The neuronal correlates of intranasal trigeminal function—an ALE meta-analysis of human functional brain imaging data

Abstract

Almost every odor we encounter in daily life has the capacity to produce a trigeminal sensation. Surprisingly, few functional imaging studies exploring human neuronal correlates of intranasal trigeminal function exist, and results are to some degree inconsistent. We utilized activation likelihood estimation (ALE), a quantitative voxel-based meta-analysis tool, to analyze functional imaging data (fMRI/PET) following intranasal trigeminal stimulation with carbon dioxide (CO2), a stimulus known to exclusively activate the trigeminal system. Meta-analysis tools are able to identify activations common across studies, thereby enabling activation mapping with higher certainty. Activation foci of nine studies utilizing trigeminal stimulation were included in the meta-analysis. We found significant ALE scores, thus indicating consistent activation across studies, in the brainstem, ventrolateral posterior thalamic nucleus, anterior cingulate cortex, insula, precentral gyrus, as well as in primary and secondary somatosensory cortices – a network known for the processing of intranasal nociceptive stimuli. Significant ALE values were also observed in the piriform cortex, insula, and the orbitofrontal cortex, areas known to process chemosensory stimuli, and in association cortices. Additionally, the trigeminal ALE statistics were directly compared with ALE statistics originating from olfactory stimulation, demonstrating considerable overlap in activation. In conclusion, the results of this meta-analysis map the human neuronal correlates of intranasal trigeminal stimulation with high statistical certainty and demonstrate that the cortical areas recruited during the processing of intranasal CO2 stimuli include those outside traditional trigeminal areas. Moreover, through illustrations of the considerable overlap between brain areas that process trigeminal and olfactory information; these results demonstrate the interconnectivity of flavor processing.

Chemosensory interaction: acquired olfactory impairment is associated with decreased taste function

“…Previous studies in patients seem to confirm that [3,17]. Very recent fMRI studies in healthy subjects seem to further corroborate this functional interdependence by showing that intranasal trigeminal stimulation co-activates central olfactory areas such as the piriform cortex, while cutaneous trigeminal stimulation solely activates the traditional trigeminal areas [1,19]. The other way around, a very recent study in rats also suggests that gustatory function influences olfactory processing, thereby giving further evidence to the hypothesis of mutual chemosensory interaction [11].…”

The human vestibular cortex revealed by coordinate-based activation likelihood estimation meta-analysis

“…This method provides a statistical description of the overlap between activation foci reported in neuroimaging studies. During the last few years, this method has been applied to identify the motor cortex involved in execution/observation of movements (Caspers et al, 2010), or to identify brain regions involved in audition (Petacchi et al, 2005), trigeminal sensation (Albrecht et al, 2010), olfaction, gustation, interoception, somatosensation, and pain (Kurth et al, 2010b). Recently, the ALE method has been applied to localize the vestibular cortex (Zu Eulenburg et al, 2012), but without identifying the cerebral networks responding differently and similarly to CVS, GVS and sounds.…”

Enhancing effect of natural borneol on the absorption of geniposide in rat via intranasal administration

“…The intranasal route can be a hopeful substitution for MCHM injection, as drugs can be absorbed sufficiently and rapidly into blood for systemic administration (Albrecht et al, 2010;Zhou et al, 2010), then transported from the nasal cavity to the central nervous system (Illum, 2003). The intranasal route is safer due to the barricade effect of the nasal mucosa.…”