What exactly does the nose know? a characterization of aversive stimulus-evoked activity in the early olfactory circuit

The ability to learn from previous experiences and use them in current circumstances is a skill that is necessary for success in any environment. This skill is dependent on our ability to learn, which requires an understanding of the relationships between encountered stimuli. Accumulating evidence shows that learning the relationship between stimuli can occur even in early sensory processing regions in the brain, even in places that seemingly lack of knowledge about stimuli occurring in other sensory modalities. To test what information an extremely early sensory region might have about other stimuli (or their outcomes for the organism), we used optical neurophysiological methods to observe neural activity in the mouse olfactory bulb during the presentation of aversive electrical stimulation of the tail. The results demonstrated that populations of PG, SA, and M/T neurons in the olfactory bulb respond not only to odors but also to tailshock. These responses are not directly evoked by peripheral input from OSNs, which did not exhibit any response to shock. Nonetheless, the response to shock in these neuronal populations were eliminated when the peripheral airflow was shunted away from the nose by a tracheotomy or when the ipsilateral airflow was prevented via naris occlusion. Pilot data demonstrated that various types of aversive stimuli besides tailshock evoked similar patterns of bulbar activity. These data demonstrate that during odor-cued fear learning, which is known to induce local, stimulus-specific plasticity in these populations of neurons in the olfactory bulb, information about an olfactory conditioned stimulus (CS) converges with activity driven by a somatosensory unconditioned stimulus (US) as early as the olfactory bulb glomeruli. This could underlie sensory changes associated with associative learning.M.S.Includes bibliographical reference