Electroencephalogram (EEG) :

An electroencephalogram (EEG or brain wave test) is a noninvasive procedure used to detect and record brain cell activity. Because normal brain waves have recognizable frequencies and amplitudes, variations or abnormalities in brain waves may suggest the following:

Attention deficit disorders (e.g., ADHD)
Seizure disorders (e.g., epilepsy)
Tumors or abscesses in the brain
Head injury
Encephalitis and other inflammatory diseases
Cerebral hemorrhages
Cerebral infarct (stroke)
Sleep disorders
Alcohol or drug abuse
Migraines (in some cases)
Hallucinations
Syncope (loss of consciousness)
Vertigo
An EEG also is used to confirm brain death in a patient who is in a coma. This neurodiagnostic test is not used to measure intelligence or diagnose mental illness.

EEG Preparation :
Patients usually are advised to wash their hair the night before the procedure, using no oils, sprays, or conditioners. Patients also should avoid caffeine for at least 8 hours prior to an EEG. If the test will be used to measure brain activity while sleeping, the patient way be asked to reduce or even eliminate their sleep time the night before. Some patients are advised to stop the use of medications before an EEG, but it is important not to do so unless directed by a physician.