Positive and Negative Retinotopic Codes in the Human Hippocampus

Abstract

The hippocampus sits at the apex of the visual hierarchy, yet little is known about the visual properties of this core memory structure. Recent work suggests that a latent, bivalent retinotopic code persists in large-scale memory networks at the cortical apex, scaffolding interactions with sensory networks. Here, we tested whether a bivalent retinotopic code also persists within the hippocampus. To do this, we leveraged high-resolution 7T functional MRI along with voxel-scale visual population receptive field (pRF) modeling in 7 densely-sampled individuals (5 female). Our findings reveal a robust, voxel-scale retinotopic code broadly distributed across subfields and along the long axis of the human hippocampus, comprised of roughly equal proportions of pRFs with positive and negative amplitude responses to visual stimulation. Hippocampal pRFs displayed canonical visual properties, including stable valence and visual field preferences across runs and a contralateral bias. Retinotopic structure also persisted at rest: hippocampal voxels with similar pRF locations were more strongly correlated than voxels representing different visual field locations. Finally, across the ventral visual stream, the prevalence of negative-amplitude pRFs increased with mnemonic involvement, culminating in the balanced, bivalent organization within the hippocampus. These findings support the view that sensory and mnemonic systems are coupled through a shared retinotopic code at the apex of the visual hierarchy. Significance Statement The hippocampus is closely coupled to the visual system, and recent work has challenged the classical view that visual coding schemes, like retinotopy, do not persist into the hippocampus. Here, we use high-resolution precision fMRI to robustly characterize a bivalent retinotopic code in the human hippocampus, consisting of both typical positive and atypical negative responses. We further show that this code predicts functional connectivity within the hippocampus even during non-visual tasks, suggesting that this bivalent retinotopic code may reflect an intrinsic organizational principle of the hippocampus relevant for perceptual-mnemonic segregation and integration.