Electroencephalography (EEG) is a method for monitoring electrical activity in the brain. It uses electrodes placed on or below the scalp to record activity with coarse spatial but high temporal resolution. EEG can be used in cognitive research or to diagnose conditions such as epilepsy and sleep disorders. An EEG, or electroencephalogram, is a test that records the electrical signals of the brain. Doctors use it to help diagnose epilepsy and sleep disorders. 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 electrical 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. The machine is only recording the activity of the brain and does not stimulate it.