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"Taste - physiology"
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Physiological Integration of Taste and Metabolism
Much of what we learned in school about how we taste is wrong. Progress in understanding how taste works is providing insights that may help in the management of obesity, diabetes, and other illnesses.
Journal Article
Tuning the value of sweet food: Blocking sweet taste receptors increases the devaluation effect in a go/no-go task
Despite the apparent simplicity of the go/no-go (GNG) task, in which individuals selectively respond or withhold responses, there is strong evidence supporting its efficacy in terms of modulating food preferences. Herein, we manipulated sweet taste perception and investigated the no-go devaluation effect that is typically observed due to GNG training with respect to sweet and savory food items. Prior to engaging in a GNG task, one group of participants rinsed their mouths with a liquid solution containing gymnemic acid, thereby transiently and selectively inhibiting sweet taste perception, while another group used a placebo solution. The participants who rinsed their mouths with gymnemic acid exhibited a stronger overall decrease in food evaluations from pre to post training. Furthermore, a pronounced no-go devaluation effect was observed for sweet foods, irrespective of the rinsing solution. Overall, our results support the notion that training in the GNG task can induce changes in the valuation of food stimuli, particularly for sweet foods.
Journal Article
The expectations humans have of a pleasurable sensation asymmetrically shape neuronal responses and subjective experiences to hot sauce
Expectations shape our perception, profoundly influencing how we interpret the world. Positive expectations about sensory stimuli can alleviate distress and reduce pain (e.g., placebo effect), while negative expectations may heighten anxiety and exacerbate pain (e.g., nocebo effect). To investigate the impact of the (an)hedonic aspect of expectations on subjective experiences, we measured neurobehavioral responses to the taste of hot sauce among participants with heterogeneous taste preferences. By identifying participants who “liked” versus those who strongly “disliked” spicy flavors and by providing contextual cues about the spiciness of the sauce to be tasted, we dissociated the effects of positive and negative expectations from sensory stimuli (i.e., visual and gustatory stimuli), which were the same across all participants. Our results indicate that positive expectations lead to modulations in the intensity of subjective experience. These modulations were accompanied by increased activity in brain regions previously linked to information integration and the placebo effect, including the anterior insula, dorsolateral prefrontal cortex, and dorsal anterior cingulate cortex, as well as a predefined “pleasure signature.” In contrast, negative expectations decreased hedonic experience and increased neural activity in the previously validated “Neurological Pain Signature” network. These findings demonstrate that hedonic aspects of one’s expectations asymmetrically shape how the brain processes sensory input and associated behavioral reports of one’s subjective experiences of intensity, pleasure, and pain. Our results suggest a dissociable impact of hedonic information: positive expectations facilitate higher-level information integration and reward processing, while negative expectations prime lower-level nociceptive and affective processes. This study demonstrates the powerful role of hedonic expectations in shaping subjective reality and suggests potential avenues for consumer and therapeutic interventions targeting expectation-driven neural processes.
Journal Article
Distinct representations of basic taste qualities in human gustatory cortex
The mammalian tongue contains gustatory receptors tuned to basic taste types, providing an evolutionarily old hedonic compass for what and what not to ingest. Although representation of these distinct taste types is a defining feature of primary gustatory cortex in other animals, their identification has remained elusive in humans, leaving the demarcation of human gustatory cortex unclear. Here we used distributed multivoxel activity patterns to identify regions with patterns of activity differentially sensitive to sweet, salty, bitter, and sour taste qualities. These were found in the insula and overlying operculum, with regions in the anterior and middle insula discriminating all tastes and representing their combinatorial coding. These findings replicated at super-high 7 T field strength using different compounds of sweet and bitter taste types, suggesting taste sensation specificity rather than chemical or receptor specificity. Our results provide evidence of the human gustatory cortex in the insula.
Previous research shows how taste types are represented across regions of the brain in non-human animals. Here, the authors examine how four basic tastes are represented in the human brain, showing evidence of the human gustatory cortex in the insula.
Journal Article
The impact of cognitive distraction on gustatory perception in volunteers with obesity
Obesity, a global health challenge, is influenced by biological, behavioral, socioeconomical, and environmental factors. In our technology-driven world, distracted eating is prevalent, yet neurocognitive mechanisms behind it remain poorly understood. This study targets individuals with overweight and obesity, exploring taste perception under distraction comprehensively. Participants formed two distinct groups based on their Body Mass Index (BMI), lean and overweight/obese. During the experiment participants received gustatory stimuli while playing a Tetris game of various difficulty levels. Participants rated taste intensity and pleasantness, with linear mixed models analyzing distraction effects. Results confirmed that high distraction levels reduced perception of taste intensity (
p
= 0.017) and taste pleasantness (
p
= 0.022), with variations influenced by gender and weight status. Individuals in the overweight/obese group exhibited most profound intensity changes during distraction (
p
= 0.01). Taste sensitivity ratings positively correlated with BMI interacting with gender (male r = 0.227,
p
< 0.001; female r = 0.101,
p
< 0.001). Overall across both groups, female participants demonstrated higher taste sensitivity compared to male participants (
p
< 0.001). This study highlights the impact of cognitive distraction during consumption on taste perception, particularly in relation to weight status and gender, underscoring their significant roles in this interplay.
Journal Article
Taste transduction and channel synapses in taste buds
The variety of taste sensations, including sweet, umami, bitter, sour, and salty, arises from diverse taste cells, each of which expresses specific taste sensor molecules and associated components for downstream signal transduction cascades. Recent years have witnessed major advances in our understanding of the molecular mechanisms underlying transduction of basic tastes in taste buds, including the identification of the bona fide sour sensor H+ channel OTOP1, and elucidation of transduction of the amiloride-sensitive component of salty taste (the taste of sodium) and the TAS1R-independent component of sweet taste (the taste of sugar). Studies have also discovered an unconventional chemical synapse termed “channel synapse” which employs an action potential-activated CALHM1/3 ion channel instead of exocytosis of synaptic vesicles as the conduit for neurotransmitter release that links taste cells to afferent neurons. New images of the channel synapse and determinations of the structures of CALHM channels have provided structural and functional insights into this unique synapse. In this review, we discuss the current view of taste transduction and neurotransmission with emphasis on recent advances in the field.
Journal Article
Differential Effect of TRPV1 Modulators on Neural and Behavioral Responses to Taste Stimuli
In our diet, we ingest a variety of compounds that are TRPV1 modulators. It is important to understand if these compounds alter neural and behavioral responses to taste stimuli representing all taste qualities. Here, we will summarize the effects of capsaicin, resiniferatoxin, cetylpyridinium chloride, ethanol, nicotine, N-geranyl cyclopropylcarboxamide, Kokumi taste peptides, pH, and temperature on neural and behavioral responses to taste stimuli in rodent models and on human taste perception. The above TRPV1 agonists produced characteristic biphasic effects on chorda tympani taste nerve responses to NaCl in the presence of amiloride, an epithelial Na+ channel blocker, at low concentrations enhancing and at high concentrations inhibiting the response. Biphasic responses were also observed with KCl, NH4Cl, and CaCl2. In the presence of multiple stimuli, the effect is additive. These responses are blocked by TRPV1 antagonists and are not observed in TRPV1 knockout mice. Some TRPV1 modulators also increase neural responses to glutamate but at concentrations much above the concentrations that enhance salt responses. These modulators also alter human salt and glutamate taste perceptions at different concentration ranges. Glutamate responses are TRPV1-independent. Sweet and bitter responses are TRPV1-independent but the off-taste of sweeteners is TRPV1-dependent. Aversive responses to acids and ethanol are absent in animals in which both the taste system and the TRPV1-trigeminal system are eliminated. Thus, TRPV1 modulators differentially alter responses to taste stimuli.
Journal Article
The neural representation of taste quality at the periphery
Using two-photon microendoscopy and genetically encoded calcium indicators the tuning properties of the first neural station of the gustatory system are explored; results reveal that ganglion neurons are matched to specific taste receptor cells, supporting a labelled line model of information transfer in the taste system.
Taste representation in the central nervous system
Individual tastes (sweet, sour, bitter, salty and umami) are detected by dedicated taste receptor cells on the tongue and palate, but how these signals are encoded and transmitted to the relevant part of the central nervous system — the gustatory cortex — is unknown. Using transgenic mice expressing a calcium indicator in neurons, Charles Zuker and colleagues characterize the tuning properties of ganglion neurons, the first neural station of the gustatory system. Ganglion neurons respond specifically to certain tastes, supporting a 'labelled line' model of information transfer in the taste system.
The mammalian taste system is responsible for sensing and responding to the five basic taste qualities: sweet, sour, bitter, salty and umami. Previously, we showed that each taste is detected by dedicated taste receptor cells (TRCs) on the tongue and palate epithelium
1
. To understand how TRCs transmit information to higher neural centres, we examined the tuning properties of large ensembles of neurons in the first neural station of the gustatory system. Here, we generated and characterized a collection of transgenic mice expressing a genetically encoded calcium indicator
2
in central and peripheral neurons, and used a gradient refractive index microendoscope
3
combined with high-resolution two-photon microscopy to image taste responses from ganglion neurons buried deep at the base of the brain. Our results reveal fine selectivity in the taste preference of ganglion neurons; demonstrate a strong match between TRCs in the tongue and the principal neural afferents relaying taste information to the brain; and expose the highly specific transfer of taste information between taste cells and the central nervous system.
Journal Article
A low-fat diet up-regulates expression of fatty acid taste receptor gene FFAR4 in fungiform papillae in humans: a co-twin randomised controlled trial
Fatty acid taste (FAT) perception is involved in the regulation of dietary fat intake, where impaired FAT is associated with increased fatty food intake. There are a number of FAT receptors identified on human taste cells that are potentially responsible for FAT perception. Manipulating dietary fat intake, and in turn FAT perception, would elucidate the receptors that are associated with long-term regulation of FAT perception. The present study aimed to assess associations between diet-mediated changes to FAT receptors and FAT perception in humans. A co-twin randomised controlled trial was conducted, where each matching twin within a pair were randomly allocated to either an 8-week low-fat (LF; <20 % energy fat) or an 8-week high-fat (HF; >35 % energy fat) diet. At baseline and week 8, fungiform papillae were biopsied in the fasted state and FAT receptor gene expressions (cluster of differentiation 36 ( CD36 ), free fatty acid receptor 2 ( FFAR2 ), FFAR4 , G protein-coupled receptor 84 ( GPR84 ) and a delayed rectifying K + channel (K + voltage-gated channel subfamily A member 2; KCNA2 )) were measured using RT-PCR; and FAT threshold (FATT) was assessed using three-alternate forced choice methodology. Linear mixed models were fitted, adjusting for correlation between co-twins. Intake was compliant with the study design, with the LF and HF groups consuming 14·8 and 39·9 % energy from fat, respectively. Expression of FFAR4 increased by 38 % in the LF group ( P = 0·023; time–diet interaction P = 0·063). Δ FFAR4 (Δ, week 8–baseline) was associated with Δfat intake (g) ( = −159·4; P < 0·001) and ΔFATT ( = −8·8; P = 0·016). In summary, FFAR4 is involved in long-term diet-mediated changes to FAT perception. Manipulating dietary fat intake, and therefore FFAR4 expression, might aid in reducing taste-mediated passive overconsumption of fatty foods.
Journal Article