Affective touch in anorexia nervosa: Exploring the role of social anhedonia and lifespan experiences

Research Progress on Neural Processing of Hand and Forearm Tactile Sensation: A Review Based on fMRI Research

Tactile perception is one of the important ways through which humans interact with the external environment. Similar to the neural processing in visual and auditory systems, the neural processing of tactile information is a complex procedure that transforms this information into sensory signals. Neuroimaging techniques, such as functional Magnetic Resonance Imaging (fMRI), provide compelling evidence indicating that different types of tactile signals undergo independent or collective processing within multiple brain regions. This review focuses on fMRI studies employing both task-based (block design or event-related design) and resting-state paradigms. These studies use general linear models (GLM) to identify brain regions activated during touch processing, or employ functional connectivity(FC) analysis to examine interactions between brain regions, thereby exploring the neural mechanisms underlying the central nervous system's processing of various aspects of tactile sensation, including discriminative touch and affective touch. The discussion extends to exploring changes in tactile processing patterns observed in certain disease states. Recognizing the analogy between pain and touch processing patterns, we conclude by summarizing the interaction between touch and pain. Currently, fMRI-based studies have made significant progress in the field of tactile neural processing. These studies not only deepen our understanding of tactile perception but also provide new perspectives for future neuroscience studies.

Neuropsychiatric considerations in treating anorexia nervosa patients with osteopathic manipulative medicine: a narrative review

Osteopathic manipulative medicine (OMM) has a growing recognition in serving as an effective treatment to promote adaptation and homeostasis of the body by addressing musculoskeletal, neural, vascular, and lymphatic structures to promote self-healing and regulation. OMM can treat the musculoskeletal tension and sympathetic hyperactivity resulting from the increased cortisol response and hypersensitivity found in varying psychiatric illnesses, including anorexia nervosa (AN). This paper addresses the considerations necessary for treating AN patients with OMM, emphasizing the need to evaluate their abnormal high-level neuronal processing of sensory information, including differences in touch perception compared to the general population. Current literature was gathered utilizing a combination of the following keywords: anorexia nervosa, perception of touch, and osteopathic manipulative medicine/treatment. No literature was found addressing the effects of OMM on treating AN patients. Eight studies addressed the change in perception of touch found in AN patients. Results of the literature review reveal that the perceptions of touch in AN patients are distorted and can lead to reduced perceived pleasantness encountered in social interactions and touch. Specific changes have been found in C-tactile (CT) afferents responsible for the positive effects of touch, thus influencing emotional regulation. The significance of addressing this topic is to provide insight into the pathophysiological processes of AN and to inform physicians of unconventional stimuli that may exacerbate AN symptoms and behaviors. Further study is required to elucidate the role and mechanism of OMM in patients with AN and whether manual therapy could worsen pathological behavior and thinking patterns seen in AN patients. Such studies could include, but are not limited to, examining biological factors such as cortisol levels in AN patients receiving OMM and collecting data about AN patients' thinking patterns and behavior during OMM treatment.

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.

Evolutionarily conserved neural responses to affective touch in monkeys transcend consciousness and change with age

Affective touch-a slow, gentle, and pleasant form of touch-activates a different neural network than which is activated during discriminative touch in humans. Affective touch perception is enabled by specialized low-threshold mechanoreceptors in the skin with unmyelinated fibers called C tactile (CT) afferents. These CT afferents are conserved across mammalian species, including macaque monkeys. However, it is unknown whether the neural representation of affective touch is the same across species and whether affective touch's capacity to activate the hubs of the brain that compute socioaffective information requires conscious perception. Here, we used functional MRI to assess the preferential activation of neural hubs by slow (affective) vs. fast (discriminative) touch in anesthetized rhesus monkeys (Macaca mulatta). The insula, anterior cingulate cortex (ACC), amygdala, and secondary somatosensory cortex were all significantly more active during slow touch relative to fast touch, suggesting homologous activation of the interoceptive-allostatic network across primate species during affective touch. Further, we found that neural responses to affective vs. discriminative touch in the insula and ACC (the primary cortical hubs for interoceptive processing) changed significantly with age. Insula and ACC in younger animals differentiated between slow and fast touch, while activity was comparable between conditions for aged monkeys (equivalent to >70 y in humans). These results, together with prior studies establishing conserved peripheral nervous system mechanisms of affective touch transduction, suggest that neural responses to affective touch are evolutionarily conserved in monkeys, significantly impacted in old age, and do not necessitate conscious experience of touch.

The perception of affective touch in women affected by obesity

Introduction

Pleasant and comforting bodily contacts characterized intimate and affective interactions. Affective touch informs us about others' emotions and intentions, sustains intimacy and closeness, protecting from loneliness and psychological distress. Previous evidence points to an altered experience of affective touch in clinical populations reporting interpersonal difficulties. However, there is no investigation of affective touch in obesity, which is often associated with negative affective-relational experiences since childhood.

Methods

This study aimed to provide the first evidence about the experience of affective touch in obesity by comparing 14 women with obesity with 14 women with healthy weight. Participants rated the pleasantness of both imagined and actual tactile stimuli, which consisted of (i) soft-brush strokes, (ii) touches of the experimenter's hand, and (iii) of a plastic stick (as control, non-affective, stimulation). Participants should report the pleasantness of each kind of touch. Moreover, we explored lifespan experiences of affective touch and interpersonal pleasure in social contexts through self-report questionnaires.

Results

No differences emerged for the pleasantness of affective touch (in both the real and imagery task) between the two groups. However, participants with obesity reported less frequent and less satisfying early experiences of affective touch when compared with the controls.

Discussion

Our results spoke in favor of a preserved experience of affective touch when experimentally probed in obesity, despite a limited early exposure to bodily affective contacts. We interpreted our results in the light of the social reconnection hypothesis. Nevertheless, we provided crucial methodological considerations for future research, considering that both the experimenter's and the brush touch may not resemble adequately real-life experiences, in which affective touch involves intimate people.

Topography and relationship-specific social touching in individuals displaying body image disturbances

Interpersonal touch is intimately related to the emotional bond between the touch giver and the touch receiver. Which bodily regions we touch in those individuals in our social network is relationship specific. Perception of interpersonal touch is altered in psychiatric disorders characterised by body image disturbances (BIDs). Here, we examined whether the 'imagined' experience of social touch in individuals with BIDs is body topography- and relationship-specific. By using an interactive media mobile App, the Virtual Touch Toolkit, high versus low levels of BIDs participants completed heatmaps of full-body virtual avatars, to indicate the body regions they find soothing/unpleasant to be touched by a loved one versus an acquaintance. Self-reports of interoceptive awareness and dysmorphic concerns were also measured. Overall, imagined touch was rated as the most soothing when received from a loved one, and also when this was delivered to 'social' body regions. The importance of the social relationship for the imagined tactile interactions was particularly evident for the high levels of BIDs group, with greater problems with interoceptive awareness predicting higher soothing touch ratings when this was received by a loved one. Despite the evidence that imagined bodily contacts between meaningful people is the most pleasant for socially acceptable bodily regions, our findings may suggest a greater sensitivity to relation-specific bodily patterns of social touch particularly in the high level of BIDs group. Heightened interoceptive awareness may also play a key role in this experience of bodily affective contacts. Future research for body-oriented therapy for BIDs is encouraged to systematically probe the efficacy of imagined social touch interaction protocols which use more plausible, ecological, scenarios where touch is delivered by loved ones and to socially acceptable bodily regions.