Electroencephalogram (EEG)

An EEG is a noninvasive test that records the brain’s electrical activity through small sensors (electrodes) placed on the scalp. It measures the rhythmic patterns of brain waves and helps identify abnormalities in brain function.

Why is this test done?

Doctors order an EEG to help diagnose or monitor:

  • Seizure disorders (like epilepsy)

  • Unexplained spells (fainting, blackouts, confusion)

  • Brain injuries or tumors

  • Sleep disorders

  • Encephalopathy (general brain dysfunction)

  • Brain activity during coma

What happens during the test

  1. Preparation:

    • Electrodes are placed on the scalp using a special paste or cap.

    • No needles or shocks are used.

  2. Recording:

    • You’ll sit or lie quietly while the EEG records your brain activity.

    • You may be asked to:

      • Open and close your eyes

      • Breathe deeply and rapidly (hyperventilate)

      • Look at flashing lights (photic stimulation)

    • These tasks can help trigger certain brain wave patterns.

  3. Duration:

    • A routine EEG lasts 20–40 minutes (plus setup time).

    • Sometimes a long-term EEG (hours to days) is done, often with video, to capture events like seizures.

What it feels like

  • Completely painless.

  • You may feel cool gel or mild pressure when the electrodes are applied.

  • Some people find the flashing lights or hyperventilation uncomfortable, but it’s safe.

After the test

  • Electrodes and paste are removed; you can return to normal activities right away.

  • No lingering side effects.