A study of the transition from spindles to spike and wave discharge in feline generalized penicillin epilepsy: EEG features

Abstract

Earlier work suggested that the epileptic bursts occurring in the form of spike and wave discharges in feline generalized penicillin epilepsy were closely related to spindles. The present study showed that after i.m. penicillin, spindles elicited by single-shock midline thalamic stimulation gradually change into spike and waves. Hybrid forms are often seen during the transition phase. The transformation of spindles into spike and waves initially involves an increase in amplitude and the development of positive phases of spindle waves. Furthermore, every second (or in cats with lesions of the midbrain reticular formation, every second and third) spindle wave is gradually eliminated and replaced by a slow wave. The remaining enhanced spindle wave becomes the spike of the spike and wave complex. In conformity with this development, spectral analysis shows that no gradual frequency shift occurs during this transformation, but that the intraburst frequency decreases by a half or a third in one step from that characteristic of spindles to that typical for spike and waves. Spindle and spike and wave frequencies vary from cat to cat, but the above ratios are constant across animals. The spike and waves of cats with lesions of the midbrain reticular formation resemble those of human generalized epilepsy more closely than those induced in intact animals. A continuous transition from spindles to spikes and wave is thus demonstrable suggesting that spike and wave bursts are elicited by the same thalamocortical volleys which normally induce spindles.