Anatomical connections of visual system with limbic cortex of monkey

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Abstract
The question of anatomical connections between the visual system and the temporo‐occipital limbic cortex was investigated in 24 squirrel monkeys (Saimiri sciureus) with the utilization of stains for showing fine degenerating cortical fibers. Lesions of various size were placed in the geniculo‐pulvinar complex by electrocoagulation. Electrodes were usually inserted in the Horsley‐Clarke frontal plane, but in two cases lesions of the lateral geniculate body were made by an extracerebral approach.With a lesion well confined to the ventrolateral part of the lateral geniculate body, heavy degeneration appeared in the inferior longitudinal fasciculus and continued into its ventromedial extension designated as band 3 in the core of the posterior hippocampal gyrus. Some degenerating fibers could be traced from band 3 into the cortex of this gyrus, as well as into adjoining cortical areas in the fusiform and lingual gyri. Sparse degeneration in the postsplenial cortex could not be excluded as arising from the lesion made by an electrode in approaching the lateral geniculate body in the frontal plane. Degeneration in band 3 did not extend as far forward as the entorhinal cortex in the anterior hippocampal gyrus. In two animals with small rostral lesions of the lateral geniculate body made by the extracerebral approach, some degeneration also extended into band 3, supporting other control observations that such degeneration is not dependent on the destruction of tissue made by an electrode in approaching the lateral geniculate body in the frontal plane.When a lesion involved the inferior pulvinar as well as the lateral geniculate body, heavier degeneration appeared in the posterior hippocampal, fusiform, and lingual cortex. With a large lesion of the inferior pulvinar, a band of degeneration appeared ventrolateral to the optic radiations and was traced into these same cortical areas.The anatomical results are discussed in the light of recent microelectrode findings of photically responsive units in the cortex of posterior hippocampal gyrus and adjoining cortical areas. The combined evidence suggests an explanation for the temporal detour made by that part of the optic radiations commonly referred to as Meyer's temporal loop.