[Compulsive manipulation of tools in the left hand following damage to the right medial frontal lobe]

In 1982, Mori and Yamadori first reported a woman who showed compulsive manipulation of tools (CMT) following an infarction in the left medial frontal lobe. When an object was shown, the patient's right hand reached, grasped and manipulated it properly against her will. Since then, there have been many similar case reports and CMT has been generally believed to occur in the right hand after damage to the left medial frontal lobe. However, there also have been a few case reports of CMT in the left hand of a patient with damage to the right medial frontal lobe. To clarify whether such a patient with CMT in the left hand is an exceptional case or not, we prospectively investigated CMT in the left hand of 10 patients with an infarction in the right medial hemisphere. All patients were examined within 6 weeks after stroke. Magnetic resonance images were used to determine the location and extension of a lesion. We found that 7 cases with a lesion involving the anterior cingulate gyrus (ACG) and the supplementary motor area (SMA) exhibited a grasp reflex and a visual grouping mainly in the left hand. Five of these 7 cases had a lesion extending into the middle and anterior parts of the ACG and displayed CMT in the left hand. Among those 5 patients, 2 with a lesion which was extensive enough into the ACG to involve almost entirely the anterior part of it adjoining the genu and anterior body of the corpus callosum showed a prominent CMT in the left hand. Two patients with a lesion principally confined to the SMA showed the grasp reflex and some subvarieties of the instinctive grasp reaction mainly in the left hand, but never showed visual grouping nor CMT. One patient with a lesion involving the posterior cingulate gyrus and medial parietal lobe but sparing both the SMA and ACG showed neither grasping responses nor CMT. From these observations, we conclude the following: (1) it is not an exceptional case that a right-handed patient with a right medial frontal lesion shows CMT in the left hand: and (2) extensive damage to the ACG involving its anterior part adjoining the genu and anterior body of the corpus callosum is most crucial for the development of CMT.