前頭葉の認知的情報処理―前頭前皮質の「脳間・脳内操作系」仮説

Cognitive processes in the frontal lobe：the“inter-and intra-brain operating system”hypothesis for prefrontal cortical functions

前頭葉の中でも高度な認知機能を担う前頭前皮質の中心的な機能は，ワーキングメモリである。前頭前皮質がワーキングメモリのセンターであることは間違いないが，最近の研究を総合すると，前頭前皮質が実際に担っているワーキングメモリ系は，「脳間・脳内操作系」と捉えなおすことができる。すなわち，前頭前皮質には，自己脳の多様な神経システムを操作し，かつ，他者の脳内システムを操作する神経システムとしての脳間・脳内操作系の過程が進行しているらしい。この「脳間・脳内操作系」概念は，前頭前皮質の担う多様な認知機能を統一的かつ総合的に理解でき，今後の多様な研究を導き得ると思われる。

The prefrontal cortex（PFC）, a neocortical area in the frontal lobe, has been implicated in working memory. Recent studies in non-human primates for working memory processes have revealed that the “working memory system” in the PFC contains at least the following six processes：1）information-selection, 2）retention and operation of selected information（“working memory” in the narrow sense）, 3）generation of goal-directed information, 4）output of control-information on other brain regions, 5）retrospective monitoring of control-outcome, and 6）generation of prospective memory based on the retrospective monitoring. The conventional “working memory system” concept has limitations for explaining/integrating these dynamic processes in the PFC. Rather, the concept of “operating system（OS）” may be better than the conventional concept of working memory（or “executive”）for explaining/integrating these processes in the PFC. This OS can be termed the “intra-brain OS” that that operates various systems in the subjective（own）brain. Further, considering several lines of studies in humans and monkeys, the PFC may contain also an “inter-brain OS” that operates neural systems in objective brains；i.e., the “objective brain-reading” and “objective brain-controlling”. The “Theory of Mind（ToM）” and lying, which are known to be mediated by the PFC, are typical functions of the inter-brain OS（objective brain-reading and objective brain-controlling, respectively）. Thus, the PFC appears to consist of two relevant systems；intra-brain OS that operates various systems in the subjective brain and inter-brain OS that operates neural systems in objective brains. The central role of intra-and inter-brain OS is to operate subjective and objective brains, thereby operating subjective and objective behaviors/minds. In addition, the intra-and inter-brain OS would be central functions of “self（ego）” for integrating various systems of the own brain and for interacting others adequately. The present intra-and inter-brain OS concept would be valid for understanding the nature/principle of primate brain and may lead further studies of neural mechanisms and evolutionary/ontogeny processes of central functions, such as self（ego）and social ability, mediated by the “highest” cortical region, PFC.