The corticopontine projection from the visual cortex in the cat. II. The projection from areas 18 and 19

Abstract

Small lesions (in most cases bilateral) were made of the cerebral cortical areas 18 and 19 in adult cats, and the ensuing degeneration in the pontine nuclei was studied with the silver impregnation methods of Nauta and of Fink and Heimer. The lesions were made by transdural thermocoagulation. Since large parts of areas 18 and 19 are buried in sulci, isolated lesions of these parts have not been achieved. The main results are as follows. (1) All parts of area 18 studied (rostral part, related to the lower visual field) project onto the pontine nuclei. (2) The fibers from area 18 terminate within mainly transverse bands in the rostral half of the pontine nuclei in the pontine regions that receive afferents from area 17. At least certain corresponding parts of areas 17 and 18 project onto identical pontine areas, and the projections from the two areas are about equally heavy. (3) There is suggestive, but not conclusive, evidence for a topical localization within the pontine projection from area 18. (4) It appears likely that all parts of area 19 situated on the convexity of the hemisphere project onto the pontine nuclei. Middle parts of area 19 (representing the central visual field) seem to project less heavily than more rostral parts. The fibers terminate mainly within a transverse band in the rostralmost part of the pontine nuclei. (5) The projections from areas 19 and 18 terminate in different parts of the pontine nuclei. No topical localization has been found within the pontine projection from area 19, but the material is inadequate to resolve this question. (6) A zone of cortex surrounding area 19 (the suprasylvian and the cingulate gyri) projects onto the same (but somewhat more extensive) pontine region as does area 19. (7) The results of the present and the preceding studies 10 are discussed with regard to physiological data on the relations between the visual cortex and the cerebellum.