Abstract
The anterior insula and rolandic operculum are key regions for flavour perception in the human brain; however, it is unclear how taste and congruent retronasal smell are perceived as flavours. The multisensory integration required for sour flavour perception has rarely been studied; therefore, we investigated the brain responses to taste and smell in the sour flavour-processing network in 35 young healthy adults. We aimed to characterise the brain response to three stimulations applied in the oral cavity—sour taste, retronasal smell of mango, and combined flavour of both—using functional magnetic resonance imaging. Effective connectivity of the flavour-processing network and modulatory effect from taste and smell were analysed. Flavour stimulation activated middle insula and olfactory tubercle (primary taste and olfactory cortices, respectively); anterior insula and rolandic operculum, which are associated with multisensory integration; and ventrolateral prefrontal cortex, a secondary cortex for flavour perception. Dynamic causal modelling demonstrated that neural taste and smell signals were integrated at anterior insula and rolandic operculum. These findings elucidated how neural signals triggered by sour taste and smell presented in liquid form interact in the brain, which may underpin the neurobiology of food appreciation. Our study thus demonstrated the integration and synergy of taste and smell.
Highlights
Flavour is a food-related perception that requires integration of different sensory systems in the brain
Significant activations for sour taste were observed in the pre- and postcentral gyrus, pallidum, prefrontal cortex, thalamus, cingulate cortex, middle temporal gyrus, and cerebellum (p < 0.05, family-wise error rate (FWE) corrected)
Our results suggest that the integration of a sour taste and mango smell first occurs at the rolandic operculum followed by the anterior insula
Summary
Flavour is a food-related perception that requires integration of different sensory systems in the brain. The latest fMRI studies reported that the multivoxel activation patterns in the insula, thalamus and other regions could reliably discriminate between sour and other tastes (18 participants) [17] and that the discriminating activation patterns between different taste qualities in the insula were affected by taste intensities (24 participants) [18]. These studies recruited between 6 and 24 participants, but recent neuroimaging guidelines have suggested that a sample size of approximately 30 participants is required for adequate power and to account for intersubject variability [19,20,21]. FMRI studies with a larger sample size (>30) would produce more representative data for the processing of sour taste, and enable an expansion of our knowledge about flavour, that is, the interaction of sour taste with congruent smell in the human brain
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