The impact of two spatial strategies on entorhinal and hippocampal involvement in visual path integration
Zhong, Yu Jimmy
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In lieu of pre-existing inconsistent neuroimaging and neuropsychological findings concerning the involvement of the hippocampal formation in path integration, the current study investigated the extent to which the hippocampus proper, the entorhinal cortex, and neocortical regions were activated based on the implementation of continuous and configural updating strategies when performing a virtual path completion task. While configural updating required allocentric encoding of the outbound path’s shape, continuous updating required constant tracking of egocentric movements with reference to a point of origin. Findings from in-lab behavioral testing (n = 50) showed that neither strategy elicited more accurate path integration performance than the other, and that gender/sex moderated strategy use. Specifically, male configural updaters outperformed female configural updaters on almost all types of path integration errors, and female continuous updaters outperformed female configural updaters in terms of mean distance error measures. Region-of-interest analysis of functional fMRI data obtained from a subset of participants (n = 38) based on a new/separate set of path integration trials showed that continuous updaters (n = 19) exhibited significant activation in the left entorhinal cortex through a contrast of activations derived from simple and complex paths [complex > simple] when returning to the start. Based on the same type of ROI analysis, marginally significant activations in the left hippocampus in both strategy groups were also found based on the same type of descriptive contrast. In each strategy group, whole-brain analysis further showed significant non-contrast-related patterns of activations (in the left parietal cortex) and deactivations (in the right medial prefrontal cortex and right lateral temporal lobe) during the homebound phase of simple paths. In addition, brain-behavior correlations associated individual differences in visual path integration with non-contrast-related functional activity changes in the occipito-parietal and inferior frontal regions. Taken together, these fMRI findings suggest that extrahippocampal attentional and perceptual processes facilitated visual path integration, and that the entorhinal cortex and hippocampus may be more involved in detecting switches in homing decisions or responses between paths of varying complexity than in monitoring performance changes over a single category of paths.