Between planning and map building: Prioritizing replay when future goals are uncertain

Despite many empirical results about hippocampal replay, its computational function remains controversial. The "value" hypothesis contends that replay plans routes to current goals, while the "map" hypothesis holds that replay builds an abstract environmental representation, distinct from immediate goals. Data appear to support either view, though the planning hypothesis is particularly challenged by recent observations of replay lagging, rather than leading, animals learning to reach current goals. However, differentiating these ideas is difficult due to a lack of formal specificity, especially about the map hypothesis. We address these gaps by extending a prominent theory of planning to include routes to future as well as current goals: effectively a map. Whether replay prefers current goals, like planning, or others, like maps, then depends on their estimated likelihood of future relevance. This account reconciles both views with one another and with much data, revealing a deep relationship between the seemingly distinct hypotheses.