The corticopontine projection from the visual cortex in the cat. I. The total projection and the projection from area 17

Abstract

Summary Large lesions of the whole visual cortex (areas 17, 18 and 19) and small lesions (in most cases bilateral) of area 17 were made 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. Most of the lesions were made by thermocoagulation. The main results are as follows. (1) The visual cortex as a whole projects onto several sharply delimited, mainly transverse bands in the rostral half of the pontine nuclei. The exact localization of these bands has been compared with the terminal areas of the corticopontine fibers from other cortical regions as determined by the present author. Only a modest degree of overlap is possible between the projection areas of the visual cortex and of the sensorimotor cortex. (2) All parts of area 17 project onto the pontine nuclei. The projection from middle parts (representing roughly the central visual field) is sparse, whereas it is heavy from rostral and caudal parts (representing peripheral parts of the visual field). (3) The total projection from area 17 covers the same pontine region as does the projection from the visual cortex as a whole (areas 17, 18 and 19). (4) A topical localization is present within the pontine projection from area 17. Rostral parts (representing the lower visual field) project more laterally within the pontine nuclei than do caudal parts (upper visual field). Medial and lateral parts of area 17 also project differently onto the pontine nuclei.