Mechanisms of interhemispheric transfer and patterns of cognitive function in acallosal patients of normal intelligence.

We investigated interhemispheric transfer and cognitive function in two boys with normal intelligence in whom agenesis of the corpus callosum was identified following minor head trauma. In patient 1, magnetic resonance imaging scan showed agenesis of the corpus callosum and absent anterior commissure. Results of visual interhemispheric transfer tasks suggested degradation in transfer of information to the left hemisphere. Results of a tactile interhemispheric transfer task suggested degradation of access to the right hemisphere. In patient 2, magnetic resonance imaging scan showed agenesis of the corpus callosum and enlarged anterior commissure. Results for both visual and tactile interhemispheric transfer tasks were normal. Dichotic listening tests showed a slight left ear advantage in both patients. These results support the hypothesis that hypertrophy of the anterior commissure is an important mechanism of functional compensation in agenesis of the corpus callosum. However, the relative subtlety of deficits in patient 1 and results of dichotic listening tests support use of other mechanisms as well. No consistent pattern of cognitive deficits was observed.