Robust and rapid air borne odor tracking without casting

Abstract

Casting behavior (zig-zagging across an odor stream) is common in air/liquid borne odor tracking in open fields; however terrestrial odor localization often involves path selection in a familiar environment. To study this we trained rats to run towards an odor source in a multi-choice olfactory arena with near-laminar air-flow. We find that rather than casting, rats run directly towards an odor port, and if this is incorrect, they serially sample other sources. This behavior is consistent and accurate in the presence of perturbations such as novel odors, background odor, unilateral nostril stitching and turbulence. We developed a model that predicts that this run-and-scan tracking of air-borne odors is faster than casting provided there are a small number of targets at known locations. Thus the combination of best-guess target selection with fallback serial sampling provides a rapid and robust strategy for finding odor sources in familiar surroundings.

Significance Statement: Our study presents a novel olfactory task making it possible to study air-borne odor tracking under well-controlled air-flow conditions, which elicit robust and spontaneous behavioral patterns in rats. The study has numerous implications for the neuroethology of odor guided target selection, and opens up interesting questions about how rats choose between strategies under different conditions that they may encounter in the field. It further sets tight constraints on olfactory sensory processing, both in terms of the sampling time, and in terms of decision-making. We speculate there may also be implications for how animals combine multisensory input for odor guided navigation and target selection.