In a dynamic environment, sensory systems must filter out irrelevant information to construct a stable percept. Animals who rely on smell need to identify and discriminate odors despite fluctuations in concentration, yet odor receptor activation is strongly concentration dependent. Here we explored how odor signals are transformed within the mouse olfactory bulb (OB) by developing an all-optical approach to identify the connectivity between odor receptor channels (glomeruli) and the mitral and tufted cells (MTCs), while monitoring their odor responses. We found that the glomeruli and MTCs activated earliest in a sniff robustly represented odor identity across concentrations, whereas MTCs connected to later activated glomeruli were concentration dependent. Furthermore, probing the responsiveness of MTCs to glomerular input found a short temporal window of excitability at a sniff’s onset, followed by prolonged odor-evoked inhibition. Our findings demonstrate, in awake animals, that the OB implements a rapid temporal filter, which is responsible for stabilizing identity across concentrations while decorrelating responses between odors. This study shows that the brain’s smell center uses precise timing and inhibition to read out early odor signals, enabling reliable odor identity across concentrations while rapidly separating (decorrelating) similar smell patterns for better discrimination.
Karadas et al. (Tue,) studied this question.