Corticocortical connections of the cat sensory areas studied by means of retrograde axonal transport of horseradish peroxidase.

Abstract

Afferent association connections to each functional cortex, i.e., the auditory, sensorimotor, visual and association cortex, was investigated in the cat with the method of retrograde axonal transport of horseradish peroxidase (HRP). After injections of HRP in various parts of the cerebral cortex, a large number of labeled cells were found within the same functional areas; while a small number of cells were labeled in other cortical areas. Small parts within the functionally uniform cortical area are evidently strongly interconnected by short association fibers. Labeled cells were found both in the cortex of the gyral surfaces and sulcal walls. Corticocortical neurons in the walls of some sulci also sent their axons to various sensory areas. Cells of origin of association fibers were mostly pyramidal in shape, occurring mainly in layer III of the various cortical areas (about 70% of the total number). Following injections of HRP suspension into the visual cortex, the majority of labeled cells (82%) were found in layers V and VI of the Clare-Bishop area; some were polygonal. Somal diameters of the labeled cells were 15.8-17.2 .mu.m (mean) .+-. 2.5-3.0 (SD).