Apraxia of the left limbs in a case of callosal disconnection: the contribution of medial frontal lobe damage.

A 40 year old right-handed woman suffered hemorrhage from an anterior cerebral artery aneurysm. CT scan showed destruction of the anterior two thirds of the corpus callosum, both cingulate gyri, and the white matter underlying the medial frontal lobes. The left limbs displayed apraxia on verbal command, in imitation, and in actual object use. There were antagonistic actions of both hands, and the patient accused her left hand of disobeying her. We interpret the leftsided apraxia as resulting from a lack of interhemispheric transfer combined with a deficit in ipsilateral motor control stemming from damage to the left supplementary motor area. Right frontal lobe damage may have impaired the motor learning capacity of the right hemisphere and thus its ability to compensate for the lack of left hemisphere motor control.