EEG is a picture of brain waves made by the process of electroencephalography.
Each brain cell (neuron)
in the brain produces a tiny electrical charge; as more neurons
become active, the sum of these tiny electrical charges can
be detected on the surface of the scalp. The electrical activity
is recorded by placing small electrodes on the scalp; activity
is magnified 1 million times and recorded as brain waves.
These brain waves provide a picture of the activity going
on under the surface, inside the brain.
Brain waves occur in various patterns, and
so EEG activity can be used to determine whether a person
is awake or in one of several sleep stages; EEG activity can
also be used to evaluate coma or brain death.
Abnormal patterns of EEG activity can be
used to help diagnose such conditions as epilepsy,
simplex encephalitis and dementia.
Before undergoing brain surgery, patients sometimes undergo
an EEG in which the electrodes are inserted under the scalp,
on the surface of the brain, to allow more precise recordings.
Further reading: Illustrated Guide to Diagnostic Tests, 2nd
edition. Springhouse Corporation, Springhouse PA, 1998
by Catherine E. Myers. Copyright © 2006 Memory Loss and the Brain