Posterior Hippocampus Contributes Differentially to Long-Term Consolidation of Contextual Memory Across Age Groups

Abstract

Event Abstract Back to Event Posterior Hippocampus Contributes Differentially to Long-Term Consolidation of Contextual Memory Across Age Groups Sicong Tu1, 2* and Michael Hornberger1, 2 1 Neuroscience Research Australia, Australia 2 University of New South Wales, Faculty of Medicine, Australia Introduction: The hippocampus is thought to be crucially involved in the consolidation of memories. Recent evidence from human neuroimaging suggests that decreased posterior hippocampal activity predicts short-term (24 hrs) memory consolidation of face-location associations [1]. This study investigated hippocampal activity over a longer time frame (4 weeks) in a group of young and elderly participants. Methods: Fifteen young and ten elderly healthy subjects explicitly learnt to criterion (90% correct) a set of 25 everyday objects presented on either the left or the right of a monitor. At test, the encoded stimuli were randomly intermixed with 25 novel stimuli and participants were asked to make an old/new recognition decision followed by a left/right source decision. Assessments were carried out after the following encoding delays: baseline (no delay), 1hr, 24hrs, 1 week, 2 weeks, and 4 weeks. Importantly, different sets of novel stimuli were employed for each test to avoid confounding target memory retrieval with previously employed foils. fMRI data was acquired at baseline and 4 weeks, and source memory performance was used as a regressor to determine retrieval of contextual information for recent (baseline) versus remote (4 weeks post-encoding) time points. Results: Behaviourally, recognition performance remained >90% for young and elderly groups over a period of 4 weeks. By contrast, contextual source memory performance decreased to <70% correct (Fig.1). Functional imaging results revealed for successful contextual memory retrieval that young and elderly age groups differed for activity in the posterior left hippocampus. Young participants showed left posterior hippocampal activations for recent and remote time points, whereas a similar activation was only found for the recent time point in the elderly. Conclusions: Our results demonstrate that contextual memory retrieval over long time delays differs between healthy young and old participant groups on a behavioural and functional imaging level. In particular, the left posterior hippocampus showed a difference between groups, which suggests that this region is in particular sensitive for the retrieval of contextual information even after longer time delays. Figure 1