Similarity and Strength of Glomerular Odor Representations Define a Neural Metric of Sniff-Invariant Discrimination Time

Abstract

Summary: The olfactory environment is first represented by glomerular activity patterns in the olfactory bulb. It remains unclear how these representations intersect with sampling behavior to account for the time required to discriminate odors. Using different chemical classes, we investigate glomerular representations and sniffing behavior during olfactory decision-making. Mice rapidly discriminate odorants and learn to increase sniffing frequency at a fixed latency after trial initiation, independent of odor identity. Relative to the increase in sniffing frequency, monomolecular odorants are discriminated within 10–40 ms, while binary mixtures require an additional 60–70 ms. Intrinsic imaging of glomerular activity in anesthetized and awake mice reveals that Euclidean distance between activity patterns and the time needed for discriminations are anti-correlated. Therefore, the similarity of glomerular patterns and their activation strengths, rather than sampling behavior, define the extent of neuronal processing required for odor discrimination, establishing a neural metric to predict olfactory discrimination time. : Bhattacharjee et al. show that mice require more neuronal processing time to discriminate odors of different similarity, irrespective of sniffing. Sniffing is invariably increased at the onset of the decision-making time window. A metric defines discrimination time as a function of similarity and strength of glomerular activity. Keywords: odor discrimination time, sniffing, olfactory bulb, intrinsic optical signal imaging, Euclidean distance