Cognitive and sensori-motor functioning in the absence of the corpus callosum: neuropsychological studies in callosal agenesis and callosotomized patients.

The aim of the present study was to investigate the role of the corpus callosum in cognitive and sensori-motor functioning as measured by a neuropsychological test battery. After a brief review and analysis of the literature, we report our own studies in acallosal subjects (n = 9) and callosotomized patients (n = 25). The main instrument of evaluation was the Michigan Neuropsychological Test Battery. This battery was supplemented by age-appropriate intelligence tests. The performance of the acallosal group was compared to that of two matched control groups: one group consisting of children and adolescents that attended the same school as the acallosals and a second group of subjects recruited from regular schools. The callosotomized patients, tested pre- and post-operatively, served as their own controls. Taken together, the results of the reviewed and personal studies suggest that absence of the corpus callosum does not necessarily impede cognitive functioning. However, samples drawn from clinical populations tend to show a larger variability as to their mental abilities. In keeping with previous findings, our results indicate that the corpus callosum does play a role in bimanual motor coordination although other pathways (probably ipsilateral and/or subcortical) may provide adequate compensation in many cases. The data further suggest that the corpus callosum may be important for interhemispheric transfer of tactuo-motor learning when a spatial component is involved. Finally, our results are consistent with a facilitatory role of the corpus callosum in cognitive and sensori-motor functioning which allows for interhemispheric compensation as part of cerebral reorganization in the case of unilateral brain damage.