The Hippocampus and Entorhinal Cortex Encode the Path and Euclidean Distances to Goals during Navigation

Summary

Background

Despite decades of research on spatial memory, we know surprisingly little about how the brain guides navigation to goals. While some models argue that vectors are represented for navigational guidance, other models postulate that the future path is computed. Although the hippocampal formation has been implicated in processing spatial goal information, it remains unclear whether this region processes path- or vector-related information.

Results

We report neuroimaging data collected from subjects navigating London’s Soho district; these data reveal that both the path distance and the Euclidean distance to the goal are encoded by the medial temporal lobe during navigation. While activity in the posterior hippocampus was sensitive to the distance along the path, activity in the entorhinal cortex was correlated with the Euclidean distance component of a vector to the goal. During travel periods, posterior hippocampal activity increased as the path to the goal became longer, but at decision points, activity in this region increased as the path to the goal became closer and more direct. Importantly, sensitivity to the distance was abolished in these brain areas when travel was guided by external cues.

Conclusions

The results indicate that the hippocampal formation contains representations of both the Euclidean distance and the path distance to goals during navigation. These findings argue that the hippocampal formation houses a flexible guidance system that changes how it represents distance to the goal depending on the fluctuating demands of navigation.

Graphical Abstract

Highlights

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  The hippocampus represents both the path and the Euclidean distances to goals

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  Entorhinal activity reflects the change in the Euclidean distance when the goal is set

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  The posterior hippocampus represents the future path at different stages en route

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  Significant correlations are abolished when travel is guided by external cues

Abstract

Howard et al. reveal that during the navigation of a simulated real-word environment, hippocampal and entorhinal activity is correlated with the distance to the goal. The posterior hippocampus encodes the path during travel, decision making, and detours. The entorhinal cortex encodes the distance along the vector when the goal is set.