The analgesic power of pleasant touch in individuals with chronic pain: Recent findings and new insights

The effects of C-tactile stimulation on temporal summation of second pain: A study of the central and peripheral neural correlates

Affective touch is mediated by specialized receptors sensitive to gentle and slow touch called C-tactile afferents (CT). The activation of these receptors has shown promise in reducing subjective pain ratings, however, how this type of touch can affect central sensitization processes is poorly studied. This work aimed to investigate if affective touch is able to modulate pain sensitization and its electrophysiological correlates during Temporal Summation of Second Pain (TSSP), a phenomenon characterized by an increase in pain perception due to repeated noxious stimuli. Thirty-seven participants underwent a TSSP protocol involving three conditions: TSSP alone, TSSP during vibrotactile stimulation, and TSSP during CT stimulation (administered with a brush mounted in a robot arm). We measured subjective pain ratings, electroencephalographic (N2-P2 complex) and electrocardiographic activity during these conditions. Participants reported a significantly lower increase of pain during CT stimulation compared to vibrotactile stimulation, but not to TSSP alone. In addition, TSSP was reduced when administered in the ipsilateral arm compared to the other somatosensory stimulation. Subjective reports of attention towards painful stimuli, amplitude of the N2-P2 complex, and heart rate were also reduced during CT stimulation. Conclusion: Our results indicated that the activation of CT receptors may reduce sensitization compared to other types of somatosensory stimulation, which is possibly related to the reduction of the attention devoted to nociceptive stimulation. Our results suggest that activation of CT receptors may alleviate the occurrence of central pain sensitization.

Visual perspective and body ownership modulate vicarious pain and touch: A systematic review

We conducted a systematic review investigating the influence of visual perspective and body ownership (BO) on vicarious brain resonance and vicarious sensations during the observation of pain and touch. Indeed, the way in which brain reactivity and the phenomenological experience can be modulated by blurring the bodily boundaries of self-other distinction is still unclear. We screened Scopus and WebOfScience, and identified 31 articles, published from 2000 to 2022. Results show that assuming an egocentric perspective enhances vicarious resonance and vicarious sensations. Studies on synaesthetes suggest that vicarious conscious experiences are associated with an increased tendency to embody fake body parts, even in the absence of congruent multisensory stimulation. Moreover, immersive virtual reality studies show that the type of embodied virtual body can affect high-order sensations such as appropriateness, unpleasantness, and erogeneity, associated with the touched body part and the toucher's social identity. We conclude that perspective plays a key role in the resonance with others' pain and touch, and full-BO over virtual avatars allows investigation of complex aspects of pain and touch perception which would not be possible in reality.

The Hedonic Experience Associated with a Gentle Touch Is Preserved in Women with Fibromyalgia

Background/Objectives: Although manual therapies can be used for pain alleviation in fibromyalgia, there is no clear evidence about the processing of gentle, affective touch in this clinical condition. In fact, persistent painful sensations and psychological factors may impact the hedonic experience of touch. Methods: This observational cross-sectional study compared the subjective experience of affective touch between 14 women with fibromyalgia (age range: 35-70; range of years of education: 5-13) and 14 pain-free women (age range: 18-30; range of years of education: 13-19). The participants rated the pleasantness of slow and fast touches delivered by a brush, the experimenter's hand, and a plastic stick. Tactile stimuli were either imagined or real to disentangle the contribution of top-down and bottom-up sensory components. Additionally, a self-report questionnaire explored the lifetime experiences of affective touch. Results: Akin to healthy counterparts, individuals with fibromyalgia rated slow touches delivered by the experimenter's hand or a brush as more pleasant than fast touches, regardless of whether they were imagined or real. However, the intensity of pain affects only the imagined pleasantness in our participants with fibromyalgia. Furthermore, despite the fibromyalgia patients reporting fewer experiences of affective touch in childhood and adolescence, this evidence was not associated with the experimental outcomes. Conclusions: The hedonic experience of affective touch seems preserved in fibromyalgia despite poor intimate bodily contact in youth. We confirmed that bottom-up and top-down factors contribute to the affective touch perception in fibromyalgia: bodily pain may impact even more the expected pleasure than the actual experience. Future investigations may introduce neurophysiological measures of the implicit autonomic responses to affective touch in fibromyalgia. To conclude, although preliminary, our evidence may be in favor of manual therapies for pain relief in fibromyalgia.

Insecure Attachment, Oxytocinergic System and C-Tactile Fibers: An Integrative and Translational Pathophysiological Model of Fibromyalgia and Central Sensitivity Syndromes

Although the pathophysiology of fibromyalgia syndrome has been better understood in recent decades, a unified model of its pathogenesis and an effective therapeutic approach are still far from being realized. The main aim of this article will be to delve into the fundamental mechanisms of the pathophysiology of fibromyalgia conceptualized as stress intolerance syndrome. Using the biopsychosocial model of chronic pain syndromes, we will describe the potential role of the attachment system, C-tactile fibers, and oxytocinergic system dysfunction in the pathophysiology of fibromyalgia syndrome and other central sensitivity syndromes. At the end of the article, the therapeutic implications of this new global and translational pathophysiological model will be briefly discussed.

CT-optimal touch and chronic pain experience in Parkinson's Disease; An intervention study

One of the most underdiagnosed and undertreated non-motor symptoms of Parkinson's Disease is chronic pain. This is generally treated with analgesics which is not always effective and can cause several side-effects. Therefore, new ways to reduce chronic pain are needed. Several experimental studies show that CT-optimal touch can reduce acute pain. However, little is known about the effect of CT-optimal touch on chronic pain. The aim of the current study is to investigate whether CT-optimal touch can reduce the chronic pain experience in Parkinson patients. In this intervention study, 17 Parkinson patients underwent three conditions; no touch, CT-optimal touch and CT non-optimal touch with a duration of one week each. During each touch week, participants received touch from their partners twice a day for 15 minutes. Results show that both types of touch ameliorate the chronic pain experience. Furthermore, it appears that it is slightly more beneficial to apply CT-optimal touch also because it is perceived as more pleasant. Therefore, we argue that CT-optimal touch might be used when immediate pain relief is needed. Importantly, this study shows that CT-optimal touch can reduce chronic pain in Parkinson's Disease and can be administered by a partner which makes it feasible to implement CT-optimal touch as daily routine.

Reconceptualizing Somatic Dysfunction in the Light of a Neuroaesthetic Enactive Paradigm

Background: Palpatory findings are considered a central element of osteopathic practice, especially when associated with a patient's altered regulative functions than with named somatic dysfunctions. Although osteopathic theories for somatic dysfunction could be plausible, the clinical applicability of the concept is debated, especially because it is largely related to simple cause-effect models of osteopathic care. In contrast to a linear kind of diagnosis of a "tissue as a producer of symptoms", this perspective article aims to provide a conceptual and operational framework in which the somatic dysfunction evaluation process is seen as a neuroaesthetic (en)active encounter between osteopath and patient. Subsections relevant to the subject: To summarize all concepts of the hypothesis, the enactive neuroaesthetics principles are proposed as a critical foundation for the osteopathic assessment and treatment of the person, specifically addressing a new paradigm for somatic dysfunction. Conclusions, and future directions: The present perspective article represents a proposition to blend technical rationality informed by neurocognitive and social sciences, and professional artistry clinical experience informed by traditional tenets, to overcome the controversy around somatic dysfunction, rather than dismissing the concept.