Abstract
Despite distinct peripheral and central pathways, stimulation of both the olfactory and the gustatory systems may give rise to the sensation of sweetness. Whether there is a common central mechanism producing sweet quality sensations or two discrete mechanisms associated independently with gustatory and olfactory stimuli is currently unknown. Here we used fMRI to determine whether odor sweetness is represented in the piriform olfactory cortex, which is thought to code odor quality, or in the insular taste cortex, which is thought to code taste quality. Fifteen participants sampled two concentrations of a pure sweet taste (sucrose), two sweet food odors (chocolate and strawberry), and two sweet floral odors (lilac and rose). Replicating prior work we found that olfactory stimulation activated the piriform, orbitofrontal and insular cortices. Of these regions, only the insula also responded to sweet taste. More importantly, the magnitude of the response to the food odors, but not to the non-food odors, in this region of insula was positively correlated with odor sweetness rating. These findings demonstrate that insular taste cortex contributes to odor quality coding by representing the taste-like aspects of food odors. Since the effect was specific to the food odors, and only food odors are experienced with taste, we suggest this common central mechanism develops as a function of experiencing flavors.
Highlights
Despite distinct peripheral and central pathways, stimulation of both the olfactory and gustatory systems gives rise to the sensation of sweetness
We have demonstrated that insular cortex shows supra-additive responses to congruent but not incongruent odor-taste mixtures, indicating that taste-odor integration occurs in the insula and that it is dependent upon experience (Small et al, 2004)
The aim of the current study was to determine if the sweet taste-like quality of odors is encoded in primary olfactory cortex, which is known to code other aspects of odor quality (Gottfried et al, 2006; Li et al, 2008) or in primary insular taste cortex, which is thought to play a role in representing taste quality (Scott and Plata-Salaman, 1999; Schoenfeld et al, 2004)
Summary
Despite distinct peripheral and central pathways, stimulation of both the olfactory and gustatory systems gives rise to the sensation of sweetness. We use fMRI to explore whether peripherally distinct sources of sweet sensation have a common central mechanism. Four lines of evidence suggest that there is a common central mechanism. Subjects conflate odor and taste sweetness, and as a result report that the overall sweetness of a taste/odor solution is approximately the sum of the sweetness of the taste alone and the odor alone. This suggests that the sweetness quality produced by stimulation of both modalities is similar
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