and slowness in movement, Parkinson’s disease occurs when nerve cells that make dopamine, a chemical that controls movement, become damaged or begin to die. Symptoms gradually worsen, often over decades. Researchers believe that Parkinson’s is caused by a combination of genetic and environmental factors. 

 

parkinsonism

A general term that refers to a group of neurological symptoms that resemble those caused by Parkinson’s, such as rigidity of limbs, slowness, stiffness and tremor, but that are caused by disorders other than Parkinson’s.

 

postural instability

An inability to balance. A common characteristic of Parkinson’s disease, postural instability worsens as the disease progresses, which increases the chances of falls.

 

prodromal phase symptoms

The early, or prodromal, phase of Parkinson’s can last up to 20 years. Symptoms of this early disease period, before the more visible muscle symptoms start, include constipation, depression and sleep problems.

 

rigidity

One of the main symptoms of Parkinson’s — along with tremor and bradykinesia — occurring in almost 90 percent of people with the disease. Stiffness of muscles in the arms, legs or trunk, and possibly those in the face.

 

tremor

Often an early symptom of Parkinson’s disease, and one of the most prevalent, this involuntary trembling tends to occur in the hands but can also occur in the arms, legs, jaw or head. Known also as resting tremor, because the tremor lessens when the affected part of the body is in use. Dystonia and tremor, distinct disorders, are often misinterpreted as Parkinson’s. “Essential tremor,” the most common adult movement disorder, and “dystonic tremor” may appear in people who have dystonia.

 

young-onset Parkinson’s disease

Although most people with Parkinson’s develop it after age 60, 5 percent to 10 percent experience onset before age 50, when it is considered early onset, or young onset.

 

For more on Parkinson's disease, click here.

A serious medical condition that occurs in the brain when something blocks the blood supply to part of the brain or a blood vessel leaks or bursts.  

 

aphasia

A disorder resulting from damage to parts of the brain involved in language. Stroke or neurological diseases such as Alzheimer’s are among possible causes. There are several types of aphasia, depending on what part of the brain is affected. For example, people with damage in the temporal lobe — behind the ears — might speak in long but meaningless sentences, unaware their words make no sense and unable to understand the meaning of what others say. Those with damage to the frontal lobe — behind the forehead — may be able to understand others but cannot say more than a few words at a time. 

 

atrial fibrillation

Atrial fibrillation, also called “afib,” is a heart rhythm abnormality. The irregular or fluttering heartbeat increases a person’s risk of stroke.

 

blood pressure

Refers to the pressure put on the large vessels of the circulatory system by the beating heart. Blood pressure measurements are given as two numbers: the first (systolic) represents the pressure when the heart beats. The second (diastolic) represents the pressure when the heart rests between beats. A blood pressure reading is considered normal when the systolic measurement is under 140 mmHg and the diastolic is under 90 mmHg. See hypertension.

 

cardiovascular, cardiovascular diseases

Cardiovascular refers to the heart and blood vessels. Cardiovascular disease is a group of disorders of the heart and blood vessels. More than 4 out of 5 cardiovascular disease deaths are due to heart attacks and strokes. 

 

cholesterol

A waxy substance made by the liver that is essential for good health. Some foods contain dietary cholesterol. Cholesterol measurements are divided into what’s informally called “bad” and “good.” High levels of the bad (low-density lipoprotein, or LDL) can lead to a buildup of fatty deposits in the arteries, and possibly stroke; high levels of the good (high-density lipoprotein, or HDL) can lower stroke risk. 

 

diabetes

Diabetes, a risk factor for stroke, is a condition in which the body does not handle insulin as it should. Type 1 diabetes means the body does not produce enough insulin. Type 2, the most common form of the condition, means the body does not use the insulin well and can’t keep the blood sugar at normal levels. High levels of blood sugar, or glucose, can lead to increased fatty deposits in blood vessels, increasing the risk of stroke.

 

hemorrhagic stroke

Occurs when an artery in the brain leaks blood or ruptures, putting too much pressure on brain cells. The less common of the two types of strokes; see also ischemic stroke.

 

hypertension (high blood pressure)

Hypertension, or high blood pressure, is when the pressure in the blood vessels causes damage to the arteries, which can decrease or block the flow of blood and oxygen to the heart and brain. Hypertension can lead to heart attack, stroke and kidney damage. A blood pressure reading is considered high when the systolic measurement is over 140 mmHg and/or the diastolic is over 90 mmHg.

 

ischemic stroke

Occurs when blood clots or other particles block the blood vessels to the brain. The more common of the two types of strokes; see also hemorrhagic stroke.

 

metabolic syndrome

A group of conditions, also known as insulin resistance syndrome, that raise one’s risk of coronary heart disease, diabetes and stroke. Characteristics include high blood pressure, high blood sugar, unhealthy cholesterol levels and abdominal fat.

 

stroke

A serious medical condition that occurs in the brain when something blocks the blood supply to part of the brain or a blood vessel leaks or bursts. There are two types of stroke: ischemic and hemorrhagic. 

 

transient ischemic attack (TIA)

Also referred to as a mini-stroke, a silent stroke or warning stroke. Unlike the two major types of stroke, in a TIA the blood flow to the brain is blocked for only a short time. The American Heart Association says that nearly 1 in 5 of those who have a TIA will have a full-blown stroke within three months. Requires an immediate emergency assessment.

 

For more on stroke, click here.

Damage to the brain from an outside force such as a blow to the head or something that pierces the skull can result in a traumatic brain injury, or TBI

 

chronic traumatic encephalopathy

A brain disease associated with repeated blows to the head over years, such as those occurring in various contact sports. CTE can be definitively diagnosed only by autopsy.

 

concussion

Caused by a sudden jolt that causes the brain to bounce inside the skull. Often referred to as a mild traumatic brain injury, a concussion — the most common type of TBI — is usually not life-threatening but can have serious health consequences. Concussions have been linked to higher risk of dementia and Parkinson’s disease in later life. 

 

contusion

Bruising or swelling of the brain either at the site of impact or on the opposite side as a result of the brain being jolted hard and quickly back and forth within the skull.

 

hematoma

A cerebral hematoma is bleeding in or around the brain caused by a ruptured blood vessel.

 

nonpenetrating TBI

TBIs that involve the entire brain being moved within the skull. Known also as closed head or blunt TBI.

 

penetrating TBI

Known also as open TBI, this refers to when an object, such as a bullet or hammer, penetrates the skull, typically causing damage to only part of the brain. 

 

traumatic brain injury

Damage to the brain caused by an outside force, such as a jolt to the head that shakes the brain within the skull, or something that pierces the skull such as a gunshot wound. TBIs are classified as mild, moderate or severe. Such injuries can be caused by falls, blunt trauma such as those caused in contact sports, car accidents or explosions. TBIs can affect learning, memory, behavior and concentration.

 

For more on traumatic brain injury, click here.

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