Intrahemispheric cortical connexions and visual guidance of hand and finger movements in the rhusus monkey

An attempt has been made to elucidate in the rhesus monkey the role of intrahemispheric cortico-cortical connexions in visual guidance of relatively independent hand and finger movements which are governed mainly from the precentral motor cortex. These movements were tested by requiring the animals to retrieve with their fingers small food pellets from a special test board in which the pellets were easily visible but were more difficult to palpate. Unilateral occipital lobectomy combined with a commissurotomy impaired the performance of the contralateral hand. The same was true for the parietal leucotomy of Myers et al. (1962) which transects the bulk of the intrahemispheric occipitofrontal cortical fibres. Tests of the visual discrimination of the leucotomized hemispheric showed that the motor impairment after this leucotomy did not represent a visual defect. In control animals no impairment was found after ablation of the cortex on the surface of the postcentral gyrus and the superior parietal lobule. A mild impairment occurred, however, when the lesion either involved also the inferior parietal lobule or was accompanied by a white matter infarct deep under the postcentral gyrus. The findings make it likely that the intrahemispheric cortical fibres to the frontal lobe play a role in visual guidance of relatively independent hand and finger movements. This conclusion is also supported by some preliminary findings after frontal lobe lesions, but further experiments are necessary to establish it firmly.