Decoding Olfactory Bulb Output: A Behavioral Assessment of Rate, Synchrony, and Respiratory Phase Coding

The olfactory system is a well-known model for studying the temporal encoding of sensory stimuli due to its rhythmic stimulus delivery through respiration. The sniff rhythm is considered critical to structuring the output of computation in the primary olfactory area, the olfactory bulb. Here, Neuropixels recording from awake, head-fixed mice confirmed that both the rate and sniff-locked spike timing are informative about odour identity. We tested the behavioural importance of these temporal features using simple closed-loop optogenetics embedded in custom behavioural paradigms. We found that mice perceive differences in evoked spike counts and discriminate between synchronous vs. asynchronous activations of the output neurons. Surprisingly, they failed to distinguish the timing of evoked activity relative to the sniff cycle. These results challenge the utility of internally generated rhythms as reference signals in the neural encoding of the environment.