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Somatosensory signals in the olfactory system

Keith Perkins and Giuliano Iurilli, PhD

July 20, 2023 | 11:00 AM ET

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Odor encoding does not happen in a vacuum. Most odor encoding occurs while animals actively explore their world and learn new stimulus-event associations. Therefore, odor processing often interacts with other sensory modalities. In particular, somatosensory stimuli can be integrated at the very early stages of olfactory processing. Understanding how this integration influences odor processing and olfactory-driven behavior will shed new light on the benefits of multisensory integration.

Characterization of non-olfactory signals in the olfactory bulb and the role of respiration
Keith Perkins
Graduate Student, McGann Laboratory
Rutgers University: - Psychology Department - Behavioral and Systems Neuroscience


Most odor encoding occurs while organisms actively explore their world and learn what odors are ecologically significant. This plasticity can improve olfactory function and support adaptive behavior in both humans and animal models. Multiple labs have shown that when a mouse learns that a particular odor predicts an aversive electrical shock corresponding neuroplasticity occurs throughout the olfactory system, including the olfactory sensory neurons and olfactory bulb circuitry. However, it remains unclear how olfactory structures could know that a particular odor correlates with a footshock unless they also receive somatosensory information. We used in vivo widefield imaging to visualize calcium dynamics in several molecularly-defined populations of neurons in the olfactory bulbs of anesthetized mice while delivering aversive somatosensory stimulations including footshock and trigeminal nerve stimulation. We observed cell-type specific, spatiotemporally complex bursts of somatosensory-evoked activity in short axon cells, mitral/tufted cells, and periglomerular cells. These responses did not resemble odor-evoked responses and were not detected in populations of olfactory sensory neuron terminals. However, but they were generally phase-locked to respiration and evolved across respiratory cycles with different cell types responding with radically different latencies. Manipulation of intranasal airflow via tracheotomy or naris occlusion disrupted some (but not all) oscillatory activity in the absence of explicit sensory stimulation and eliminated neural responses to somatosensory stimulation in the olfactory bulb. Ongoing respiration-driven synchrony may thus dynamically gate centrifugal somatosensory signaling to the bulb. Understanding the convergence of olfactory, somatosensory, and respiratory information in the olfactory bulb will help us understand how the brain links olfactory stimuli to the rest of the body across time and sensory modalities.

Solving the sampling/sensation problem in the olfactory system
Giuliano Iurilli, Ph.D.
Principal Investigator
Center for Neuroscience and Cognitive systems - Italian Institute of Technology – Rovereto (Italy)


A fundamental problem for sensory systems is that sampling can distort sensory representations. For example, inhalations draw volatile odorants into the nose, but the airflow also stimulates a significant fraction of olfactory sensory neurons regardless of the identity and concentration of the odorant. It has been previously shown that this mechanosensory stimulus has a detrimental impact on olfactory encoding. Different airflow speeds generated by different inhalation speeds alter the responses of mitral/tufted neurons to the same olfactory stimulus. Therefore, like other sensory systems, the olfactory system has a sampling/sensation problem. And yet, the perception of odor intensity within a range of concentrations remains invariant to the inhalation speed. Therefore, the brain found a solution to the sampling/sensation problem. We investigated whether this problem persists in the piriform cortex. We found that individual neurons change their response to the same odor concentration based on the inhalation speed. However, a population code makes odor concentration representations sniff-invariant. This outcome is possible because cortical neurons encode the intensity of the airflow-generated stimulus; however, the mechanosensory and concentration tuning curves are uncorrelated. Therefore, the population representation of odor concentration is orthogonal to the population representation of the inhalation speed. We are now gathering evidence that embedding an uncorrelated motion-dependent signal during the encoding stage, like in the olfactory system, could be a canonical solution to the sampling/sensation problem adopted by other sensory systems too.