LATERAL DIVISION OF THE LATERAL POSTERIOR REGION - CONNECTIONS WITH AREA-18 IN CATS

To establish the topography of the lateral division of the lateral pos terior region (LP1) projections to area 18, up to five different anato mical 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 ros tral nuclei and were topological, organized in patterns that indicate that lower visual space is represented anteroventrally, and more centr al and upper visual space is represented caudodorsally. In the caudal LP1 nucleus, patches of labeled cells formed bands that ran parallel t o the medial and lateral LP1 borders and encompassed medial portions o f the nucleus. In rostral LP1, the patches of labeled cells formed clu sters giving the connections with area 18 a more modular appearance, a nd were nearer the lateral LP1 border. Injections made nearest area ce ntralis representations in area 18 labeled more neurons than injection s in cortex representing more peripheral visual space. Also, neighbori ng 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, t hat two retinotopically organized nuclei constitute LP1.