Abstract
We reported 7 patients who exhibited imitation behavior following damage to the medial frontal lobe. On the basis of symptomatological features of imitation behavior, the patients were divided into 2 groups (A and B). In group A (4 patients), imitation behavior appeared in both upper extremities and other body parts. It showed no signs of inhibition and seemed to be related to the patient's own will. In group B (3 patients), on the other hand, imitation behavior appeared only in the right upper extremity in response to visual stimulus and was inhibited by the left hand. It seemed to be a kind of compulsive behavior against the patient's will. In group A, when generalized attention was reduced, the category of stimuli which induce imitation behavior, body parts involved and patterns of behavior tended to become more extensive and varying. The lesions of group A were located in the middle and posterior parts of the anterior cingulate gyrus, whereas in group B the lesions in the anterior part of the anterior cingulate gyrus seemed to be important in inducing imitation behavior. The anterior cingulate gyrus seems to control the activities of the parietal lobe and premotor cortex in response to sensory stimuli. Results further suggested that there are differences in function between the anterior part of the anterior cingulate gyrus, and its middle and posterior parts.
