Epilepsy

An irritable focus in the brain will activate that part of the brain intermittently. When it is in the motor area (which controls muscle movement) it shows as the classic "Grand mal" shaking seizure and may result in the person passing stool or urine during the attack. In other areas it may simply cause spells where people seem to "space out" (called absence seizures).

The EEG brain wave test to diagnose seizures is often only positive during a seizure and normal between attacks, so a negative EEG offers little useful information.