海馬の「空間地図説」対「時間処理説」の検討 (第五百五十號記念特集號)

Abstract

A recent progress of the hippocampal function was reviewed in this article, examining the spatial mapping and temporal processing function in particular. Spatial mapping theory is sustained by a fact that the animals with hippocampal lesions make frequent re-entrance errors to the already visited arms in the radial maze task. A number of recent findings also has been reported that the hippocampal neurons respond to spatial characteristics. However, those failures in the radial maze task could be argued by loss of working memory, since hippocampal animals could retain their reference memory as normal. In addition, hippocampal neurons enhance their response when a meaningful stimulus approaches close in time even in the task such as a classical conditioning experiment in which no particular spatial factors are involved. These facts lead to a notion of hippocampal function as a temporal processing. Even though both of these theories are concerned with a memory process, one might consider that the spatial mapping theory is mainly related to the problem of what is being processed, while the temporal processing theory is related to the controlling mechanism of hippocampal function. As already noticed in many studies, hippocampal lesioned animals are suffered in context dependent behavior. It was hypothesized in this article tentatively that this structure might be related to a matching of behavioral plan in spatial-temporal sequence with those of current performance stage of the animal. When the matching is completed animals are released from the behavioral sequence, or reset the performance, thus forming a behavioral sequence as a unit.