Sleep spindles in the human hippocampus: normal or epileptic activity?

Spindles of 12-14 Hz were recorded in the hippocampus of 13 epileptics during sleep. This activity was more prominent in patients in whom the hippocampal region was not the site of the primary focus and in whom the electrical activity was normal during wakefulness. Spindles were more numerous during stage 2 non-rapid-eye-movement sleep, especially in patients who had seizures in this stage. It is postulated that this activity is either a normal activity of human brain or an evoked response of the hippocampus to an epileptic afferent discharge. In either case, hippocampal spindles may contribute to the triggering of nocturnal seizures.