Abstract
Episodic memories are constructed from sequences of events. When recalling such a memory, we not only recall individual events, but we also retrieve information about how the sequence of events unfolded. Here, we focus on the role of the hippocampal-entorhinal region in processing and remembering sequences of events, which are thought to be stored in relational networks. We summarize evidence that temporal relations are a central organizational principle for memories in the hippocampus. Importantly, we incorporate novel insights from recent studies about the role of the adjacent entorhinal cortex in sequence memory. In rodents, the lateral entorhinal subregion carries temporal information during ongoing behavior. The human homologue is recruited during memory recall where its representations reflect the temporal relationships between events encountered in a sequence. We further introduce the idea that the hippocampal-entorhinal region might enable temporal scaling of sequence representations. Flexible changes of sequence progression speed could underlie the traversal of episodic memories and mental simulations at different paces. In conclusion, we describe how the entorhinal cortex and hippocampus contribute to remembering event sequences-a core component of episodic memory.
Highlights
Episodic memories are classically thought to comprise information about specific events as well as about where and when these events occurred (Tulving, 1972, 1983)
The timeline of events could be reconstructed from multivoxel patterns in the anterior-lateral entorhinal cortex (Bellmund et al, 2019). These findings suggest that anterior-lateral entorhinal cortex forms holistic representations of the temporal relations between different elements in an event sequence
We have focused on memory for event sequences
Summary
Episodic memories are classically thought to comprise information about specific events as well as about where and when these events occurred (Tulving, 1972, 1983). The analysis of fMRI multivoxel patterns further suggests that hippocampal activity in response to retrieval cues carries information about the temporal relationships of memories. These studies suggest that hippocampal activity patterns during retrieval carry information about the relative sequence position at which different events were encountered.
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