Forebrain Commissures and Vision

Abstract

The splenium of the corpus callosum has two functions in vision which have been clearly defined: depth discrimination (Mitchell and Blakemore, 1970) and control of ocular vergence movements (Westheimer and Mitchell, 1969), both utilizing information concerning image disparity on the two retinae for objects lying on the visual axis. The splenial system also undoubtedly mediates some unification of the two halves of the visual field, a process particularly difficult in mammals, such as the rabbit (Thompson et al., 1950; see below), that have laterally directed eyes and an ipsilateral retinocortical projection widely separated from the contralateral projection in its representation of the visual field. The splenium also carries information between the limbic and visual systems pertinent to recognition of the significance of visual stimuli, as for fearful or edible objects (Downer, 1962; Horel and Keating, 1969; Doty et al., 1971). In addition to these functions in sensorial analysis or efferent integration, the corpus callosum has a major mnemonic function. This mnemonic processing is required to achieve full utilization of the capabilities of the cerebral hemispheres by giving access from each hemisphere to information stored in the other (i.e., engram “read out”). Electrical stimulation of the corpus callosum, including the splenium, in man produces confusion of higher neural functions such as speech (Schaltenbrand et al., 1970).