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How do we know where to go? While most of our day-to-day navigation is usually automatised, new or complex situations require localising oneself in the environment, choosing a goal, and deciding of the best route to reach it. This type of navigation is believed to rely on an internal representation of places called a ‘cognitive map’. The cognitive map is thought to involve a number of brain regions, at the centre of which is the hippocampus and its ‘place cells’. Place cells sometimes reactivate in fast sequences that might represent past or future paths, called ‘replay’. While place cells – and their reactivations – are ubiquitous in any kind of environment, the map is thought to be most needed in situations of detours, shortcuts, or new trajectories to a known goal.
How do place cells guide navigation in these cases? Does the map incorporate relevant aspects of a complex environment, such as its connectivity? Can hippocampal replay select the optimal path to a goal when the connectivity changes? To answer these questions, I will present findings from hippocampal recordings in rats during flexible navigation, including during navigation in a four-room environment, and in a hexagonal maze providing two paths to a goal. I will also briefly dive into one of the paradigms at the origin of the cognitive map theory: the Sunburst maze, often used as a demonstration of shortcutting in rats even though it has not been consistently replicated.
We find that, during flexible navigation, place cells remain relatively stable in the face of (non-sensory) connectivity changes in the environment, raising the question of how connectivity information might be stored in service of navigation. Hippocampal replay sequences tend to reflect connectivity updates, but this seems to be a result of behavioural change, rather than a forward-looking planning mechanism. Overall, the hippocampal cognitive map appears to be used as a repository of experiences, rather than in direct support of navigational decisions, leaving this planning role to other brain regions.
