An electroencephalogram (EEG) is a test that detects, measures, and records patterns of electrical activity in the brain. Neurologists may use an EEG to investigate the cause of certain neurological conditions, including seizures.
An EEG device consists of electrodes, or sensors, that attach to the scalp. These electrodes detect and transmit brain activity data to an external machine that displays the data on a graph.
An EEG is generally very safe. However, the procedure may include stimuli that can induce seizure activity in people with epilepsy. A person who experiences a seizure during an EEG will receive immediate medical treatment.
This article describes how an EEG can detect seizures and what happens during the procedure. It also provides information on preparing for an EEG, the risks involved, and some other methods of diagnosing seizures. Finally, the article answers some frequently asked questions about EEGs for seizures.
Nerve cells within the brain
An EEG consists of small electrodes that attach to the scalp and connect to an external machine via electrical cables. The machine displays the brain’s electrical currents as waves on a graph.
Medical professionals refer to the shape and pattern of the waves as a “trace.” Some factors that can affect the trace include:
- whether the person is awake or asleep
- how tired the person is
- whether the person talks or
movesduring the test
- whether the person is currently having an epileptic seizure
- the stimuli the person is exposed to during the test
- certain medications, such as benzodiazepines
If a person has an epileptic seizure during an EEG, their brain activity fits a pattern that doctors refer to as epileptiform brain activity (EBA). This brain activity produces a spike-and-wave pattern on an EEG graph, meaning the waves appear high and steep.
Other ways EBA
People can also have EEG abnormalities without epilepsy.
An EEG is a tool doctors use to help investigate the cause of certain neurological conditions,
A doctor may use an EEG to:
- assess the type of seizures a person has
- find the cause of seizures or determine where the seizures originate in the brain
- rule out other conditions that may mimic seizures, such as a stroke or central nervous system (CNS) conditions
An EEG to diagnose seizures typically consists of the following
- Step 1: A technician sets up the EEG machine in a quiet room with controllable lighting.
- Step 2: The person relaxes in a reclining chair or lies on a bed.
- Step 3: The technician uses a special paste to attach the electrodes to the person’s scalp. Alternatively, the technician asks the person to wear a cap, which has the electrodes attached to it.
- Step 4: The technician instructs the person to close their eyes, relax, and remain still.
- Step 5: The technician runs the first brain wave recording while the person is at rest.
Once the technician records the person’s brain activity, they introduce different stimuli to trigger epileptiform brain waves. The technician then records any associated changes to the EEG pattern.
Sometimes a person
Below are some EEG stimuli a technician may administer when recording brain activity during an EEG.
A technician may perform an EEG when the person is drowsy or asleep. Doing so helps doctors detect EBA more easily in a person with epilepsy.
Technicians may also record a person’s EEG trace while the person sleeps overnight. In such cases, a person may need to reduce their sleep the night before the test, or not sleep at all.
During the EEG, the technician may expose the person to a bright flashing light or flickering lights. Medical professionals refer to this kind of stimuli as photic stimulation.
The technician may ask the person to breathe deeply and rapidly for a few minutes at a time.
A doctor will
An EEG is generally very safe and does not cause pain or discomfort.
Doctors typically ask people to avoid the following before an EEG:
- consuming foods or drinks containing caffeine within 8–12 hours of the EEG
- fasting, since low blood sugar levels may influence the results of the EEG
- using hair conditioner or hairstyling products before the EEG, as this can prevent the electrodes from sticking to the scalp
- taking any medication that can interfere with the EEG, though people should not stop taking a medication unless their doctor advises them to do so
A person does not need to shave their head for an EEG.
There is no single test doctors use to diagnose epilepsy in people who experience seizures. An EEG only shows if a person has a seizure at the time of the test, not if they have had seizures before.
An EEG also looks for abnormalities that may indicate they are at risk of seizures. Therefore, even if a person’s EEG results do not show any unusual brain activity, it will not rule out epilepsy.
Likewise, people without epilepsy can have EEG results that show irregular brain activity.
Ultimately, doctors use a person’s EEG results together with their symptoms and medical history to diagnose seizures or determine their cause.
In rare cases, the stimuli a technician administers during an EEG can trigger seizures in people with seizure disorders. If a person experiences a seizure during an EEG, they will receive immediate treatment.
Some factors doctors may consider when diagnosing seizures include:
- the person’s medical history
- information about the person’s seizures, such as triggers, or what happens during the seizure
- brain scans, such as MRI or CAT scans
Below are answers to some frequently asked questions about EEG for seizures.
Do all seizures show up on an EEG?
Any seizure normally causes a change to an EEG reading. However, an EEG reading cannot prove that a person does or does not have epileptic seizures unless they experience a seizure during the test.
How soon after a seizure can an EEG be done?
Doctors recommend performing an EEG as soon as possible after a person has a seizure. Doing so increases the chances that abnormal patterns of brain activity will still be detectable on the EEG reading.
For routine EEGs, a doctor typically interprets the results within
Can an EEG predict seizures?
An electroencephalogram (EEG) is a test that detects and measures patterns of electrical activity in the brain. Neurologists may recommend an EEG to help diagnose seizures or determine their cause.
An EEG is generally a very safe procedure. However, to find evidence of seizure activity in the brain, technicians may need to use stimuli that can induce seizures in people with epilepsy. Anyone who experiences a seizure during an EEG will receive immediate medical treatment.
There is no single test to diagnose epilepsy. Instead, doctors typically use EEG results along with a person’s symptoms, medical history, and other tests. A person can talk with their doctor for more information on EEGs for seizures.