From psychophysics to the clinic: missteps and advances

Neural responses to oral administration of erythritol vs. sucrose and sucralose explain differences in subjective liking ratings

INTRODUCTION

High sugar intake is associated with many chronic diseases. However, non-caloric sweeteners (NCSs) might fail to successfully replace sucrose due to the mismatch between their rewarding sweet taste and lack of caloric content. The natural NCS erythritol has been proposed as a sugar substitute due to its satiating properties despite being non-caloric. We aimed to compare brain responses to erythritol vs. sucrose and the artificial NCS sucralose in a priori taste, homeostatic, and reward brain regions of interest (ROIs).

METHODS

We performed a within-subject, single-blind, counterbalanced fMRI study in 30 healthy men (mean ± SEM age:24.3 ± 0.8 years, BMI:22.3 ± 0.3 kg/m2). Before scanning, we individually matched the concentrations of both NCSs to the perceived sweetness intensity of a 10% sucrose solution. During scanning, participants received 1 mL sips of the individually titrated equisweet solutions of sucrose, erythritol, and sucralose, as well as water. After each sip, they rated subjective sweetness liking.

RESULTS

Liking ratings were significantly higher for sucrose and sucralose vs. erythritol (both pHolm = 0.0037); water ratings were neutral. General Linear Model (GLM) analyses of brain blood oxygen level-depended (BOLD) responses at qFDR<0.05 showed no differences between any of the sweeteners in a priori ROIs, but distinct differences were found between the individual sweeteners and water. These results were confirmed by Bayesian GLM and machine learning-based models. However, several brain response patterns mediating the differences in liking ratings between the sweeteners were found in whole-brain multivariate mediation analyses. Both subjective and neural responses showed large inter-subject variability.

CONCLUSION

We found lower liking ratings in response to oral administration of erythritol vs. sucrose and sucralose, but no differences in neural responses between any of the sweeteners in a priori ROIs. However, differences in liking ratings between erythritol vs. sucrose or sucralose are mediated by multiple whole-brain response patterns.

Neural Representation of Valenced and Generic Probability and Uncertainty

Representing the probability and uncertainty of outcomes facilitates adaptive behavior by allowing organisms to prepare in advance and devote attention to relevant events. Probability and uncertainty are often studied only for valenced (appetitive or aversive) outcomes, raising the question of whether the identified neural machinery also processes the probability and uncertainty of motivationally neutral outcomes. Here, we aimed to dissociate valenced from valence-independent (i.e., generic) probability (p; maximum at p = 1) and uncertainty (maximum at p = 0.5) signals using human neuroimaging. In a Pavlovian task (n = 41; 19 females), different cues predicted appetitive, aversive, or neutral liquids with different probabilities (p = 0, p = 0.5, p = 1). Cue-elicited motor responses accelerated, and pupil sizes increased primarily for cues that predicted valenced liquids with higher probability. For neutral liquids, uncertainty rather than probability tended to accelerate cue-induced responding and decrease pupil size. At the neural level, generic uncertainty signals were limited to the occipital cortex, while generic probability also activated the anterior ventromedial prefrontal cortex. These generic probability and uncertainty signals contrasted with cue-induced responses that only encoded the probability and uncertainty of valenced liquids in medial prefrontal, insular, and occipital cortices. Our findings show a behavioral and neural dissociation of generic and valenced signals. Thus, some parts of the brain keep track of motivational charge while others do not, highlighting the need and usefulness of characterizing the exact nature of learned representations.

Sodium Replacement with KCl and MSG: Attitudes, Perception and Acceptance in Reduced Salt Soups

Sodium intake is linked to multiple negative health outcomes, particularly hypertension, the leading cause of premature death globally. Sodium intake levels in human populations are high, due in part to our desire for palatable salty-tasting foods. Two leading salt replacement strategies are the use of potassium chloride (KCl) and monosodium glutamate (MSG), the latter of which still contains some sodium, but both of which can replace some salty taste in foods while reducing net sodium levels. In this report, we employed a trained descriptive sensory panel to optimize saltiness in sodium-reduced aqueous samples using various concentrations of KCl and MSG. Following this, we assessed consumer attitudes to sodium-reduction strategies in a model food, canned soup, known to typically be high in sodium. Finally, in a large consumer test, we verified that these optimized levels of KCl and MSG did not lead to a drop in liking for the reduced-sodium soups with saltiness subsidized in this manner. Our results showed that sodium can be readily reduced in soups by 18% while actually scoring higher in liking, and in some cases being perceived as even more salty tasting, but that consumers are more open to sodium reduction in this manner when sodium replacements are not specifically highlighted, and when percentage sodium reduction is stated over absolute levels.

Examining the Influence of Chemosensation on Laryngeal Health and Disorders

Inhaled airborne stimuli are associated with laryngeal disorders affecting respiration. Clinically, several themes emerged from the literature that point to specific gaps in the understanding and management of these disorders. There is wide variation in the types of airborne stimuli that trigger symptoms, lack of standardization in provocation challenge testing using airborne stimuli, and vague reporting of laryngeal symptoms. Scientifically, evidence exists outside the field of voice science that could prove useful to implement among patients with impaired laryngeal-respiration. To expand this area of expertise, here we provide a thematic overview of relevant evidence and methodological tools from the discipline of chemosensory sciences. This review provides distinctions across the three chemosensory systems of olfaction, trigeminal chemesthesis, and gustation, guidance on selecting and delivering common chemosensory stimuli for clinical testing, and methods of quantifying sensory experiences using principles of human psychophysics. Investigating the science of chemosensation reveals that laryngeal responses to inhaled airborne stimuli have explanations involving physiological mechanisms as well as higher cognitive processing. Fortunately, these findings are consistent with current pharmacological and nonpharmacological interventions for impaired laryngeal-respiration. Based on the close relationships among inhaled airborne stimuli, respiration, and laryngeal function, we propose that new perspectives from chemosensory sciences offer opportunities to improve patient care and target areas of future research.

Desenvolvimento e validação de medidas psicofísicas de sensibilidade ao contraste de segunda-ordem

A medida de sensibilidade ao contraste (SC) de primeira ordem é frequentemente utilizada para avaliação da percepção espacial. Nosso objetivo foi desenvolver e validar um teste de SC de segunda ordem para aplicação clínica. Modificações metodológicas foram realizadas na rotina psicofísica para redução do tempo de testagem e no primeiro experimento validamos a nova metodologia. Em um segundo experimento, dezesseis participantes foram testados nas mesmas condições do primeiro experimento. As medidas de consistência interna por alfa de Cronbach foram robustas para a medida de primeira ordem sendo α= 0,788, segunda ordem por ruído branco α= 0,668 e por ruído rosa α= 0,717. O desenvolvimento e validação deste novo experimento para medidas de SC de segunda ordem permitirá avançar nos estudos dos mecanismos básicos da percepção de espaço para estímulos complexos, assim como a aplicação clínica em diversas doenças.

Perspective: Measuring Sweetness in Foods, Beverages, and Diets: Toward Understanding the Role of Sweetness in Health

Various global public health agencies recommend minimizing exposure to sweet-tasting foods or beverages. The underlying rationale is that reducing exposure to the perception of sweet tastes, without regard to the source of sweetness, may reduce preferences for sweetness, added sugar intake, caloric intake, and body weight. However, the veracity of this sequence of outcomes has yet to be documented, as revealed by findings from recent systematic reviews on the topic. Efforts to examine and document the effects of sweetness exposure are needed to support evidence-based recommendations. They require a generally agreed-upon methodology for measuring sweetness in foods, beverages, and the overall diet. Although well-established sensory evaluation techniques exist for individual foods in laboratory settings, they are expensive and time-consuming, and agreement on the optimal approach for measuring the sweetness of the total diet is lacking. If such a measure could be developed, it would permit researchers to combine data from different studies and populations and facilitate the design and conduct of new studies to address unresolved research questions about dietary sweetness. This narrative review includes an overview of available sensory techniques, their strengths and limitations, recent efforts to measure the sweetness of foods and diets across countries and cultures, and a proposed future direction for improving methods for measuring sweetness toward developing the data required to support evidence-based recommendations around dietary sweetness.

Prolonged Exposure to Monosodium Glutamate in Healthy Young Adults Decreases Perceived Umami Taste and Diminishes Appetite for Savory Foods

Background

Research suggests that increased consumption of sweet, salt, or fat is associated with diminished perceived taste intensity and shifted preferences for the respective stimulus. It is unknown whether a similar effect occurs with the consumption of umami.

Objective

The aim of the study was to investigate the influence of habitual exposure to umami stimuli on umami taste perception, hedonics, and satiety.

Methods

Fifty-eight healthy men (n = 16) and women (n = 42) participated in a parallel-group, randomized controlled study. The normal-weight [mean ± SD body mass index (kg/m2): 21.8 ± 2.2] group of young adults (mean ± SD age: 22.7 ± 6.2 y) consumed vegetable broth daily for 4 wk. The broth for the treatment group (n = 28) was supplemented with 3.8 g monosodium glutamate (MSG), whereas the control group (n = 30) consumed a sodium-matched broth without MSG. Perceived umami taste intensity and discrimination in MSG solutions; liking, wanting, and preference of a variety of umami-rich foods; satiation and satiety from an ad libitum meal; and anthropometric measures were evaluated at baseline and at week 4. General linear models assessed the effect of treatment on change from baseline for all outcomes and tested for effect modification of sex.

Results

Relative to controls, increased consumption of MSG for 4 wk diminished umami taste in women (8.4 units on generalized Labeled Magnitude Scale; 95% CI: -13.8, -3.1 units; P = 0.013). The desire for and intake of savory foods decreased after MSG treatment in both sexes with an ad libitum meal (desire: -7.7 units; 95% CI: -13.7, -1.7 units; P = 0.04; intake: -36 g; 95% CI: -91, 19 g; P = 0.04).

Conclusion

Our results highlight that a month-long diet high in umami stimuli attenuates perceived umami taste and appetite for savory foods in a young, healthy population. Our findings contribute to the understanding of food choice, a factor in the development and maintenance of obesity, as well as the etiology of protein-related health conditions such as osteoporosis and kidney disease. This study is registered at www.clinicaltrials.gov as NCT03010930.

Differences in Our Sensory Worlds

People use intensity descriptors to compare sensory differences: “This tastes strong to me; is it strong to you?” These comparisons are deceptive because they assume that intensity descriptors like strong denote the same absolute perceived intensities to everyone. This assumption is false. Visual-analogue and category scales are labeled with intensity descriptors, and whenever there are systematic differences across groups in the absolute perceived intensity denoted by these descriptors, across-group comparisons will be invalid. We have explored this problem using studies of taste perception. When intensity descriptors are falsely assumed to have universal meaning, real differences can be blunted, abolished, or reversed. One solution to this problem is to express sensations of interest relative to an unrelated standard; any variation in this standard will be equivalent across groups, allowing valid group comparisons. The importance of detecting and correcting these measurement errors is not limited to sensory comparisons, but applies to hedonic comparisons as well.

Oral sensory nerve damage: Causes and consequences

Oral sensations (i.e., taste, oral somatosensation, retronasal olfaction) are integrated into a composite sense of flavor, which guides dietary choices with long-term health impact. The nerves carrying this input are vulnerable to peripheral damage from multiple sources (e.g., otitis media, tonsillectomy, head injury), and this regional damage can boost sensations elsewhere in the mouth because of central interactions among nerve targets. Mutual inhibition governs this compensatory process, but individual differences lead to variation in whole-mouth outcomes: some individuals are unaffected, others experience severe loss, and some encounter sensory increases that may (if experienced early in life) elevate sweet-fat palatability and body mass. Phantom taste, touch, or pain sensations (e.g., burning mouth syndrome) may also occur, particularly in those expressing the most taste buds. To identify and treat these conditions effectively, emerging clinical tests measure regional vs. whole-mouth sensation, stimulated vs. phantom cues, and oral anatomy. Scaling methods allowing valid group comparisons have strongly aided these efforts. Overall, advances in measuring oral sensory function in health and disease show promise for understanding the varied clinical consequences of nerve damage.

Behavioral measures of risk tasking, sensation seeking and sensitivity to reward may reflect different motivations for spicy food liking and consumption

Based on work a quarter century ago, it is widely accepted personality traits like sensation seeking are related to the enjoyment and intake of spicy foods; however, data supporting this belief is actually quite limited. Recently, we reported strong to moderate correlations between remembered spicy food liking and two personality traits measured with validated questionnaires. Here, participants consumed capsaicin-containing strawberry jelly to generate acute estimates of spicy food liking. Additionally, we used a laboratory-based behavioral measure of risk taking (the mobile Balloon Analogue Risk Task; mBART) to complement a range of validated self-report measures of risk-related personality traits. Present data confirm Sensation Seeking correlates with overall spicy meal liking and liking of the burn of a spicy meal, and extends prior findings by showing novel correlations with the liking of sampled stimuli. Other personality measures, including Sensitivity to Punishment (SP), Sensitivity to Reward (SR), and the Impulsivity and Risk Taking subscales of the DSM5 Personality Inventory (PID-5) did not show significant relationships with liking of spicy foods, either sampled or remembered. Our behavioral risk taking measure, the mBART, also failed to show a relationship with remembered or sampled liking. However, significant relationships were observed between reported intake of spicy foods and Sensitivity to Reward, and the Risk Taking subscale of the PID-5 (PID5-RT). Based on the observed patterns among various personality measures, and spicy food liking and intake, we propose that personality measures may exert their influence on intake of spicy food via different mechanisms. We also speculate that Sensation Seeking may reflect motivations for consuming spicy foods that are more intrinsic, while the motivations for eating spicy foods measured by SR and PID5-RT may be more extrinsic.

The Measurement of Pleasure and Pain

Pleasure and pain are among our most salient experiences, and we want to know how our pleasures and pains stack up against those of others. Older psychophysical methods fail to provide valid comparisons of pleasure and pain across individuals or groups. We are making progress in measurement, but we still have a ways to go.

Taste damage (otitis media, tonsillectomy and head and neck cancer), oral sensations and BMI

Otitis media and tonsillectomy are associated with enhanced palatability of energy dense foods and with weight gain. Otitis media can damage the chorda tympani nerve (CN VII); tonsillectomy and head and neck radiation treatment can damage the glossopharyngeal nerve (CN IX). Both of these nerves function prominently in taste sensation. The present study utilizes these sources of damage to study central interactions among the nerves that mediate oral sensations. Mild damage restricted to one of these nerves can actually intensify sensations evoked from undamaged nerves (i.e., whole-mouth taste, oral tactile sensations evoked by fats and irritants). These intensifications may result from disruption of central inhibitory taste circuits, as taste damage appears to disinhibit other oral sensory nerves. In addition, mild damage restricted to one taste nerve can intensify odors perceived from foods in the mouth during chewing and swallowing (i.e., retronasal olfaction); this may be a secondary consequence of the intensification of whole-mouth taste. Damage to both nerves leads to widespread oral sensory loss. At present, the link between sensory alterations and weight gain has not been established for adults (e.g., does increased fat preference occur in individuals with oral sensory intensifications, those with losses, or both?). Finally, pain in non-oral locations is also related to taste loss. When participants rated "the most intense pain of any kind they had ever experienced," those with the greatest taste loss gave the highest ratings. These effects suggest that taste loss significantly influences long-term health outcomes.

Taste evaluation in adolescents and pediatric patients with benign migratory glossitis

OBJECTIVE

Benign migratory glossitis (BMG) is a disease that affects the tongue and is considered an inflammatory disorder well recognized. It is characterized by the appearance of erosive areas on the dorsum and lateral border of the tongue that can be isolated or multiple. The aim of this study was to assess whether the perception of taste to the four basic tastes is altered due to the presence of BMG.

METHODS

Forty individuals of both sexes with a mean age of 12.1 years were divided into two groups (20 BMG patients and 20 healthy controls) and had their taste function assessed in relation to four basic tastes: bitter, sour, sweet, and salty.

RESULTS

All participants in the case group exhibited lesions over the dorsum, edges and tip of the tongue with a possible extension to the surface below. No statistic difference was observed between BMG patients and controls for the taste scores (Mann-Whitney U test: P=0.0955). The percentage of correctly identified taste strips for the highest concentrations was 100% for all tastes. For the lowest concentrations it was 85% for sweet, 50% for sour, 95% for salty, and 95% for bitter. Three patients with BMG and three control subjects showed hypogeusia.

CONCLUSION

This study revealed that BMG is not able to change the perception of taste for salty, sweet, sour and bitter.

Two decades of supertasting: where do we stand?

Oral chemosensation can vary greatly across individuals, both in terms of the lowest concentration that can be detected (threshold) and in the magnitude of perceived intensity for stimuli at higher concentrations (suprathreshold response). Individuals who experience greater taste intensity are often termed supertasters, and this phenotype has typically been measured via the suprathreshold bitterness of the tastant propylthiouracil (PROP). Notably, supertasting extends beyond bitterness and other tastants to include oral somatosensation and retronasal olfaction, and it may also include finer acuity as well. Here, we describe the evolution of the supertasting concept over the last 20 years, and summarize the current state of the field. Alternative phenotyping approaches that are not dependent on PROP are reviewed, and the molecular genetics of broadly tuned heightened taste and orosensory response are discussed. We conclude by initiating a conversation on nomenclature as we look toward the next 20 years of chemosensory research.

Effect of Liberibacter infection (huanglongbing or "greening" disease) of citrus on orange juice flavor quality by sensory evaluation

Some anecdotal reports suggest that infection of citrus trees with Candidatus Liberibacter asiaticus (Las), the suspected causal agent of huanglongbing (HLB) disease, imparts off flavor to orange juice. It is of interest to the industry to know how Las infection affects juice quality with respect to cultivar, maturity, or processing method. Hamlin, Midsweet, and Valencia oranges were harvested over 2 y from trees that tested negative (Las-) or positive (Las+) for Las from different groves and included normal looking (nonsymptomatic) and symptomatic fruit (small, green, and lopsided) from Las+ trees. In the 1st year, fruit were manually juiced, while in the 2nd year, a commercial process was used. Juice from Las+ trees was compared to juice from Las- trees in difference-from-control tests, and by descriptive analysis. Results showed large variability due to tree, harvest date, and cultivar. Juice from Hamlin Las+ trees tended to be more bitter and sour than its Las- counterpart. In contrast, hand processed Valencia juice from Las+ trees was perceived to have some off-flavor and bitterness compared to control, but the following year, commercially processed Valencia juice from Las+ trees was perceived to be only slightly more sour than juice from Las- trees for the April harvest, and to be sweeter for the June harvest. When juice from individual replicates was pooled to be more representative of a commercial situation, there was no difference between Las+ and Las- juice in Valencia. Trained panel differences were noted for juice from Hamlin Las+ fruit, especially for symptomatic fruit.

PRACTICAL APPLICATION

Assumptions that juice made from oranges harvested from Huanglongbing (from infection with Liberibacter sp.) affected trees is off-flavored appeared to be generally more true for Hamlin juice than for Midsweet or Valencia, especially for Hamlin juice made from symptomatic fruit. For Midsweet and Valencia, flavor differences between juice made from fruit harvested from diseased or healthy trees varied greatly between trees, season, and even processing method. Under a commercial processing situation, where juice is blended from several varieties, seasons, and multiple locations, it is expected that off-flavor will not be a major problem.

Explaining variability in sodium intake through oral sensory phenotype, salt sensation and liking

Our sodium-rich food supply compels investigation of how variation in salt sensation influences liking and intake of high-sodium foods. While supertasters (those with heightened propylthiouracil (PROP) bitterness or taste papillae number) report greater saltiness from concentrated salt solutions, the non-taster/supertaster effect on sodium intake is unclear. We assessed taster effects on salt sensation, liking and intake among 87 healthy adults (45 men). PROP bitterness showed stronger associations with perceived saltiness in foods than did papillae number. Supertasters reported: greater saltiness in chips/pretzels and broth at levels comparable to regular-sodium products; greater sensory and/or liking changes to growing sodium concentration in cheeses (where sodium ions mask bitterness) and broths; and less frequently salting foods. PROP effects were attenuated in women. Compared with men, women reported more saltiness from high-sodium foods and greater liking for broth at salt levels comparable to regular-sodium products. Across men and women, Structural Equation Models showed PROP and papillae number independently explained variability in consuming high-sodium foods by impacting salt sensation and/or liking. PROP supertasters reported greater changes in sensation when more salt was added to broth, which then associated with greater changes in broth liking, and finally with more frequent high-sodium food intake. Greater papillae number was associated with less frequent high-sodium food intake via reduced liking for high-fat/high-sodium foods. In summary, variation in sensations from salt was associated with differences in hedonic responses to high-sodium foods and thus sodium intake. Despite adding less salt, PROP supertasters consumed more sodium through food, as salt was more important to preference, both for its salty taste and masking of bitterness.

Derivation and evaluation of a labeled hedonic scale

The objective of this study was to develop a semantically labeled hedonic scale (LHS) that would yield ratio-level data on the magnitude of liking/disliking of sensation equivalent to that produced by magnitude estimation (ME). The LHS was constructed by having 49 subjects who were trained in ME rate the semantic magnitudes of 10 common hedonic descriptors within a broad context of imagined hedonic experiences that included tastes and flavors. The resulting bipolar scale is statistically symmetrical around neutral and has a unique semantic structure. The LHS was evaluated quantitatively by comparing it with ME and the 9-point hedonic scale. The LHS yielded nearly identical ratings to those obtained using ME, which implies that its semantic labels are valid and that it produces ratio-level data equivalent to ME. Analyses of variance conducted on the hedonic ratings from the LHS and the 9-point scale gave similar results, but the LHS showed much greater resistance to ceiling effects and yielded normally distributed data, whereas the 9-point scale did not. These results indicate that the LHS has significant semantic, quantitative, and statistical advantages over the 9-point hedonic scale.

Coactivation of gustatory and olfactory signals in flavor perception

It is easier to detect mixtures of gustatory and olfactory flavorants than to detect either component alone. But does the detection of mixtures exceed the level predicted by probability summation, assuming independent detection of each component? To answer this question, we measured simple response times (RTs) to detect brief pulses of one of 3 flavorants (sucrose [gustatory], citral [olfactory], sucrose-citral mixture) or water, presented into the mouth by a computer-operated, automated flow system. Subjects were instructed to press a button as soon as they detected any of the 3 nonwater stimuli. Responses to the mixtures were faster (RTs smaller) than predicted by a model of probability summation of independently detected signals, suggesting positive coactivation (integration) of gustation and retronasal olfaction in flavor perception. Evidence for integration appeared mainly in the fastest 60% of the responses, indicating that integration arises relatively early in flavor processing. Results were similar when the 3 possible flavorants, and water, were interleaved within the same session (experimental condition), and when each flavorant was interleaved with water only (control conditions). This outcome suggests that subjects did not attend selectively to one flavor component or the other in the experimental condition and further supports the conclusion that (late) decisional or attentional strategies do not exert a large influence on the gustatory-olfactory flavor integration.

Do past pain events systematically impact pain ratings of healthy subjects or fibromyalgia patients?

We previously reported that 3 different electronic visual analogue and numerical pain scales are useful in providing refined capacity to discriminate discrete levels of pain intensity. Using the same subjects and scales, we now investigated whether pain scaling is influenced by past pain events and by recalled memories of these events in the rating of pain. Normal control subjects (NC: 19 male, 30 female) and female fibromyalgia (FM) (n = 17) patients received 5-second suprathreshold heat stimuli (45-49 degrees C) to both forearms. The participants rated these experimental heat stimuli using the previously described electronic pain scales. Subsequently, they were asked to report whether they used any prior pain experiences during the process of rating their pain. Out of 49 NC, only 6 females (12.2%) and 7 males (14.3%), and out of 17 FM patients, only 3 females (17.6%) stated that they had used past pain experiences during scaling. Notably, pain ratings of experimental heat stimuli did not statistically differ between subjects who used past pain experiences during scaling as compared to those who did not. Furthermore, ratings of their most severe past pains were not significantly correlated with ratings of experimental pain stimuli. These results do not provide support for the strong assertion that pain rating scales are elastic, ie, being used differently depending on the severity of past pain events such as childbirth.

PERSPECTIVE

Less than 25% of subjects used memories of past pain events during pain scaling. In addition, if they were used, these pain memories did not influence pain scaling with electronic eVAS and eNUM scales. Thus, use of these scales allows reliable comparisons of experimental and clinical pain ratings within and between subjects.

Perspectives on population-based epidemiological studies of olfactory and taste impairment

Epidemiological studies of the senses of olfaction (smell) and gustation (taste) are needed since impairments in these senses have important implications for health. Only a few attempts have been made to measure the prevalence of olfactory and gustatory or taste dysfunction, and many methodological challenges remain to be addressed. These challenges differ from those faced in studies based in the clinic or research laboratory. Epidemiological studies of smell and taste represent translational research, because they can be used to understand how findings from laboratory or clinical studies apply to the general population. This paper briefly reviews existing methods for "how" to measure smell and taste dysfunction and then illustrates findings based on prior epidemiological studies to indicate "why" we wish to measure smell and taste functioning in population-based samples. Self-reported information collected on smell and taste loss in a national sample, the 1994-1995 Disability Sample (phase I screening) of the National Health Interview Survey, is contrasted with results provided by an exam-based measure of olfactory impairment in an epidemiological study conducted in Beaver Dam, WI. The comparison of self-reported and exam-based measures of smell or taste loss leads to the question of how to best define smell or taste impairment in population samples, since unlike other sensory domains (namely, vision and hearing), there are no internationally accepted standards of impairment for the chemosenses. In addition to highlighting existing epidemiological studies, the current development of an NIH Toolbox of brief exam measures is described. Through this symposium, we hope to advance the nascent field of olfactory and taste epidemiology.

Measuring taste impairment in epidemiologic studies: the Beaver Dam Offspring Study

Taste or gustatory function may play an important role in determining diet and nutritional status and therefore indirectly impact health. Yet there have been few attempts to study the spectrum of taste function and dysfunction in human populations. Epidemiologic studies are needed to understand the impact of taste function and dysfunction on public health, to identify modifiable risk factors, and to develop and test strategies to prevent clinically significant dysfunction. However, measuring taste function in epidemiologic studies is challenging and requires repeatable, efficient methods that can measure change over time. Insights gained from translating laboratory-based methods to a population-based study, the Beaver Dam Offspring Study (BOSS) will be shared. In this study, a generalized labeled magnitude scale (gLMS) method was used to measure taste intensity of filter paper disks saturated with salt, sucrose, citric acid, quinine, or 6-n-propylthiouracil, and a gLMS measure of taste preferences was administered. In addition, a portable, inexpensive camera system to capture digital images of fungiform papillae and a masked grading system to measure the density of fungiform papillae were developed. Adult children of participants in the population-based Epidemiology of Hearing Loss Study in Beaver Dam, Wisconsin, are eligible for this ongoing study. The parents were residents of Beaver Dam and 43-84 years of age in 1987-1988; offspring ranged in age from 21-84 years in 2005-2008. Methods will be described in detail and preliminary results about the distributions of taste function in the BOSS cohort will be presented.

Epidemiological studies of taste function: discussion and perspectives

Efforts to quantify the public health impact of chemosensation present significant challenges, including a strong need for testing methods suitable for field assessment. This discussion highlights several promising approaches to the population-based study of taste function; it also identifies key principles that should be considered when adapting laboratory-based taste tests for field use.

Metallic taste phantom predicts oral pain among 5-year survivors of head and neck cancer

Chronic pain following cancer-related treatment is emerging as a major concern. Heretofore, the pain level among 5-year survivors of head and neck cancer has received limited attention. This study proposes a predictive model for understanding factors associated with the elevated levels of chronic oral pain. Cancer survivors were drawn from a pool of 5-year survivors. A listed sample matched on sex, age, and zip code was purchased and served as a comparison group. Telephone interviews were conducted by a professional call center. Oral pain levels and the presence of metallic taste phantoms were significantly higher in the cancer survivor group than among the comparison group. The prevalence of chronic oral pain among the 5-year survivors was 43% compared to 13% for the comparison group. Hierarchical linear regression showed that among the 5-year survivors, the predictive model for spontaneous pain accounted for 24% of the variance, and for function-related pain the model accounted for 34% of the variance, with the presence of a phantom metallic taste making a significant independent contribution in both models. In the function-related pain model, depression and level of oral function quality of life (QOL) made significant independent contributions. The presence of oral pain is a significant problem among head and neck cancer survivors. The presence of metallic phantoms is an important new piece of evidence suggesting neural damage following cancer-directed treatment. Routine assessment of oral pain levels could improve current analgesic approaches among head and neck cancer survivors.

Thermal taste, PROP responsiveness, and perception of oral sensations

Differences between 6-n-propylthiouracil (PROP) taster groups have long been the focus of studies on individual variation in perception of oral sensation. Recently, "thermal taste" was described, the phenomenon whereby some individuals perceive "phantom" taste sensations after thermal stimulation of small areas of the tongue. As with PROP taster status (PTS), thermal taster status (TTS) has been proposed as a proxy for general responsiveness to oral stimuli. Here we examined the influence of PTS and TTS, independently, on the perceived intensity of sweet, sour, salty, bitter, astringent, and metallic stimuli, and temperature on heating or cooling the tongue. Interactions between PTS and TTS were also examined, and fungiform papillae (FP) density and salivary flow rate (SFR) were determined. Both PTS and TTS were associated with perceived stimulus intensities. PROP super-tasters (pSTs) rated all oral stimuli as more intense than PROP non-tasters (pNTs). Thermal tasters (TTs) gave higher logged ratings than thermal non-tasters (TnTs) for all oral sensations including temperature, with the exception of metallic flavour (at low concentration) and PROP. Examination of ETA-squared values showed that PTS had a greater effect on perceived intensities than did TTS for most sensations. No PTSTTS interaction was found for any oral stimuli. In contrast with PTS, TTS was not associated with FP density, and neither PTS nor TTS were associated with SFR. We conclude that pSTs and TTs possess greater responsiveness across a range of taste and trigeminal stimuli and concentrations.

Stimulating the development of mechanism-based, individualized pain therapies

Biomedical science has greatly improved our understanding of pain in recent decades, but few novel molecular entities that address fundamentally new pain mechanisms have entered the clinic, despite dramatically increased pharmaceutical investment. Indeed, virtually all new analgesics approved over the past 25 years are derivatives or reformulations of opioids or aspirin-like drugs, existing drugs given for a new indication or older drugs given by a different route of administration. Here, we discuss factors contributing to this lack of innovation in therapies for pain and advocate public-private partnerships (PPPs) to translate new knowledge into more efficacious and safer treatments.

Influence and stability of pain scale anchors for an investigation of cold pressor pain tolerance

Variable use of pain scale anchors may influence recalled pain ratings, rating consistency, and agreement between actual rating change and ratings of pain relief. This investigation examined change in events that represent maximal pain scale anchors. Participants (N = 68, 50% women) provided events for maximal anchors of 0 to 100 pain scales, and cold pressor pain was rated by using self-selected event/s and an investigator-provided event. Participants then were allowed to change their self-selected event/s. The revised event/s or original events were then used to rate a second cold pressor trial. Forty-one percent of participants changed event/s, and the new event/s was more likely to involve cold or heat, but the painfulness of events and the pain ratings of the second trial did not change. The cold pressor pain ratings were higher when rated on the basis of self-selected event/s than the investigator-provided event for intensity (mean = 80.13, SD = 19.30; mean = 60.81, SD = 27.45) and unpleasantness (mean = 80.84, SD = 19.07; mean = 59.07, SD = 27.53), which could be due to the submaximal painfulness of the investigator-provided event. Therefore, the width of numerical scales is stable with maximal events regardless of the actual events.

PERSPECTIVE

This report identifies change in physical events that are used by participants to represent maximal pain scale anchors and suggests that the maximal nature of the events' painfulness is more important than variability in the actual events. We conclude that the numerical pain scales we used are understandable and stable, but we suggest that instructional sets for pain measurement may be improved by evaluation of the painfulness of events that respondents use to conceptualize maximal pain scale anchors.

Variation in oral sensation: implications for diet and health

PURPOSE OF REVIEW

Important advances in our understanding of how taste, smell and somatosensation contribute to oral sensation are reviewed and the nutritional and health implications associated with variation in oral sensation are discussed.

RECENT FINDINGS

Oral sensation is a central integration of taste (salty, sweet, sour, bitter, umami), retronasal olfaction (i.e. smelling through the mouth), and somatosensation (touch, temperature, pain) by the orbitofrontal cortex. There is normal variation in oral sensation across individuals, ranging from those living in a neon orosensory world to those living in a pastel world. Historically, study of this variation revolved around genetically mediated bitterness of phenylthiocarbamide or propylthiouracil, but now it encompasses additional phenotypes (e.g. fungiform papillae number, bitterness of quinine) and emerging receptor genotypes. Aging and exposure to pathogens interact with genetics to further influence oral sensation. Orosensory variation is associated with differences in preference for high-fat foods, sweets, vegetables, and alcoholic beverages. Emerging data suggest this variation influences intake of these foods/beverages and thus diet-related chronic diseases (cardiovascular diseases, certain cancers, obesity).

SUMMARY

Oral sensation varies with genetics and gene-environment interactions. As this variation explains some of the differences in what we like/dislike to eat, attempts to reduce disease risk through diet should consider food/beverage preference to promote health and food enjoyment.

Revisiting sugar-fat mixtures: sweetness and creaminess vary with phenotypic markers of oral sensation

Genetic variation in oral sensation presumably influences ingestive behaviors through sensations arising from foods and beverages. Here, we investigated the influence of taste phenotype [6-n-propylthiouracil (PROP) bitterness, fungiform papillae (FP) density] on sweet and creamy sensations from sugar/fat mixtures. Seventy-nine subjects (43 males) reported the sweetness and creaminess of water or milk (skim, whole, heavy cream) varying in sucrose (0-20% w/v) on the general Labeled Magnitude Scale. Sweetness grew with sucrose concentration and when shifting from water to milk mixtures--the growth was greatest for those tasting PROP as most bitter. At higher sucrose levels, increasing fat blunted the PROP-sweet relationship, whereas at lower levels, the relationship was effectively eliminated. Perceived sweetness of the mixture exceeded that predicted from the sum of components at low sucrose concentrations (especially for those tasting PROP most bitter) but fell below predicted at high concentrations, irrespective of fat level. Creaminess increased greatly with fat level and somewhat with sucrose. Those tasting PROP most bitter perceived greater creaminess in the heavy cream across all sucrose levels. Perceived creaminess was somewhat lower than predicted, irrespective of PROP bitterness. The FP density generally showed similar effects as PROP on sweetness and creaminess, (but to a lesser degree) and revealed potential taste-somatosensory interactions in weakly sweet stimuli. These data support that taste phenotype affects the nature of enhancement or suppression of sweetness and creaminess in liquid fat/sugar mixtures. Taste phenotype effects on sweetness and creaminess likely involve differential taste, retronasal olfactory, and somatosensory contributions to these perceptual experiences.

Smell images and the flavour system in the human brain

Flavour perception is one of the most complex of human behaviours. It involves almost all of the senses, particularly the sense of smell, which is involved through odour images generated in the olfactory pathway. In the human brain, the perceptual systems are closely linked to systems for learning, memory, emotion and language, so distributed neural mechanisms contribute to food preference and food cravings. Greater recognition of the role of the brain's flavour system and its connection with eating behaviour is needed for a deeper understanding of why people eat what they do, and to generate better recommendations about diet and nutrition.

The effect of taste and palatability on lingual swallowing pressure

There is evidence that a strong, unpalatable, sour bolus improves swallowing in neurogenic dysphagia. It is not known whether other tastes may alter swallowing physiology. This study investigated the effect of moderate versus high taste concentrations (sweet, sour, salty, bitter) and barium taste samples on lingual swallowing pressure in ten healthy young adults, using a three-bulb lingual pressure array secured to the hard palate. Palatability of the samples was analyzed using the nine-point hedonic scale. Results showed that moderate sucrose, high salt, and high citric acid elicited significantly higher lingual swallowing pressures compared with the pressures generated by water. Pressures in the anterior bulb were significantly higher than those recorded from the middle or posterior bulb. There was no significant effect of palatability on lingual swallowing pressures. High salt and citric acid are known to elicit chemesthesis mediated by the trigeminal nerve. These results suggest that chemesthesis may play a crucial role in swallowing physiology. If true, dysphagia diet recommendations that include trigeminal irritants such as carbonation may be beneficial to individuals with dysphagia. However, before this recommendation more research is needed to examine how food properties and their perception affect swallowing in individuals with and without dysphagia.

Psychophysics of sweet and fat perception in obesity: problems, solutions and new perspectives

Psychophysical comparisons seem to show that obese individuals experience normal sweet and fat sensations, they like sweetness the same or less, but like fat more than the non-obese do. These psychophysical comparisons have been made using scales (visual analogue or category) that assume intensity labels (e.g. extremely) which denote the same absolute perceived intensity to all. In reality, the perceived intensities denoted by labels vary because they depend on experiences with the substances to be judged. This variation makes comparisons invalid. Valid comparisons can be made by asking the subjects to rate their sensory/hedonic experiences in contexts that are not related to the specific experiences of interest. Using this methodology, we present the evidence that the sensory and hedonic properties of sweet and fat vary with body mass index. The obese live in different orosensory and orohedonic worlds than do the non-obese; the obese experience reduced sweetness, which probably intensifies fat sensations, and the obese like both sweet and fat more than the non-obese do. Genetic variation as well as taste pathology contribute to these results. These psychophysical advances will impact experimental as well as clinical studies of obesity and other eating disorders.

Individual responder analyses for pain: does one pain scale fit all?

The outcomes of clinical trials are based on the mean responses of large numbers of subjects but fail to address inter-individual differences. The molecular mechanisms that underlie pain vary among individuals over time and among different types of pain to produce wide inter-individual variations in pain perception and response. Gender, ethnicity, temperament and genetic factors also contribute to individual variation in pain sensitivity and responses to analgesics. Pain measurement scales can be used differently across individuals based on the past pain experiences of individuals. We propose that individual responder analyses could be used in clinical trials to better detect analgesic activity across patient groups and within sub-groups, and to identify molecular-genetic mechanisms that contribute to individual variation.

Psychophysics: a journey from the laboratory to the clinic

Pfaffmann, famous for pioneering work in taste neurophysiology, was a great supporter of psychophysics. He wrote: "Indeed it can be said that without behavioral study, hand in hand with physiological and anatomical methods, one gets only a partial insight: telling where, and to some degree how, but not for what!" [The Psychologists, 1974; Chem Senses Flavour 1 (1974) 61]. The psychophysical studies he initially encouraged concerned mechanism (e.g. taste quality coding), but later methodological advances permitted valid comparisons of taste sensations across groups. Quantification of genetic as well as pathological variation permits the demonstration of links between oral sensory variation, food preferences, diet and health.

Association between 6-n-propylthiouracil (PROP) bitterness and colonic neoplasms

Inadequate vegetable intake appears to increase colon cancer risk. Since genetic variation in taste influences vegetable preference, we tested associations between bitterness of 6-n-propylthiouracil (PROP), a measure of taste genetics, and number of colonic polyps, a measure of colon cancer risk, in 251 men who underwent screening lower endoscopy. Patients used the general Labeled Magnitude Scale to rate bitterness of 1.6 mg PROP delivered via filter paper. A subset of 86 patients reported weekly vegetable intakes, excluding salad or potatoes. PROP bitterness correlated significantly with polyp number, an effect separate from age-associated increases in polyp number. The PROP-polyp relationship was strongest in men over 66 years, and older men with polyps were most likely to be overweight or obese. In the subset reporting vegetable intake, men who tasted PROP as more bitter consumed fewer vegetables. These preliminary findings suggest that taste genetics may influence colon cancer risk, possibly through intake of vegetables.

Development and testing of a labeled magnitude scale of perceived satiety

Satiety ratings are often made using VAS or simple category scales. In order to establish a simple, more quantitative technique to index perceived hunger and/or fullness, research was undertaken to develop and test a labeled magnitude scale of satiety. Thirty-seven subjects rated the semantic meaning of 47 phrases describing different levels of hunger/fullness using magnitude estimation. Eleven phrases were then selected using criteria of response consistency, symmetry, bipolarity, and inclusion of the end-point anchors of 'greatest imaginable hunger (fullness)'. These phrases were placed along a vertical line scale at positions corresponding to their geometric mean magnitude estimates to create a labeled magnitude scale of satiety. This Satiety Labeled Intensity Magnitude (SLIM) scale was compared to VAS scales for sensitivity and reliability in two studies. In one image-based study, ANOVA with post-hoc tests showed the SLIM scale to have greater sensitivity and to have an average reliability coefficient of 0.90. In a second study using three different foods replicated on two consecutive weeks, reliability was found to be highest for the SLIM scale. It is concluded that the SLIM scale is a sensitive, reliable, and easy-to-use scale for measuring perceived satiety that has several advantages over other, more commonly used satiety scales.