A neural system for encoding odor valence which influences approach behaviors

Odors may elicit strong emotional and behavioral responses which are known to be strengthened through learning. Presumably subserving this, olfactory structures are well-known for their experience-dependent plasticity, yet the specific cellular systems involved and the actual influence of these systems on behavior are less understood. Here we investigated the transformation of odor information throughout the association of odors with learned-rewarded outcomes and also sought to link those neural systems with displays of reinforcement-based approach behaviors. First, we investigated the representation of odor-reward associations, also known as valence, within two areas recipient of dense olfactory bulb input, the posterior piriform cortex (pPCX) and olfactory tubercle (OT), using simultaneous multi-site electrophysiological recordings from mice engaged in a reward-based olfactory learning task. As expected, neurons in both regions represented the reward-associated valence of odors, yet both the proportion of neurons recruited by conditioned rewarded odors and the magnitudes of their recruitment were distinctly pronounced in the OT. Using fiber photometry we found that odor valence coding in the OT occurs among D1- but not D2-type dopamine receptor expressing neurons. In both the recordings and imaging, statistically meaningful changes in activity occurred prior to instrumental behavior responses. Finally, using optogenetics we show that OT D1-receptor expressing neurons strongly influence reward-motivated approach behavior. Together our results contribute to a model whereby OT D1 neurons support olfactory valence and ultimately hedonic-based behavioral responses.