using-facial-electromyography-to-assess-facial-muscle-reactions-to

Using Facial Electromyography to Assess Facial Muscle Reactions to Experienced and Observed Affective Touch in Humans

"Affective" touch is believed to be processed in a manner distinct from discriminatory touch and to involve activation of C-tactile (CT) afferent fibers. ...

University of Oslo

Touch is important for individuals' subjective well-being, is typically rewarding, and is one of few sensory stimuli which are experienced as pleasant for a rather long time. This study tracked brain activation during slow stroking stimulation of the arm that was applied continuously for 40min - a much longer time than what previous studies have investigated.

Temporal dynamics of brain activation during 40 minutes of pleasant touch.

Expectancy and certainty regarding an outcome are important factors during performance monitoring. However, the separate contributions of expected and unexpected uncertainty on different measures of performance monitoring, including feedback-related negativity (FRN) and P300 components, are not well established. The current study investigated their relationship to fearless-dominance, a personality construct described by high social potency and low anxiety. Accurately predicting environmental outcomes in certain and uncertain situations might be a prerequisite of social potency, therefore it may be associated with increased performance monitoring and its ERP correlates. Consequently, expected-uncertain and unexpected-uncertain feedback (by violating previously learned certain and expected feedback) was introduced in addition to expected-certain feedback in healthy individuals during a probabilistic gambling task. In both FRN and P300 components, difference waves were more pronounced for unexpected-uncertain and expected-uncertain compared to expected-certain feedback. Moreover, more fearless-dominant individuals showed diminished feedback processing specifically in expected-uncertain trials, but concurrently enhanced attentional processing in expected-certain trials. These findings indicate adaptive and situation-appropriate utilization of performance monitoring resources in individuals with more pronounced fearless-dominance personality traits. The results indicate that a precise differentiation of expected and unexpected uncertainty in fearless-dominant individuals is mandatory in order to better understand the underlying personality construct and related behavior.

Processing expected and unexpected uncertainty is modulated by fearless-dominance personality traits - An exploratory ERP study on feedback processing.

Touch has been found to entail positive effects in the person receiving it, whereas effects on the person giving touch have previously been unexplored. We investigated whether stroking the partner also is a pleasant experience for the person performing it, and whether it has similar effects on well-being and autonomic nervous function as being stroked or stroking oneself. Furthermore, we compared the hedonic and autonomic nervous effects of stroking the partner and self-stroking.

Touch between romantic partners: Being stroked is more pleasant than stroking and decelerates heart rate.

The present study explores whether long-lasting pleasant touch has positive effects on the stress response, reward sensitivity, mood, and interoceptive awareness.

Heart rate variability is enhanced by long-lasting pleasant touch at CT-optimized velocity.

Touch is a common occurrence in our lives, where affective and inter-personal aspects of touch are important for our well-being. We investigated whether touch exposure affects hedonic and discriminative aspects of tactile perception. The perceived pleasantness and intensity of gentle forearm stroking, over different velocities, was assessed in individuals reporting to seldom receive inter-personal touch, and in controls who received touch often. The groups did not differ in their stroking intensity judgements, nor in tactile discrimination sensitivity; however, individuals with low touch exposure evaluated the pleasantness of touch differently. These individuals did not differentiate pleasantness over the stroking velocities in the same way as the control group. The pleasantness curve for the low touch exposure group was significantly flatter and they rated 3cm/s stroking as significantly less pleasant. Other physiological and questionnaire measures were obtained and the appreciation of touch from familiar persons was positively related to the pleasantness of touch in controls, but this was not found in low touch exposure individuals. This suggests that the association of human caresses from well-known individuals, with the pleasure derived, may depend on continued exposure to it.

Exposure shapes the perception of affective touch.

Field studies have demonstrated that humans become more generous, helpful and compliant after having been touched by another person. Here, we explored whether these effects are larger for touch activating the C-tactile (CT) fibres, as it is ascribed a particular role in establishing and maintaining bonds and affiliative interactions. The role of CT-targeted and non-targeted touch on prosocial behaviour was investigated in three different experiments using a trust game and a task measuring individual differences in social value orientations (the SVO task). Whereas participants in general acted prosocially, there was no influence of CT-targeted touch on prosocial behaviour, both in comparison to non-CT-targeted control touch and visual (non-tactile) stimulation. The null findings were further corroborated by Bayesian statistics. Thus, under the controlled laboratory conditions employed, CT-targeted touch did not play a particular role in prosocial behaviour. This indicates that touch does not increase prosocial behaviour in the absence of meaningful social and psychological connotations. Any touch related effects on prosocial behaviour likely depends on the ecological validity of the situation.

Slow touch targeting CT-fibres does not increase prosocial behaviour in economic laboratory tasks.

Caress-like touch is thought to rely on C-tactile (CT) fiber signaling. Here, the arousing and emotional effects of CT-optimal touch were assessed via participants' skin conductance level (SCL), facial electromyography (EMG) responses and subjective ratings of pleasantness and intensity. Temporal facial EMG analysis was based on the conduction velocity of CT-fibers. 45 healthy participants received CT-optimal touch, control touch and visual control input during 2-minute trials. CT optimal touch was significantly more pleasant and intense than control touch. In the initial 700 ms of stimulation there was no difference in facial EMG responses to touch. Between 700 and 6300 ms there was a significant reduction of corrugator activity in response to CT optimal touch only, possibly reflecting the affective value of CT optimal touch. Based on the temporal dynamics of the reduced corrugator activity, we suggest that CT fibers are involved in mediating a reduction in corrugator activity.

Touch targeting C-tactile afferent fibers has a unique physiological pattern: A combined electrodermal and facial electromyography study.

Depression is associated with difficulties in interpersonal relationships, of which communication is an integral part. Communication can not only be effected by verbal means, but also non-verbally by touch. Against this background, the aim of the present study was to investigate the relationship between depression, interpersonal problems and the attitude towards social touch.

Article	Year
Temporal dynamics of brain activation during 40 minutes of pleasant touch. NeuroImage\| PubMed ID: 27338514	2016
Processing expected and unexpected uncertainty is modulated by fearless-dominance personality traits - An exploratory ERP study on feedback processing. Physiology & behavior\| PubMed ID: 27789252	2017
Touch between romantic partners: Being stroked is more pleasant than stroking and decelerates heart rate. Physiology & behavior\| PubMed ID: 28478031	2017
Heart rate variability is enhanced by long-lasting pleasant touch at CT-optimized velocity. Biological psychology\| PubMed ID: 28723347	2017
Exposure shapes the perception of affective touch. Developmental cognitive neuroscience\| PubMed ID: 28818429	2019
Slow touch targeting CT-fibres does not increase prosocial behaviour in economic laboratory tasks. Scientific reports\| PubMed ID: 29769551	2018
Touch targeting C-tactile afferent fibers has a unique physiological pattern: A combined electrodermal and facial electromyography study. Biological psychology\| PubMed ID: 30468895	2019
Depression predicts interpersonal problems partially through the attitude towards social touch. Journal of affective disorders\| PubMed ID: 30584957	2019

Uta Sailer

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