Olfaction is traditionally considered a ‘slow’ sense, but recent evidence demonstrates that rodents are capable of making extremely difficult odor discriminations rapidly, in as little as a single sniff. To understand the temporal aspects of olfactory information processing, we combine electrophysiological, optogentic, and behavioral approaches.
We found that odorants evoked precisely sniff-locked activity in mitral/tufted cells in the olfactory bulb of awake mouse. Individual cells expressed odor-specific temporal patterns of activity and responses were more tightly time-locked to the sniff phase than to the time after inhalation onset. Precise locking to sniff phase may facilitate ensemble coding by making synchrony relationships across neurons robust to variation in sniff rate.
Relative timing of activity may represent information in the olfactory system. To test whether mice perceive the timing of olfactory activation relative to the sniff cycle, we used optogenetics in gene-targeted mice to generate spatially constant, temporally controllable olfactory input. We show that mice can discriminate between light-evoked inputs that are shifted in timing relative to the sniff cycle by as little as 10 ms, which is similar to the temporal precision of olfactory bulb odor responses. Our work provides evidence that the mammalian olfactory system can read temporal patterns, and suggests that timing of activity relative to sampling behavior is a potent cue that may enable accurate olfactory percepts to form quickly.