Unlike vision and audition, in olfaction we do not understand how physical properties of a stimulus are translated into perceptual characteristics. While most studies focus on the olfactory system as the primary mechanism for detecting airborne chemicals and facilitating odor perception, most volatile stimuli at high concentrations activate both olfactory sensory neurons (OSNs) and chemosensory trigeminal fibers. The trigeminal system elicits sensations such as cooling, warming, pricking, or irritation when stimulated by odorants, but it also interacts with the olfactory system at peripheral and central levels of the nervous system.
To gain insights into the interplay between the olfactory and trigeminal systems, we compared physiological and perceptual responses in mice and humans. In both systems, the olfactory stimulus was 2-phenethylalcohol (PEA, rose), which does not activate the trigeminal system while the trigeminal stimulus was CO2, which does not elicit an olfactory response. By varying the concentrations of CO2, we aimed to determine the impact of trigeminal activation on the olfactory signal. In a mouse model, co-stimulation of these systems influenced the generation of olfactory signals in the olfactory epithelium (OE) measured with the electro-olfactogram (EOG) technique.

Similarly, the effects of trigeminal activation on odor perception were evident among trained human participants who rated the perceived intensity of binary mixtures of PEA and CO2. Combining animal electrophysiology and human psychophysics allowed us to explore the integration of both olfactory and trigeminal components in odor intensity encoding. Ultimately, the findings from this research will lay the groundwork for developing a model that encompasses multiple molecular and sensory factors, benefiting both the scientific community and industries involved in scent-related applications.

This work was supported by the Monell Chemical Senses Center Seed Fundings Program.