Taste sensitivities mediate differential snack choices across BMI groups: a study with New Zealand young male individuals.

OBJECTIVE: This study aimed to: 1) test for the link between snack choices and BMI using a novel sensory-based classification method; and 2) elucidate the role of gustatory sensitivity in orienting snack choices. METHODS: The study employed a dual approach involving sensory and nutritional assessments. Ninety-eight European male individuals were tested for gustatory sensitivities to sweetness, saltiness, umami, and lipid perception. Participant food intake was measured over 4 days. A separate cohort of 327 participants categorized the recorded snacks based on taste patterns, enabling profiling of snack choices across body-weight groups. RESULTS: Results showed clear differentiations in snack choices across the BMI groups: Individuals with a higher BMI consumed more "Sweet" and "Sweet+Fat" snacks and less "Savory" snacks compared with the lower-BMI group (p < 0.05). Mediation analyses confirmed a significant effect of gustatory sensitivity, showing that the greater choice for "Sweet" and "Sweet+Fat" snacks among those with a higher BMI was mediated by sensitivities to sweetness and lipid perception (p = 0.008-0.044). CONCLUSIONS: Our study revealed that gustatory sensitivity can mediate the relationship between BMI and energy consumption from different snacks. These findings highlight the significance of taste perception in shaping snack choice, suggesting potential strategies for interventions aimed at addressing gustatory sensitivity to promote healthier dietary preferences.

A review of assessment methods for measuring individual differences in oral somatosensory perception.

While taste and smell perception have been thoroughly investigated, our understanding of oral somatosensory perception remains limited. Further, assessing and measuring individual differences in oral somatosensory perception pose notable challenges. This review aimed to evaluate the existing methods to assess oral somatosensory perception by examining and comparing the strengths and limitations of each method. The review highlighted the lack of standardized assessment methods and the various procedures within each method. Tactile sensitivity can be assessed using several methods, but each method measures different tactile dimensions. Further investigations are needed to confirm its correlation with texture sensitivity. In addition, measuring a single textural attribute may not provide an overall representation of texture sensitivity. Thermal sensitivity can be evaluated using thermal-change detection or temperature discrimination tests. The chemesthetic sensitivity tests involve either localized or whole-mouth stimulation tests. The choice of an appropriate method for assessing oral somatosensory sensitivity depends on several factors, including the specific research objectives and the target population. Each method has its unique intended purpose, strengths, and limitations, so no universally superior approach exists. To overcome some of the limitations associated with certain methods, the review offers alternative or complementary approaches that could be considered. Researchers can enhance the comprehensive assessment of oral somatosensory sensitivity by carefully selecting and potentially combining methods. In addition, a standardized protocol remains necessary for each method.

Gustatory cortex: Taste coding and decision making in one.

A new study reveals that, as mice learn a taste discrimination task, taste responses in gustatory cortex undergo plasticity such that they reflect taste identity and predict the upcoming decision in separate response epochs.

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.

Salivary buffering capacity is correlated with umami but not sour taste sensitivity in healthy adult Japanese subjects.

OBJECTIVE: Saliva serves multiple important functions crucial for maintaining a healthy oral and systemic environment. Among them, the pH buffering effect, which is primarily mediated by bicarbonate ions, helps maintain oral homeostasis by neutralizing acidity from ingested foods. Therefore, higher buffering capacity, reflecting the ability to neutralize oral acidity, may influence taste sensitivity, especially for sour taste since it involves sensing H+ ions. This study aims to explore the relationship between salivary buffering capacity and taste sensitivities to the five basic tastes in healthy adult humans. DESIGN: Eighty seven healthy adult students participated in this study. Resting saliva volume was measured using the spitting method. The liquid colorimetric test was used to assess salivary buffering capacity. The whole-mouth taste testing method was employed to determine the recognition threshold for each tastant (NaCl, sucrose, citric acid, quinine-HCl, monosodium glutamate). RESULTS: Taste recognition thresholds for sour taste as well as sweet, salty, and bitter tastes showed no correlation with salivary buffering capacity. Interestingly, a negative relationship was observed between recognition threshold for umami taste and salivary buffering capacity. Furthermore, a positive correlation between salivary buffering capacity and resting saliva volume was observed. CONCLUSIONS: Salivary buffering capacity primarily influences sensitivity to umami taste, but not sour and other tastes.

Neural circuits for taste sensation.

The sense of taste arises from the detection of chemicals in food by taste buds, the peripheral cellular detectors for taste. Although numerous studies have extensively investigated taste buds, research on neural circuits from primary taste neurons innervating taste buds to the central nervous system has only recently begun owing to recent advancements in neuroscience research tools. This minireview focuses primarily on recent reports utilizing advanced neurogenetic tools across relevant brain regions.

Taste of common prebiotic oligosaccharides: impact of molecular structure.

Prebiotic oligosaccharides are naturally occurring nondigestible carbohydrates with demonstrated health benefits. They are also a chemically diverse class of nutrients, offering an opportunity to investigate the impact of molecular structure on oligosaccharide taste perception. Accordingly, a relevant question is whether these compounds are detected by the human gustatory system, and if so, whether they elicit sweet or "starchy" taste. Here, in 3 psychophysical experiments, we investigated the taste perception of 3 commercially popular prebiotics [fructooligosaccharides (FOS), galactooligosaccharides (GOS), xylooligosaccharides (XOS)] in highly pure form. Each of these classes of prebiotics differs in the type of glycosyl residue, and position and type of bond between those residues. In experiments I and II, participants were asked to discriminate a total of 9 stimuli [FOS, GOS, XOS; degree of polymerization (DP) of 2, 3, 4] prepared at 75 mM in the presence and absence of lactisole, a sweet receptor antagonist. We found that all 9 compounds were detectable (P < 0.05). We also found that GOS and XOS DP 4 were discriminable even with lactisole, suggesting that their detection was not via the canonical sweet receptor. Accordingly, in experiment III, the taste of GOS and XOS DP 4 were directly compared with that of MOS (maltooligosaccharides) DP 4-6, which has been reported to elicit "starchy" taste. We found that GOS and MOS were perceived similarly although narrowly discriminable, while XOS was easily discriminable from both GOS and MOS. The current findings suggest that the molecular structure of oligosaccharides impacts their taste perception in humans.

Taste the music: Modality-general representation of affective states derived from auditory and gustatory stimuli.

Prior studies have extensively examined modality-general representation of affect across various sensory modalities, particularly focusing on auditory and visual stimuli. However, little research has explored the modality-general representation of affect between gustatory and other sensory modalities. This study aimed to investigate whether the affective responses induced by tastes and musical pieces could be predicted within and across modalities. For each modality, eight stimuli were chosen based on four basic taste conditions (sweet, bitter, sour, and salty). Participants rated their responses to each stimulus using both taste and emotion scales. The multivariate analyses including multidimensional scaling and classification analysis were performed. The findings revealed that auditory and gustatory stimuli in the sweet category were associated with positive valence, whereas those from the other taste categories were linked to negative valence. Additionally, auditory and gustatory stimuli in sour taste category were linked to high arousal, whereas stimuli in bitter taste category were associated with low arousal. This study revealed the potential mapping of gustatory and auditory stimuli onto core affect space in everyday experiences. Moreover, it demonstrated that emotions evoked by taste and music could be predicted across modalities, supporting modality-general representation of affect.

The larva and adult of Helicoverpa armigera use differential gustatory receptors to sense sucrose.

Almost all herbivorous insects feed on plants and use sucrose as a feeding stimulant, but the molecular basis of their sucrose reception remains unclear. Helicoverpa armigera as a notorious crop pest worldwide mainly feeds on reproductive organs of many plant species in the larval stage, and its adult draws nectar. In this study, we determined that the sucrose sensory neurons located in the contact chemosensilla on larval maxillary galea were 100-1000 times more sensitive to sucrose than those on adult antennae, tarsi, and proboscis. Using the Xenopus expression system, we discovered that Gr10 highly expressed in the larval sensilla was specifically tuned to sucrose, while Gr6 highly expressed in the adult sensilla responded to fucose, sucrose and fructose. Moreover, using CRISPR/Cas9, we revealed that Gr10 was mainly used by larvae to detect lower sucrose, while Gr6 was primarily used by adults to detect higher sucrose and other saccharides, which results in differences in selectivity and sensitivity between larval and adult sugar sensory neurons. Our results demonstrate the sugar receptors in this moth are evolved to adapt toward the larval and adult foods with different types and amounts of sugar, and fill in a gap in sweet taste of animals.

Influence of flavor information on visual search: Attentional capture by and suppression of flavor-associated colors.

Numerous studies have demonstrated the impact of flavor cues on visual search, yet the underlying mechanisms remain elusive. In this experiment, we used event-related potentials (ERPs) to examine whether, and if so, how flavor information could lead to attentional capture by, and suppression of, flavor-associated colors. The participants were asked to taste certain flavored beverages and subsequently complete a shape-based visual search task, while their neural activities were simultaneously recorded. The behavioral results revealed that the participants made slower responses when a distractor in the flavor-associated color (DFAC) was present, suggesting an attentional bias toward the flavor-associated color. The ERP results revealed that the N2pc was detected if the target and the DFAC were shown in the same visual field (e.g. both target and DFCA on the right side of the screen), when the pairings between flavor cues and target colors were incongruent. However, the N2pc was not observed if the target and the DFAC were shown in the opposite visual fields (e.g. target on the right and DFCA on the left side of the screen) for the incongruent color-flavor pairings. Moreover, the distractor positivity (Pd) was observed if the target and the DFAC were shown in the opposite visual field for the congruent color-flavor pairings. These results suggest that both attentional capture and suppression are involved in the influence of flavor information on visual search. Collectively, these findings provide initial electrophysiological evidence on the mechanisms of the crossmodal influence of flavor cues on visual search.

Learning enhances representations of taste-guided decisions in the mouse gustatory insular cortex.

Learning to discriminate overlapping gustatory stimuli that predict distinct outcomes-a feat known as discrimination learning-can mean the difference between ingesting a poison or a nutritive meal. Despite the obvious importance of this process, very little is known about the neural basis of taste discrimination learning. In other sensory modalities, this form of learning can be mediated by either the sharpening of sensory representations or the enhanced ability of "decision-making" circuits to interpret sensory information. Given the dual role of the gustatory insular cortex (GC) in encoding both sensory and decision-related variables, this region represents an ideal site for investigating how neural activity changes as animals learn a novel taste discrimination. Here, we present results from experiments relying on two-photon calcium imaging of GC neural activity in mice performing a taste-guided mixture discrimination task. The task allows for the recording of neural activity before and after learning induced by training mice to discriminate increasingly similar pairs of taste mixtures. Single-neuron and population analyses show a time-varying pattern of activity, with early sensory responses emerging after taste delivery and binary, choice-encoding responses emerging later in the delay before a decision is made. Our results demonstrate that, while both sensory and decision-related information is encoded by GC in the context of a taste mixture discrimination task, learning and improved performance are associated with a specific enhancement of decision-related responses.

Biophysical investigations using atomic force microscopy can elucidate the link between mouthfeel and flavour perception.

Food texture, along with taste and odour, is an important factor in determining food flavour. However, the physiological properties of oral texture perception require greater examination and definition. Here we explore recent trends and perspectives related to mouthfeel and its relevance in food flavour perception, with an emphasis on the biophysical point of view and methods. We propose that atomic force microscopy, combined with other biophysical techniques and more traditional food science approaches, offers a unique opportunity to study the mechanisms of mouthfeel at cellular and molecular levels. With this knowledge, food composition could be modified to develop healthier products by limiting salt, sugar, fat and calories while maintaining sensory qualities and consumer acceptance.

The Obese Taste Bud study: Objectives and study design.

AIMS: Taste modifies eating behaviour, impacting body weight and potentially obesity development. The Obese Taste Bud (OTB) Study is a prospective cohort study launched in 2020 at the University of Leipzig Obesity Centre in cooperation with the HI-MAG Institute. OTB will test the hypothesis that taste cell homeostasis and taste perception are linked to obesity. Here, we provide the study design, data collection process and baseline characteristics. MATERIALS AND METHODS: Participants presenting overweight, obesity or normal weight undergo taste and smell tests, anthropometric, and taste bud density (TBD) assessment on Day 1. Information on physical and mental health, eating behaviour, physical activity, and dental hygiene are obtained, while biomaterial (saliva, tongue swap, blood) is collected in the fasted state. Further blood samples are taken during a glucose tolerance test. A stool sample is collected at home prior to Day 2, on which a taste bud biopsy follows dental examination. A subsample undergoes functional magnetic resonance imaging while exposed to eating-related cognitive tasks. Follow-up investigations after conventional weight loss interventions and bariatric surgery will be included. RESULTS: Initial results show that glycated haemoglobin levels and age are negatively associated with TBD, while an unfavourable metabolic profile, current dieting, and vegan diet are related to taste perception. Olfactory function negatively correlates with age and high-density lipoprotein cholesterol. CONCLUSION: Initial findings suggest that metabolic alterations are relevant for taste and smell function and TBD. By combining omics data from collected biomaterial with physiological, metabolic and psychological data related to taste perception and eating behaviour, the OTB study aims to strengthen our understanding of taste perception in obesity.

Locus Ceruleus Dynamics Are Suppressed during Licking and Enhanced Postlicking Independent of Taste Novelty.

Attending to salient sensory attributes of food, such as tastes that are new, displeasing, or unexpected, allows the procurement of nutrients without food poisoning. Exposure to new tastes is known to increase norepinephrine (NE) release in taste processing forebrain areas, yet the central source for this release is unknown. Locus ceruleus norepinephrine neurons (LC-NE) emerge as a candidate in signaling salient information about taste, as other salient sensory stimuli (e.g., visual, auditory, somatosensation) are known to activate LC neurons. To determine if LC neurons are sensitive to features of taste novelty, we used fiber photometry to record LC-NE activity in water-restricted mice that voluntarily licked either novel or familiar substances of differential palatability (saccharine, citric acid). We observed that LC-NE activity was suppressed during lick bursts and transiently activated upon the termination of licking and that these dynamics were independent of the familiarity of the substance consumed. We next recorded LC dynamics during brief and unexpected consumption of tastants and found no increase in LC-NE activity, despite their responsiveness to visual and auditory stimuli, revealing selectivity in LC's responses to salient sensory information. Our findings suggest that LC activity during licking is not influenced by taste novelty, implicating a possible role for non-LC noradrenergic nuclei in signaling critical information about taste.

Does presbygeusia really exist? An updated narrative review.

This review critically assessed the existence of presbygeusia, i.e., the impairment in taste perception occurring in the elderly, as a natural part of the aging process and its potential clinical implications. Several factors might contribute to age-related taste alterations (TAs), including structural changes in taste buds, alterations in saliva composition, central nervous system changes, and oral microbiota dysbiosis. A comprehensive literature review was conducted to disentangle the effects of age from those of the several age-related diseases or conditions promoting TAs. Most of the included studies reported TAs in healthy elderly people, suggesting that presbygeusia is a relatively frequent condition associated with age-related changes in the absence of pathological conditions. However, the impact of TAs on dietary preferences and food choices among the elderly seems to be less relevant when compared to other factors, such as cultural, psychological, and social influences. In conclusion, presbygeusia exists even in the absence of comorbidities or drug side effects, but its impact on dietary choices in the elderly is likely modest.

Metabolic sensing in AgRP regulates sucrose preference and dopamine release in the nucleus accumbens.

Hunger increases the motivation for calorie consumption, often at the expense of low-taste appeal. However, the neural mechanisms integrating calorie-sensing with increased motivation for calorie consumption remain unknown. Agouti-related peptide (AgRP) neurons in the arcuate nucleus of the hypothalamus sense hunger, and the ingestion of caloric solutions promotes dopamine release in the absence of sweet taste perception. Therefore, we hypothesised that metabolic-sensing of hunger by AgRP neurons would be essential to promote dopamine release in the nucleus accumbens in response to caloric, but not non-caloric solutions. Moreover, we examined whether metabolic sensing in AgRP neurons affected taste preference for bitter solutions under conditions of energy need. Here we show that impaired metabolic sensing in AgRP neurons attenuated nucleus accumbens dopamine release in response to sucrose, but not saccharin, consumption. Furthermore, metabolic sensing in AgRP neurons was essential to distinguish nucleus accumbens dopamine response to sucrose consumption when compared with saccharin. Under conditions of hunger, metabolic sensing in AgRP neurons increased the preference for sucrose solutions laced with the bitter tastant, quinine, to ensure calorie consumption, whereas mice with impaired metabolic sensing in AgRP neurons maintained a strong aversion to sucrose/quinine solutions despite ongoing hunger. In conclusion, we demonstrate normal metabolic sensing in AgRP neurons drives the preference for calorie consumption, primarily when needed, by engaging dopamine release in the nucleus accumbens.

Multisensory Integration Underlies the Distinct Representation of Odor-Taste Mixtures in the Gustatory Cortex of Behaving Rats.

The perception of food relies on the integration of olfactory and gustatory signals originating from the mouth. This multisensory process generates robust associations between odors and tastes, significantly influencing the perceptual judgment of flavors. However, the specific neural substrates underlying this integrative process remain unclear. Previous electrophysiological studies identified the gustatory cortex as a site of convergent olfactory and gustatory signals, but whether neurons represent multimodal odor-taste mixtures as distinct from their unimodal odor and taste components is unknown. To investigate this, we recorded single-unit activity in the gustatory cortex of behaving female rats during the intraoral delivery of individual odors, individual tastes, and odor-taste mixtures. Our results demonstrate that chemoselective neurons in the gustatory cortex are broadly responsive to intraoral chemosensory stimuli, exhibiting time-varying multiphasic changes in activity. In a subset of these chemoselective neurons, odor-taste mixtures elicit nonlinear cross-modal responses that distinguish them from their olfactory and gustatory components. These findings provide novel insights into multimodal chemosensory processing by the gustatory cortex, highlighting the distinct representation of unimodal and multimodal intraoral chemosensory signals. Overall, our findings suggest that olfactory and gustatory signals interact nonlinearly in the gustatory cortex to enhance the identity coding of both unimodal and multimodal chemosensory stimuli.

Relationship between olfactory and gustatory functions: The Iwaki health promotion project 2019.

OBJECTIVE: Olfactory and gustatory functions are important sensory aspects in humans. Although they are believed to influence each other, their interrelationship is not well understood. In this study, we aimed to investigate the relationship between the olfactory and gustatory functions based on the results of a large-scale epidemiological study (Iwaki Health Promotion Project) of the general local population. METHODS: We analyzed 565 participants who underwent taste and olfactory tests in the 2019 Iwaki Project. Gustatory function was tested for four taste qualities (sweet, sour, salty, and bitter) using whole-mouth taste tests. Olfactory function was tested using the University of Pennsylvania Smell Identification Test modified for Japanese (UPSIT-J). We evaluated sex-related differences between olfactory and gustatory functions and the effects of various factors on olfactory identification using multivariate analysis. Furthermore, we compared the percentage of accurate UPSIT-J responses between the normal and hypogeusia groups. We also analyzed the effects of taste and olfactory functions on eating. RESULTS: Olfactory and gustatory functions were lower in men than in women. Among the four taste qualities, salty taste was the most closely associated with olfactory identification ability, with lower olfactory scores of salty taste in the hypogeusia group than in the normal group. Moreover, the hyposmia group had higher daily salt intake than the normal olfaction group in women. CONCLUSION: These results suggest that olfactory identification tests may be useful in predicting elevated salt cognitive thresholds, leading to a reduction in salt intake, which may contribute to hypertension prevention.

Structural basis for sugar perception by Drosophila gustatory receptors.

Insects rely on a family of seven transmembrane proteins called gustatory receptors (GRs) to encode different taste modalities, such as sweet and bitter. We report structures of Drosophila sweet taste receptors GR43a and GR64a in the apo and sugar-bound states. Both GRs form tetrameric sugar-gated cation channels composed of one central pore domain (PD) and four peripheral ligand-binding domains (LBDs). Whereas GR43a is specifically activated by the monosaccharide fructose that binds to a narrow pocket in LBDs, disaccharides sucrose and maltose selectively activate GR64a by binding to a larger and flatter pocket in LBDs. Sugar binding to LBDs induces local conformational changes, which are subsequently transferred to the PD to cause channel opening. Our studies reveal a structural basis for sugar recognition and activation of GRs.