The spread of after-discharge from stimulation of the rhinencephalon in the cat

Abstract

1. 1. The spread of after-discharge following electrical stimulation of the dorsal and ventral hippocampus, septum, basal and lateral amygdaloid nuclei, and the anterior sigmoid gyrus has been studied in locally anesthetized cats and in animals anesthetized with Dial. 2. 2. From each stimulated focus after-discharge was found to spread diffusely to subcortical and paleocortical areas, but the overall epileptoid response varied in character and some areas remained negative. Propagation of after-discharge to the dorsolateral isocortex was less diffuse than that to subcortical brain levels. 3. 3. Following stimulation of each area investigated, rhythmic after-discharge of high amplitude was recorded from certain brain structures and these corresponded with the same areas that fired at liminal stimulation of the same foci in animals anesthetized with Dial. These were predominantly rhinencephalic and hypothalamic nuclei when rhinencephalic areas were stimulated and structures of the pyramidal and extrapyramidal systems when the anterior sigmoid gyrus was stimulated. 4. 4. The medial geniculate body, ventrolateral reticular formation and associational thalamic nuclei responded prominently to each of the rhinencephalic structures stimulated. 5. 5. After-discharge of certain areas appeared to be distinctive, such as: activation of the ventral thalamus following ventral hippocampal stimulation; the intralaminar thalamic nuclei after dorsal hippocampal stimulation; the sensorimotor cortex after basal amygdaloid stimulation; and superior colliculus and lateral geniculate nucleus after stimulation of the septum. 6. 6. It is concluded that each area stimulated has a pattern of ictal projection to the subcortex, paleo- and juxtallocortex and neocortex that is sufficiently distinctive, but that there is considerable overlap in the main projection areas of each rhinencephalic focus. There is a strong contrast between the propagation pattern of after-discharge from the rhinencephalon and that originating in the anterior sigmoid gyrus. 7. 7. The possible correlation of certain features of rhinencephalic after-discharge with autonomic and behavioral effects generally known to follow rhinencephalic stimulation or ablation, and with clinical effects of psychomotor epilepsy have been discussed.