Adding cocoa to sucrose: the effect on cold pain tolerance

Chocolate intake and muscle pain sensation: A randomized experimental study

BACKGROUND

Chocolate, as a cocoa-derived product rich in flavanols, has been used for medical and anti-inflammatory purposes. Therefore, the aim of this study was to investigate if the ingestion of different percentages of cocoa products affects the experimentally induced pain caused by intramuscular hypertonic saline injections in the masseter muscle of healthy men and women.

METHODS

This experimental randomized, double-blind, and controlled study included 15 young, healthy, and pain-free men and 15 age-matched women and involved three visits with at least a 1-week washout. Pain was induced twice at each visit with intramuscular injections of 0.2 mL hypertonic saline (5%), before and after intake of one of the different chocolate types: white (30% cocoa content), milk (34% cocoa content), and dark (70% cocoa content). Pain duration, pain area, peak pain, and pressure pain threshold (PPT) were assessed every fifth minute after each injection, up until 30 min after the initial injection. Descriptive and inferential statistics were performed using IBM® SPSS (Version 27); significance level was set to p<0.05.

RESULTS

This study showed that intake of chocolate, no matter the type, reduced the induced pain intensity significantly more than no intake of chocolate (p<0.05, Tukey test). There were no differences between the chocolate types. Further, men showed a significantly greater pain reduction than women after intake of white chocolate (p<0.05, Tukey test). No other differences between pain characteristics or sexes were revealed.

CONCLUSION

Intake of chocolate before a painful stimulus had a pain-reducing effect no matter the cocoa concentration. The results indicate that perhaps it is not the cocoa concentration (e.g., flavanols) alone that explains the positive effect on pain, but likely a combination of preference and taste-experience. Another possible explanation could be the composition of the chocolate, i.e. the concentration of the other ingredients such as sugar, soy, and vanilla. ClinicalTrials.gov Identifier: NCT05378984.

Acute and Chronic Pain from Facial Skin and Oral Mucosa: Unique Neurobiology and Challenging Treatment

The oral cavity is a portal into the digestive system, which exhibits unique sensory properties. Like facial skin, the oral mucosa needs to be exquisitely sensitive and selective, in order to detect harmful toxins versus edible food. Chemosensation and somatosensation by multiple receptors, including transient receptor potential channels, are well-developed to meet these needs. In contrast to facial skin, however, the oral mucosa rarely exhibits itch responses. Like the gut, the oral cavity performs mechanical and chemical digestion. Therefore, the oral mucosa needs to be insensitive, to some degree, in order to endure noxious irritation. Persistent pain from the oral mucosa is often due to ulcers, involving both tissue injury and infection. Trigeminal nerve injury and trigeminal neuralgia produce intractable pain in the orofacial skin and the oral mucosa, through mechanisms distinct from those seen in the spinal area, which is particularly difficult to predict or treat. The diagnosis and treatment of idiopathic chronic pain, such as atypical odontalgia (idiopathic painful trigeminal neuropathy or post-traumatic trigeminal neuropathy) and burning mouth syndrome, remain especially challenging. The central integration of gustatory inputs might modulate chronic oral and facial pain. A lack of pain in chronic inflammation inside the oral cavity, such as chronic periodontitis, involves the specialized functioning of oral bacteria. A more detailed understanding of the unique neurobiology of pain from the orofacial skin and the oral mucosa should help us develop novel methods for better treating persistent orofacial pain.

Pain, Smell, and Taste in Adults: A Narrative Review of Multisensory Perception and Interaction

Every day our sensory systems perceive and integrate a variety of stimuli containing information vital for our survival. Pain acts as a protective warning system, eliciting a response to remove harmful stimuli; it may also be a symptom of an illness or present as a disease itself. There is a growing need for additional pain-relieving therapies involving the multisensory integration of smell and taste in pain modulation, an approach that may provide new strategies for the treatment and management of pain. While pain, smell, and taste share common features and are strongly linked to emotion and cognition, their interaction has been poorly explored. In this review, we provide an overview of the literature on pain modulation by olfactory and gustatory substances. It includes adult human studies investigating measures of pain threshold, tolerance, intensity, and/or unpleasantness. Due to the limited number of studies currently available, we have structured this review as a narrative in which we comment on experimentally induced and clinical pain separately on pain–smell and pain–taste interaction. Inconsistent study findings notwithstanding, pain, smell, and taste seem to interact at both the behavioral and the neural levels. Pain intensity and unpleasantness seem to be affected more by olfactory substances, whereas pain threshold and tolerance are influenced by gustatory substances. Few pilot studies to date have investigated these effects in clinical populations. While the current results are promising for the future, more evidence is needed to elucidate the link between the chemical senses and pain. Doing so has the potential to improve and develop novel options for pain treatment.

Smell and taste dissociations in the modulation of tonic pain perception induced by a capsaicin cream application

BACKGROUND

Pain is a subjective experience characterized by sensory (intensity) and emotional (unpleasantness) aspects. Although literature reports behavioural effects on pain due to smell and taste influence, to our knowledge the relationship between tonic pain induced by a capsaicin cream and these chemosensory systems has never been explored before. The aim of this study was to investigate the modulation of olfactory and gustatory substances having different valence on tonic pain perception mediated by a capsaicin cream application.

METHODS

Sixty healthy volunteers were included in two separated experiments (N = 30 smell; N = 30 taste) and underwent different valence smell and taste stimulations, while receiving painful stimuli. Perception of pain intensity (the sensory component) and unpleasantness (the affective component) was measured with a numerical rating scale, both during the two aforementioned experiments.

RESULTS

Pain unpleasantness rating showed differences only in the smell experiment between the two odourous conditions. In particular, pleasant odour induced lower ratings of pain unpleasantness, while no significant results were found for intensity. Regarding taste, we could not observe significant effects nor for pain unpleasantness or intensity.

CONCLUSIONS

These findings highlight the potential role of pleasant odours in influencing the affective aspects of pain perception induced by this kind of tonic pain. Such evidence might provide new insight for using chemosensory substances as analgesics for modulating the cognitive aspects of neuropathic pain.

SIGNIFICANCE

This work shows the effect of smell on the emotional component of tonic pain, experimentally induced by capsaicin cream application. Previous literature investigated tonic pain in interaction with smell and/or taste stimuli, but mainly with physical methods such as temperature. Our findings add new information in this field, contributing to a deeper insight on the role of olfaction on this particular kind of tonic pain perception. This approach could open to new investigations aimed to consider odours for pain management.

Perception of phasic pain is modulated by smell and taste

BACKGROUND

Pain perception is a multimodal experience composed of sensory, emotional and cognitive dimensions. Accumulating evidence suggests that the chemical senses can influence pain perception, but their relation with phasic pain is still unknown. The aim of this study was to investigate the influence of smell and taste having different valence on phasic pain.

METHODS

Twenty-eight healthy volunteers received sweet, bitter and neutral odours or gustatory substances while receiving painful stimuli consisting of electrical shocks. Tactile threshold, pain threshold and pain tolerance were collected using the psychophysical method of limits at baseline and in association with smell and taste. Perception of pain intensity and unpleasantness was measured with a numerical rating scale.

RESULTS

Sweet smell induced lower ratings of pain intensity than bitter smell when stimuli were delivered at pain threshold. Sweet smell also induced lower ratings of pain unpleasantness than neutral smell when stimuli were delivered at pain tolerance. Sweet taste induced lower ratings of pain unpleasantness than bitter taste when stimuli were delivered at pain threshold. Conversely, pain threshold and pain tolerance per se were not affected by smell and taste.

CONCLUSIONS

These findings highlight an effect of sweet substances in reducing the subjective perception of pain intensity and unpleasantness associated to phasic pain.

SIGNIFICANCE

By demonstrating the link between smell, taste and phasic pain this study may have a translational impact in clinical conditions characterized by so-called shock-like pain, such as neuropathic pain.

A pain in the bud? Implications of cross-modal sensitivity for pain experience

There is growing evidence that enhanced sensitivity to painful clinical procedures and chronic pain are related to greater sensitivity to other sensory inputs, such as bitter taste. We examined cross-modal sensitivities in two studies. Study 1 assessed associations between bitter taste sensitivity, pain tolerance, and fear of pain in 48 healthy young adults. Participants were classified as non-tasters, tasters and super-tasters using a bitter taste test (6-n-propythiouracil; PROP). The latter group had significantly higher fear of pain (Fear of Pain Questionnaire) than tasters (p=.036, effect size r = .48). There was only a trend for an association between bitter taste intensity ratings and intensity of pain at the point of pain tolerance in a cold pressor test (p=.04). In Study 2, 40 healthy young adults completed the Adolescent/Adult Sensory Profile before rating intensity and unpleasantness of innocuous (33 °C), moderate (41 °C), and high intensity (44 °C) thermal pain stimulations. The sensory-sensitivity subscale was positively correlated with both intensity and unpleasantness ratings. Canonical correlation showed that only sensitivity to audition and touch (not taste/smell) were associated with intensity of moderate and high (not innocuous) thermal stimuli. Together these findings suggest that there are cross-modal associations predominantly between sensitivity to exteroceptive inputs (i.e., taste, touch, sound) and the affective dimensions of pain, including noxious heat and intolerable cold pain, in healthy adults. These cross-modal sensitivities may arise due to greater psychological aversion to salient sensations, or from shared neural circuitry for processing disparate sensory modalities.

Cocoa agronomy, quality, nutritional, and health aspects

The history of cocoa and chocolate including the birth and the expansion of the chocolate industry was described. Recent developments in the industry and cocoa economy were briefly depicted. An overview of the classification of cacao as well as studies on phenotypic and genetic diversity was presented. Cocoa agronomic practices including traditional and modern propagation techniques were reviewed. Nutrition-related health benefits derived from cocoa consumption were listed and widely reviewed. The specific action of cocoa antioxidants was compared to those of teas and wines. Effects of adding milk to chocolate and chocolate drinks versus bioavailability of cocoa polyphenols were discussed. Finally, flavor, sensory, microbiological, and toxicological aspects of cocoa consumption were presented.

Direct comparison of the generalized Visual Analog Scale (gVAS) and general Labeled Magnitude Scale (gLMS)

Hundreds of studies have used the generalized Labeled Magnitude Scale (gLMS) to collect intensity data. Recent work on generalized affective scales like the Labeled Affective Magnitude (LAM) scale and Labeled Hedonic Scale (LHS) suggest a substantial proportion of participants fail to use the entire range of generalized scales, marking only at the adjective labels. This categorical behavior (i.e., clustering) is not limited to affective ratings, as it is well known anecdotally among users of the gLMS. One way to stop this behavior would be to retain a generalized top anchor and cross modal orientation procedure while stripping away the internal adjectives. Several published studies have already used this variant, the generalized Visual Analog Scale (gVAS). Because there are no reports directly comparing the gVAS and gLMS head to head, we did so in two experiments. In Experiment 1, participants (n=87) were randomized to 1 of 3 conditions to test effects of scaling instructions and scale structure. In Experiment 2, participants (n=58) assessed perceived ease of use and resolving power for each scale in a two-session crossover design. gLMS data showed evidence of categorical behavior, while gVAS data did not. Explicitly instructing participants to rate between adjectives did not reduce this behavior. The gLMS was easier to use according to participants, but resulted in non-normal data due to clustering near the adjective labels. gVAS data did not show categorical behavior, as there are no adjectives to cluster around, but the gVAS sacrifices semantic information about the magnitude of response. Regardless of scale type, participants felt the cross-modal orientation procedure helped them understand how to use the scale. Both scales were able to discriminate between sucrose samples in a concentration series. Relative tradeoffs between the two methods suggest the choice of one scale over the other depends on the specific goals and context of the project.