“Associative and Episodic Memory from Pre-Structured Spatial Scaffolds in the Hippocampus”

Ila Fiete, PhD
Associate Investigator, McGovern Institute
Professor, Brain and Cognitive Sciences, MIT
Director, K. Lisa Yang ICoN Center, MIT

Hippocampal circuits in the brain enable two distinct cognitive functions: the construction of spatial maps for navigation and the storage of sequential episodic memories. This dual role remains an enduring enigma. While there have been significant advances in modeling spatial representations in the hippocampus, we lack good models of its role in episodic memory. Additionally, we now know that the spatial codes in grid and hippocampal cells generalize to represent non-spatial cognitive domains, but it is unclear why this arrangement might be advantageous. In this talk, I’ll discuss a neocortical-entorhinal-hippocampal network model that implements a high-capacity and flexible general associative memory, spatial memory, and episodic memory based on a scaffold of rigid, low-dimensional dynamics in grid cells and fixed random projections to the hippocampus. The circuit factorizes the problem of content storage from the problem of generating error-correcting stable states. Unlike existing neural memory models, which exhibit a memory cliff, the circuit exhibits a graceful tradeoff between the number of stored items and detail. The scaffold is also critical for constructing episodic memory: it enables high-capacity sequence memory by simplifying the chaining problem into one of learning low-dimensional transitions. The model recapitulates a number of hippocampal physiology results, and interestingly provides a potential explanation for the striking efficacy of the “memory palaces” technique of memory athletes.