Visual Control of Limb Movement Following Section of Optic Chiasm and Corpus Callosum in the Monkey

Abstract

Hand preference tests were given to four monkeys following section of the optic chiasm and anterior commissure and also after additional section of the corpus callosum. Using a stationary food reward and testing under conditions of binocular and monocular vision, no change was found, in hand preference with changes in visual input following chiasmal section. Marked preference for using the hand contralateral to the seeing eye was shown following additional section of the corpus callosum with enforced monocular vision, and abnormalities in the use of the hand ipsilateral to the open eye were evident. These results indicate that deficits in visuomotor control occur in the “split-brain” monkey independently from visual pattern learning situations and suggest a direct cortical link between visual input and crossed corticospinal fibers, giving dexterity to finger movements. A comparison of the speed of retrieval of a moving target was made between normal monkeys, those with optic chiasm sectioned and those with optic chiasm, corpus callosum and anterior commissure sectioned. With binocular vision, only the “split-brain” animals differed from normal, being slower and more erratic in their performance. With monocular testing the animals with only the optic chiasm sectioned showed a slight initial deficit, attributed to the adjustment to their visual field deficit. The “split-brain” animals showed marked disturbance of performance of the tasks. On occluding the first eye by lid suture and testing over a period of one to several weeks, their two hands performed initially at the same rate, then a marked deficit of the hand ipsilateral to the open eye became evident, then again improved. On changing directly to occlusion of the second eye a marked deficit or refusal to perform the task was shown using either forelimb; then over time a gradual improvement was evident, particularly with the forelimb contralateral to the open eye. These findings lead to a theory of gradual bias of subcortical visuomotor linkages under the influence of lateralised vision in the absence of the corpus callosum. The repeated use of new visuomotor linkages disrupts unused, previously established, linkages. The utilisation of intrahemispheric visuomotor links can delay or disrupt the simultaneous formation of the apparently weaker interhemispheric linkages in the “split-brain” animal.