SPLTRAK Abstract Submission
Odor mixture representation in cortical feedback projections to the olfactory bulb
Joseph D. Zak & Venkatesh N. Murthy
Harvard University, Cambridge, MA, United States

The olfactory bulb not only receives input from the sensory periphery, but also integrates dense top-down information from the piriform cortex. The piriform cortex is thought to be involved in computations related to odor identity, quality, and predictive coding; however, it is unknown to what degree these cognitive aspects of odor processing are transmitted back to the olfactory bulb. We have begun to investigate how projections from the piriform cortex to the olfactory bulb respond to behaviorally relevant odor mixtures. We used multiphoton microscopy to visualize odor responses from cortical axon terminals expressing GCaMP6f. Individual boutons had diverse responses to monomolecular odorants, as well as to complex odor mixtures. The activity of individual boutons >16000 bouton-odor pairs) could be increased or suppressed by stimulation with monomolecular odorants. For nearly all boutons, response polarity was preserved across all responsive odors. We next considered how these feedback projections would respond to odors at different concentrations. For many boutons, we observed strong concentration dependence to the responses, with the highest odor concentration (10%) eliciting the largest positive, as well as negative signals; however, a subset of boutons were concentration invariant. Lastly, we examined bouton responses to odor mixtures containing 2-12 components. Our preliminary analysis points to highly non-linear mixture interactions. We found that the fraction of boutons with enhanced responses increased with the number of mixture components, while the fraction of suppressed boutons remained constant. In summary, complex information about odor composition is broadcast to the olfactory bulb, and ongoing experiments are aimed at dissecting the nature of this information.