Episodic and associative memory from spatial scaffolds in the hippocampus

Sarthak Chandra; Sugandha Sharma; Rishidev Chaudhuri; Ila Fiete

doi:10.1038/s41586-024-08392-y

Episodic and associative memory from spatial scaffolds in the hippocampus

Nature. 2025 Jan 15. doi: 10.1038/s41586-024-08392-y. Online ahead of print.

Authors

Sarthak Chandra^#¹, Sugandha Sharma^#¹, Rishidev Chaudhuri^{2

3}, Ila Fiete⁴

Affiliations

¹ Department of Brain and Cognitive Sciences and McGovern Institute, MIT, Cambridge, MA, USA.
² Center for Neuroscience, Department of Neurobiology, Physiology and Behavior, University of California Davis, Davis, CA, USA.
³ Department of Mathematics, University of California Davis, Davis, CA, USA.
⁴ Department of Brain and Cognitive Sciences and McGovern Institute, MIT, Cambridge, MA, USA. fiete@mit.edu.

^# Contributed equally.

PMID: 39814883
DOI: 10.1038/s41586-024-08392-y

Abstract

Hippocampal circuits in the brain enable two distinct cognitive functions: the construction of spatial maps for navigation, and the storage of sequential episodic memories^1-5. Although there have been advances in modelling spatial representations in the hippocampus^6-10, we lack good models of its role in episodic memory. Here we present a neocortical-entorhinal-hippocampal network model that implements a high-capacity general associative memory, spatial memory and episodic memory. By factoring content storage from the dynamics of generating error-correcting stable states, the circuit (which we call vector hippocampal scaffolded heteroassociative memory (Vector-HaSH)) avoids the memory cliff of prior memory models^11,12, and instead exhibits a graceful trade-off between number of stored items and recall detail. A pre-structured internal scaffold based on grid cell states is essential for constructing even non-spatial episodic memory: it enables high-capacity sequence memorization by abstracting the chaining problem into one of learning low-dimensional transitions. Vector-HaSH reproduces several hippocampal experiments on spatial mapping and context-based representations, and provides a circuit model of the 'memory palaces' used by memory athletes¹³. Thus, this work provides a unified understanding of the spatial mapping and associative and episodic memory roles of the hippocampus.