Electroencephalogram | Procedure and Working of EEG

Electroencephalogram (EEG)

The Electroencephalogram (EEG) is a test that measures the electrical activity in the brain.

An EEG measures brain waves through small button electrodes that are placed on the scalp.

Electroencephalogram (EEG) procedure is painless and can help diagnose a number of conditions such as

  • Degeneration of brain tissue
  • Certain disorders of the central nervous system
  • Stroke
  • Brain tumour
  • Sleep disorders (such as narcolepsy)
  • Head injuries
  • Brain infection
  • Hormonal conditions that affect brain tissue
  • Brain haemorrhage
  • Metabolic conditions that affect brain tissue

Electroencephalogram (EEG) procedure:

Your hair must be thoroughly clean and recently shampooed. You lie down on the examining table or bed while eight to 20 electrodes are attached to your scalp.

A gel may be applied to help the electrodes to stick firmly in place. You will need to lie quietly to avoid any electrical interference from muscle contractions. Sometimes, you are asked to relax and lie first with your eyes open, and then closed.

You may be asked to breathe deeply and fastly or to watch at a flashing light both of which produce changes in the brain-wave patterns.  An EEG normally takes from 30 to 60 minutes to complete. Sometimes, a sleep recording is also required.

Immediately after the Electroencephalogram (EEG) procedure:

Once the test is complete, the electrodes are removed and the glue that held them in place is washed away with acetone. The results need to be analysed at a later stage by a neurologist.

Generally, if there is no abnormality to the brain's electrical activity, the pattern of 'peaks and valleys' charted by the EEG should be fairly regular. If excited, the pattern will show considerable variation, and any departure from the regular pattern can indicate abnormalities.

How Electroencephalogram (EEG) works:

Electrical signals produced by the brain neurons are picked up by the electrodes and sent to a polygraph, where they produce separate graphs on moving paper using an ink writing pen or on a computer screen.


  • It's highly informative.
  • It's noninvasive.


  • Electroencephalogram (EEG) is less helpful than imaging techniques in determining the location of injuries or their precise nature for some diseases such as stroke.
  • a person with epilepsy may experience a seizure, triggered by the various stimuli used in the procedure, including the flashing lights.

Taking care of yourself at home:

Electroencephalogram (EEG) is a safe procedure. Take advice from the doctor, but generally, there are no special instructions for after-care. However, you need to wash your hair thoroughly to remove all traces of gel and other fluids.


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