Electroencephalogram (EEG)

An electroencephalogram (EEG) is a diagnostic test that records the electrical activity of the brain by placing small sensors on the scalp.

Brain cells communicate with each other through tiny electrical signals. The EEG picks up these signals through sensors called electrodes, which are attached to the skin of the scalp with a sticky gel or paste. The signals are then displayed as wavy lines on a screen or paper. A neurologist — a doctor who specialises in the brain and nervous system — studies these wave patterns to see whether the brain's electrical activity looks normal or shows signs of a problem.

Doctors order an EEG when they need to understand what is happening inside the brain's electrical system. It is most commonly used to investigate seizures (sudden bursts of uncontrolled electrical activity in the brain), but it helps with a range of other neurological conditions as well.

• Epilepsy — to confirm a diagnosis, identify the type of seizure, or guide treatment decisions
• A first unexplained seizure — to check whether the brain's electrical pattern puts a person at risk of further seizures
• Fainting spells or blackouts that may be coming from the brain rather than the heart
• Sleep disorders such as narcolepsy (sudden uncontrollable sleepiness) or unusual movements during sleep
• Encephalitis (inflammation of the brain) or encephalopathy (general disruption of brain function), to assess severity
• Monitoring a patient who is in a coma or under heavy sedation in an intensive care setting
• Checking the level of brain activity when brain death is being assessed

An EEG is generally not the right test when the symptoms are clearly caused by a structural problem — such as a tumour, stroke damage, or a bleed — that is better seen with imaging tests like MRI or CT. Your doctor will decide which test, or combination of tests, best fits your situation.

An EEG is a non-invasive test — nothing enters the body — and it carries almost no physical risk. The electrodes only record electrical signals; they do not send any electricity into the brain.

• Mild scalp irritation or redness where the gel or paste was applied — this usually fades within a few hours
• Tangles or temporary stickiness in the hair from the electrode gel, which washes out easily
• In a sleep-deprived EEG, where the patient is asked to stay awake through the night beforehand, tiredness and difficulty concentrating on the day of the test are expected
• In a photic stimulation (flashing light) part of the test, a very small number of people who already have photosensitive epilepsy may experience a brief seizure — medical staff are present and trained to respond immediately
• Anxiety or distress during the test, particularly in children or people who feel uncomfortable in enclosed or clinical settings — the procedure is painless, but the environment can feel unfamiliar

Preparing well helps produce a clearer recording and makes the appointment run smoothly. Your doctor or the EEG department will give you specific instructions; the points below describe what is typically advised.

On the day before and the day of the test, wash your hair thoroughly but do not apply conditioner, hair oil, spray, or styling products afterwards. These coat the scalp and make it harder for the electrodes to pick up signals. Avoid caffeine — found in coffee, tea, energy drinks, and some soft drinks — for at least several hours before the test, as caffeine affects brain activity. You do not usually need to fast (go without food) for a standard EEG, but confirm this with your doctor. If a sleep-deprived EEG has been requested, you will be asked to stay awake through the night before the test.

Do not stop taking any regular medication unless your doctor has specifically told you to. Some medications can be adjusted beforehand for certain types of EEG, but that decision belongs to your doctor. Let the EEG team know about every medication you are taking, including herbal supplements.

Before the EEG, the team may check a brief medical history and note any symptoms. No blood tests or imaging scans are needed as routine preparation for an EEG itself.

During the procedure, the steps typically follow this order:

• You sit in a reclining chair or lie on a bed in a quiet room.
• A technician measures your head and marks the correct positions for the electrodes using a soft pencil or removable marker.
• The skin at each marked spot is lightly cleaned, and a small amount of conductive gel or paste is applied.
• The electrodes — usually between 20 and 30 small metal discs — are attached to the marked spots and held in place with the gel, a cap, or light adhesive.
• You are asked to lie still, relax, and breathe normally. Closing your eyes is often encouraged.
• The technician may ask you to do specific tasks during the recording: breathe deeply and rapidly for a few minutes (hyperventilation), look at a flashing light (photic stimulation), or — if a sleep study component is included — try to fall asleep.
• The recording runs for the time your doctor has requested, which can range from around 20 minutes for a routine EEG to many hours for a prolonged or ambulatory study.
• Once the recording is complete, the electrodes are removed and any gel is cleaned from your scalp and hair.

Because an EEG records rather than treats, recovery is minimal for most people. You can usually return to normal activities the same day, though there are a few things to be aware of depending on how the test was conducted.

• If you had a sleep-deprived EEG and stayed awake all night, you will feel tired after the test. Arrange for someone else to drive you home, as drowsy driving is dangerous.
• If a sedative (a calming medication) was given to help a child or anxious adult sleep during the test, the person will need to be supervised until the medication has fully worn off, and driving is not allowed on that day.
• You can wash your hair as normal after leaving the clinic to remove any remaining gel.
• Resume all regular medications as usual unless your doctor has given different instructions.
• There are no dietary restrictions or wound care requirements after a standard EEG.
• The raw recording will be reviewed and interpreted by a neurologist; results are not usually given at the time of the test itself. Ask the clinic how and when you will receive the report.
• A follow-up appointment with your referring doctor or neurologist is typical, so that the EEG findings can be explained in the context of your full clinical picture and next steps can be discussed.