Neural and cognitive mechanisms underlying episodic memory formation in humans.

摘要

Episodic memories not only allow one to reminisce about past events and experiences, but they also give rise to a coherent concept of one's self and guide adaptive strategies for future goals. An intriguing and still largely unanswered question is how the building blocks of our experiences are assembled and converted into durable memory traces so that we can, at any time in the near or remote future, recollect those experiences in great detail. Although the pivotal role of the medial temporal lobe (MTL) for successful memory formation is well established, the division of labor among the anatomically and functionally distinct MTL subregions in the service of memory formation has remained elusive. The work presented in this dissertation aims at elucidating the precise contributions of two key MTL subregions, the hippocampus and the adjacent perirhinal cortex (PrC), to episodic memory. The results of three functional magnetic resonance imaging (fMRI) studies reveal a clear distinction between these two subregions along the dimensions of stimulus domain and representational integrity of the to-be-remembered information. First, PrC mechanisms seem to be specific to the encoding of item- or object-related information, supporting subsequent item recognition as well as memory for item-related event details (an associated item color), but not for contextual event details (a surrounding task context). Conversely, hippocampal encoding mechanisms seem to be domain-general, supporting subsequent memory for both item-related and contextual event details. However, involvement of the hippocampus during successful episodic binding was found to be directly modulated by the level of representational integrity of the constituent event details, suggesting that a core function of the hippocampus is to mnemonically overcome discontiguities across the elements of our experience. In sum, the research presented herein elucidates some of the key mechanisms through which the building blocks of our rich everyday life experiences, including multiple event details of various modalities and representational formats, are converted into durable episodic memory traces.