Smell perception serves to provide information not only about odor quality (i.e., what the odor is), but also about the emotional meaning of the odor to an observer: besides being potentially musky or fruity, odors can be experienced as pleasant or aversive, dependent in part on past experience of the observer. Brain imaging research in human subjects has demonstrated that olfactory cortex-owing to its connectivity to neural systems involved in learning, memory and emotion-plays a central role in representing odor valence. However, the cellular processes underlying the transformation of odor quality coding to behaviorally-relevant odor valence coding is as of yet unknown. The present proposal combines electrophysiological recordings with behavioral measures of odor valence to probe responses of small ensembles of olfactory cortical neurons to a set of odors with a known range of valences. A first set of experiments is designed to test how and when valence-related neural firing patterns appear in olfactory cortex. Based on previous work from our lab investigating valence coding in the taste system, the specific hypothesis is that odor quality and valence are both encoded in the dynamic response patterns of single olfactory cortex neurons. The validity of the results obtained from these experiments will then be tested by changing the valence of an odor-pairing it with sweet taste, and observing whether the previously- identified valence-related response patterns change accordingly. Finally, the source of valence-related firing patterns will be determined by combining optogenetic inactivation of a range of candidate regions with electrophysiological recordings of odor responses in olfactory cortex. Guided by the extant literature as well as a wealth of preliminary data, inactivation of taste cortex, the amygdala and orbitofrontal cortex is hypothesized to affect valence-related firing patterns in olfactory cortex. The results obtained from these experiments will influence our understanding of emotion, memory, and a variety of clinical syndromes known to affect perception of valenced stimuli (most notably autism).
Odors are not only floral or musky, woody or fruity, they also have intrinsic valence-that is, they are pleasant or aversive, preferred or shunned. Olfactory cortex codes both the quality and valence of odors, but how it does so is not yet known. Combining cutting-edge neuro-recording and molecular techniques with novel computational and behavioral analyses, I will test several hypotheses as to how, where, and when valence-related neural firing appears in the brain. The data provided by these experiments will influence our understanding of emotion, memory, and a variety of clinical syndromes known to affect perception of valenced stimuli (most notably autism).