Neural mechanisms of stereo olfaction

Abstract

Rodents primarily rely on odor information for navigation. As air-borne odor molecules constantly drift away from the source, they form a non-uniform and a fluctuating concentration gradient. To navigate in such a dynamically changing odor environment, the animal needs to extract instantaneous information about aspects of odor gradients. This is achieved by bilateral odor sampling that has been demonstrated in many species. In principle, bilateral comparison strategy could provide the animal with the knowledge of fast changing odor environment. The key assumptions for bilateral comparison are Symmetry: bilateral equivalence at all levels of the olfactory processing and Laterality: bilateral distinction of the information. Absence of any one of these prerequisites might upset the efficiency of odor localization behavior. In this study, we have checked for the extent of these attributes in early olfactory processing in the rat. We first established behavioral readouts of precisely controlled bilateral odorant stimuli. We found that rats could rapidly and accurately report the direction of a wide range of odor gradients, presented in a random sequence. Then, we measured the nasal airflow and found that the air flow was symmetric over long periods. Further, our study suggests that sampling from the two nostrils in the behavioral task were highly lateralized. Finally, we observed strong lateralization of odor elicited responses from both the receptor epithelium and the glomerular layer of the olfactory bulb. Taken together, these results suggest that the olfactory system is symmetric and the bilateral information flow is lateralized. Therefore, this forms the basis for a simple, single-sniff bilateral comparison mechanism to determine odor direction.