Interhemispheric connections of visual cortex in the owl monkey, Aotus trivirgatus, and the bushbaby, Galago senegalensis

Abstract

Anatomical techniques have been used to map within visual cortex th pattern of degenerating axonal terminals produced by surgical section of the splenium of the corpus callosum in the owl monkey, Aotus trivirgatus, and the bushbaby, Galago senegalensis. Previous studies in other species have shown that callosal inputs terminate preferentially in regions where the vertical meridian of the visual field is represented. Such a correspondence can serve as a useful aid for locating the boundaries of visual areas. The goals of this study have been (1) to assess the degree of correspondence between callosal inputs and previously identified vertical meridian representations in the owl monkey and bushbaby, and (2) to gain information from the pattern of callosal inputs concerning the existence and organization of as yet unidentified extrastriate visual areas. In both the owl monkey and the bushbaby, a discrete band of degenerating axonal terminals corresponds precisely to the vertical meridian representation at the V1-V2 border, and a less precise increase in the density of degenerating axonal terminals corresponds to the vertical meridian representation of extrastriate area MT. A well-defined band of degeneration on the ventral surface of the owl monkey's cerebral hemisphere corresponds to a previously unknown vertical meridian representation which is shared by two newly identified extrastriate visual areas. Elsewhere in visual cortex the pattern of callosal connections is more complex. Although this pattern may still reflect visual topography, it is not immediately useful for distinguishing areal boundaries.