What happens during an electroencephalogram (EEG)?
During an EEG, you lie down on the exam table or bed, and a technician puts about 20 small sensors on your scalp. These sensors, called electrodes, pick up activity from cells inside your brain called neurons and send them to a machine, where they show up as a series of lines recorded on moving paper or displayed on a computer screen.
You'll relax with your eyes open first, then with them closed. The technician may ask you to breathe deeply and rapidly or to stare at a flashing light, because both of these can change your brain wave patterns.
From: What Is an EEG (Electroencephalogram)? WebMD Medical Reference
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