The pattern of interhemispheric connections and its relationship to extrastriate visual areas in the macaque monkey

Abstract

The distribution of interhemispheric connections was studied in extrastriate visual cortex of the macaque monkey. Callosal fiber terminations were identified by staining for anterograde degeneration following transection of the splenium of the corpus callosum. Retrogradely labeled cell bodies of callosal projection neurons were identified histochemically following application of horseradish peroxidase to the cut surface of the callosum. Results were displayed on unfolded, two-dimensional representations of the cortex, which permitted spatial and topological relationships between callosal recipient and callosal free cortical regions to be discerned readily.The overall pattern of callosal inputs to visual cortex can be subdivided into nine callosal recipient zones which surround seven callosal free regions in the occipital, temporal, and parietal lobes. This pattern provides reliable and useful landmarks for identifying the borders of at least five topographically organized extrastriate visual areas. There is a pronounced dorsoventral asymmetry in callosal projections, not recognized in previous studies, which reflects an asymmetry in the organization of visual areas in dorsal versus ventral halves of the occipital lobe.The pattern of callosal fiber terminations is mirrored by a very similar distribution of callosal projection neurons. There are significant regional differences in the laminar distribution of callosal projection cells, and these differences may reflect functionally distinct cortical subdivisions.A considerable degree of individual variability was found in the relationship of callosal connections to gyral and sulcal landmarks as well as in the fine structure of individual callosal recipient strips, suggesting that each animal has a unique "callosal fingerprint." These findings emphasize the usefulness of the callosal pathway in elucidating the functional organization of extrastriate visual cortex.

Visual Field Map Organization in Human Visual Cortex

“…Feedforward and feedback information from each VFM must be passed on to other maps up and down the hierarchy of visual processing [18]. The retinotopic human visual system processes portions of visual space in parallel, requiring connections for one type of processing in any particular location of the visual field to be passed to the same location of visual space in the next VFM for the next step in visual processing [102]. An elegant solution to this connectivity problem would be to maintain visuospatial organization in the white matter tracts between clusters.…”

Evidence for Activity-Dependent Cortical Wiring: Formation of Interhemispheric Connections in Neonatal Mouse Visual Cortex Requires Projection Neuron Activity

“…Interhemispheric axon projections across the corpus callosum are among long-range efferent fibers derived from cortical neurons, connecting neurons in the left and right cerebral hemispheres. The pattern of interhemispheric (callosal) connections in the visual cortex (VC) is highly organized; the density of callosal connections is highest at the borders between the primary and secondary VC, in which the vertical midline of the visual field is represented, and lowest in regions representing peripheral visual portions (Hubel and Wiesel, 1967;Shatz, 1977;Van Essen et al, 1982;Blakemore et al, 1983;Olavarria and Montero, 1984;Innocenti et al, 1986). This organized pattern of interhemispheric connections in VC is thought to ensure higher visual information processing (Stryker and Antonini, 2001) and develops during the prenatal and early postnatal periods (Olavarria et al, 1987;Innocenti and Price, 2005).…”

Segregation and overlap of callosal and association neurons in frontal and parietal cortices of primates: a spectral and coherency analysis

“…In some fields these callosal and association terminal stripes interdigitate (Jones et al, 1979;Goldman-Rakic and Schwartz, 1982). In other fields, as in the visual cortex (Zeki, 1978;Van Essen et al, 1982), overlap of callosal and association terminal fields seems to be the rule. The cells of origin of these sets of fibers show a more complex pattern of tangential distribution.…”