Global and Local Head Direction Coding in the Human Brain

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Abstract Orientation-specific head direction (HD) cells increase their firing rate to indicate one’s facing direction in the environment. Rodent studies suggest HD cells in distinct areas of thalamus and retrosplenial cortex (RSC) code either for global (relative to the wider environment) or local (e.g., room-specific) reference frames. To investigate whether similar neuroanatomical dissociations exist in humans, we reanalysed functional magnetic resonance imaging data in which participants learned the orientation of unique images in separate local environments relative to distinct global landmarks (Shine, Valdés-Herrera, Hegarty, & Wolbers, 2016). The environment layout meant that we could establish two separate multivariate analysis models in which the HD on individual trials was coded relative either to global (North, South, East, West) or local (Front, Back, Right, Left) reference frames. Examining the data first in key regions of interest (ROI) for HD coding, we replicated our previous results and found that global HD was decodable in the thalamus and precuneus; the RSC, however, was sensitive only to local HD. Extending recent findings in both humans and rodents, V1 was sensitive to both HD reference frames. Additional small volume-corrected searchlight analyses supported the ROI results and indicated that the anatomical locus of the thalamic global HD coding was located in the medial thalamus, bordering the anterior thalamus, a region critical for global HD coding in rodents. Our findings elucidate further the putative neural basis of HD coding in humans, and suggest that distinct brain regions code for different frames of reference in HD. Significance statement Head direction (HD) cells provide a neural signal as to one’s orientation in the environment. HD can be coded relative to global or local (e.g., room-specific) reference frames, with studies suggesting that distinct areas of thalamus and retrosplenial cortex (RSC) code for this information. We reanalysed fMRI data where human participants associated images with global HDs before undergoing scanning. The design enabled us to examine both global and local HD coding. Supporting previous findings, global HD was decodable in thalamus, however the RSC coded only for local HD. We found evidence also for both reference frames in V1. These findings elucidate the putative neural basis of HD coding in humans, with distinct brain regions coding for different HD reference frames.

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