The role of ventral medial wall motor areas in bimanual co-ordination - A combined lesion and activation study

Two patients with midline tumours and disturbances of bimanual co-ordinatio n as the presenting symptoms were examined. Both reported difficulties when ever the two hands had to act together simultaneously, whereas they had no problems with unimanual dexterity or the use of both hands sequentially. In the first patient the lesion was confined to the cingulate gyrus; in the s econd it also invaded the corpus callosum and the supplementary motor area. Kinematic analysis of bimanual in-phase and anti-phase movements revealed an impairment of both the temporal adjustment between the hands and the ind ependence of movements between the two hands. A functional imaging study in six volunteers, who performed the same bimanual in-phase and anti-phase ta sks, showed strong activations of midline areas including the cingulate and ventral supplementary motor area. The prominent activation of the ventral medial wall motor areas in the volunteers in conjunction with the bimanual co-ordination disorder in the two patients with lesions compromising their function is evidence for their pivotal role in bimanual co-ordination.