A low-cost open-architecture taste delivery system for gustatory fMRI and BCI experiments

Experiencing sweet taste is associated with an increase in prosocial behavior

Taste may be the first sense that emerged in evolution. Taste is also a very important sense since it signals potential beneficial or dangerous effects of foods. Given this fundamental role of taste in our lives, it is not surprising that taste also affects our psychological perception and thinking. For example, previous research demonstrated remarkable psychological effects of sweet taste experiences, suggesting that sweetness may be a source domain for prosocial functioning. Recent research reports that briefly experiencing sweet taste made participants more helpful in their intentions and behavior. The current study aims to test this hypothesis and to examine the neural underpinnings of this effect by using an fMRI approach. Participants were asked to taste sweet, salty, and neutral taste while lying in the fMRI scanner. Subsequently their prosocial behavior was tested by playing the dictator game, a measure of prosocial behavior. Results showed that sweet taste was associated with an increase in prosocial behavior compared with previously experiencing salty taste but did not affect control stimuli ratings. FMRI results revealed a modulation of the dorsal anterior cingulate cortex associated with this sweetness effect. This brain area is known to play a central role for monitoring conflicts and decisions and has been directly linked to selfish and prosocial economic decisions. The results demonstrate that sweet taste has complex psychological effects including positive and socially desirable outcomes. We discuss the results with other studies on psychological sweetness effects and suggest possible implications of these findings.

Sex differences in the taste-evoked functional connectivity network

The central gustatory pathway encompasses multiple subcortical and cortical regions whose neural functional connectivity can be modulated by taste stimulation. While gustatory perception has been previously linked to sex, whether and how the gustatory network differently responds to basic tastes between men and women is unclear. Here, we defined the regions of the central gustatory network by a meta-analysis of 35 fMRI taste activation studies and then analyzed the taste-evoked functional connectivity between these regions in 44 subjects (19 women) in a separate 3 Tesla activation study where sweet and bitter solutions, at five concentrations each, were administered during scanning. From the meta-analysis, a network model was set up, including bilateral anterior, middle and inferior insula, thalamus, precentral gyrus, left amygdala, caudate and dorsolateral prefrontal cortex. Higher functional connectivity than in women was observed in men between the right middle insula and bilateral thalami for bitter taste. Men exhibited higher connectivity than women at low bitter concentrations and middle-high sweet concentrations between bilateral thalamus and insula. A graph-based analysis expressed similar results in terms of nodal characteristics of strength and centrality. Our findings add new insights into the mechanisms of taste processing by highlighting sex differences in the functional connectivity of the gustatory network as modulated by the perception of sweet and bitter tastes. These results shed more light on the neural origin of sex-related differences in gustatory perception and may guide future research on the pathophysiology of taste perception in humans.

3D-Printed Pacifier-Shaped Mouthpiece for fMRI-Compatible Gustometers

Gustometers have made it possible to deliver liquids in functional magnetic resonance imaging (fMRI) settings for decades, and mouthpieces are a critical part of these taste delivery systems. Here, we propose an innovative 3D-printed fMRI mouthpiece inspired by children's pacifiers, allowing human participants to swallow while lying down in an MRI scanner. We used a large sample to validate the effectiveness of our method. The results suggest that the mouthpiece can be used to deliver taste stimuli by showing significant clusters of activation in the insular and piriform cortex, which are regions that have been consistently identified in taste processing. This mouthpiece fulfills several criteria guaranteeing a gustatory stimulus of quality, making the delivery precise and reliable. Moreover, this new pacifier-shaped design is simple and cheap to manufacture, hygienic, comfortable to keep in the mouth, and flexible to use in diverse cases. We hope that this new method will promote and facilitate the study of taste and flavor perception in the context of reward processing in affective neuroscience, and thus, help provide an integrative approach to the study of the emotional nature of rewards.

Intensity-related distribution of sweet and bitter taste fMRI responses in the insular cortex

The human gustatory cortex analyzes the chemosensory properties of tastants, particularly the quality, intensity, and affective valence, to determine whether a perceived substance should be ingested or rejected. Among previous studies, the spatial distribution of taste intensity-related activations within the human insula has been scarcely addressed. To spatially characterize a specialized or distributed nature of the cortical responses to taste intensities, a functional magnetic resonance imaging study was performed at 3 T in 44 healthy subjects where sweet and bitter tastants were administered at five increasing concentrations and cortex-based factorial and parametric analyses were performed. Two clusters in the right middle-posterior and left middle insula were found specialized for taste intensity processing, exhibiting a highly nonlinear profile across concentrations. Multiple clusters were found activated by sweet and bitter taste stimuli at most concentrations, in the anterior, middle-posterior, and inferior portion of the bilateral insula. Across these clusters, respectively, for the right and left insula, a superior-to-inferior and an anterior-to-posterior spatial gradient for high-to-low concentrations were observed for the most responsive intensity of both tastes. These findings may gather new insights regarding how the gustatory cortex is spatially organized during the perceptual processing of taste intensity for two basic tastants.

Neuroimaging of smell and taste

The senses of taste and smell developed early in evolution and are of high ecological and clinical relevance in humans. Chemosensory systems function, in large part, as hazard avoidance systems, thereby ensuring survival. Moreover, they play a critical role in nutrition and in determining the flavor of foods and beverages. Their dysfunction has been shown to be a key element of early stages of a number of diseases, including Alzheimer's and Parkinson's diseases. Advanced neuroimaging methods provide a unique means for understanding, in vivo, neural and psychological processing of smell, taste, and flavor, and how diseases can impact such processing. This chapter provides, from a neuroimaging perspective, a comprehensive overview of the anatomy and physiology involved in the odor and taste processing in the central nervous system. Some methodological challenges associated with chemosensory neuroimaging research are discussed. Multisensory integration, the mechanisms that enable holistic sensory experiences, is emphasized.