Spatial and visuomotor performance with agenesis of the corpus callosum.

The extent to which the cerebral hemispheres and their ipsilateral projection systems compensate for congenital absence of the corpus callosum was studied in an intelligent young adult with radiologically verified total agenesis. She was found to have bilateral speech and the ability to readily integrate visual, tactile, and verbal information simultaneously presented to both hemispheres. However, spatial performance, as demonstrated in blind tactile form board learning, was subnormal compared to normal controls. The results further suggest this impairment, especially severe in the nondominant hand, reflects ipsilateral projection of kinesthetic input, thus maximizing hemispheric competition for motor control of the minor hand. In contrast, the agenic's performance on a simple visuomotor discrimination task (with reduced opportunity for hemispheric interaction) was almost normal. Moreover, she exhibited a doubling of attentional and processing capacity in comparison to the control group. Both hands simultaneously performed this task as rapidly and as accurately as either hand alone. The findings affirm the functionally important, yet limited compensatory role of a developmentally elaborated ipsilateral somatosensory projection system in agenesis of the corpus callosum.