An electroencephalogram (EEG) is a test that records the brain’s electrical activity. Healthcare professionals use it to help assess and understand neurological conditions, sleep disorders, and brain trauma.

A person may undergo an EEG if they have seizures, blackouts, or migraine to help identify the underlying causes.

This article discusses why doctors may use an EEG.

It also outlines 10 conditions that an EEG helps doctors understand.

A doctor fixing EEG electrodes to a person's head.Share on Pinterest
FG Trade/Getty Images

An EEG is a test that an EEG technologist performs to assess neurological conditions such as epilepsy, dementia, and others.

Doctors can also use it to understand the brain’s activity after a brain trauma such as a head injury or brain tumor. An EEG looks at what is happening in the brain for the duration of the test rather than the brain’s physical structure.

To perform the EEG, the technologist attaches electrodes to the person’s head, which picks up electrical signals from the brain’s cells. A computer records these signals and shows the electrical activity of the brain.

The electrodes attach to different parts of the head to locate precisely where activity is happening. An EEG is painless and safe.

A routine EEG procedure usually lasts 1 hour, including preparation before the test and 20–40 minutes of recording a person’s brain activity. There are several types of EEGs that have varying lengths.

Doctors use EEGs alongside other tests to build a complete picture of a person’s condition. The following sections outline 10 conditions that an EEG can help doctors understand.

Epilepsy is a neurological seizure condition that occurs in one of several parts of the brain. The main symptom of epilepsy is recurrent seizures due to unusual electrical brain activity.

A doctor may use an EEG to look for abnormal brain waves and determine which part of the brain the seizure originates from. This helps them diagnose the type of epilepsy a person has.

Read about how doctors diagnose epilepsy.

Sleep disorders include problems with the amount or quality of sleep a person has, often due to an underlying physical or emotional cause. A sleep disorder can impair a person’s cognitive functions, leading to poor physical or mental health and impaired quality of life.

Sleep disorders that may require an EEG include:

Resources for healthy sleep

To discover more evidence-based information and resources on the science of healthy sleep, visit our dedicated hub.

Was this helpful?

Head injuries, or traumatic brain injuries (TBIs), occur when a strong force to the head causes damage to the brain, resulting in temporary or permanent impairment of cognitive, physical, and psychosocial functions.

Doctors may use EEGs when a person has a mild traumatic brain injury (mTBI) to help them assess and monitor cognitive function. However, using EEGs in this way is not commonplace, and research is ongoing into their use in this area.

Read about the causes and effects of TBI.

Brain inflammation, or encephalitis, primarily occurs after a viral infection. Other causes may involve the immune system mistakenly attacking brain tissue. In rare cases, an attack comes from bacteria, fungi, or parasites.

A brain abscess is a serious and potentially life threatening condition that develops due to bacterial or fungal infection in the brain.

In encephalitis, an EEG may show sharp waves in one or both temporal lobes and abnormalities in people who experience seizures. Doctors may also use an EEG to understand when a person is seizure-free after receiving treatment.

Read more about encephalitis here.

Dementia involves a decline in a person’s cognitive abilities, including symptoms such as forgetfulness and impaired decision-making ability. Dementia is not a disease itself but is due to diseases such as Alzheimer’s disease and Lewy body dementia.

Dementia happens due to brain cell damage, and an EEG may detect abnormal brain activity. Dementia increases the risk of seizures, and an EEG can show whether a person with dementia experiences them.

Alzheimer’s and dementia resources

To discover more evidence-based information and resources for Alzheimer’s and dementia, visit our dedicated hub.

Was this helpful?

A degenerative disease describes when body parts, such as organs or tissue, lose function and deteriorate over time. A neurodegenerative disease occurs in the central nervous system (CNS). Alzheimer’s disease is the most common neurodegenerative disease, affecting more than 6.7 million Americans.

Other common degenerative diseases include:

A brain tumor is a growth of abnormal cells in the brain. Brain tumors may also form in other parts of the CNS, such as the spine. A brain tumor can be harmful (malignant) or unharmful (benign). It can affect the brain’s ability to perform functions such as thought, speech, movement, and memory.

To diagnose a brain tumor, a doctor may perform an MRI or CT scan. They may also use an EEG to detect abnormal brain activity and assess a person’s risk of seizures.

A stroke is a cerebrovascular disease that occurs when oxygen levels to the brain decrease, often resulting from a blockage in blood supply or a bleed. More than 795,000 people in the United States have a stroke each year, with 610,000 having one for the first time.

A doctor can use an EEG to determine whether a person’s symptoms are more likely from a stroke or a seizure.

A metabolic condition involves the body experiencing abnormalities in its ability to produce certain chemicals it needs to function. Metabolism refers to the many different chemical processes in the body. A metabolic condition can cause a buildup of chemicals that may lead to brain damage.

Metabolic conditions that can affect the brain include:

Doctors can use an EEG to understand how various metabolic conditions affect the brain.

A hormonal condition, or endocrine disorder, involves a disruption to the body’s hormone production.

Endocrine conditions typically cause high or low levels of certain hormones resulting in the body not responding correctly. This can sometimes affect the brain’s tissue and cause brain tumors.

Hormonal conditions that can affect the brain include:

Doctors may use an EEG to understand how various hormonal conditions affect the brain.

An EEG is a test that records the electrical activity of the brain. Doctors use it alongside other examinations and tests to diagnose neurological conditions, degenerative diseases, head injuries, and other conditions that affect the brain.

An EEG can help determine how a condition affects the brain and inform treatment decisions.