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Electroencephalography (EEG) (cont.)

During the Procedure

A standard noninvasive EEG takes about 1 hour. The patient will be positioned on a padded bed or table, or in a comfortable chair. To measure the electrical activity in various parts of the brain, a nurse or EEG technician will attach 16 to 20 electrodes to the scalp. The brain generates electrical impulses that these electrodes will pick up. To improve the conduction of these impulses to the electrodes, a gel will be applied to them. Then a temporary glue will be used to attach them to the skin. No pain will be involved.

The electrodes only gather the impulses given off by the brain and do not transmit any stimulus to the brain. The technician may tell the patient to breathe slowly or quickly and may use visual stimuli such as flashing lights to see what happens in the brain when the patient sees these things. The brain's electrical activity is recorded continuously throughout the exam on special EEG paper.

  • Sleep EEG: During a specialized sleep EEG, the patient will be placed in a room that encourages relaxation and asked to fall asleep while the brain's electrical activity is recorded. The sleep EEG will last about 2 to 3 hours.
  • Ambulatory EEG: During a specialized ambulatory (moving from place to place, walking) EEG, the electrodes are placed on the patient's scalp and attached to a portable cassette recorder. The patient will be allowed to go home and resume normal activities while the EEG continuously records. The ambulatory EEG typically lasts 24 hours.
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