Olfactory and Trigeminal Systems Interact in the Periphery

The olfactory and trigeminal systems are intimately connected as most odorants stimulate both sensory systems. They interact by mutually suppressing and enhancing each other. However, the location and the degree of their interaction remain unclear. One method to test sensitivity in the trigeminal system is the odor localization task: when an odorant is presented to one nostril, we are able to localize the stimulated nostril only if the odorant stimulates the trigeminal nerve. Our objective was to evaluate the interaction between olfactory and trigeminal system by measuring the effect of an olfactory co-stimulation on the ability to localize a trigeminal stimulus. More specifically, we evaluated the influence of an olfactory co-stimulation with pure odors (phenyl ethanol, vanillin), presented either ipsilaterally or contralaterally, on the localization of predominantly trigeminal stimuli (mustard oil, eucalyptol). The ipsilateral, but not the contralateral, olfactory co-stimulation with a pure odorant increased the capacity to localize a trigeminal stimulus. These results suggest an interaction between the olfactory and trigeminal systems at peripheral, that is, mucosal, levels.