Retinotopic organization of macaque pulvinar

The retinotopic organization of the inferior and lateral pulvinar in rhesus monkeys was investigated using tungsten microelectrodes and extracellular recordings. The animals were immobilized with gallamine triethiodide and anesthetized with a nitrous oxide-oxygen mixture. Both the inferior and lateral nuclei were found to be visually responsive. Two complete representations of the contralateral hemifield occupy most of this territory. One representation lies mainly within the inferior pulvinar but extends somewhat into the adjacent lateral pulvinar. The vertical meridian lies in the dorsal and lateral margins of the inferior pulvinar while the periphery is found in the medial margin adjacent to the medial geniculate body. The fovea and central vision are represented laterally and posteriorly. A second representation of the hemifield lies entirely within the lateral pulvinar and partially surrounds the first along its dorsal, lateral, ventral, and caudal aspects. The lower quadrant of te second map lies in the dorsal half of the lateral pulvinar, the upper quadrant is found almost completely separated in the ventral half. A double representation of the horizontal meridian forms the outer boundary of the second representation and lies in the external margin of the pulvinar. The two maps share a common representation of the vertical meridian and the pattern of topography reverses in crossing this joint boundary from one map to the other. The physiologically defined boundary between the two representations, i.e., the representation of the vertical meridian, does not coincide with the cytoarchitectonic boundary between the inferior and lateral nuclei but, instead, coincides with the medial edge of a fiber system that fills the external half of the lateral pulvinar. Both visuotopic maps encompass virtually the entire visual hemifield. Receptive-field size for cell clusters in te two visuotopic zones is the same and, for both regions, increases with increasing eccentricity.