Interpretation of the electroencephalogram.

The background pattern is described in terms of frequency and amplitude. Waves of varying frequencies may be normal or abnormal, depending on the patient's age and state of wakefulness. Specific features sought in the EEG are slowing of frequency, asymmetry of frequency or amplitude, paroxysmal disturbances, and spikes and sharp waves. Certain abnormalities may be present only after provocation by hyperventilation, sleep deprivation or induction, photic stimulation or drugs.