The subcortex and hypothalamic after-discharge in the cat.

Abstract 1. 1. Using adequate electrical stimuli, seizure activity (EEG) can be induced in the hypothalamus, from stimulation of telecephalic, diencephalic, and mesencephalic structures. 2. 2. Structures which are most effectively epileptogenic for hypothalamic activity are topographically diffuse but are primarily rhinecephalic. These strucutres are: the hippocampus, basal and cortical amygdalar nuclei, the septum, and basal olfactory areas. 3. 3. Structures which produce ictal activity in the hypothalamus, and for which evidence of direct connection is not generally known or is lacking, are: the gyrus cinguli, prepyriform, pyriform and hippocampal cortices, claustrum, lateral amygdaloid nucleus, anterior thalamic nuclei, and olfactory striatum. 4. 4. Structures which are not generally known to be connected to either the rhinencephalon or hypothalamus, but which when stimulated, produce seizure potentials in the hypothalamus are: the lateral anterior, pulvinar, lateral posterior, and lateral geniculate thalamic nuclei, the superior colliculus, putamen and central gray matter. The neural pathways over which they produce this activity are not clear, except that the thalamic nuclei mentioned most likely produce their effect indirectly through the temporal cortex, as discussion of the anatomical literature suggests. 5. 5. Voltage and frequency thresholds for the production of ictal after-discharge in the hypothalamus were obtained for the hippocampus, amygdalar nuclei, septum, and basal olfactory region. On the basis of the least voltage and frequency values necessary to activate the hypothalamus, these structures are irritable in the order mentioned; namely, hippocampal structures first, followed by amygdalar and septal areas, and finally the olfactory region. 6. 6. Concerning the epileptoid activity produced in the hypothalamus, study of the EEG records provides the following characteristic features. Most consistent findings showed that: (a) the dorsal hippocampus preferentially fires the mammillary body, whose ictal potentials are more often of gradual onset; (b) highest potentials are obtained from stimulation of the basal amygdala, hippocampus, and septum; (c) the fastest hypothalamic fit frequencies are obtained from the stimulation of the septum and hippocampus; (d) the ventromedial hypothalamic nucleus fires most frequently at higher potentials from stimulation of the majority of rhinencephalic structures than does the mammillary body, and the latter is more actively responsive than the preoptic region; (e) ictal response of the hypothalamus to stimulation of the gyrus cinguli often occurs late. 7. 7. By reason of their different threshold irritabilities, the possibility exists that several rhinencephalic systems, in their natural function, can affect the hypothalamus selectively, thus accounting in some way for the varied patterns of autonomic response in the expression of various emotions. 8. 8. Distinct organizations within the rhinencephalic and limbic systems probably exist, and anatomical considerations alone would attest to their mutual influence. All such systems, however, have a common terminus, the hypothalamus. The latter, though perhaps adequate for autonomic balance in sterotyped metabolic and thermal regulations, cannot be considered as the highest integrator of the varied and phasic autonomic effects accompanying emotional and behavioral phenomena. 9. 9. Due to the widespread distribution of rhinencephalic-limbic mechanisms in the brain, each having their influence on the hypothalamus, it is understandable how autonomic and behavioral mechanisms, though not always detected, could scarcely be lacking in the various types of epilepsy, regardless of the location of the epileptogenic lesion. For the same reason, so-called purely autonomic epilepsy can have a varied origin and particular pathologic physiology.