Forward processing of spatiotemporal maps across hippocampal subfields in common marmosets

Abstract

Episodic memory requires distinguishing similar events occurring at the same location but at different times. While the hippocampus integrates "where" and "when," the specific roles of the primate dentate gyrus (DG) and CA3 remain elusive. We recorded single-unit activity from freely moving marmosets navigating a spatial maze in a visually impoverished environment. Both hippocampal subfields robustly encoded self-position via neurons selective for stationary epochs at platforms and movement along trajectories, whereas gaze-related coding was minimal. While DG signaled stationary and dynamic self-positions independently, CA3 integrated these elements into conjunctive representations. Critically, only CA3 neurons exhibited strong temporal-order modulation. These findings reveal a feedforward disambiguation process in which CA3 transforms discrete spatial inputs from DG into the integrated spatiotemporal maps essential for episodic memory.