展望記憶と虚記憶に関する臨床神経心理学的検討(人間の記憶に関する学際的パースペクティブ,第24回大会 シンポジウム2)

抄録

Prospective memory is to remember the future intentions or plans in every day life. We used prospective memory training for two brain-damaged amnesic patients to investigate the neural mechanism of two component of prospective remembering: remembering to remember and remembering content. The results provide strong evidence that these two remembering components have independent neural bases, with the basal forebrain and right medial frontal lobe being required for remembering to remember and the medial temporal lobe being required for remembering content. The amnesic patients often develop a spontaneous and fantastic confabulation which is an extreme type of false memory. To elucidate the mechanism of confabulation, we investigated the neural basis and psychological process of false memory. Neuroimaging studies of human memory demonstrated that the prefrontal cortex (PFC) is activated during episodic memory retrieval. We focused on the role of anterior and posterior prefrontal cortex in false recognition by neuropsychological studies and by event-related functional magnetic resonance imaging (MRI) and the functional connectivity method. In the neuropsychological study, we administered the typical false recognition paradigm to eight patients with ventromedial prefrontal cortex (VMPFC) lesion. The VMPFC patients showed significantly higher false alarm rate than the normal subjects for lure words, suggesting that the VMPFC patients were more likely to fail to retrieve past similar events. In fMRI study, subjects were first asked to try to remember a series of associate-word lists outside the MRI scanner in preparation for a later recognition test. In the MRI scanning phase, they were asked to make recognition judgments in regard to old words, semantically related lure words, and unrelated new words. The right anterior PFC showed a greater signal change for false alarm than for hit and correct rejection. The signal increase in the right anterior PFC was greater for false alarm responses led us to speculate that the excessively high sensitivity to familiarity in the right anterior PFC may be a cause of the frequent occurrence of false alarm responses. The finding of a greater signal change in the left anterior PFC for correct rejection than for hit and false alarm suggests a major contribution of the left anterior PFC to systematic source monitoring or conscious recollection. The analysis of functional connectivity revealed that the posterior PFC in each hemisphere had strong functional interconnections with the contralateral posterior PFC, whereas the anterior PFC in each hemisphere had only weak functional interconnections with the contralateral anterior PFC.