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. Sniff-locked activity is pervasive in the primary olfactory area, the olfactory bulb, and is considered critical to structuring the output of its computation. We tested the behavioral importance of these temporal features using simple closed-loop optogenetics embedded in custom behavioral 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 suggest that, beyond the first steps of olfactory processing, sniff rhythms play a more nuanced role, with greater reliance on the spike rate and synchrony for the neural encoding of the environment, consistent with a gradual transformation of encoding format at successive stages of sensory processing.