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Title: Neurobiological mechanisms of affective touch and their role in depression
Author: Trotter, Paula Diane
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2011
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The aim of this investigation was to determine whether i) affective touch has a role in mediating beneficial social influences on resilience to depression and ii) whether affective touch acts through specific skin CT afferents to enhance central serotonin function. To develop and validate the Touch Experiences and Attitudes Questionnaire (TEAQ), 117 items about experiences and attitudes to touch were completed online by 618 participants. Principal components analysis reduced this to 57 items and 6 factors. Three factors concerned touch experienced; in social situations (CST), in intimate relationships (CIT) and during childhood (ChT) and 3 factors concerned attitude to touch; in intimate relationships (AIT), with unfamiliar people (AUT) and in Skin Care (ASkC). The shortened TEAQ was completed by a second sample of 704 participants. Confirmatory factor analysis found the 6 factor structure to be a good fit of the data, suggesting the TEAQ to be valid and reliable. Participants completed some demographic questions and some questionnaires to determine their current psychiatric symptoms, social circumstances, recent life events, childhood adversity and personality alongside the TEAQ. Currently depressed participants had lower touch scores for all factors compared to healthy controls. Remitted depressed participants had significantly lower touch scores on all factors except CST, ASkC and AIT compared to healthy controls. A multiple regression analysis found neuroticism, satisfaction with social support, recent life events, CIT and childhood adversity (CHA) to be predictive of depression, whereas extraversion, number of social supports, ChT and CST, did not significantly predict depression score. Logistic regression analysis found ChT, CHA and neuroticism to predict vulnerability to depression, but not AIT or AUT. It was concluded that CIT was the most important aspect of affective touch for promoting resilience to depression. The CNS effects of pleasant and unpleasant touch were investigated using fMRI in healthy female volunteers. It has been hypothesised that a novel class of CT afferent fibres in hairy skin encodes affective touch. Therefore, CNS responses to pleasant stroking of the forearm with stroking of the fingers were compared. No differential CNS effects of forearm stroking over finger stroking were seen. Indeed, more brain regions were activated by pleasant brush stroking of the fingers which lack CT afferents. Pleasant brush responses in left inferior frontal gyrus were attenuated by tryptophan depletion. However, the midbrain raphe was activated by unpleasant brush stroking and de-activated by pleasant and this effect was abolished by tryptophan depletion. This study found little evidence that CT afferents in hairy skin have a specific role in affective touch and serotonin cells of the raphe appear engaged by unpleasant stimuli rather than pleasant. In conclusion, the results of the questionnaire study indicated touch (hugs, kisses, stroking) in intimate relationships may promote resilience to depression whereas touch with other social contacts does not, suggesting type of affective touch to be important. It is suggested that future studies of the role of current social support and of early adversity in depression should include assessments of the correlated dimension of affective touch. The fMRI study found little evidence for a specific peripheral touch receptor encoding pleasant affective touch. The median raphe nucleus was inhibited by pleasant touch and this is in keeping with the idea that that aversive stimuli activate serotonin projections to the forebrain but not that this is strengthened by affective touch. Further investigation is required to identify CNS mechanisms of affective touch.
Supervisor: Deakin, Bill Sponsor: Biotechnology and Biological Sciences Research Council (BBSRC) ; Unilever
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: affective touch ; tryptophan depletion ; serotonin ; depression ; social support ; fMRI