Bridging skin, brain, and behavior to understand pleasurable social touch

Psychometric evaluation of the Social Touch Questionnaire in Chinese adolescents

Social touch promotes psychological well-being through inducing positive effects on social affiliation and stress alleviation, especially in adolescence. However, there is a scarcity of instruments available for evaluating adolescents' attitude toward social touch in China. The present study aimed to investigate the validity and reliability of the Social Touch Questionnaire (STQ) in Chinese adolescents. A total of 2839 high school students were enrolled, ranging in age from 11 to 19 years. The dimensions of the scale were conducted by exploratory factor analysis, and validated by confirmatory factor analysis. A three-factor model showed the best fit and consisted of the following subgroups: liking of informal social touch, liking of general social touch, and dislike of social touch. Furthermore, positive associations were found between social touch and interaction anxiety, fear of negative evaluation, depressive and anxiety symptoms, and sleep quality. Short-term prediction of dislike of social touch in anxiety symptoms was determined, while no significant predictor of depressive symptoms was found. The STQ demonstrates reliability and validity as a self-report questionnaire designed to assess behaviors and attitudes toward social touch. It effectively adapts to the nuances of the Chinese context among adolescents.

A failure to discriminate social from non-social touch at the circuit level may underlie social avoidance in autism

Social touch is critical for communication and to impart emotions and intentions. However, certain autistic individuals experience aversion to social touch, especially when it is unwanted. We used a novel social touch assay and Neuropixels probes to compare neural responses to social vs. non-social interactions in three relevant brain regions: vibrissal somatosensory cortex, tail of striatum, and basolateral amygdala. We find that wild type (WT) mice showed aversion to repeated presentations of an inanimate object but not of another mouse. Cortical neurons cared most about touch context (social vs. object) and showed a preference for social interactions, while striatal neurons changed their preference depending on whether mice could choose or not to interact. Amygdalar and striatal neurons were preferentially modulated by forced object touch, which was the most aversive. In contrast, the Fmr1 knockout (KO) model of autism found social and non-social interactions equally aversive and displayed more aversive facial expressions to social touch when it invaded their personal space. Importantly, when Fmr1 KO mice could choose to interact, neurons in all three regions did not discriminate social valence. Thus, a failure to differentially encode social from non-social stimuli at the circuit level may underlie social avoidance in autism.

Virtual social grooming in macaques and its psychophysiological effects

Allogrooming is a widespread, pervasive activity among non-human primates. Besides its hygienic function, it is thought to be instrumental in maintaining social bonds and establishing hierarchical structures within groups. However, the question arises as to whether the physiological and social benefits derived from social touch stem directly from body stimulation, or whether other mechanisms come into play. We address this question by analyzing an elaborate social behavior that we observed in two adult male macaques. This behavior demonstrates the existence of a persistent motivation to interact through a form of simulated grooming, as the animals were housed in adjacent enclosures separated by a glass panel preventing direct tactile contact. We find that such virtual grooming produces similar physiological sensations and social effects as allogrooming. We suggest that this behavior engages affective and reward brain circuits to the same extent as real social touch, and that this is probably achieved through high level processes similar to those involved in bodily illusions or synaesthetic phenomena previously described in humans. This observation reveals the unsuspected capacity of non-human primates to invent alternative, quasi-symbolic strategies to obtain effects similar to those provided by direct bodily interaction, which are so important for maintaining social bonds.

Out of touch? How trauma shapes the experience of social touch - Neural and endocrine pathways

Trauma can shape the way an individual experiences the world and interacts with other people. Touch is a key component of social interactions, but surprisingly little is known about how trauma exposure influences the processing of social touch. In this review, we examine possible neurobiological pathways through which trauma can influence touch processing and lead to touch aversion and avoidance in trauma-exposed individuals. Emerging evidence indicates that trauma may affect sensory touch thresholds by modulating activity in the primary sensory cortex and posterior insula. Disturbances in multisensory integration and oxytocin reactivity combined with diminished reward-related and anxiolytic responses may induce a bias towards negative appraisal of touch contexts. Furthermore, hippocampus deactivation during social touch may reflect a dissociative state. These changes depend not only on the type and severity of the trauma but also on the features of the touch. We hypothesise that disrupted touch processing may impair social interactions and confer elevated risk for future stress-related disorders.

A narrative review of research linking non-sexual social touch to sleep quality

This narrative review describes the current state of the literature that has examined associations between non-sexual social touch (i.e., affectionate touch, touch therapies, touch with animals and inanimate objects that mimic social touch) and sleep quality. It also highlights areas for future research to clarify the links and to identify underlying mechanisms. Most existing studies have focussed on and shown positive effects of touch therapies (e.g., massage, therapeutic touch) on sleep quality in clinical populations. Although there are fewer studies examining how other forms of social touch are linked with sleep quality, the existing research provides preliminary evidence supporting affectionate touch (e.g., hugging, skin-to-skin contact) and tactile contact with animals (e.g., dogs) and objects that mimic social touch (e.g., robots, weighted blankets) as predictors of better sleep quality, while touch deprivation and touch aversion are associated with worse sleep quality. Informed by the existing literature, we additionally reviewed potential relational-cognitive (e.g., felt-security) and neurobiological (e.g., oxytocin) mechanisms likely to underlie associations between social touch and sleep quality. Overall, current research supports associations between non-sexual social touch and sleep quality. However, future research is needed to establish these links for specific forms of social touch (and in various populations), to test explanatory mechanisms, and to identify boundary conditions. Understanding associations between non-sexual social touch and sleep quality can inform the development of touch-based interventions to improve sleep quality and health.

Spatial factors influencing the pain-ameliorating effect of CT-optimal touch: a comparative study for modulating temporal summation of second pain

Recent studies show that CT-optimal touch, gentle slow stroking of the skin, can reduce pain. However, much is unknown regarding the factors influencing its pain-ameliorating effect, such as tactile attention and touch application site. The current study investigates in 36 healthy individuals, whether CT-optimal touch can reduce temporal summation of second pain (TSSP) compared to CT non-optimal touch and tapping the skin. TSSP refers to activation of the C-nociceptors; by stimulating these fibers a burning and/or tingling sensation can be elicited. All participants underwent three conditions on both the contralateral and ipsilateral side of pain induction. The results show that tapping the skin did not reduce TSSP, meaning that pain reduction through touch cannot be explained by tactile attention effects. CT non-optimal touch only reduced TSSP when applied on the ipsilateral side. Importantly, CT-optimal touch effectively reduced TSSP when applied on the contralateral or ipsilateral side. Furthermore, CT-optimal touch was more effective in reducing TSSP compared to CT non-optimal touch and Tapping. This study shows that that CT-optimal touch can reduce TSSP and this effect appears to be independent of touch application site, which is highly relevant for implementing CT-optimal touch as a treatment.

Human sweat contains oxytocin

BACKGROUND

Oxytocin (OT) has been detected in various body fluids, including blood, urine, saliva, breastmilk, and spinal fluid. Consistent with models that regard skin as a social organ and in line with studies demonstrating that skin cells express both OT and its receptor, our study sought to examine the presence of OT in human sweat.

METHODS

Overall, 553 individuals participated in a pilot study and three experiments. Firstly, 50 participants provided sweat after engaging in various sports for different durations. Secondly, 26 participants provided sweat from forehead, upper-chest, forearm, and underarm, including 11 in natural setting and 15 following OT administration and a 30-minute exercise. Thirdly, of 435 volunteers, 97 provided sufficient axillary sweat for assaying. Of these, 84 participated in a naturalistic experiment that involved saliva and sweat collection in response to physical activity in either solitary or social settings. OT and testosterone (TS) were assayed in sweat and saliva.

RESULTS

Intense activity for at least 25 min was required to produce sufficient sweat for OT analysis. Highest OT levels were found in axillary sweat compared to sweat from the forehead, upper-chest, and forearm. Salivary OT and TS increased after both solitary and social physical activity; however, higher sweat OT was found after solitary sports. Post-hoc preliminary findings indicate that highly extroverted individuals exercising in solitary environments showed the highest sweat OT levels.

CONCLUSIONS

Findings demonstrate, for the first time, the presence of OT in human sweat and show the feasibility of its measurement. Much further research is required to illuminate how sweat OT is impacted by personality and social context and to uncover the role of the skin in OT production.

Early tactile stimulation influences the development of Alzheimer's disease in gestationally stressed APP NL-G-F adult offspring NL-G-F/NL-G-F mice

Alzheimer's disease (AD) is associated with cerebral plaques and tangles, reduced synapse number, and shrinkage in several brain areas and these morphological effects are associated with the onset of compromised cognitive, motor, and anxiety-like behaviours. The appearance of both anatomical and behavioural symptoms is worsened by stress. The focus of this study was to examine the effect of neonatal tactile stimulation on AD-like behavioural and neurological symptoms on APP NL-G-F/NL-G-F mice, a mouse model of AD, who have been gestationally stressed. Our findings indicate that neonatal tactile stimulation improves cognition, motor skills, and anxiety-like symptoms in both gestationally stressed and non-stressed adult APP mice and that these alterations are associated with reduced Aβ plaque formation. Thus, tactile stimulation appears to be a promising non-invasive preventative strategy for slowing the onset of dementia in aging animals.

Distinct acute stressors exert an antagonistic effect on complex grooming during novelty habituation in rats

Grooming is a common readout in multiple rat models of neuropsychiatric diseases. It is usually associated with distress and negative emotionality, but also with emotional de-arousal after stress. These seemingly conflicting interpretations may result from specific grooming sequences appearing at different arousal levels and during distinct phases of the stress response. To further explore this hypothesis, we analyzed how distinct stressors affect grooming syntaxis and kinetics. To that end, we explored the independent and interacting effects of foot shocks, corticosterone (CORT), and novelty on exploratory activity, grooming, and ultrasonic vocalizations (USVs) in an open-field test (OF). Wistar rats were intraperitoneally injected either with vehicle or CORT, placed in a chamber where half of them were foot-shocked and then assessed in the OF. The next day, animals were re-exposed to the shock chamber and then tested in the OF without receiving any treatment. On day 1, foot shocks and -to a less extent CORT- increased freezing and inhibited rearing in the chamber, but only foot shocks increased distress USVs. In the OF, both treatments suppressed complex grooming, with foot-shocks also inhibiting exploration and CORT marginally reducing rearing. On day 2, foot-shocked rats showed conditioned fear when re-exposed to the chamber. When tested in the OF, foot-shocked and CORT-treated animals still showed low levels of complex grooming, with the former group also showing increased distress USVs. In this study, all different stressors inhibited complex grooming, suggesting an inverse association between these grooming subtypes and negative emotionality.

Neural mechanisms of comforting: Prosocial touch and stress buffering

Comforting is a crucial form of prosocial behavior that is important for maintaining social unity and improving the physical and emotional well-being of social species. It is often expressed through affiliative social touch toward someone in distress, providing relief for their distressed state. In the face of increasing global distress, these actions are paramount to the continued improvement of individual welfare and the collective good. Understanding the neural mechanisms responsible for promoting actions focused on benefitting others is particularly important and timely. Here, we review prosocial comforting behavior, emphasizing synthesizing recent studies carried out using rodent models. We discuss its underlying behavioral expression and motivations, and then explore both the neurobiology of prosocial comforting in a helper animal and the neurobiology of stress relief following social touch in a recipient as part of a feedback loop interaction.

Socio-sexual touch: On the hunt for a pleasure signal in the mouse brain

Skin-to-skin contact is widespread during social interactions and essential for establishing intimate relationships. To understand the skin-to-brain circuits underlying pleasurable touch, a new study has used mouse genetic tools to specifically target and study sensory neurons that transmit social touch and their role during sexual behavior in mice.

Touch neurons underlying dopaminergic pleasurable touch and sexual receptivity

Pleasurable touch is paramount during social behavior, including sexual encounters. However, the identity and precise role of sensory neurons that transduce sexual touch remain unknown. A population of sensory neurons labeled by developmental expression of the G protein-coupled receptor Mrgprb4 detects mechanical stimulation in mice. Here, we study the social relevance of Mrgprb4-lineage neurons and reveal that these neurons are required for sexual receptivity and sufficient to induce dopamine release in the brain. Even in social isolation, optogenetic stimulation of Mrgprb4-lineage neurons through the back skin is sufficient to induce a conditioned place preference and a striking dorsiflexion resembling the lordotic copulatory posture. In the absence of Mrgprb4-lineage neurons, female mice no longer find male mounts rewarding: sexual receptivity is supplanted by aggression and a coincident decline in dopamine release in the nucleus accumbens. Together, these findings establish that Mrgprb4-lineage neurons initiate a skin-to-brain circuit encoding the rewarding quality of social touch.

Social behavior: Closing the gap for close encounters

Social touch can launch a cascade of emotions with enormous impact on the development and maintenance of emotional, cognitive and social functioning. A recent study identifies a novel pathway that facilitates physical contact via its direct impact on brain circuits controlling social behavior.

Hearing, touching, and multisensory integration during mate choice

Mate choice is a potent generator of diversity and a fundamental pillar for sexual selection and evolution. Mate choice is a multistage affair, where complex sensory information and elaborate actions are used to identify, scrutinize, and evaluate potential mating partners. While widely accepted that communication during mate assessment relies on multimodal cues, most studies investigating the mechanisms controlling this fundamental behavior have restricted their focus to the dominant sensory modality used by the species under examination, such as vision in humans and smell in rodents. However, despite their undeniable importance for the initial recognition, attraction, and approach towards a potential mate, other modalities gain relevance as the interaction progresses, amongst which are touch and audition. In this review, we will: (1) focus on recent findings of how touch and audition can contribute to the evaluation and choice of mating partners, and (2) outline our current knowledge regarding the neuronal circuits processing touch and audition (amongst others) in the context of mate choice and ask (3) how these neural circuits are connected to areas that have been studied in the light of multisensory integration.

The effects of coloring therapy on patients with generalized anxiety disorder

Generalized anxiety disorder (GAD) has harmful effects on physical and mental health and quality of life. Coloring therapy has been reported to have a positive effect on improving patient anxiety and depression. But there are no reported clinical trials examining their effectiveness as a treatment for GAD. This study was planned to evaluate the effectiveness of coloring therapy combined with conventional therapy in improving anxiety, depression, and positive and negative emotions with GAD. This randomized controlled study comprising 88 GAD patients was selected for intervention in different wards. The control group (n = 45) was given conventional antianxiety medication and physical therapy, and the experimental group (n = 43) received coloring therapy combined with conventional therapy. The Self-Rating Depression Scale, Self-Rating Anxiety Scale (SAS), Hamilton Depression Scale, Hamilton Anxiety Scale (HAMA), and Positive and Negative Affect Scale were assessed in both groups before and 3 weeks after the intervention. After the intervention, there were statistical differences in intra- and inter-group comparisons of anxiety, depression, and positive and negative mood scales in the experimental and control groups (p < .05). The minus in anxiety/positive emotions pre- and postintervention in the experimental group was statistically significant compared to that in anxiety/positive emotions pre- and postintervention in the control group (HAMA: d = 1.45, 95% confidence interval [CI] (0.34, 2.57), p = .011; SAS: d = 3.87, 95% CI (1.73,6.00), p = .001; positive: d = 1.76, 95% CI (0.17, 3.34), p = .030). The minus in depressive/negative emotions pre- and postintervention in the experimental group was not statistically significant compared with that in depressive/negative emotions pre- and postintervention in the control group (p > .05). For GAD patients, adding coloring therapy based on conventional drug therapy and physical therapy can not only reduce depression and negative emotions but also have better effects on reducing anxiety and improving positive emotions than conventional therapy.