Positive and Negative Retinotopic Codes in the Human Hippocampus

The hippocampus is thought to coordinate sensory-mnemonic information streams in the brain, representing both the apex of the visual processing hierarchy and the central hub of mnemonic processing. Yet, the mechanisms underlying sensory-mnemonic interactions in the hippocampus are poorly understood. Recent work in cortex suggests that a retinotopic code - typically thought to be exclusive to visual areas - may help organize internal and external information at the cortical apex via opponent interactions. Here, we leverage high-resolution 7T functional MRI to test whether a bivalent retinotopic code structures activity within the human hippocampus and mediates hippocampal-cortical interactions. In seven densely-sampled individuals, we defined the retinotopic preferences of individual voxels within the hippocampus and cortex during a visual mapping task, as well as their functional connectivity during independent runs of resting-state fixation. Our findings reveal a robust retinotopic code in the hippocampus, characterized by stable population receptive fields (pRFs) with consistent preferred visual field locations across experimental runs. Notably, this retinotopic code is comprised of roughly equal proportions of positive and negative pRFs, aligning with the hypothesized role of negative pRFs in mnemonic processing. Finally, the signed amplitude of hippocampal pRFs predicts functional connectivity between retinotopic hippocampal and cortical voxels. Taken together, these results suggest that retinotopic coding may scaffold internal mnemonic and external sensory information processing within the hippocampus, and across hippocampal-cortical interactions.