EEG (Electroencephalography)

What is EEG (electroencephalography)?

The brain’s billions of nerve cells communicate through tiny electrical signals. When large groups of cells work together, these signals form rhythmic patterns called brain waves. An electroencephalogram (EEG) records these waves from the surface of the scalp and displays them as lines on a screen.

Brain waves change with age and with the state of the brain — wakefulness, drowsiness and sleep. A specialist reading the EEG looks at the background rhythm, its symmetry between the two halves of the brain, and any abnormal patterns. In epilepsy, characteristic epileptiform discharges — sharp waves, spikes or spike-and-wave complexes — may be seen, even between seizures.

An EEG does not measure intelligence, thoughts or emotions, and it does not deliver any electricity into the head. It only listens to the activity that the brain naturally produces.

What an EEG can and cannot show

• It can support a diagnosis of epilepsy and help determine the type of epilepsy
• It can show whether seizures start in one area of the brain (focal) or in both hemispheres at once (generalised)
• It can reveal slowing of brain activity in encephalopathy, infections or after a head injury
• A normal EEG does not rule out epilepsy — abnormal activity may not appear during a short recording
• An abnormal EEG alone does not always mean epilepsy; findings are always interpreted together with the clinical history

When is it requested?

An EEG is commonly requested in the following situations:

• A first seizure or suspected epileptic seizure
• Follow-up of known epilepsy, especially when considering changes or withdrawal of medication
• Brief absences, staring spells or unexplained episodes of unresponsiveness
• Fainting or loss of consciousness where the cause is unclear
• Sudden jerks, unusual movements or sensations
• Confusion, altered consciousness or suspected encephalopathy
• Memory problems or behavioural changes in certain situations
• After a head injury, brain infection or stroke when seizures are suspected

Who needs EEG (electroencephalography)?

An EEG can be performed safely at any age, from newborns to older adults, and during pregnancy. There is no radiation and no injection. People with epilepsy can usually continue their medication as normal unless their doctor advises otherwise.

Types of EEG

• Routine EEG: a 20–40 minute recording while awake, including activation procedures
• Sleep-deprived EEG: after a shortened night of sleep, to increase the chance of capturing abnormal activity
• Long-term (ambulatory) EEG: recording over 24–72 hours at home
• Video-EEG monitoring: EEG recorded together with video to capture and characterise actual episodes

How to prepare

• Wash your hair the night before or on the morning of the test; do not use oil, gel, conditioner or hairspray
• Eat as usual — low blood sugar can affect the recording
• Continue your regular medicines unless told otherwise, and bring a list of them
• Avoid caffeine on the day of the test if asked
• If a sleep-deprived EEG is planned, follow the instructions about how much to sleep the night before
• Bring any previous EEG and MRI reports
• If possible, bring a video of your episodes recorded by a family member

How is EEG (electroencephalography) performed?

• You sit in a comfortable chair or lie on a bed
• The technician measures your head and places about 20 small electrodes on the scalp using a conductive paste or a cap
• You are asked to relax with your eyes closed; at intervals you open and close your eyes
• Hyperventilation: you breathe deeply and quickly for about three minutes
• Photic stimulation: a flashing light at different frequencies is shown in front of your eyes
• If you fall asleep during the recording, this is useful — some abnormalities appear more clearly during sleep
• The electrodes are removed and the paste is wiped away

The activation procedures (deep breathing and flashing lights) increase the chance of detecting abnormal activity. Very rarely, they can trigger a seizure in a person with epilepsy; the test is always performed under supervision and with appropriate precautions.

Duration, results and your stay in Istanbul

Preparation takes 15–20 minutes and the recording itself 20–40 minutes; the whole appointment lasts about an hour. The EEG is analysed by a neurologist and the report is usually ready within one or two days, and often on the same day for international patients.

For patients travelling from abroad, the consultation and EEG can usually be completed in one day in Istanbul, with the results explained in English.

What the EEG report contains

The report describes the conditions of the recording (wakefulness, sleep, activation procedures), whether the background rhythm of the brain is normal for your age, any slowing, and the type and location of any epileptiform abnormalities. The technical terms in the report are explained at the consultation in relation to your own symptoms.

After the test

• You can return to your normal activities immediately
• Wash your hair to remove any remaining paste
• If you had a sleep-deprived EEG, avoid driving until you have rested
• The results are discussed together with your history and examination at the consultation

Risks and safety

EEG is a very safe test. There is no pain, radiation or electricity applied to the brain. The paste may cause mild skin irritation in people with sensitive skin. In people with epilepsy, hyperventilation, flashing lights or sleep deprivation may rarely provoke a seizure; this is why the test is performed under the supervision of trained staff.

Frequently asked questions about EEG (electroencephalography)