Intranasal Trigeminal Stimulation Research Articles

Odor-induced sound localization bias under unilateral intranasal trigeminal stimulation.

As a stereo odor cue, internostril odor influx could help us in many spatial tasks, including localization and navigation. Studies have also revealed that this benefit could be modulated by the asymmetric concentrations of both influxes (left nose vs right nose). The interaction between olfaction and vision, such as in object recognition and visual direction judgment, has been documented; however, little has been revealed about the impact of odor cues on sound localization. Here we adopted the ventriloquist paradigm in auditory-odor interactions and investigated sound localization with the concurrent unilateral odor influx. Specifically, we teased apart both the "nature" of the odors (pure olfactory stimulus vs. mixed olfactory/trigeminal stimulus) and the location of influx (left nose vs. right nose) and examined sound localization with the method of constant stimuli. Forty-one participants, who passed the Chinese Smell Identification Test, perceived sounds with different azimuths (0°, 5°, 10°, and 20° unilaterally deflected from the sagittal plane by head-related transfer function) and performed sound localization (leftward or rightward) tasks under concurrent, different unilateral odor influxes (10% v/v phenylethyl alcohol, PEA, as pure olfactory stimulus, 1% m/v menthol as mixed olfactory/trigeminal stimulus, and propylene glycol as the control). Meanwhile, they reported confidence levels of the judgments. Results suggested that unilateral PEA influx did not affect human sound localization judgments. However, unilateral menthol influx systematically biased the perceived sound localization, shifting toward the odor source. Our study provides evidence that unilateral odor influx could bias perceived sound localization only when the odor activates the trigeminal nerves.

Frequent minty chewing gum use is associated with increased trigeminal sensitivity: An fMRI study

Repeated sensory exposure through frequent consumption of certain foods leads to changes in the processing of sensory cues. We investigated the influence of frequent minty chewing gum consumption on the neurobehavioral processing of intranasal trigeminal and olfactory stimuli. fMRI responses to a trigeminal minty odor (L-menthol), a non-trigeminal minty odor (L-carvone), and a non-trigeminal non-minty odor (strawberry) were assessed in 29 young adults (mean age = 23 years, SD = 4.3 years; mean BMI = 22.7, SD = 1.9; thirteen females), who were divided into a minty chewing gum high frequency (N = 18) and a low infrequency (N = 11) groups based on their self-reported frequency of chewing gum consumption. Participants’ performance for odor lateralization, ratings for perceived odor intensity, pleasantness, familiarity, and pungency were also collected. Compared to the low frequency group, the high frequency group rated L-menthol as more familiar and performed better during the L-menthol lateralization test. The high frequency group compared to low frequency group showed stronger activation in trigeminal and somatosensory brain regions during perception of trigeminal component. These findings suggest an association between frequent minty odor exposure and increased neurobehavioral sensitivity to intranasal trigeminal stimulation.

Central Processing of Trigeminal Activation in Humans

Although numerous fMRI studies have been performed on the processing of olfactory information, the intranasal trigeminal system so far has not received much attention. In a pilot study stimulants were presented within a constantly flowing airstream birhinally to activate the olfactory (phenylethyl alcohol, H(2)S) or the trigeminal (CO(2)) nerves. Both olfactory and trigeminal stimulation activated the ventral insular cortex. Intranasal trigeminal stimulation additionally led to an activation of the midbrain, superior temporal gyrus, anterior caudate nucleus, and the dorsolateral orbitofrontal cortex. Cerebellar activation was reduced relative to odorous stimuli. For all stimuli, right-sided activity was more pronounced. These results suggested that processing of intranasal activation follows a pattern which is, at least to some degree, similar for both trigeminal and olfactory stimulation. This and results from several other studies emphasize the fact that there is a high degree of interaction between the different aspects of the chemical senses, also in the sense that chemosensory-induced activation in the nasal cavity is processed in similar cortical networks. Interactions between the olfactory and trigeminal system can also be seen in patients with acquired olfactory loss, who exhibit reduced trigeminal sensitivity, possibly due to the lack of a central-nervous interaction. Both the orbitofrontal cortex and the rostral insula appear to be of significance in the amplification of trigeminal input, which is missing in patients with olfactory loss.

PET‐based investigation of cerebral activation following intranasal trigeminal stimulation

The present study aimed to investigate cerebral activation following intranasal trigeminal chemosensory stimulation using O15-H2O-PET. A total of 12 healthy male participants underwent a PET scan presented with four scanning conditions; two left-sided intranasal CO(2)-stimuli and two matched baseline conditions consisting of odorless air. CO(2) was used as it produces burning and stinging sensations. Stimulation started 20 s before intravenous injection of the isotope and lasted for the first 60 s of the 5 min scan time. A comparison between CO(2) and baseline showed a pronounced activation of the trigeminal projection area at the base of the postcentral gyrus (primary and secondary somatosensory cortex) which was more intense for the right hemisphere, contralateral to the side of stimulation. In addition, activation was also found in the piriform cortex which is typically activated following odor presentation and thus thought of as primary olfactory cortex. In conclusion, and in line with previously published work, our data suggest that intranasal trigeminal stimulation not only activates somatosensory projection areas, but that it also leads to activation in cerebral areas associated with the processing of olfactory information. This may be interpreted in terms of the intimate relation between the intranasal chemosensory systems.

New Whiffs About Chemesthesis. Focus on “TRPM5-Expressing Solitary Chemosensory Cells Respond to Odorous Irritants”

In the recent article by Lin and collaborators (2008), they show that solitary chemosensory cells dispersed in the respiratory epithelium of the mouse nasal cavity could comprise a new transduction system for some noxious stimuli. Chemical sensitivity in the nasal cavity is not limited to smelling

Intranasal trigeminal sensitivity in subjects with allergic rhinitis

Trigeminal nerve endings of the human nasal mucosa are activated by chemical, physical or thermal stimuli. Activation of these A(delta) and C fibers can be quantified through the recording of chemo-somatosensory event-related potentials (ERP). The aim of this study was to investigate whether allergy-related activation of trigeminal nerve endings leads to changes in their responsiveness to intranasal trigeminal stimulation. Gaseous carbon dioxide (CO(2)) stimuli were applied in three sessions (baseline, after NaCl solution and after allergen application) to the nasal mucosa of 13 subjects with allergic rhinitis. Chemo-somatosensory ERP were recorded, and subjects rated the intensity of rhinitis symptoms. Administration of allergen produced a significant shortening of chemo-somatosensory ERP peak latencies P1 and N1. Observed changes of latencies were in line with rhinitis symptoms subjects indicated during the session. In addition, there was a negative relation between the general symptom score and ERP peak latencies, obtained both at baseline and after allergen exposure. In conclusion, it is hypothesized that in patients suffering from allergic rhinitis, nasal itching and sneezing after allergen exposure are, at least in part, clinical correlates of the activation of trigeminal nerve endings due to local inflammatory mechanisms. The correlations between ERP latencies and the patients' symptoms indicate that ERP latencies may possess a predictive value of the subjects' responsiveness to allergens.

Functional MRI of Intranasal Chemosensory Trigeminal Activation

Numerous brain imaging studies using positron emission tomography or functional magnetic resonance imaging (fMRI) have provided considerable information regarding the processing of sensory information. While many studies have also been performed on olfactory mediated sensations, cerebral activation following intranasal trigeminal stimulation has not been systematically addressed. The aim of this pilot study was to look at cerebral activation following trigeminally induced activation using CO2, a stimulant which almost exclusively activates the trigeminal system. This activation was compared to effects of stimulation with ‘pure’ olfactory stimuli [i.e. H2S and phenyl ethyl alcohol (PEA)]. Based upon the intimate connections between the trigeminal and olfactory systems (Doty et al., 1978; Hummel and Livermore, 2002), we hypothesized that there would be overlap between central activation induced by separate stimulation of the olfactory and trigeminal systems. We expected that olfactory stimulation would produce activation in, for example, the insular, piriform and orbitofrontal cortices, as well as in the cerebellum and gyrus rectus (Savic, 2002). We sought to determine which, if any, of these structures were activated by trigeminal stimulation. In terms of lateralization, stronger activation of the right hemisphere was expected (Hummel et al., 1995; Hari et al., 1997).

Olfactory and intranasal trigeminal event-related potentials in anosmic patients.

The aim of this study was to investigate the usefulness of chemosensory event-related potentials (CSERPs) in response to both olfactory and intranasal trigeminal stimulation in the diagnosis of anosmia. Forty-four patients participated. Gaseous CO2 was used for trigeminal stimulation, vanillin and H2S were used as olfactory stimulants. Event-related potentials to olfactory stimuli could not be obtained in any of the anosmic patients, indicating the complete loss of the sense of smell. However, all patients responded to stimulation of the trigeminal nerve with CO2. These data clearly demonstrate the clinical significance of CSERPs in the assessment of anosmia.

Intranasal trigeminal stimulation from odorous volatiles: Psychometric responses from anosmic and normal humans

Psychometric ratings of the perceived intensity, pleasantness, coolness, warmth, and presumptive safety of high concentrations of 47 nasally-inhaled chemicals commonly used in olfactory research were established for three groups of human observers (n = 15/group): (1) anosmics lacking olfactory (CN I), but not trigeminal (CN V), nerve function; (2) normals asked to rate only intranasal trigeminal (CN V) sensations (trigeminal focus group); and (3) normals asked to rate the overall odor experience in the traditional fashion. Forty-five of the 47 compounds were detected by at least some proportion of the anosmics in a forced-chice test. Although differences in the rated intensities of the stimuli were present between the three experimental groups, the relative rankings of the intensity responses were quite similar (rs ranging from 0.92 to 0.97). The pleasantness and presumed safety of the chemicals varied inversely with the perceived intensity in all three groups. The use of 11 to 13 readily-available and computer-derived molecular descriptors in linear learning machine pattern recognition analyses separated the 47 stimuli correctly into four discrete intensity classes. A multiple linear regression equation based upon such molecular descriptors (multiple R = .88) proved successful in predicting the perceived trigeminal intensities of 12 chemical stimuli similar in general structure to members of the original stimulus set (r = .80 between predicted and observed intensities). These results emphasize the importance of trigeminal input in human nasal chemoreception and support the notion that the perceived intensities of nasally-inhaled stimulants can be mathematically predicted from relatively simple physicochemical and molecular structural parameters.