Abstract
Recently, various unilateral disconnection syndromes accompanying agenesis of the corpus callosum (ACC) have been reported ; however, these have been restricted to visuo-spatial tasks dependent on parietal lobe function. In ACC patients, it is known that there are no pathways compensating not only parietal lobe function but also frontal lobe function. Therefore, unilateral disconnection syndrome may possibly occur in tasks dependent on frontal lobe functions. However, the disconnection syndromes reported in previous studies of frontal lobe tasks were bilateral syndromes such as reaction-time or bimanual-movement tasks. In this paper, we examined the possibility of unilateral disconnection syndrome of frontal lobe function in a high-mentality ACC patient using a mirror-drawing test, which is thought to be a unilateral frontal-lobe-dependent task, based on a functional imaging study. The patient was a 35-year-old ambidextrous female. In the dichotic listening test, a left-ear advantage (LEA) was detected. In the intelligence test, she scored above normal. In the mirror-drawing task, she was asked to trace a fixed shape in a mirror using each hand, and the results were compared with those of the control subjects. The finding indicated that while the control subjects showed no differences between hands, there was a marked difference in the subject's performance with the right and left hands. Her left-hand (dominant hand) performance was normal compared to the control subjects, but her right-hand (non-dominant hand) performance was markedly impaired. We believe that this phenomenon is a previously unidentified clinical sign of unilateral disconnection syndrome in ACC patients.
