Turbulent airflow imposes strong intensity fluctuations onto natural odour plumes. It has been hypothesised that such fluctuations could carry information about odour source composition or distance. We have recently shown that mice can indeed extract information from odour concentration fluctuations of a bandwidth up to at least 40 Hz. However, it is largely unknown how neurons in the olfactory system can encode temporal features of the odour stimulus.
To understand how neurons in the mouse olfactory bulb (OB) encode temporal features of odour stimuli, we performed in-vivo extracellular and patch clamp recordings while administering precisely controlled temporally fluctuating odours at multiple frequencies between 2 Hz and 20Hz. We observed that, despite the heterogeneous activity profiles, a substantial fraction of OB neurons demonstrated frequency coupling in their sub-threshold domain for 2 Hz (29/70) and 20Hz (24/70) odour stimuli. Furthermore, mitral and tufted cells showed differential coupling of their membrane potential to odour concentration fluctuations, with tufted cells showing stronger coupling for the 20Hz stimuli compared to the mitral cells. Frequency coupling was largely independent of odour quality. Upon administering odour mixtures, we observed that neurons that coupled well to the mixtures also coupled well to at least one of the individual components of the mixture. Interestingly, pharmacological blocking of the inhibitory circuitry strongly modulated frequency coupling of cell-odour pairs at both 2Hz and 20Hz.
Overall, we conclude that the mouse olfactory system has the capacity to perceive rapid changes in odour concentrations, and this challenges the typical thinking of slow sensory processing in the olfactory system. Further, projection neurons in the mouse olfactory bulb can encode aspects of the temporal structure of the odour stimulus.