EEG measures the activity of brain. In this test electrodes are applied over the patients head and voltage differences in various parts of the brain are recorded. These voltage differences represent activity in that region of the brain. The test is completed in 30-40 minutes. The machine has an attached video camera which helps in visualizing the abnormal movements of the patient during the recording. EEG is most useful in patients of epilepsy; especially in diagnosing the type of epilepsy, in localizing the focus of seizures, in prognosticating the patient, in helping the physician in choosing the appropriate drug for the patient. EEG is a very important parameter in diagnosing brain death. It is also helpful in patients of encephalopathy, encephalitis, brain tumors etc.