Remembering episodes: a selective role for the hippocampus during retrieval

Abstract

Some memories are linked to a specific time and place, allowing one to re-experience the original event, whereas others are accompanied only by a feeling of familiarity. To uncover the distinct neural bases for these two types of memory, we measured brain activity during memory retrieval using event-related functional magnetic resonance imaging. We show that activity in the hippocampus increased only when retrieval was accompanied by conscious recollection of the learning episode. Hippocampal activity did not increase for items recognized based on familiarity or for unrecognized items. These results indicate that the hippocampus selectively supports the retrieval of episodic memories.

Memory orientation and success: separable neurocognitive components underlying episodic recognition

“…Thus, activation in the hippocampus and PHG was clearly selective for source retrieval success, with perirhinal cortex demonstrating a more complex pattern. Eldridge et al [28], using the "remember/know" paradigm, observed a conceptually similar pattern [28]. In that study, only correct endorsements accompanied by subjective reports of remembering resulted in hippocampal activation.…”

“…Thus, correct and incorrect source recognition should yield differential hippocampal activation. In contrast, from one perspective [28,35], retrieval success effects should not be observed within the hippocampus during recency recognition, as such judgments in the current paradigm are hypothesized to be largely non-recollective.…”

“…For the main comparison of source and recency tasks, a region was considered significant if it consisted of five or more contiguous voxels and exceeded an alpha threshold of 0.001 (Z > 3.09, uncorrected). For accuracy (retrieval success or failure) comparisons, in which the number of observations in each condition for each subject was markedly reduced and for which the medial temporal regions of interest are known to provide a relatively modest signal to noise ratio compared to lateral neocortical structures, the threshold was lowered to an alpha of 0.005 (Z > 2.58, uncorrected) [28,[44][45][46].…”

“…With respect to retrieval outcome, recognition tests that require the retrieval of contextual specifics may be particularly sensitive to hippocampal damage [26][27][28][29][30][31][32] and the hippocampal formation has been specifically postulated as a critical component in successful conscious episodic retrieval [33,34]. Thus, correct and incorrect source recognition should yield differential hippocampal activation.…”

Retrieval of emotional memories.

“…The retrieval attempt, in which the participant mounts a strategic effort to remember, elicits activity in the PFC (Buckner & Wheeler, 2001). 6 Activity in the hippocampus (Eldridge, Knowlton, Furmanski, Bookheimer, & Engel, 2000;Henson et al, 1999) and the posterior parietal cortex (Wagner et al, 2005) correlates with successful retrieval. 7 Neural areas also track the retrieval of information across the different sensory domains differently, such that the recollection of a visual scene may result in the activity of visual cortices even in the absence of visual stimulation (M. E. Wheeler, Petersen, & Buckner, 2000).…”