Encoding Innately Recognized Odors via a Generalized Population Code

Odors carrying intrinsic values often trigger instinctive aversive or attractive responses. Innate valence is thought to be conveyed through hardwired circuits along the olfactory pathway, insulated from influences of other odors. Here we show that in mice, mixing of innately aversive or attractive odors with a neutral odor abolishes the behavioral responses. Surprisingly, mixing of two odors with the same valence also abolishes the expected responses. Recordings from the olfactory bulb indicate that odors are not masked at the level of peripheral activation and glomeruli independently encode components in the mixture. However, crosstalk among the mitral/tufted cells changes their patterns of activity such that those elicited by the congruent mixtures can no longer be decoded as separate components. The changes in behavioral and mitral/tufted cell responses are associated with reduced activation of brain areas linked to odor preferences. Thus, interactions of odor channels at the earliest processing stage in the olfactory pathway lead to re-coding of odor identity. These results are inconsistent with insulated labeled lines and support a model of a common mechanism of odor recognition for both innate and learned valence associations.