Dynamic ensemble odor coding in the mammalian olfactory bulb: sensory information at different timescales.

Neural firing discharges are often temporally patterned, but it is often ambiguous as to whether the temporal features of these patterns constitute a useful code. Here we show in the mouse olfactory bulb that ensembles of projection neurons respond with complex odor- and concentration-specific dynamic activity sequences developing below and above sniffing frequency. Based on this activity, almost optimal discrimination of presented odors was possible during single sniffs, consistent with reported behavioral data. Within a sniff cycle, slower features of the dynamics alone (>100 ms resolution, including mean firing rate) were sufficient for maximal discrimination. A smaller amount of information was also observed in faster features down to 20-40 ms resolution. Therefore, mitral cell ensemble activity contains information at different timescales that could be separately or complementarily exploited by downstream brain centers to make odor discriminations. Our results also support suggestive analogies in the dynamics of odor representations between insects and mammals.