Abstract
Topological networks lie at the heart of our cities and social milieu. However, it remains unclear how and when the brain processes topological structures to guide future behaviour during everyday life. Using fMRI in humans and a simulation of London (UK), here we show that, specifically when new streets are entered during navigation of the city, right posterior hippocampal activity indexes the change in the number of local topological connections available for future travel and right anterior hippocampal activity reflects global properties of the street entered. When forced detours require re-planning of the route to the goal, bilateral inferior lateral prefrontal activity scales with the planning demands of a breadth-first search of future paths. These results help shape models of how hippocampal and prefrontal regions support navigation, planning and future simulation.
Highlights
Topological networks lie at the heart of our cities and social milieu
Consistent with this pattern, and with our theoretical prediction that lateral prefrontal cortex (PFC) regions might be responsible, we found that bilateral inferior lateral PFC was significantly correlated with our measure of breadthfirst search (BFS)-planning demands in the first layer of the street network at Detours, but not at Decision Points, and significantly more correlated with planning demands at Detours than Decision Points (n 1⁄4 24, GLM Po0.001 uncorrected for ROI; Fig. 5b and Supplementary Table 11)
We show evidence that when entering a street during navigation the right posterior hippocampal activity tracks changes in the number of available path options, the right anterior hippocampus tracks changes related to the closeness centrality of the street and, at forced detours, lateral prefrontal activity scales with the planning demands consistent with a BFS of the street network
Summary
Topological networks lie at the heart of our cities and social milieu. it remains unclear how and when the brain processes topological structures to guide future behaviour during everyday life. While the hippocampus is thought to support retrieval of memory representations to simulate future possibilities, the role of evaluating possible future states for action is argued to be the preserve of the prefrontal cortex (PFC) This is based on evidence that damage to the PFC impairs planning and problem solving[9,10]. Our analysis reveals that the right posterior hippocampus tracks the changes in the local connections in the street network, the right anterior hippocampus tracks changes in the global properties of the streets and the bilateral lateral prefrontal activity scales with the demands of a BFS These responses were only present when long-term memory of the environment was required to guide navigation
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