Abstract
A 55-year-old right-handed woman, with an infarction of the left anterior cingulate gyrus that encroached upon part of the left supplementary motor area and the truncus of the corpus callosum, showed “compulsive use” phenomenon in the right hand. We examined her symptoms by administering tests under various conditions and by analyzing her introspection written in her diary. During the tests, compulsive use appeared in tactile-and-visual and tactile conditions. However, she did not show compulsive use but pantomimed correctly when the examiner asked her to pantomime in response to seeing an object. She also showed “compulsive pantomime” after hearing an object name. She reported that she felt urged to use the object even when she succeeded in suppressing compulsive use or pantomime. From her diary, we found at least three distinctive ways in which she experienced her problems : (1) compulsive use occurring against her will ; (2) compulsive use derived from an obsessive intent to use the object ; and (3) instantaneous action immediately after thinking about it.
These phenomena can be explained by introducing the concept of dual mechanism for action-selection formed by intent and will. It is believed that the supplementary motor area generates intent for a particular action, whereas the prefrontal area generates will that decides whether or not to perform an action. Each of these areas independently subserves the selection of an action to be performed. Moreover, will appears to regulate intent. The subject's compulsiveness may result from dysfunction of the mechanism for action-selection, from dysfunction of control of will over intent, or from both.
