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An atypical social touch system in Anorexia Nervosa? Towards a novel non-invasive brain stimulation intervention

Bellard, A (2024) An atypical social touch system in Anorexia Nervosa? Towards a novel non-invasive brain stimulation intervention. Doctoral thesis, Liverpool John Moores University.

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As outlined in Chapter 1, affective touch is a pleasant interoceptive stimulus facilitated by the activation of a specialised system of mechanosensitive cutaneous afferents C-tactile afferents (CTs), which respond when an individual receives gentle touch to the skin. The purpose of CTs is to encode the rewarding sensation of the touch that has been received. This type of touch is important for communication, bonding, and typical development. Numerous investigations have outlined that this process is associated with the activation of the Insula Cortex. In particular, the anterior and posterior regions respond when an individual receives affective touch to their hairy skin. In addition to this region, other brain regions specifically involved in social perception and social cognition, such as the medial Prefrontal Cortex (mPFC), have been implicated in affective touch processing. Furthermore, the role of the primary Somatosensory Cortex (S1), a key brain region for discriminatory touch processing, has been debated in terms of affective touch processing. More recently, investigations have shifted their focus from the general population to atypical responses to affective touch in clinical populations, specifically Anorexia Nervosa (AN). AN is an eating pathology characterised by restricted eating, body image distortions and impaired socio-cognitive abilities. It has been suggested that altered responses to affective touch may contribute to the aetiology and maintenance of this disorder. Based on this evidence, study 1 (Chapter 3) aimed to examine whether women with high and low EDs risk differed in their responses to third-party vicarious social touch, delivered to various body regions at CT-optimal vs. non-CT optimal velocities. Forty-five women reporting high EDs risk symptoms vs. 40 women reporting low EDs risk symptoms viewed a sequence of video clips depicting one individual being touched by another, which was delivered to five body sites (cheek, back, ventral forearm, upper arm vs. palm). Participants were asked to rate how pleasant they perceived the touch to be when delivered at CT-optimal (5 cm/s) vs. CT non-optimal velocities (0 cm/s and 30 cm/s) for self-directed and other-directed touch. Self-report measures of body image concerns, interoceptive awareness and touch experiences and attitudes were also collected (outlined in Chapter 2). Surprisingly, touch pleasantness did not differ between both groups for both self-directed and other-directed touch. For high EDs risk females, eating disorder traits and specific interoceptive awareness facets impacted pleasantness of touch for both the upper arm and back. Findings suggest that EDs traits and body awareness negatively affect ratings of social touch for specific body sites. However, results should be handled cautiously, given that women in this investigation did not have a clinical diagnosis of AN. Therefore, given that women in study 1 did not have a formal AN diagnosis, study 2 (Chapter 4) investigated whether women with a current diagnosis of AN, recovered from AN (RAN) and Healthy Controls (HCs) responded differently to vicarious social touch also delivered at CT-optimal vs. non-CT optimal velocities. Thirty-five HCs, 27 AN and 29 RAN provided third-party pleasantness evaluations for two different tasks, one concerning self (self-directed touch) and one focused on touch to another person (other-directed touch). As in study 1, measures of body image concerns, interoceptive awareness and touch experiences and attitudes were administered through various questionnaires (outlined in Chapter 2). Results from this investigation revealed that both AN and RAN did not differ to HCs in their evaluations of touch directed to another person. However, both clinical populations rated self-directed CT-optimal touch as less pleasant compared to HCs. Thus, suggesting that both clinical groups display atypical responses to affective touch, when this touch is directed towards the self and not another person. In particular, that a learnt experience may contribute towards pleasantness responses to other-directed touch, as individuals with AN or RAN may be aware through experience that touch is pleasantly experienced by another, even if this is not the case for them. Moreover, given that in study 2 individuals with AN demonstrated atypical responses to self-directed touch, study 3 (Chapter 5) examined whether this type of touch is mediated by the social relationship of that touch. Specifically, whether individuals with high and low levels of Body Image Disturbances (BIDs) differed in their responses to ‘imagined’ social touch. This was achieved through the use of an interactive mobile application, the ‘Virtual Touch Toolkit’ (See Chapter 2 for details). Sixty-nine high vs. low levels of BIDs completed heatmaps of front and back full body avatars, to indicate the intimate and social regions they find soothing/unpleasant to receive touch from a loved one vs. an acquaintance. In addition to this, various self-reports of interoceptive awareness and dysmorphic concerns were also collected. The results from this study revealed that both groups rated touch from a loved one as soothing, compared to touch from an acquaintance which was rated as unpleasant. For the high levels of BIDs group, greater emotional awareness predicted higher soothing ratings for touch provided from a loved one. Thus, findings support the idea that pleasantness responses to social touch are mediated by the relationships shared between the touch provider and receiver. Lastly, study 4 (Chapter 6) aimed to understand the neural underpinnings related to atypical responses to social touch in AN. This study explored whether the primary somatosensory cortex (S1) and the ventromedial prefrontal cortex (mPFC) are involved in affective touch processing. In order to investigate this, 18 healthy control participants received offline continuous theta burst Transcranial Magnetic Stimulation (cTBS), a form of repetitive transcranial magnetic stimulation (rTMS) to the right vmPFC, S1 and Vertex (control). After this, participants provided ratings of self-directed vicarious touch and other-directed touch. In addition, self-report measures of interoception, body image concerns and touch experiences and attitudes were collected (Detailed in Chapter 2). Findings from this study revealed that vmPFC-cTBS reduced pleasantness ratings for other directed touch but not for self-directed touch. S1-cTBS increased pleasantness ratings for self-directed touch but had no effect on pleasantness ratings for other-directed touch. The reduction in pleasantness for other-directed touch and the increase in pleasantness for self-directed touch was not CT-specific. Overall, results from this study imply that both S1 and vmPFC have distinctive roles in social touch processing and the processing of CT-optimal touch occurs outside of these social brain regions. This study offers important consideration for future non-pharmacological intervention which could improve touch processing in individuals with AN regardless of CT-optimality (Chapter 6). Taken together, findings from these investigations suggest that women with AN and recovered from AN display comparable intact evaluations when comparing touch for another person, similar to HCs. However, atypical responses to affective touch occur when asked to make judgements for touch to the self, with both clinical groups rating this touch as less pleasant than HCs (Chapter 4). These results do not extend to high EDs risk, who display typical and comparable responses to self and other-directed touch to HCs (Chapter 3). Overall, responses to social touch have been found to be modulated by the relationship shared with the touch provider, with more familiar individuals being more positive and more distant being more unpleasant (Chapter 5). Furthermore, although there is some distinctive involvement of vmPFC and S1 in social touch processing, it is evident that the processing of CT-optimal touch occurs outside of these regions, such as the orbitofrontal cortex (OFC) and anterior cingulate cortex (ACC). Overall, results from these investigations offer valuable insight into responses to vicarious social touch in women at risk of EDs, women with AN and recovered from AN (Chapters 3 and 4). Based on this, results offer the potential for future pilot studies to be developed, incorporating both TMS and mobile applications as an intervention for atypical responses to self-directed touch in individuals with AN (discussed in Chapter 7).

Item Type: Thesis (Doctoral)
Uncontrolled Keywords: Anorexia Nervosa; Vicarious Social Touch; Non-invasive brain stimulation
Subjects: B Philosophy. Psychology. Religion > BF Psychology
Divisions: Psychology (from Sep 2019)
SWORD Depositor: A Symplectic
Date Deposited: 07 Mar 2024 12:13
Last Modified: 07 Mar 2024 12:13
Supervisors: Cazzato, V, Trotter, P and McGlone, F
URI: https://researchonline.ljmu.ac.uk/id/eprint/22745
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