Taste and Smell Perception in Aging1

The taste and smell experience of other human beings cannot be known directly. Thus our understanding of age-related changes in the perception of taste and smell is derived inferentially. Inferences based on verbal reports and on the performance of tasks involving taste and smell stimuli suggest that some older individuals are impaired. The perceptual disadvantage of older adults appears to be more marked or more easily measured for complex than for simple stimuli. Some difference between older and younger adults may not be primarily sensory; others may arise from differences only incidentally associated with aging. The study of taste and smell perception in aging continues to challenge the psychophysical investigator to define the nature and extent of age-related change and to demonstrate its underlying mechanisms.     

Involvement of the Calcium-sensing Receptor in Human Taste Perception

By human sensory analyses, we found that various extracellular calcium-sensing receptor (CaSR) agonists enhance sweet, salty, and umami tastes, although they have no taste themselves. These characteristics are known as “kokumi taste” and often appear in traditional Japanese cuisine. Although GSH is a typical kokumi taste substance (taste enhancer), its mode of action is poorly understood. Here, we demonstrate how the kokumi taste is enhanced by the CaSR, a close relative of the class C G-protein-coupled receptors T1R1, T1R2, and T1R3 (sweet and umami receptors). We identified a large number of CaSR agonist γ-glutamyl peptides, including GSH (γ-Glu-Cys-Gly) and γ-Glu-Val-Gly, and showed that these peptides elicit the kokumi taste. Further analyses revealed that some known CaSR agonists such as Ca²⁺, protamine, polylysine, l-histidine, and cinacalcet (a calcium-mimetic drug) also elicit the kokumi taste and that the CaSR-specific antagonist, NPS-2143, significantly suppresses the kokumi taste. This is the first report indicating a distinct function of the CaSR in human taste perception.     

Changes in Hemodynamic Response to Mental Stress with Heart Rate Feedback Training

This study was designed to examine underlying hemodynamic changes that accompany observed reductions in heart rate (HR) response to mental stress following HR feedback training. Twenty-five college males, assigned to either a HR feedback training group (FB+) or a control group (FB–), were presented with a videogame and mental arithmetic challenge, as HR, blood pressure, and impedance cardiography-derived measures of hemodynamic functioning were recorded. During training, the FB+ group received HR feedback and the FB– group was not provided with HR feedback while playing a videogame. At posttraining, results revealed that the FB+ group exhibited significantly lower HR, systolic blood pressure, stroke volume, and total peripheral resistance responses to the videogame compared to that at pretraining. There was no evidence that the acquired skills generalized to a mental arithmetic task. These results suggest that HR feedback training is an effective method for reducing cardiovascular and hemodynamic responses to a mental stressor; however, the generalizability of this effect remains questionable.     

Taste Perception in Kallmann Syndrome,A Model of Congenital Anosmia

ObjectiveTo investigate taste, a component of flavor perception, using electrogustometry (EG) in patients with congenital anosmia associated with Kallmann syndrome (KS).MethodsFour patients with KS and 4 control subjects participated in this study. During the first phase of the investigation, the study subjects were administered the University of Pennsylvania Smell Identification Test. During the second phase of the study, EG testing of 2 regions on the anterior tongue tip was performed through an electrode.ResultsPatients with KS, as expected, scored in the anosmic range on the University of Pennsylvania Smell Identification Test, whereas the control group had a normal sense of smell. The difference in the olfaction scores was significant between the 2 study groups (P < 0.015). The result of taste assessment of patients with KS and control subjects with use of EG was not significantly different between the 2 study groups (P = 0.874).ConclusionThe current study demonstrates that patients with KS have a normal sense of taste, as determined by EG. This finding is consistent with the fact that the deficit in KS is purely olfactory. Because flavor perception is not a common complaint in patients with this condition, it may be postulated that persons with KS compensate for the absent sense of smell. Further studies need to be undertaken to explore how patients with KS compensate for the olfactory dysfunction, information that should contribute to the understanding of the interplay of the various components of flavor perception. (Endocr Pract. 2007;13:716-720)     

Perception of Suicide Risk in Mental Health Professionals

This study employed an independent-groups design (4 conditions) to investigate possible biases in the suicide risk perception of mental health professionals. Four hundred participants comprising doctors, nurses and social workers viewed a vignette describing a fictitious patient with a long-term mental illness. The case was presented as being drawn from a sample of twenty similar clinical case reports, of which 10 were associated with an outcome of suicide. The participant tasks were (i) to decide whether the presented vignette was one of those cases or not, and (ii) to provide an assessment of confidence in that decision. The 4 conditions were used to investigate whether the presence of an associated face, and the nature of the emotional state expressed by that face, affected the response profile. In fact, there were no significant differences between conditions, but there was a significant bias across all conditions towards associating the vignette with suicide, despite the base rate being pre-determined at 50%. The bias was more pronounced in doctors and in male respondents. Moreover, many participants indicated substantial confidence in their decisions. The results are discussed in terms of availability bias and over-confidence bias.     

Marked Increase in PROP Taste Responsiveness Following Oral Supplementation with Selected Salivary Proteins or Their Related Free Amino Acids

The genetic predisposition to taste 6-n-propylthiouracil (PROP) varies among individuals and is associated with salivary levels of Ps-1 and II-2 peptides, belonging to the basic proline-rich protein family (bPRP). We evaluated the role of these proteins and free amino acids that selectively interact with the PROP molecule, in modulating bitter taste responsiveness. Subjects were classified by their PROP taster status based on ratings of perceived taste intensity for PROP and NaCl solutions. Quantitative and qualitative determinations of Ps-1 and II-2 proteins in unstimulated saliva were performed by HPLC-ESI-MS analysis. Subjects rated PROP bitterness after supplementation with Ps-1 and II-2, and two amino acids (L-Arg and L-Lys) whose interaction with PROP was demonstrated by ¹H-NMR spectroscopy. ANOVA showed that salivary levels of II-2 and Ps-1 proteins were higher in unstimulated saliva of PROP super-tasters and medium tasters than in non-tasters. Supplementation of Ps-1 protein in individuals lacking it in saliva enhanced their PROP bitter taste responsiveness, and this effect was specific to the non-taster group.¹H-NMR results showed that the interaction between PROP and L-Arg is stronger than that involving L-Lys, and taste experiments confirmed that oral supplementation with these two amino acids increased PROP bitterness intensity, more for L-Arg than for L-Lys. These data suggest that Ps-1 protein facilitates PROP bitter taste perception and identifies a role for free L-Arg and L-Lys in PROP tasting.     

Genetic and Molecular Basis of Individual Differences in Human Umami Taste Perception

Umami taste (corresponds to savory in English) is elicited by L-glutamate, typically as its Na salt (monosodium glutamate: MSG), and is one of five basic taste qualities that plays a key role in intake of amino acids. A particular property of umami is the synergistic potentiation of glutamate by purine nucleotide monophosphates (IMP, GMP). A heterodimer of a G protein coupled receptor, TAS1R1 and TAS1R3, is proposed to function as its receptor. However, little is known about genetic variation of TAS1R1 and TAS1R3 and its potential links with individual differences in umami sensitivity. Here we investigated the association between recognition thresholds for umami substances and genetic variations in human TAS1R1 and TAS1R3, and the functions of TAS1R1/TAS1R3 variants using a heterologous expression system. Our study demonstrated that the TAS1R1-372T creates a more sensitive umami receptor than -372A, while TAS1R3-757C creates a less sensitive one than -757R for MSG and MSG plus IMP, and showed a strong correlation between the recognition thresholds and in vitro dose - response relationships. These results in human studies support the propositions that a TAS1R1/TAS1R3 heterodimer acts as an umami receptor, and that genetic variation in this heterodimer directly affects umami taste sensitivity.     

Changes in Visuospatial Perception in Emotional Pathology

In patients with maniacal-depressive disease, peculiarities of perception of sizes of horizontal lines and of depth of space as well as of reflection of space in drawings were studied. It was shown the maniacal state to be characterized by underestimation of distant object sizes and by preference of remote space field; this was manifested as moving objects away from an observer, i.e., overestimation of distances at depth perception and using an exaggerative linear perspective in drawings. The depressive state was characterized by overestimation of sizes of distant object or by constancy of their perception and by preference of the near space field; this was manifested as approaching objects to an observer, i.e., underestimation of the distances at depth perception and using an inverse perspective in drawings. The data obtained confirm the hypothesis that distortion of perception of space is based on a shift of balance of the interhemispheric activity.     

Receptor Polymorphism and Genomic Structure Interact to Shape Bitter Taste Perception

The ability to taste bitterness evolved to safeguard most animals, including humans, against potentially toxic substances, thereby leading to food rejection. Nonetheless, bitter perception is subject to individual variations due to the presence of genetic functional polymorphisms in bitter taste receptor (TAS2R) genes, such as the long-known association between genetic polymorphisms in TAS2R38 and bitter taste perception of phenylthiocarbamide. Yet, due to overlaps in specificities across receptors, such associations with a single TAS2R locus are uncommon. Therefore, to investigate more complex associations, we examined taste responses to six structurally diverse compounds (absinthin, amarogentin, cascarillin, grosheimin, quassin, and quinine) in a sample of the Caucasian population. By sequencing all bitter receptor loci, inferring long-range haplotypes, mapping their effects on phenotype variation, and characterizing functionally causal allelic variants, we deciphered at the molecular level how a subjects’ genotype for the whole-family of TAS2R genes shapes variation in bitter taste perception. Within each haplotype block implicated in phenotypic variation, we provided evidence for at least one locus harboring functional polymorphic alleles, e.g. one locus for sensitivity to amarogentin, one of the most bitter natural compounds known, and two loci for sensitivity to grosheimin, one of the bitter compounds of artichoke. Our analyses revealed also, besides simple associations, complex associations of bitterness sensitivity across TAS2R loci. Indeed, even if several putative loci harbored both high- and low-sensitivity alleles, phenotypic variation depended on linkage between these alleles. When sensitive alleles for bitter compounds were maintained in the same linkage phase, genetically driven perceptual differences were obvious, e.g. for grosheimin. On the contrary, when sensitive alleles were in opposite phase, only weak genotype-phenotype associations were seen, e.g. for absinthin, the bitter principle of the beverage absinth. These findings illustrate the extent to which genetic influences on taste are complex, yet arise from both receptor activation patterns and linkage structure among receptor genes.     

Changes in Self-Efficacy Following Obesity Treatment

Self-efficacy is an important component in the treatment of obesity. However, there is limited research examining changes in self-efficacy following obesity treatment. In this quasi-experimental study, 26 obese subjects demonstrated significant improvement on the Weight Efficacy Life-Style Questionnaire (WEL) following participation in a 26-week multidisciplinary VLCD program. Subjects demonstrated significant improvement from pre- to post-treatment on total WEL scores and on all five of the situational factors: Negative Emotions, Availability, Social Pressure, Physical Discomfort and Positive Activities. These results provide further construct validity for the WEL and offer guidelines for the amount of change that subjects may demonstrate on the WEL following obesity treatment.