Brain networks underlying episodic memory retrieval

Abstract

The importance of the medial temporal lobe to episodic memory has been recognized for decades. Recent human fMRI findings have begun to delineate the functional roles of different MTL regions, most notably the hippocampus, for the retrieval of episodic memories. Importantly, these studies have also identified a network of cortical regions--each interconnected with the MTL--that are also consistently engaged during successful episodic retrieval. Along with the MTL these regions appear to constitute a content-independent network that acts in concert with cortical regions representing the contents of retrieval to support consciously accessible representations of prior experiences.

Figure 1

Retrieval-related hippocampal activity co-varies with amount of retrieved contextual information [56]. The data are shown for test items endorsed as familiar (K) or recollected (R), further segregated by the confidence and accuracy of a subsequent source memory judgment made on recollected items. R-high and R-mod refer to accurate source judgments made with high and moderate levels of confidence respectively. R-weak refers to source judgments made with low confidence or that were inaccurate.

Figure 2

The general recollection network. The figure illustrates the outcome of the contrast between accurately recognized test words endorsed as ‘Remember’ or ‘Know’ in an unpublished study (n=19) of Wang and Rugg. The words had been studied either as pictures or as words in the context of two different encoding tasks. Shown are regions where recollection was associated with enhanced activity at test regardless of the encoding condition.