Rhinencephalic spikes and beta waves in the cat under pentobarbital

Abstract

Spontaneous electrical activity of the rhinencephalon was studied in the cat under varying depths of pentobarbital anesthesia. Under light anesthesia a distinctive electrical pattern, characterized by an amplitude of over 50 µv and a predominant frequency of 15–50 cycles/sec, has been localized to three structures—the hippocampus, prepyriform cortex, and ventromedial nucleus of the hypothalamus. With increasing depth of anesthesia this pattern is replaced, in each of these structures, by a low-frequency spikelike one. The frequency of both the light and deep anesthesia patterns is highest in the prepyriform cortex, and the deep anesthesia spikes of the hippocampus and ventromedial nucleus are synchronous with prepyriform spikes. Light and deep anesthesia patterns of the prepyriform cortex and hippocampus have their maximum potential gradient in the region of the pyramidal cell layer. Although the spike pattern is not bilaterally synchronous, with very deep levels of anesthesia flat intervals appear between trains of spikes, and these intervals are bilaterally synchronous.