Components of episodic memory: connecting human behavior and electrophysiology to a rodent model

Abstract

Episodic memory encoding and retrieval rely on integration of information about what an item was, as well as when and where it was encountered. Previous research from animal lesion studies using a novelty preference paradigm found that the hippocampus and medial prefrontal cortex were critical for different aspects of recollection of episodic events (DeVito & Eichenbaum, 2010). The present study attempts to adapt this paradigm to assess these components behaviorally and electrophysiologically in humans using a memory recognition task. Participants studied two virtual “rooms” containing images of women, with each image presented consecutively in a random location for 5 s. Between rooms, participants engaged in a go/no-go distractor task for either 15 s (“short” retention interval) or 3 m (“long”). After both rooms were studied, participants made old/new judgments with half of the items being new. Half of the images appeared in the same location as during the study phase (“stationary”) with the others appearing in a new location (“displaced”). Behavioral results showed no difference in reaction time (RT) between old and new items, but significantly longer RTs for displaced items relative to stationary, and significantly longer RTs for items seen before long retention intervals than short. Electrophysiological (EEG) results show no main effect of old/new status in a memory-related ERP in the left parietal area, but did show a main effect of displacement, with items that were displayed eliciting smaller amplitudes than items that were stationary. Additionally, trial-by-trial regression analyses uncovered sets of electrodes that were responsive to manipulations in retention interval and study room (memory for “when”), as well as displacement at test (“where”).