SPLTRAK Abstract Submission
Separating Respiration, Trigeminal and Olfactory Effects at the Cortical Level
Florian Fischmeister1, Christina Kumpitsch3, Cinzia Cecchetto1,2, Christine Moissl-Eichinger2,3, Veronika Schöpf1,2
1University of Graz, Graz, Austria
2BioTechMed, Graz, Austria
3Internal Medicine, Graz, Austria

Human odor perception is based on the tight interplay between the olfactory and the trigeminal system since most odorants stimulate both systems simultaneously. Additionally, odor perception is modulated by breathing, which also affects neuronal activity. To overcome possible biases in studies using intranasal chemosensory stimulation various experimental schemes using respiration triggering were proposed. Yet, such designs are technically demanding and prone to errors. Here we aim to separate respiration, trigeminal and odorant effects in a pseudo-free breathing paradigm. In this fMRI study, normosmic and hyposmic participants performed simple guided breathing where they had to match their breathing cycle to an expanding or shrinking ball. During the inhale-phase an odor stimulus (rose and peppermint), or diluted CO2 as trigeminal stimulus were presented birhinally using a computer controlled olfactometer. Data were analyzed using a standard GLM with the individual breathing pattern as an additional regressor.  Preliminary results of 5 participants already show that olfactory stimuli activated primary and secondary olfactory regions, while CO2 activated somatosensory regions and breathing the basal ganglia, cerebellum, and frontal areas. Direct comparison of odor versus breathing exhibited stronger and more distinct activation within both piriform cortices as well as within the parahippocampal and entorhinal cortices, both not found in the direct contrast. In hyposmic participants, a similar pattern evolved at a very lean threshold. CO2 compared to breathing revealed strong activation within the insular cortex and the supramarginal gyrus in both groups. These results further previous literature and emphasize the importance of the tight control of respiration pattern in olfactory science.