Mice navigate scent trails using predictive policies

Many terrestrial animals accurately follow odor trails, but their navigation strategies remain unclear. We presented mice with dynamic, non-repeating odor trails using a paper treadmill, and found that they rapidly learned to track trails effectively. Odor detections by one or both nostrils during inhalation evoked rapid, stereotyped motor responses. Blocking one nostril led to biased tracking, while disconnecting interhemispheric neural communication disrupted tracking almost entirely. We found that trail tracking is more than a reflex, with mice adapting their movements according to a memory of recently encountered trail geometry. A Bayesian model captures these behaviors, suggesting mice combine bilateral olfactory input with short-term memory to guide navigation actively. Functional perturbations and neural recordings from behaving animals implicate an early olfactory cortical region in trail tracking. These results lay the groundwork to uncover the computational architecture of sensorimotor integration in naturalistic tasks.