Visuotopic organization of projections from striate cortex to inferior and lateral pulvinar in rhesus monkey

Abstract

Anatomical material from two series of monkeys Macaca mulattawas used to determine the full extent and visuotopic organization of striate projections to the pulvinar. One series was processed for degeneration by the Fink‐Heimer procedure following unilateral lesions of lateral, posterior, or medial striate cortex (representing the central, peripheral, and far peripheral visual field, respectively); collectively, the lesions included all of area 17. The second series was processed for autoradiography following tritiated amino‐acid injections into striate sites representing the center of gaze and eccentricities ranging from 0.5° to greater than 30° from fixation in both the upper and lower fields. The results indicate the existence of two separate striate projection zones within the pulvinar. One, the PI/PL zone, is located primarily within the inferiorpulvinar (PI) but extends into the adjacentlateral pulvinar (PL). The other, the PL zone, is located entirely within the lateral pulvinar and partially surrounds the first zone along its dorsal, lateral, and ventral aspects. Within the PI/PL zone, striate projections are topographically organized and represent the entire contralateral visual field. Central vision is represented laterally and posteriorly, with the fovea represented at the caudal pole of the nucleus; conversely, far peripheral vision is found medially and anteriorly, adjacent to the medial geniculate nucleus. The representation of the horizontal meridian runs obliquely across PI/PL, such that the upper visual field is located ventrolaterally and the lower visual field dorsomedially. The representation of the vertical meridian is located along the lateral margin of PI in anterior sections of the pulvinar, but within PL in posterior sections. Thus, the vertical meridian appears to form the border between the lateral margin of the PI/PL zone and the medial margin of the PL zone. At the lateral margin of the PL zone is the representation of its horizontal meridian. Striate projections to the PL zone, unlike those to the PI/PL zone, are limited to the representation of central vision. These results suggest that striate inputs contribute to the visual properties of neurons (Bender, 1981 a) throughout the PI/PL zone, but are insufficient to explain the visual properties of neurons outside of the central visual field representation in the PL zone. Copyright © 1983 Alan R. Liss, Inc.