Figure 1.

Top, Schematic representation of the highly lateralized visual projection system. The visual information from each visual hemifield is projected to the visual cortex of the contralateral hemisphere; it is transmitted from the retina along the optic nerve through the optic chiasm, where fibers from the nasal retinal nerve cells cross to join the fibers from the temporal retinal nerve cells of the other eye. This way, the brain merges visual information from one visual hemifield to form an optic tract, which travels from the chiasm to the lateral geniculate nucleus (LGN) in the thalamus and then along the optic radiation fibers to the visual cortex of each cerebral hemisphere. Bottom, Illustration of posterior corpus callosum fibers, and cingulate fiber bundles for interhemispheric and intrahemispheric integration of visuomotor information within dynamically co-operating brain networks. Our results indicate that at the cortical level, between-hemisphere visuomotor integration is mediated cooperatively via posterior corpus callosum fibers and within-hemisphere integration is conveyed via left posterior cingulate fibers in an inhibitory fashion. Individual variation of white matter fiber structure modulates visuomotor integration dynamically and in interaction with a dominant left-hemispheric motor output system. Subtle white matter fiber degradation, as seen in alcoholism, contributes to an attenuation of the normal functional brain asymmetry.