Genetic Taster Status as a Mediator of Neural Activity and Swallowing Mechanics in Healthy Adults

Comparing Taste Perception Across Modalities in Healthy Adults: Liquids Versus Dissolvable Taste Strips

Taste stimulation has rehabilitative value in dysphagia management, as it activates salient underlying afferent pathways to swallowing which may evoke feedforward effects on swallow biomechanics. Despite its potential beneficial effects on swallow physiology, taste stimulation's clinical application is limited for persons unsafe to orally consume food/liquid. This study aimed to create edible, dissolvable taste strips matched to flavor profiles previously used in research assessing taste's effects on swallowing physiology and brain activity, and to evaluate how similar their perceived intensity and hedonic, or palatability, ratings were between their liquid counterparts. Plain, sour, sweet-sour, lemon, and orange flavor profiles were custom-made in taste strips and liquid modalities. The generalized Labeled Magnitude Scale and hedonic generalized Labeled Magnitude Scale were used to assess intensity and palatability ratings for flavor profiles in each modality. Healthy participants were recruited and stratified across age and sex. Liquids were rated as more intense than taste strips; however, there was no difference in palatability ratings between the modalities. There were significant differences across flavor profiles in intensity and palatability ratings. Collapsed across liquid and taste strip modalities, pairwise comparisons revealed all flavored stimuli were rated as more intense than the plain profile, sour was perceived as more intense and less palatable than all other profiles, and orange was rated as more palatable than sour, lemon, and plain tastants. Taste strips have useful implications for dysphagia management, as they could offer safe and patient-preferred flavor profiles to potentially provide advantageous swallowing and neural hemodynamic responses.

The Effect of Genetic Taste Status on Swallowing: A Literature Review

PURPOSE

Swallowing and taste share innervation pathways and are crucial to nutritive intake. Individuals vary in their perception of taste due to factors such as genetics; however, it is unclear to what extent genetic taste status influences swallowing physiology and function. The purpose of this review article is to provide background on genetic taste status, review the evidence on the association between genetic taste status and swallowing, and discuss research and clinical implications.

METHOD

A comprehensive literature review was conducted using search terms related to swallowing and genetic taste status. Studies were included if they investigated the main effect of genetic taste status on swallowing or the interaction of genetic taste status with other variables. Studies were grouped by participant population (healthy participants or persons with a swallowing disorder), swallowing-related outcome measure, and method of genetic taste status measurement.

RESULTS

The results were mixed, with five of 10 reviewed studies reporting a statistically significant main or interaction effect on swallowing. Most studies included healthy participants, with only one study investigating participants with dysphagia. Additionally, swallowing-related outcome measures and methods of determining genetic taste status varied greatly between studies conducted on separate cohorts.

CONCLUSIONS

Few studies have incorporated genetic taste status as a variable in swallowing research, and results are mixed. Future research on sensation and swallowing should consider the potential effect of genetic taste status and follow standardized procedures for its determination. Despite the limited evidence, clinicians may consider how individual differences in perception shape swallowing outcomes.

Brain activity associated with taste stimulation: A mechanism for neuroplastic change?

PURPOSE

Neuroplasticity may be enhanced by increasing brain activation and bloodflow in neural regions relevant to the target behavior. We administered precisely formulated and dosed taste stimuli to determine whether the associated brain activity patterns included areas that underlie swallowing control.

METHODS

Five taste stimuli (unflavored, sour, sweet-sour, lemon, and orange suspensions) were administered in timing-regulated and temperature-controlled 3 mL doses via a customized pump/tubing system to 21 healthy adults during functional magnetic resonance imaging (fMRI). Whole-brain analyses of fMRI data assessed main effects of taste stimulation as well as differential effects of taste profile.

RESULTS

Differences in brain activity associated with taste stimulation overall as well as specific stimulus type were observed in key taste and swallowing regions including the orbitofrontal cortex, insula, cingulate, and pre- and postcentral gyri. Overall, taste stimulation elicited increased activation in swallowing-related brain regions compared to unflavored trials. Different patterns of blood oxygen level-dependent (BOLD) signal were noted by taste profile. For most areas, sweet-sour and sour trials elicited increases in BOLD compared to unflavored trials within that region, whereas lemon and orange trials yielded reductions in BOLD. This was despite identical concentrations of citric acid and sweetener in the lemon, orange, and sweet-sour solutions.

CONCLUSIONS

These results suggest that neural activity in swallowing-relevant regions can be amplified with taste stimuli and may be differentially affected by specific properties within very similar taste profiles. These findings provide critical foundational information for interpreting disparities in previous studies of taste effects on brain activity and swallowing function, defining optimal stimuli to increase brain activity in swallowing-relevant regions, and harnessing taste to enhance neuroplasticity and recovery for persons with swallowing disorders.

The effect of taste on swallowing: A scoping and systematic review

Consuming foods and liquids for nutrition requires the coordination of several muscles. Swallowing is triggered and modified by sensory inputs from the aerodigestive tract. Taste has recently received attention as a potential modulator of swallowing physiology, function, and neural activation; additionally, taste impairment is a sequela of COVID-19. This review presents factors impacting taste and swallowing, systematically summarizes the existing literature, and assesses the quality of included studies. A search was conducted for original research including taste stimulation, deglutition-related measure(s), and human participants. Study design, independent and dependent variables, and participant characteristics were coded; included studies were assessed for quality and risk of bias. Forty-eight articles were included after abstract and full-text review. Synthesis was complicated by variable sensory components of stimuli (taste category and intensity, pure taste vs. flavor, chemesthesis, volume/amount, consistency, temperature), participant characteristics, confounding variables such as genetic taster status, and methods of measurement. Most studies had a high risk of at least one type of bias and were of fair or poor quality. Interpretation is limited by wide variability in methods, taste stimulation, confounding factors, and lower-quality evidence. Existing studies suggest that taste can modulate swallowing, but more rigorous and standardized research is needed.

An examination into the effect of genetic taste status and intensity of carbonation on swallowing and palatability in healthy young adults

BACKGROUND

Dysphagia is a highly prevalent condition and affects a wide range of cohorts. A common compensatory strategy to manage dysphagia is diet modification. However, this technique is often associated with poor patient quality of life and adverse long-term effects. Carbonated liquids have shown promise as an alternative compensatory strategy for the management of dysphagia.

AIMS

To examine the effect of genetic taste status and intensity of carbonation on swallowing and palatability in a healthy young adult population. To examine the palatability of carbonated liquids over time.

METHODS & PROCEDURES

A total of 35 healthy young adults were recruited for this prospective, quantitative cohort study. They each drank 150 ml of still water (SW), lightly carbonated water (LCW) and highly carbonated water (HCW). Swallow function, palatability and genetic taste status were assessed using the timed water swallow test, the hedonic general labelled magnitude scale and participant ratings of the bitterness of propylthiouracil strips, respectively. Participants were divided into groups of supertasters, moderate tasters and non-tasters.

OUTCOMES & RESULTS

A significant difference was found between SW and HCW on three tests of swallow function. Average time per swallow increased (p = 0.03), average swallow velocity decreased (p = 0.001) and average volume per swallow decreased (p = 0.017) on HCW compared with SW. HCW had a greater impact on swallow function than LCW. A significant mean difference in palatability ratings was found across intensity levels of carbonated fluids (p = 0.002), specifically between SW and HCW (p = 0.001). HCW was less palatable than SW. The palatability of carbonated liquids, investigated within a subgroup of five participants, did not decrease after a 24-h period during which participants only drank carbonated liquids (p = 0.102). A significant difference was found between supertasters' (n = 9) (mean = 13.33) and non-tasters' (n = 20) (mean = -24.5) palatability ratings of HCW (p = 0.03). Despite differences in swallow function between SW and HCW, no differences were detected between supertasters' and non-tasters' swallow function on SW, LCW or HCW.

CONCLUSIONS & IMPLICATIONS

Carbonated liquids have the ability to alter swallow function in a healthy young adult population; however, liquids must be highly carbonated in order to have an effect. Additionally, highly carbonated liquids are less palatable than SW, but the palatability of carbonated liquids does not decrease over time. Furthermore, supertasters find HCW more palatable than non-tasters. These findings suggest that carbonated liquids alter swallowing in a healthy population. Further research in a clinical population is needed to better understand the potential role of sensory stimulation as a dysphagia intervention.

WHAT THIS PAPER ADDS

What is already known on the subject Several studies have found that carbonated liquids have the ability to alter swallow function in both healthy and clinical populations. However, there is a lack of evidence around the optimum intensity of CO₂ in carbonated liquids and the palatability of carbonated liquids as well as the palatability of carbonated fluids over time. What this paper adds to existing knowledge The findings from this study suggest that carbonated liquids can alter swallow function in a healthy young adult population, but liquids must be highly carbonated in order to have an effect. HCW is less palatable than SW, but the palatability of carbonated liquids does not decrease over time. Additionally, supertasters find HCW more palatable than non-supertasters (non-tasters). What are the potential or actual clinical implications of this work? The findings from this study suggest that carbonated liquids may be suitable for use as a sensory stimulation technique for people with dysphagia, as their palatability does not decrease over time; however, further research in a clinical population is needed in order to determine this. Additionally, intensity of stimulus is an important factor to consider during dysphagia evaluation to identify what intensity is required to optimize swallowing.