The author referred to the “cognitive process” and “conscious process” in patients with higher brain dysfunction. Two processes could be dissociated at least in the implicit recognition phenomena, anosognosia and interhemispheric disconnection. The former should be considered as “externalization of inner psychological process and trial to treat it as information processing” and the latter as “self-awareness process which should be grasped as arisen from inner subjective process accompanying with brain activity” . The latter have to be distinguished from the former on the aspect of its self-awareness and self-reference nature. We should respect the two processes as distinguished ones and grasp them as integrated way. It is just the “Clinical View Point” insisted on by the author.

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This paper aims to describe the methods of rehabilitation from aphasia within the framework of neural networks. The literature shows that three cortical regions are responsible for language processing : the semantic, mediate, and word-sentence generating systems. In addition to these areas, it is strongly indicated that the basal ganglia may play an important role in language processing. The author proposes a neural network model of word production which consists of dual-route pathways, the cortical and basal ganglia circuits. In this model, it is proposed that units in the cortical pathway are trained by back-propagation algorithm. It is also postulated that units in the basal ganglia are able to represent the conditional probabilities of sensory input via a self-organizing process, and that the number of units activated simultaneously is restricted via a k-winners-take-all circuit, which is intended to represent the sparse coding frequently observed in the brain. The model shows aphasic symptoms when units in the semantic and mediate regions are corrupted. Simulation indicates that reactivation is more effective when brain damage is not so severe. On the other hand, when brain damage is severe in the mediate region, reorganization and relearning may induce better recovery than reactivation. These results are thought to be consistent with actual therapy on aphasic patients.

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   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.

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