This brief study was made as a corollary to previous experimental work on additional motor areas of the macaque monkey. The region of the island cortex is shown in figures 6A and B, as it relates to the opercular areas of the matching cerebrum. Although there is not general agreement as to the homology of the insula (von Bonin and Bailey, '47, Frontera, '56) of monkey with that of man, it appears that two varieties of cortex can be distinguished in both. Von Bonin and Bailey ('47) describe agranular cortex at the limen as the dominant histologic feature, although some granular cortex is found in the caudal part of the insula. Several authors (von Bonin and Bailey, '47; Kaada, Pribram and Epstein, '49 and Kaada, '51) emphasized the presence of discernible rostra1 motor cortex and caudal sensory cortex in the island.Frontera's ('55) description of the macaque insula will be used as reference here. Branches of the middle cerebral artery divide the island into a dorsorostral portion and a ventrocaudal portion without there being evidence of true gyri and sulci ( fig. 6A). The dorsorostral insula is covered by the frontoparietal operculum of the Walker ('40) areas 6, 4, and 1, and the ventrocaudal region by the temporal operculum of area 22 of the superior temporal gyrus ( fig. 6B).
Cardiovascular and respiratory changes resulting from systematic stimulation of the hippocampal formation of the monkey were recorded. Stimulation of the anterior portion of the hippocampus resulted in a marked depression or cessation of respiratory excursions, but without apparent changes in respiratory rate. Respiratory changes were minimal to absent when posterior regions of the hippocampus were activated. Anterior hippocampal stimulation resulted in an initial depression of blood pressure accompanied by a small drop in pulse rate, followed by a rise in blood pressure which lasted throughout the period of stimulation and then gradually returned to former levels. The duration of the rise in blood pressure following cessation of stimulation was directly correlated with hippocampal activity. Posterior hippocampal stimulation did not show the secondary rise in pressure, only the depression. Marked pulse changes occurred only when the hippocampal gyrus was secondarily activated or stimulated directly. The neuron pathways which mediated these responses fall into two general groups, the fornix system and a hippocampotemporal system or both. A hypothesis that both systems may be concerned in visceral responses is presented.
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