Abstract
The hippocampus integrates over timescales, modalities, and events to generate abstract representations for memory-guided behaviour. But for our memories to guide perception and action, the hippocampus must map its abstractions back into the concrete sensory topographies that are ‘in touch’ with the outside world. Here, I identify topographic hippocampus-visual connectivity by means of connective field mapping. Specifically, this method models fMRI timecourses as originating from distinct topographic locations in V1. If topographic V1-hippocampus connectivity plays a functional role in our understanding of the visual world, one would expect to find this topographic connectivity in naturalistic vision. This connectivity, then, should be even stronger in the resting state when activations are dominated by top-down influences.
Using the 7T HCP retinotopy, movie, and resting state fMRI datasets (totalling 2.5 hours for 181 subjects each), I show that there is topographic connectivity between hippocampus and V1 during movie watching, covering the entire visual field. This connectivity is localised to hippocampal output subregions. The spatial pattern of connectivity is stable: a voxel's topographic connectivity pattern during movie watching predicts the selfsame spatial pattern in the resting state. Moreover, the strength of V1-hippocampus topographic connectivity is stronger in resting state vs movie watching, indicative of enhanced top-down processing. Conversely, an opposite relation holds for topographic connectivity between V1 and thalamus, colliculus and cerebellum, indicating that for these regions connectivity is dominated by bottom-up and oculomotor processing.
These findings show that the hippocampus connects topographically to visual cortex, bridging recent animal studies into visual-hippocampal connectivity and human imaging. The uncovered visual-hippocampal connections are likely to play an essential role in both naturalistic vision and mind-wandering.