A common hippocampal gradient for semantic and spatial information

Poster Session C - Sunday, March 30, 2025, 5:00 – 7:00 pm EDT, Back Bay Ballroom/Republic Ballroom

Anikka G. Jordan¹ (anikka@uchicago.edu), Joel L. Voss¹, James E. Kragel¹; ¹University of Chicago

Memories differ in precision from highly detailed to vague, but the neural basis of this spectrum is not yet known. Current theories suggest that memory-relevant processing increases in resolution from the anterior to posterior hippocampus. However, it remains unclear whether semantic and spatial memory share a functional gradient. To relate hippocampal function to behavioral measures with high temporal resolution, we recorded eye movements during fMRI while participants (N = 29) learned visuospatial sequences of objects. They detected mismatching test sequences that differed along spatial and semantic dimensions. Critically, we manipulated the magnitude of these mismatches, allowing us to examine how they affected memory-guided behaviors and long-axis organization. The degree of mismatch affected accuracy on the task, with better detection of mismatching sequences that were either spatially or semantically far from targets (F(1,27.7) = 39.0, p < 0.001). Eye-movement behavior also reflected spatial and semantic memory. Participants made more predictive eye movements to repeated compared to mismatched object locations (F(1,28.0) = 48.8, p < 0.001). Fixation durations increased for unexpected objects compared to objects presented in unexpected locations (F(1,25.5) = 257.0, p < 0.001), reflecting semantic memory. Neural pattern similarity decreased along the hippocampal long axis for both semantic and spatial mismatches (F(1,22.3) = 3.00, p = 0.003). Additional fMRI connectivity analyses utilizing these behaviors relate semantic and spatial hippocampal gradients to distributed brain networks. Taken together, these findings suggest a common gradient of memory precision in the hippocampus.

Topic Area: LONG-TERM MEMORY: Episodic