Diagonistic dyspraxia: case report and movement-related potentials.

We report unusual motor behavior of the left hand dissociated from conscious volition in a 51-year-old right-handed man. This patient had sustained damage to the anterior two-thirds of the corpus callosum, the rostral and lower parts of the right medial frontal lobe, and a small portion of the left medial frontal lobe. He subsequently showed 4 types of abnormal motor behavior in the left hand that were triggered by voluntary activities of the right hand: symmetric or antagonistic left hand movements; irrelevant movements of the left hand to the right hand; and a tendency to close the fingers of the left hand into a fist. Recordings of movement-related potentials revealed a marked attenuation of the Bereitschaftspotential (BP) over the right hemisphere observed only when the patient initiated voluntary activity with the right hand. Since the BP is believed to represent a cerebral cortical activity preparatory for voluntary movement, we infer that the level of dysfunction in this patient is at the motor preparatory level caused by a disconnection of the right hemisphere from the left.