Exploring egocentric boundary activity and population receptive field mapping with human functional magnetic resonance imaging in a virtual open field foraging paradigm
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Abstract
Navigation is a cognitive process important for all species from insects to humans, whether it is navigating to a watering hole, migrating back to breeding grounds, or finding one’s way to class in a new building. The process of navigating within an environment entails the utilization of two distinct reference frames: allocentric, i.e. centered on the external world, and egocentric, i.e. centered on oneself. Individuals must rely on both their perception of the surrounding space and their own orientation or perspective to effectively navigate from one point to another. The goal of this dissertation was to examine population level coding of allocentric and egocentric navigational information in humans using a novel virtual field foraging paradigm. Experiment One investigated whether we could find signatures of spatiotopic population receptive field activity in the hippocampus. Our hypothesis was that, in line with rodent studies, we would see the size of receptive fields increasing as we move posterior to anterior along the long axis of the hippocampus. Eighteen participants performed a novel, virtual open-field coin foraging study modeled after similar studies done in rodents. While results from this experiment were inconclusive, there is reason to believe that the hippocampus may still have some form of organization of spatiotopic receptive fields. While the hypothesis and analysis technique were sound, it’s possible that current limitations of neuroimaging technology may make finding conclusive evidence infeasible at this time.
Experiment Two was a separate analysis of the same task and participants from Experiment One, with a focus on coding of egocentric information rather than allocentric, and with a focus on retrosplenial cortex and parahippocampal cortex rather than hippocampus. For this experiment, we leveraged tuning curves, linear regression, and behavioral measures of cognitive tests of egocentric to allocentric transformations. In line with findings from rodent studies, the results demonstrate that the retrosplenial and parahippocampal cortices exhibit a sensitivity to both egocentric distance and bearing. Moreover, the strength of these egocentric signals was found to be associated with a behavioral measure of navigation, which necessitates the transformation between reference frames.
Taken together, these experiments demonstrate that retrosplenial cortex and parahippocampal cortex code for aspects of egocentric navigation while future work is needed to further explore the possibility of spatiotopic receptive fields in the hippocampus.
Description
2024
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Attribution-NonCommercial-NoDerivatives 4.0 International