Abstract
Although the brain structures involved in integrating odorant and trigeminal stimuli are well-documented, there is still a need to clarify (1) how emotional response is represented in the human brain during cross-modal interaction between odors and trigeminal stimuli, and (2) whether the degree of congruency between the two types of stimuli influences these emotional responses and their neural processing. These questions were explored combining psychophysics, event-related potentials (ERP) and fMRI in the same group of 17 subjects under a “congruent condition” (intranasal carbon dioxide mixed with the smell of orange, a combination found in soda drinks, for example), and an “incongruent condition” (intranasal carbon dioxide mixed with the smell of rose, a combination not encountered in everyday life). Responses to the 3 constituent stimuli (carbon dioxide, orange, and rose) were also measured. Hedonic and intensity ratings were collected for all stimulations. The congruent bimodal stimulus was rated as more pleasant than the incongruent. This behavioral effect was associated with enhanced neural activity in the hippocampus and anterior cingulate gyrus, indicating that these brain areas mediate reactivation of pleasant and congruent olfactory-trigeminal associations.
Highlights
Chemosensation comprises three main sensory modalities: olfaction and gustation, involved in discrimination and identification of, respectively, odorant and tastant stimuli, and the trigeminal system involved in detecting the irritating, fresh or painful component of chemosensory stimuli [see Lundstrom et al (2011) for a review]
The mechanisms and brain structures involved in the neural integration of odors and tastes have been well-documented in the last decade (Dalton et al, 2000; De Araujo et al, 2003; Small et al, 2004; Small and Prescott, 2005), but there is still a need to understand how emotional responses are represented in the human brain during cross-modal interaction of odors and trigeminal stimuli
Psychophysics, fMRI and electroencephalography were combined in the same subjects under congruent and incongruent conditions relevant to food: in the “congruent” condition, intranasal carbon dioxide was mixed with the smell of orange, and in the “incongruent condition” intranasal carbon dioxide was mixed with the smell of rose
Summary
Chemosensation comprises three main sensory modalities: olfaction and gustation, involved in discrimination and identification of, respectively, odorant and tastant stimuli, and the trigeminal system involved in detecting the irritating, fresh or painful component of chemosensory stimuli [see Lundstrom et al (2011) for a review]. The chemical senses provide a special window onto the cross-modal integration of emotion: chemosensory stimuli are mixtures of various compounds stimulating the olfactory, gustatory and trigeminal systems; each system may evoke particular affective states. The mechanisms and brain structures involved in the neural integration of odors and tastes have been well-documented in the last decade (Dalton et al, 2000; De Araujo et al, 2003; Small et al, 2004; Small and Prescott, 2005), but there is still a need to understand how emotional responses are represented in the human brain during cross-modal interaction of odors and trigeminal stimuli. Past and recent studies suggest that congruency is a key factor in modulating the cross-modal integration of chemosensory stimuli, especially when the sensory cues belong to the same object
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