Abstract
The medial temporal lobes play an important role in episodic memory, but over time, hippocampal contributions to retrieval may be diminished. However, it is unclear whether such changes are related to the ability to retrieve contextual information, and whether they are common across all medial temporal regions. Here, we used functional neuroimaging to compare neural responses during immediate and delayed recognition. Results showed that recollection-related activity in the posterior hippocampus declined after a 1-day delay. In contrast, activity was relatively stable in the anterior hippocampus and in neocortical areas. Multi-voxel pattern similarity analyses also revealed that anterior hippocampal patterns contained information about context during item recognition, and after a delay, context coding in this region was related to successful retention of context information. Together, these findings suggest that the anterior and posterior hippocampus have different contributions to memory over time and that neurobiological models of memory must account for these differences.
Highlights
The medial temporal lobes (MTL) are known to play a key role in the formation of lasting memories, but there has been considerable debate about whether their involvement in memory retrieval is stable over time
One question involves the role of the perirhinal cortex (PRC) and parahippocampal cortex (PHC) in immediate and delayed recollection
Neuroscience supported recollection immediately and after a 1-day delay, but that patterns in the PRC but not the PHC were sensitive to shared context information
Summary
The medial temporal lobes (MTL) are known to play a key role in the formation of lasting memories, but there has been considerable debate about whether their involvement in memory retrieval is stable over time. Some functional magnetic resonance imaging (fMRI) studies have shown that, when both encoding and retrieval are controlled in the laboratory, retrieval-related activity in the HF declines from immediate to delayed test with even a 1-day delay (Bosshardt et al, 2005a; Takashima et al, 2006, 2009; but see Stark and Squire, 2000) These findings are echoed by work demonstrating that a night of sleep, or even a brief nap, can alter the neural bases of memory (Takashima et al, 2006; Gais et al, 2007; Sterpenich et al, 2007) and have long-term consequences for memory (Diekelmann and Born, 2010). These findings are often interpreted as reflecting the early stages of memory systems consolidation, it has remained a challenge to separate changes in neural representation
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