Lateral division of the lateral posterior region: connections with area 18 in cats.

Abstract

To establish the topography of the lateral division of the lateral posterior region (LP1) projections to area 18, up to five different anatomical tracers were injected in separate rostrocaudal locations in area 18 of four adult cats, and patterns of retrogradely labeled LP1 cells were identified. LP1 inputs to area 18 arose from both caudal and rostral nuclei and were topological, organized in patterns that indicate that lower visual space is represented anteroventrally, and more central and upper visual space is represented caudodorsally. In the caudal LP1 nucleus, patches of labeled cells formed bands that ran parallel to the medial and lateral LP1 borders and encompassed medial portions of the nucleus. In rostral LP1, the patches of labeled cells formed clusters giving the connections with area 18 a more modular appearance, and were nearer the lateral LP1 border. Injections made nearest area centralis representations in area 18 labeled more neurons than injections in cortex representing more peripheral visual space. Also, neighboring injections in area 18 labeled overlapping patches of cells, but no double-labeled cells were observed. These findings are consistent with previous conclusions based on electrophysiological mapping studies, that two retinotopically organized nuclei constitute LP1.