Abstract
Olfactory sensitivity is influenced by intranasal trigeminal sensation. For instance, sniffing is central to how humans and animals perceive odorants. Here, we investigated the influence of olfactory costimulation on the perception of intranasal somatosensory stimulation. In this study, 22 healthy human subjects, with normal olfactory function, performed a localization task for stimulation using weak air puffs, a pure odorant, phenyl ethyl alcohol (PEA; rose odor), or their combination. Visual cues were used to inform participants to briefly hold their breath while weak, poorly localizable, air puffs and/or PEA were delivered to either nostril. Although PEA alone could not be localized to the correct nostril, when it accompanied a weak air puff in the ipsilateral nostril, localization accuracy significantly improved, relative to presentation of the air puff without the odorant. The enhancement of localization was absent when the air puff and PEA were presented to opposite nostrils. Since ipsilateral but not contralateral costimulation with PEA increased the accuracy of weak air puff localization, the results argue against a non-specific alerting effect of PEA. These findings suggest an interaction between olfactory and intranasal somatosensory stimuli leading to their integration.
Highlights
The intranasal trigeminal system processes chemosensory as well as somatosensory trigeminal stimulation conveyed via the trigeminal nerve
phenyl ethyl alcohol (PEA) could not be localized above chance, it enhanced the localizability of weak air-puffs delivered to the same, but not opposite nostril
The observed enhancement argues against a non-specific alerting effect by the odorant, which would have been expected to lead to similar effects whether PEA and airpuffs were delivered to the same or opposite nostrils
Summary
The intranasal trigeminal system processes chemosensory as well as somatosensory trigeminal stimulation conveyed via the trigeminal nerve. Olfactory information is processed via the olfactory nerve (cranial nerve I), but most odorants stimulate both sensory systems via mutually suppressing and enhancing interactions between each other (Brand 2006; Doty et al 1978; Friedland and Harteneck 2017). Chemosensory trigeminal stimuli are perceived to be at higher intensities when presented with olfactory co-stimulation (Cain and Murphy 1980; Livermore et al 1992). Active sniffing as well as when odorants are delivered into participants’ nostrils using air-puffs (i.e., passive sniffing) improve olfactory perception (Frasnelli et al 2009). Whether olfactory costimulation can modulate the intranasal somatosensory trigeminal perception still remains unclear
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