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Retinotopic coding by human hippocampus? An evaluation using intracranial electroencephalography.

Poster Session D - Monday, March 9, 2026, 8:00 – 10:00 am PDT, Fairview/Kitsilano Ballroom

Kenneth Rostowsky¹ (), Joel Voss, James Kragel; ¹University of Chicago

By representing both space and ongoing experience, the hippocampus supports memory and spatial learning. Recent functional magnetic resonance imaging (fMRI) studies show contralateral hippocampal responses to visual stimuli, pointing to retinotopic coding as one such form of spatial representation. However, fMRI is an indirect indicator of neural activity and provides low temporal resolution, and so it is unclear which, if any, aspects of neural activity demonstrate retinotopic coding in hippocampus. In visual cortex, prominent alpha oscillations are retinotopically organized; we hypothesized that hippocampal theta would similarly demonstrate retinotopic sensitivity. We tested this hypothesis by examining direct hippocampal recordings from epilepsy patients (N=12) undergoing presurgical monitoring while they completed the Human Connectome Project visual field mapping task (N=98 hippocampal contacts; 40% in left hippocampus). Analyses focused on slow (1-5 Hz) and fast (6-12 Hz ) theta activity. Both slow and fast theta power were significantly modulated by visual stimulation (linear-mixed effects model for slow theta: Beta=0.03, 95% CI=[0.02, 0.04], chi^2(1)=21.45 p=0.02, corrected; for fast theta Beta=0.03, 95% CI=[0.02, 0.04], chi^2(1)=23.21 , p=0.02, corrected). Few visually sensitive contacts had activity that correlated significantly with stimulus hemifield (5%, p<0.05, corrected). Linear mixed effects modeling failed to identify modulation of theta activity by contralateral visual stimulation. In contrast, behavior during an ongoing change-detection task significantly modulated hippocampal theta (p<0.05), including microsaccades, fixation-cross color changes, and button presses. Thus, hippocampal theta is visually responsive, but concurrent behaviors may be responsible for apparent visuospatial sensitivity.

Topic Area: LONG-TERM MEMORY: Episodic