Abstract
The brain is capable of registering a constellation of events, encountered only once, as an episodic memory that can last for a lifetime. As evidenced by the clinical case of the patient HM, memories preserving their episodic nature still depend on the hippocampal formation, several years after being created, while semantic memories are thought to reside in neocortical areas. The neurobiological substrate of one-time learning and life-long storing in the brain, that must exist at the cellular and circuit level, is still undiscovered. The breakthrough is delayed by the fact that studies jointly investigating the rodent hippocampus and entorhinal cortex are mostly targeted at understanding the spatial aspect of learning. Here, we present the concept of an entorhinal cortical module, termed EPISODE module, that could explain how the representations of different elements constituting episodic memories can be linked together at the stage of encoding. The new model that we propose here reconciles the structural and functional observations made in the entorhinal cortex and explains how the downstream hippocampal processing organizes the representations into meaningful sequences.
Highlights
As the clinical case of the patient HM has proven, the medial temporal lobe memory system, including the hippocampus proper and the adjacent entorhinal, perirhinal, and parahippocampal cortices, is critically concerned in the retention of new episodic memories (Scoville and Milner, 1957; Tulving, 2002; Squire, 2009)
That observation is fully compatible with our model that locates the source of the hippocampal phase precession in the entorhinal ring attractors of Significant occurrence detector ring (SODeR) cells and such phase precession is assumed to be independent of experience, while, on the other hand, organized theta sequences are proposed here to arise in the CA3, might be projected back to the EC via the CA1 region
We describe a new functional unit in the entorhinal cortex that we term the EPISODE module
Summary
As the clinical case of the patient HM has proven, the medial temporal lobe memory system, including the hippocampus proper and the adjacent entorhinal, perirhinal, and parahippocampal cortices, is critically concerned in the retention of new episodic memories (Scoville and Milner, 1957; Tulving, 2002; Squire, 2009). The concept and the in silico simulation presented by Navratilova et al (2012) is built on a 1-dimensional ring attractor, it incorporates the intrinsic resonance and other physiologically realistic properties of MECII stellate cells, thereby it explains the grid-like firing activity and the emergence of phase precession.
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