Percutaneous recording of the electrical potentials associated with cerebral activity confirms that an epileptic attack is associated with a sudden abnormal electrical discharge form cerebral neuroses. Sub threshold paroxysms may be demonstrable between clinical attacks. The EEG phenomena indicate that the differences in type of seizure are due to the site of the initial abnormal discharge of cerebral neurons and the mode of spread. One group originates in the upper brain stem (termed the cent encephalon by Penfield) the simultaneously disturbed function in both cerebral hemispheres; the site of discharge is believed to be the upper reticular formation because in grand mal and petit mal suspension of consciousness is invariable.