Determinants for positive and negative experiences of interpersonal touch: context matters.

The goal of the study was to determine which aspects of interpersonal touch interactions lead to a positive or negative experience. Previous research has focused primarily on physical characteristics. We suggest that this may not be sufficient to fully capture the complexity of the experience. Specifically, we examined how fulfilment of psychological needs influences touch experiences and how this relates to physical touch characteristics and situational factors.In two mixed-method studies, participants described their most positive and most negative interpersonal touch experience within a specific time frame. They reported fulfilment of nine needs, affect, intention, and reason for positivity/negativity, as well as the body part(s) touched, location, type of touch, interaction partner, and particular touch characteristics (e.g. humidity).Positive and negative touch experiences shared similar touch types, locations, and body parts touched, but differed in intended purpose and reasons. Overall, the valence of a touch experience could be predicted from fulfilment of relatedness, the interaction partner and initiator, and physical touch characteristics. Positive affect increased with need fulfilment, and negative affect decreased.The results highlight the importance of relatedness and reciprocity for the valence of touch, and emphasise the need to incorporate psychological needs in touch research.

Social and non-social feedback stimuli lead to comparable levels of reward learning and reward responsiveness in an online probabilistic reward task.

Social stimuli seem to be processed more easily and efficiently than non-social stimuli. The current study tested whether social feedback stimuli improve reward learning in a probabilistic reward task (PRT), in which one response option is usually rewarded more often than the other via presentation of non-social reward stimuli. In a pre-registered online study with 305 participants, 75 participants were presented with a non-social feedback stimulus (a star) and information about gains, which is typically used in published PRT studies. Three other groups (with 73-82 participants each) were presented with one of three social feedback stimuli: verbal praise, an attractive happy face, or a "thumbs up"-picture. The data were analysed based on classical signal detection theory, drift diffusion modelling, and Bayesian analyses of null effects. All PRT variants yielded the expected behavioural preference for the more frequently rewarded response. There was no processing advantage of social over non-social feedback stimuli. Bayesian analyses further supported the observation that social feedback stimuli neither increased nor decreased behavioural preferences in the PRT. The current findings suggest that the PRT is a robust experimental paradigm independent of the applied feedback stimuli. They also suggest that the occurrence of a processing advantage for social feedback stimuli is dependent on the experimental task and design.

Single-centre, non-randomised clinical trial at a tertiary care centre to investigate 1-year changes in social experiences and biomarkers of well-being after bariatric surgery in individuals with severe obesity: protocol for the Bariatric Surgery and Social Experiences (BaSES) study.

INTRODUCTION: Obesity is linked to increased loneliness and less enjoyment of social interactions. While bariatric surgery is the most effective treatment targeting severe obesity, there is limited understanding as to whether patients experience social interactions differently after surgery. The Bariatric Surgery and Social Experiences study is designed to assess potential changes in how much patients enjoy and engage in daily social interactions 1 year after Roux-en-Y gastric bypass (RYGB) or sleeve gastrectomy (SG). METHODS AND ANALYSIS: Single-centre, non-randomised clinical trial carried out at the Department of Endocrinology, Obesity and Nutrition at Vestfold Hospital Trust, Norway. Eligible patients (N=113) will undergo either RYGB, SG or single anastomosis sleeve ileal (SASI) bypass. The primary outcome measure is change in the social experience score (assessed with a questionnaire) from a presurgery to a follow-up assessment 1 year after RYGB and SG. The respective changes after SASI bypass will be assessed and considered exploratory. ETHICS AND DISSEMINATION: The most recent protocol version of this study was reviewed and approved by the Regional Committee for Medical Research Ethics South East Norway (REK sør-øst A) on 29 August 2022 (ref: 238406). The results will be disseminated to academic and health professional audiences and the public via publications in international peer-reviewed journals and conferences. TRIAL REGISTRATION NUMBER: NCT05207917.

Affectionate touch and diurnal oxytocin levels: An ecological momentary assessment study.

Background: Affectionate touch, which is vital for mental and physical health, was restricted during the Covid-19 pandemic. This study investigated the association between momentary affectionate touch and subjective well-being, as well as salivary oxytocin and cortisol in everyday life during the pandemic. Methods: In the first step, we measured anxiety and depression symptoms, loneliness and attitudes toward social touch in a large cross-sectional online survey (N = 1050). From this sample, N = 247 participants completed ecological momentary assessments over 2 days with six daily assessments by answering smartphone-based questions on affectionate touch and momentary mental state, and providing concomitant saliva samples for cortisol and oxytocin assessment. Results: Multilevel models showed that on a within-person level, affectionate touch was associated with decreased self-reported anxiety, general burden, stress, and increased oxytocin levels. On a between-person level, affectionate touch was associated with decreased cortisol levels and higher happiness. Moreover, individuals with a positive attitude toward social touch experiencing loneliness reported more mental health problems. Conclusions: Our results suggest that affectionate touch is linked to higher endogenous oxytocin in times of pandemic and lockdown and might buffer stress on a subjective and hormonal level. These findings might have implications for preventing mental burden during social contact restrictions. Funding: The study was funded by the German Research Foundation, the German Psychological Society, and German Academic Exchange Service.

Hungry for compliments? Ghrelin is not associated with neural responses to social rewards or their pleasantness.

The stomach-derived hormone ghrelin motivates food search and stimulates food consumption, with highest plasma concentrations before a meal and lowest shortly after. However, ghrelin also appears to affect the value of non-food rewards such as interaction with rat conspecifics, and monetary rewards in humans. The present pre-registered study investigated how nutritional state and ghrelin concentrations are related to the subjective and neural responses to social and non-social rewards. In a cross-over feed-and-fast design, 67 healthy volunteers (20 women) underwent functional magnetic resonance imaging (fMRI) in a hungry state and after a meal with repeated plasma ghrelin measurements. In task 1, participants received social rewards in the form of approving expert feedback, or non-social computer reward. In task 2, participants rated the pleasantness of compliments and neutral statements. Nutritional state and ghrelin concentrations did not affect the response to social reward in task 1. In contrast, ventromedial prefrontal cortical activation to non-social rewards was reduced when the meal strongly suppressed ghrelin. In task 2, fasting increased activation in the right ventral striatum during all statements, but ghrelin concentrations were neither associated with brain activation nor with experienced pleasantness. Complementary Bayesian analyses provided moderate evidence for a lack of correlation between ghrelin concentrations and behavioral and neural responses to social rewards, but moderate evidence for an association between ghrelin and non-social rewards. This suggests that ghrelin's influence may be restricted to non-social rewards. Social rewards implemented via social recognition and affirmation may be too abstract and complex to be susceptible to ghrelin's influence. In contrast, the non-social reward was associated with the expectation of a material object that was handed out after the experiment. This may indicate that ghrelin might be involved in anticipatory rather than consummatory phases of reward.

Caressed by music: Related preferences for velocity of touch and tempo of music?

Given that both hearing and touch are 'mechanical senses' that respond to physical pressure or mechanical energy and that individuals appear to have a characteristic internal or spontaneous tempo, individual preferences in musical and touch rhythms might be related. We explored this in two experiments probing individual preferences for tempo in the tactile and auditory modalities. Study 1 collected ratings of received stroking on the forearm and measured the velocity the participants used for stroking a fur. Music tempo preferences were assessed as mean beats per minute of individually selected music pieces and via the adjustment of experimenter-selected music to a preferred tempo. Heart rate was recorded to measure levels of physiological arousal. We found that the preferred tempo of favorite (self-selected) music correlated positively with the velocity with which each individual liked to be touched. In Study 2, participants rated videos of repeated touch on someone else's arm and videos of a drummer playing with brushes on a snare drum, both at a variety of tempos. We found that participants with similar rating patterns for the different stroking speeds did not show similar rating patterns for the different music beats. The results suggest that there may be a correspondence between preferences for favorite music and felt touch, but this is either weak or it cannot be evoked effectively with vicarious touch and/or mere drum beats. Thus, if preferences for touch and music are related, this is likely to be dependent on the specific type of stimulation.

Sex difference in human olfactory sensitivity is associated with plasma adiponectin.

Energy deprivation as well as hormones that regulate appetite and eating can influence olfactory function. This study investigated olfactory sensitivity for a food-related and a non-food odour prior to and after a meal, and its relationship to the energy-regulating hormones ghrelin and adiponectin. The olfactory sensitivity for orange and rose (PEA) odour in healthy, normal-weight volunteers (19 women, 45 men, 1 undisclosed individual) was not affected by the consumption of a meal. Olfactory sensitivity was not associated with concentrations of circulating ghrelin. However, olfactory sensitivity was higher for women than for men, indicating better olfactory performance. This difference between women and men was related to concentrations of plasma adiponectin, an adipose-specific hormone. Adiponectin may thus explain why sex differences in olfactory sensitivity emerge, and may also account for some of the inconsistencies in previous findings on sex differences. Our findings add to the limited literature on the impact of stomach and adipose tissue-derived hormones on olfactory sensitivity. Further studies are needed to establish a causal link between circulating adiponectin and a sex difference in olfactory sensitivity.

Dynamics of Affective Habituation to Touch Differ on the Group and Individual Level.

Slow stroking touch activates C-tactile (CT) fibres in the human skin and is typically described as pleasant. Over a longer duration of stroking, affective habituation sets in, indicated by a reduction in rated pleasantness. However, it is not clear whether the group level effect is represented on an individual level. We analyse the stability of individual ratings of slow stroking touch and their relationship to behavioural and physiological measures. Forty-eight participants (23 women) were repeatedly stroked with a velocity maximally activating CT fibres. The perceived pleasantness was rated on a visual analogue scale. In order to examine the stability of pleasantness ratings, the experiment was repeated after a couple of days. During the experiment, electrocardiogram (ECG) and facial-electromyography (EMG) data were recorded. On the group-level, previous results of affective habituation to touch were replicated and stable across sessions. On the individual level, however, less than half of the participants showed a significant reduction of pleasantness in the course of the experiment. Moreover, the remaining participants showed either no change, random rating behaviour or even an increase in pleasantness ratings during the course of the experiment. The individual response patterns were variable across sessions but stable above the chance level. Furthermore, the response patterns could not be explicitly associated with any of the behavioural or physiological measures. Our findings indicate a lack of group-to-individual generalizability for affective habituation to touch. The variability of rating patterns over time indicates that they are not conclusively determined by stable individual characteristics. Future research investigating touch should favour a more individual approach to the more commonly applied group analysis.

Individual Variability of Pleasantness Ratings to Stroking Touch Over Different Velocities.

Many studies have investigated the perception of tactile pleasantness over a range of stroking velocities. On average, pleasantness is low at slow (e.g. 0.3 cm/s) and fast (e.g. 30 cm/s) stroking velocities, but is rated highest at velocities between 1 and 10 cm/s. On a group level, this results in an inverted-U shape pleasantness ratings curve, which is described statistically by a negative quadratic equation. We reanalyzed the data from five earlier studies to investigate whether the inverted-U shape pleasantness curve at the group level is also present at the level of the individual, - a precondition for using tactile pleasantness perception as a diagnostic marker. We pooled the data from five studies with a total of 127 participants. Each study included a 'standard condition' of stroking on the dorsal forearm over different velocities (0.3, 1, 3, 10, 30 cm/s) and participants rated the pleasantness. Factors other than stroking velocity were also varied in these studies. On the whole-group level and in each study, pleasantness ratings produced a significant negative quadratic pleasantness curve over the stroking velocities. In individual participants, ratings varied greatly and only 42% of the participants showed a significant negative quadratic curve. The steepness of the inverted-U correlated only moderately across other experimental conditions, showing that the experimental circumstances can influence pleasantness ratings. Our findings have important implications for future work, where differences in the tactile pleasantness curve should not be used to predict or diagnose issues at an individual level.

Calming Effects of Touch in Human, Animal, and Robotic Interaction-Scientific State-of-the-Art and Technical Advances.

Small everyday gestures such as a tap on the shoulder can affect the way humans feel and act. Touch can have a calming effect and alter the way stress is handled, thereby promoting mental and physical health. Due to current technical advances and the growing role of intelligent robots in households and healthcare, recent research also addressed the potential of robotic touch for stress reduction. In addition, touch by non-human agents such as animals or inanimate objects may have a calming effect. This conceptual article will review a selection of the most relevant studies reporting the physiological, hormonal, neural, and subjective effects of touch on stress, arousal, and negative affect. Robotic systems capable of non-social touch will be assessed together with control strategies and sensor technologies. Parallels and differences of human-to-human touch and human-to-non-human touch will be discussed. We propose that, under appropriate conditions, touch can act as (social) signal for safety, even when the interaction partner is an animal or a machine. We will also outline potential directions for future research and clinical relevance. Thereby, this review can provide a foundation for further investigations into the beneficial contribution of touch by different agents to regulate negative affect and arousal in humans.

Pleasantness Only?

When gently stroked with velocities between 0.1 and 30 cm/s, participants typically rate velocities around 3 cm/s as most pleasant, and the ratings follow an inverted u-shape. This pleasantness curve correlates often, but not always, with the firing rate of unmyelinated C-tactile (CT) afferents, leading to the notion that CT afferents code for the hedonic or emotional aspect of gentle touch. However, there is also evidence that CT firing does not necessarily equal pleasantness, and the range of attributes that CT afferents code for is not known. Here, participants were stroked with different velocities assumed to activate CT afferents to a different extent while they rated the touch on several sensory and emotional attributes. We expected an inverted u-shaped rating curve for pleasantness and other emotional attributes, but not for sensory attributes. Inverted u-shaped rating patterns were found for the emotional attributes "pleasant" and "not burdensome," but also for the sensory attribute "rough." CT-directed stimulation is thus not only experienced as hedonic. The sensations arising from CTs together with all other types of mechanoreceptors might be centrally integrated into a percept that represents those aspects which are most salient for the stimulation at hand.

Right between the eyes: Corrugator muscle activity tracks the changing pleasantness of repeated slow stroking touch.

Subjective reports and physiological responses provide different appraisals of sensory input. The coherence between subjective and physiological responses to repeated pleasant stimuli remains largely unexplored, and is particularly important in situations where subjective responses are prone to cognitive or contextual bias. Here, we investigate how subjective and physiological responses to repeated gentle touch correspond at two separate sessions and compare these to responses obtained when smelling an odorant. Forty-eight participants underwent 60 trials of skin-to-skin slow stroking touch directed to the forearm. We collected subjective pleasantness reports, recorded facial electromyography (EMG) of the corrugator and zygomaticus muscles and heart-rate variability (HRV). With increasing touch repetitions, mean ratings of pleasantness decreased and corrugator muscle activity increased during session 1, whereas zygomaticus activity remained largely unchanged during both sessions. HRV was significantly higher during the first session, but did not increase from baseline during either sessions. Touch was rated as more pleasant than odor, and demonstrated greater resilience to satiety than the odor responses. Facial EMG recordings of the corrugator muscle appear to be a relevant measure for capturing satiety effects in skin-to-skin touch. Zygomaticus and HRV responses were independent of the subjective appraisal of the gentle touch. Rather than being blueprints of the subjective reports, physiological responses appear to reflect different parts of the subjective experience. As such, an improved understanding of the subjective and physiological responses to pleasant stimuli may improve our understanding of the dynamic interactions that take place in shaping complex emotional phenomena, such as aversion and pleasantness.

Ghrelin Induces Place Preference for Social Interaction in the Larger Peer of a Male Rat Pair.

Social interaction is important for survival in most social species including humans. To ensure social activities, individuals experience reward from social interaction, generating a powerfully reinforcing process. Here we hypothesized that reward from social interaction in a juvenile male rat pair may be enhanced by ghrelin, a circulating hormone that has been shown to enhance reward from other natural (e.g. food, sex) as well as artificial reinforcers (e.g. alcohol and other drugs of abuse). To this end, we assessed the impact of ghrelin and a ghrelin antagonist on preference for a chamber previously paired to the presence of a social partner in a conditioned place preference paradigm. We found that ghrelin increased and a ghrelin antagonist decreased preference for social interaction, but only in the heavier partner in a social pair. In addition, we found that administered ghrelin induced a positive association between preference for social interaction and body weight difference within socially interacting pairs, where larger ghrelin treated rats preferred social interaction, whereas smaller ghrelin treated rats avoided it, which raises the question if ghrelin could have a role in implementing social hierarchies in rats. In summary, we conclude that ghrelin signaling increases the reward from social interaction in a manner that reflects the degree of divergence in body weight between the social pair.

The "Longing for Interpersonal Touch Picture Questionnaire": Development of a new measurement for touch perception.

Touch is a crucial factor of physiological and psychological health in humans. A lack of touch in contrast is associated with adverse implications on mental health. A new "Longing for Interpersonal Touch Picture Questionnaire (LITPQ)" was developed and tested for its concurrent, predictive, discriminant and face validity as well as its relation to psychological distress. Six different types of touch were depicted and touch frequency and touch wish concerning different interaction partners assessed. A sample of 110 participants aged 18-56 years completed the LITPQ as well as an existing touch deprivation questionnaire and a questionnaire on mental health. Frequency and wish for touch were higher for close interaction partners than for strangers. For 72.7% of the participants, their touch wish exceeded the reported touch frequency. The LITPQ correlated moderately with the existing questionnaire for touch deprivation and was independent of relationship status or gender but positively correlated with depressiveness, anxiety and somatization. Measuring longing for touch is a very complex task considering the many aspects of subjective touch perception and confounds in the method of self-report of touch. In our view, the LITPQ provides promising insights into this matter.

Touch aversion in patients with interpersonal traumatization.

BACKGROUND: Interpersonal touch is a key aspect of human interaction and a usually very comforting experience. For patients suffering from posttraumatic stress disorders (PTSD) caused by interpersonal traumatization, such touch is affectively ambiguous. METHODS: In two studies, we investigated the experience and neural processing of various types of interpersonal and impersonal touch in patients as compared with healthy controls. RESULTS: Patients strongly disliked show, interpersonal skin-to-skin stroking, while controls appreciated this kind of touch. No group differences were observed for ratings of impersonal touch. Similarly, the neural activation differed between groups for interpersonal, but not for impersonal touch. The interpersonal touch aversion in patients was accompanied by enhanced blood-oxygen-level-dependent response in the superior temporal gyrus and by a pronounced reduction of response in the hippocampus. This reduction was significantly correlated to symptoms of negative alterations and arousal within the patients. CONCLUSION: We interpret the hippocampal suppression as an attempt to control traumatic memories, evoked by interpersonal touch. This mechanism may maintain the aversion of interpersonal touch in patients with interpersonal trauma-related PTSD.

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. Touch that optimally activates CT fibers is consistently rated as hedonically pleasant. Patient groups with impaired social-emotional functioning also show disordered affective touch ratings. However, relying on self-reported ratings of touch has many limitations, including recall bias and communication barriers. Here, we describe a methodological approach to study affective responses to touch via facial electromyography (EMG) that circumvents the reliance on self-report ratings. Facial EMG is an objective, quantitative, and non-invasive method to measure facial muscle activity indicative of affective responses. Responses can be assessed across healthy and patient populations without the need for verbal communication. Here, we provide two separate datasets demonstrating that CT-optimal and non-optimal touch elicit distinct facial muscle reactions. Moreover, facial EMG responses are consistent across stimulus modalities, e.g. tactile (experienced touch) and visual (observed touch). Finally, the temporal resolution of facial EMG can detect responses on timescales that supersede that of verbal reporting. Together, our data suggest that facial EMG is a suitable methodology for use in affective tactile research that can be used to supplement, or in some cases, supplant, existing measures.

Exposure shapes the perception of affective touch.

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.

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

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.

Depression predicts interpersonal problems partially through the attitude towards social touch.

INTRODUCTION: 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. METHODS: 147 individuals (115 females; 21-71 years old) seeking treatment in a clinic for outpatient psychotherapy took part in the survey. Three questionnaires evaluating the level of depression (Beck Depression Questionnaire), the degree of interpersonal problems (Inventory of Interpersonal Problems) and the attitude towards social touch (Social Touch Questionnaire, were administered. RESULTS: Highly depressed individuals had a more negative attitude towards social touch than non-to lowly depressed individuals. Highly depressed individuals particularly reported to dislike physical touch by not well-known people, but not by close ones. Highly depressed individuals also reported more interpersonal problems, with the level of depression predicting the degree of interpersonal problems. This relationship was partially mediated by the attitude towards social touch in general and, to a greater extent, by the dislike of physical touch by people not well-known in particular. DISCUSSION: Given the role of social touch in the relationship between depression and interpersonal problems, the attitude towards touch may be taken into consideration in the therapy of depressed patients. We assume that a more positive attitude towards social touch can influence the ability to create and maintain interpersonal relationships.

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

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.