Pain tolerance predicts human social network size

Social support and the association between post-traumatic stress disorder and risk for long-term prescription opioid use

ABSTRACT

Post-traumatic stress disorder (PTSD) is common in patients with chronic pain, adversely affects chronic pain outcomes, and is associated with opioid use and adverse opioid outcomes. Social support is a robust predictor of PTSD incidence and course as well as chronic pain outcome. We determined whether the association between PTSD and persistent opioid use was modified by emotional support in a cohort of patients receiving opioids for noncancer pain. Eligible participants were ≥18 years and had completed a new period of prescription opioid use lasting 30 to 90 days. Bivariate associations between cohort characteristics and each key variable was assessed using χ 2 tests for categorical variables and t -tests for continuous variables. Interaction between PTSD and emotional support was assessed by a priori stratification on low vs high emotional support. Participants (n = 808) were 53.6 (SD ± 11.6) years of age, 69.8% female, 69.6% White, and 26.4% African American. Overall, 17.2% had probable PTSD. High emotional support was significantly ( P < 0.0001) more common among those without probable PTSD. Prescription opioid use at 6-month follow-up was significantly ( P = 0.0368) more common among patients with vs without probable PTSD. In fully adjusted models, PTSD was no longer associated with opioid use at 6-month follow-up among participants with high emotional support. Among those with lower emotional support, PTSD was significantly associated with opioid use at 6-month follow-up in unadjusted (odds ratio = 2.40; 95% confidence interval: 1.24-4.64) and adjusted models (odds ratio = 2.39; 95% confidence interval: 1.14-4.99). Results point to the hypothesis that improvement of emotional support in vulnerable patients with chronic pain and PTSD may help reduce sustained opioid use.

Only empathy-related traits, not being mimicked or endorphin release, influence social closeness and prosocial behavior

Seminal studies suggest that being mimicked increases experienced social closeness and prosocial behavior to a mimicking confederate (i.e., interaction partner). Here we reexamine these results by considering the role of empathy-related traits, an indirect proxy for endorphin uptake, and their combined effects as an explanation for these results. 180 female participants were mimicked or anti-mimicked in an interaction with a confederate. The effects of being mimicked versus anti-mimicked in relation to empathy-related traits and endorphin release (assessed indirectly via pain tolerance) on experienced closeness and prosocial behavior were assessed using Bayesian analyses. Our results suggest that high individual empathy-related traits increase social closeness to the anti-mimicking and mimicking confederate and to one's romantic partner, as compared to mimicry alone. Results furthermore strongly suggest that high individual empathy-related traits increase prosocial behavior (donations and willingness to help) as compared to mimicry alone. These findings extend previous work by highlighting that empathy-related traits are more influential in creating positive effects on social closeness and prosocial behavior than a one-shot mimicking encounter.

Sociability in a non-captive macaque population is associated with beneficial gut bacteria

The relationship between social behaviour and the microbiome is known to be reciprocal. Research in wild animal populations, particularly in primate social groups, has revealed the role that social interactions play in microbial transmission, whilst studies in laboratory animals have demonstrated that the gut microbiome can affect multiple aspects of behaviour, including social behaviour. Here we explore behavioural variation in a non-captive animal population with respect to the abundance of specific bacterial genera. Social behaviour based on grooming interactions is assessed in a population of rhesus macaques (Macaca mulatta), and combined with gut microbiome data. We focus our analyses on microbiome genera previously linked to sociability and autistic behaviours in rodents and humans. We show in this macaque population that some of these genera are also related to an individual's propensity to engage in social interactions. Interestingly, we find that several of the genera positively related to sociability, such as Faecalibacterium, are well known for their beneficial effects on health and their anti-inflammatory properties. In contrast, the genus Streptococcus, which includes pathogenic species, is more abundant in less sociable macaques. Our results indicate that microorganisms whose abundance varies with individual social behaviour also have functional links to host immune status. Overall, these findings highlight the connections between social behaviour, microbiome composition, and health in an animal population.

Peptidomimetics and Their Applications for Opioid Peptide Drug Discovery

Despite various advantages, opioid peptides have been limited in their therapeutic uses due to the main drawbacks in metabolic stability, blood-brain barrier permeability, and bioavailability. Therefore, extensive studies have focused on overcoming the problems and optimizing the therapeutic potential. Currently, numerous peptide-based drugs are being marketed thanks to new synthetic strategies for optimizing metabolism and alternative routes of administration. This tutorial review briefly introduces the history and role of natural opioid peptides and highlights the key findings on their structure-activity relationships for the opioid receptors. It discusses details on opioid peptidomimetics applied to develop therapeutic candidates for the treatment of pain from the pharmacological and structural points of view. The main focus is the current status of various mimetic tools and the successful applications summarized in tables and figures.

Physical, Emotional, and Social Pain During COVID-19 Pandemic-Related Social Isolation

The socio-emotional condition during the COVID-19 pandemic subsidises the (re)modulation of interactive neural circuits underlying risk assessment behaviour at the physical, emotional, and social levels. Experiences of social isolation, exclusion, or affective loss are generally considered some of the most “painful” things that people endure. The threats of social disconnection are processed by some of the same neural structures that process basic threats to survival. The lack of social connection can be “painful” due to an overlap in the neural circuitry responsible for both physical and emotional pain related to feelings of social rejection. Indeed, many of us go to great lengths to avoid situations that may engender these experiences. Accordingly, this work focuses on pandemic times; the somatisation mentioned above seeks the interconnection and/or interdependence between neural systems related to emotional and cognitive processes such that a person involved in an aversive social environment becomes aware of himself, others, and the threatening situation experienced and takes steps to avoid daily psychological and neuropsychiatric effects. Social distancing during isolation evokes the formation of social distress, increasing the intensity of learned fear that people acquire, consequently enhancing emotional and social pain.

A randomised, double-blind study investigating the relationship between early childhood trauma and the rewarding effects of morphine

Experiences of childhood trauma (abuse and neglect) are disproportionately higher in those with opioid use disorder (OUD). Childhood trauma may affect the reinforcing and rewarding properties of opioid drugs and responses to pain, potentially via developmental changes to the endogenous opioid system. This has been supported by preclinical research, yet this has not been investigated in non-addicted humans. Physically healthy participants with either a history of severe childhood trauma or no previous history of childhood trauma attended two sessions where they received either an intramuscular active dose of morphine (0.15 mg/kg) or a very low dose control (0.01 mg/kg) in a randomised, double-blind crossover design. Sessions were held 1 week apart. Participants' physical pain threshold and tolerance were measured pre- and post-drug administration using the cold water pressor test, alongside acute subjective and behavioural responses over 2.5 h. The trauma group reported liking the effects of morphine, feeling more euphoric and wanting more of the drug over the session, as well as feeling less nauseous, dizzy, and dislike of the effects of morphine compared to the non-trauma comparison group. Morphine increased pain threshold and tolerance, yet this did not differ between the groups. Childhood trauma may therefore sensitise individuals to the pleasurable and motivational effects of opioids and reduce sensitivity to the negative effects, providing compelling evidence for individual differences in opioid reward sensitivity. This may explain the link between childhood trauma and vulnerability to OUD, with consequent implications on interventions for OUD, the prescribing of opioids, and reducing stigmas surrounding OUD.

Laughter influences social bonding but not prosocial generosity to friends and strangers

Humans deploy a number of specific behaviours for forming social bonds, one of which is laughter. However, two questions have not yet been investigated with respect to laughter: (1) Does laughter increase the sense of bonding to those with whom we laugh? and (2) Does laughter facilitate prosocial generosity? Using changes in pain threshold as a proxy for endorphin upregulation in the brain and a standard economic game (the Dictator Game) as an assay of prosociality, we show that laughter does trigger the endorphin system and, through that, seems to enhance social bonding, but it does not reliably influence donations to others. This suggests that social bonding and prosociality may operate via different mechanisms, or on different time scales, and relate to different functional objectives.

Neurobiological Bases of Social Networks

A social network is a web that integrates multiple levels of interindividual social relationships and has direct associations with an individual’s health and well-being. Previous research has mainly focused on how brain and social network structures (structural properties) act on each other and on how the brain supports the spread of ideas and behaviors within social networks (functional properties). The structure of the social network is correlated with activity in the amygdala, which links decoding and interpreting social signals and social values. The structure also relies on the mentalizing network, which is central to an individual’s ability to infer the mental states of others. Network functional properties depend on multilayer brain-social networks, indicating that information transmission is supported by the default mode system, the valuation system, and the mentalizing system. From the perspective of neuroendocrinology, overwhelming evidence shows that variations in oxytocin, β-endorphin and dopamine receptor genes, including oxytocin receptor (OXTR), mu opioid receptor 1 (OPRM1) and dopamine receptor 2 (DRD2), predict an individual’s social network structure, whereas oxytocin also contributes to improved transmission of emotional and behavioral information from person to person. Overall, previous studies have comprehensively revealed the effects of the brain, endocrine system, and genes on social networks. Future studies are required to determine the effects of cognitive abilities, such as memory, on social networks, the characteristics and neural mechanism of social networks in mental illness and how social networks change over time through the use of longitudinal methods.

Clustering of Social and Physical Pain Variables and Their Association With Mortality in Two Population-Based Cohorts

OBJECTIVE

Social pain and physical pain are related bidirectionally, but how these variables cluster in the population is unknown.

METHODS

This study included 2833 women from the Study of Women's Health Across the Nation (SWAN), a community-based cohort of middle-aged women, and 3972 women from the Pathways Study, a population-based cohort of women diagnosed with American Joint Committee on Cancer stages I-IV breast cancer diagnosed between 2005 and 2013. Women provided data on measures related to social pain (social network size, social support, loneliness, social well-being) and physical pain (sensitivity to pain, bodily pain) at study baseline. Analyzing each cohort separately, we used latent class analysis to evaluate social-physical pain clusters, logistic regression to evaluate predictors of categorization into clusters, and Cox proportional hazards models to evaluate associations of clusters with all-cause mortality. We also performed a meta-analysis to combine cohort mortality associations.

RESULTS

Each cluster analysis produced a "low social-physical pain" cluster (SWAN, 48.6%; Pathways, 35.2%) characterized by low social and pain symptoms, a "high social-physical pain" cluster (SWAN, 17.9%; Pathways, 17.9%) characterized by high symptoms, and a "low social/high physical pain" cluster of women with high pain and compromised social functioning but otherwise low social symptoms (SWAN, 33.5%; Pathways, 46.9%). In meta-analysis, categorization into the high social-physical pain cluster was associated with elevated mortality (adjusted hazard ratio = 1.34, 95% confidence interval = 1.05-1.71, Q statistic = 0.782), compared with those in the low social-physical pain cluster.

CONCLUSIONS

In two cohorts of women, latent class analysis produced similar sets of social-physical pain clusters, with the same proportion having both high social and pain symptoms; women in this cluster had elevated mortality.

Opposing effects of antibiotics and germ-free status on neuropeptide systems involved in social behaviour and pain regulation

Background

Recent research has revealed that the community of microorganisms inhabiting the gut affects brain development, function and behaviour. In particular, disruption of the gut microbiome during critical developmental windows can have lasting effects on host physiology. Both antibiotic exposure and germ-free conditions impact the central nervous system and can alter multiple aspects of behaviour. Social impairments are typically displayed by antibiotic-treated and germ-free animals, yet there is a lack of understanding of the underlying neurobiological changes. Since the μ-opioid, oxytocin and vasopressin systems are key modulators of mammalian social behaviour, here we investigate the effect of experimentally manipulating the gut microbiome on the expression of these pathways.

Results

We show that social neuropeptide signalling is disrupted in germ-free and antibiotic-treated mice, which may contribute to the behavioural deficits observed in these animal models. The most notable finding is the reduction in neuroreceptor gene expression in the frontal cortex of mice administered an antibiotic cocktail post-weaning. Additionally, the changes observed in germ-free mice were generally in the opposite direction to the antibiotic-treated mice.

Conclusions

Antibiotic treatment when young can impact brain signalling pathways underpinning social behaviour and pain regulation. Since antibiotic administration is common in childhood and adolescence, our findings highlight the potential adverse effects that antibiotic exposure during these key neurodevelopmental periods may have on the human brain, including the possible increased risk of neuropsychiatric conditions later in life. In addition, since antibiotics are often considered a more amenable alternative to germ-free conditions, our contrasting results for these two treatments suggest that they should be viewed as distinct models.

Gut microbiome composition and diversity are related to human personality traits

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Investigation of gut microbiome composition and diversity with respect to human personality.

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Analyses targeted bacterial genera linked to behaviour in animal and human psychiatric studies.

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Bacterial genera were modelled (using negative binomial regression) with respect to personality.

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Genera linked to autism are also related to social behaviour in the general population.

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Sociability is associated with higher diversity, and anxiety and stress with reduced diversity.

The gut microbiome has a measurable impact on the brain, influencing stress, anxiety, depressive symptoms and social behaviour. This microbiome–gut–brain axis may be mediated by various mechanisms including neural, immune and endocrine signalling. To date, the majority of research has been conducted in animal models, while the limited number of human studies has focused on psychiatric conditions. Here the composition and diversity of the gut microbiome is investigated with respect to human personality. Using regression models to control for possible confounding factors, the abundances of specific bacterial genera are shown to be significantly predicted by personality traits. Diversity analyses of the gut microbiome reveal that people with larger social networks tend to have a more diverse microbiome, suggesting that social interactions may shape the microbial community of the human gut. In contrast, anxiety and stress are linked to reduced diversity and an altered microbiome composition. Together, these results add a new dimension to our understanding of personality and reveal that the microbiome–gut–brain axis may also be relevant to behavioural variation in the general population as well as to cases of psychiatric disorders.

A novel theory on the predictive value of variation in the β-endorphin system on the risk and severity of PTSD

Despite growing interest in genetic and psychosocial indicators of heightened susceptibility to posttraumatic stress disorder (PTSD), a predictive model, which explains why some individuals develop PTSD in response to life-threatening traumatic events, while others, when faced with the same or similar experiences, do not, has thus far remained out of reach. In this paper, we review the literature on gene-environment interactions in β-endorphin system functioning with regard to PTSD and suggest that variation, both genetic and with regard to environmental stimuli, in systems which, like the β-endorphin system, distort human perception of life-threatening traumatic experiences may account for some of the variance in resilience to the disorder. Given the role of β-endorphin in both social connections and physical exercise, this becomes especially relevant with regard to military selection, training, and leadership processes.

Does information about toughness decrease fighting? Experimental evidence

Will fights erupt when resources are scarce and the rules regulating their distribution are absent or ignored? We conjecture that the answer depends on whether credible information about individuals' toughness is available. When people send credible signs and signals of their toughness disputes may be solved without violence. We use a laboratory experiment in which subjects create information about their toughness and decide whether to take others' resources and resist in case others' attempt to take theirs. Subjects perform a potentially painful but safe physical exercise to create information and to determine who wins and loses fights. This, realistically, ranks subjects according to their toughness and implicates toughness, a quality important in real conflict, in fighting. We find that, consistent with theory, information reduces fighting. This suggests that, in addition to the theories traditionally used to explain prisoner behavior, the availability of credible information about toughness influences prison conflict.

The peer effect on pain tolerance

Background and aims Twin studies have found that approximately half of the variance in pain tolerance can be explained by genetic factors, while shared family environment has a negligible effect. Hence, a large proportion of the variance in pain tolerance is explained by the (non-shared) unique environment. The social environment beyond the family is a potential candidate for explaining some of the variance in pain tolerance. Numerous individual traits have previously shown to be associated with friendship ties. In this study, we investigate whether pain tolerance is associated with friendship ties. Methods We study the friendship effect on pain tolerance by considering data from the Tromsø Study: Fit Futures I, which contains pain tolerance measurements and social network information for adolescents attending first year of upper secondary school in the Tromsø area in Northern Norway. Pain tolerance was measured with the cold-pressor test (primary outcome), contact heat and pressure algometry. We analyse the data by using statistical methods from social network analysis. Specifically, we compute pairwise correlations in pain tolerance among friends. We also fit network autocorrelation models to the data, where the pain tolerance of an individual is explained by (among other factors) the average pain tolerance of the individual's friends. Results We find a significant and positive relationship between the pain tolerance of an individual and the pain tolerance of their friends. The estimated effect is that for every 1 s increase in friends' average cold-pressor tolerance time, the expected cold-pressor pain tolerance of the individual increases by 0.21 s (p-value: 0.0049, sample size n=997). This estimated effect is controlled for sex. The friendship effect remains significant when controlling for potential confounders such as lifestyle factors and test sequence among the students. Further investigating the role of sex on this friendship effect, we only find a significant peer effect of male friends on males, while there is no significant effect of friends' average pain tolerance on females in stratified analyses. Similar, but somewhat lower estimates were obtained for the other pain modalities. Conclusions We find a positive and significant peer effect in pain tolerance. Hence, there is a significant tendency for students to be friends with others with similar pain tolerance. Sex-stratified analyses show that the only significant effect is the effect of male friends on males. Implications Two different processes can explain the friendship effect in pain tolerance, selection and social transmission. Individuals might select friends directly due to similarity in pain tolerance, or indirectly through similarity in other confounding variables that affect pain tolerance. Alternatively, there is an influence effect among friends either directly in pain tolerance, or indirectly through other variables that affect pain tolerance. If there is indeed a social influence effect in pain tolerance, then the social environment can account for some of the unique environmental variance in pain tolerance. If so, it is possible to therapeutically affect pain tolerance through alteration of the social environment.

Non-medical prescription opioid users exhibit dysfunctional physiological stress responses to social rejection

Non-medical prescription opioid use (NMPOU) recently increased dramatically, especially in the U.S. Although chronic opioid use is commonly accompanied by deficits in social functioning and dysregulation of the hypothalamic-pituitary adrenergic (HPA) stress axis, little is known about the impact of NMPOU on psychosocial stress responses. Therefore, we measured physiological responses of the autonomic nervous system and the HPA axis to social rejection using the Cyberball paradigm. We compared 23 individuals with NMPOU, objectively confirmed by hair and urine analyses, with 29 opioid-naïve, healthy controls. As expected, heart rate variability (HRV), an index of parasympathetic activity, increased significantly during exclusion within controls, while in the NMPOU group only a trend in the same direction was found. However, increased HRV was robustly moderated by opioid craving indicating worse emotion regulation to social exclusion specifically in individuals with high opioid craving. Greater levels of the adrenocorticotropic hormone and cortisol responses to social rejection were found in the NMPOU group indicating hyperreactivity of the HPA axis to social exclusion. Self-ratings suggest that opioid users were aware of rejection, but less emotionally affected by exclusion. Furthermore, controls showed greater negative mood after the Cyberball confirming the task's validity. Moreover, NMPOU individuals reported a smaller social network size compared to controls. Present findings suggest that chronic NMPOU is associated with dysfunctional physiological responses to psychosocial stressors such as social rejection. In sum, NMPOU was associated with poorer regulation of the parasympathetic nervous system, especially under opioid craving highlighting its potential importance in relapse prevention.

The Effect of Fatigue and Pain Self- Efficacy on Health-Related Quality of Life Among Patients with Multiple Sclerosis

Introduction:

Health-related quality of life is a major issue among patients with Multiple sclerosis (MS).

Aim:

To explore the effect of fatigue and pain self-efficacy on health-related quality of life among patients with MS.

Methods:

Between March and May 2018, 85 MS patients from a large Hospital of Athens region completed the questionnaires: a) Missoula-VITAS Quality of Life Index-15, which examines 5 dimensions of quality of life, b) Pain Self Efficacy Questionnaire which measures the pain self-efficacy that an individual perceives, c) Fatigue Assessment Scale (FAS) which measures fatigue, d) a questionnaire about the sociodemographic elements. Statistical analysis was performed using the IBM SPSS Statistics version 21. The significance level was set up to 0.001.

Results:

Fatigue might predict the dimension of quality of life “Function” while Pain Self-Efficacy might, also, predict the dimension of quality of life “Interpersonal”. A strong correlation was found between the dimensions of quality of life “Well-being” and “Transcendent” and between “Interpersonal” and Pain Self-Efficacy. The total score of fatigue was strongly correlated with Physical Fatigue and very strongly correlated with Mental Fatigue.

Conclusion:

Fatigue and Pain Self-Efficacy are important predictors of the dimensions of quality of life among patients with MS. Pain in MS has to be taken into serious consideration in every patient with MS.

Pre-operative pressure pain thresholds do not meaningfully explain satisfaction or improvement in pain after knee replacement: a cohort study

OBJECTIVES

Pain sensitization could be a risk factor for poor outcomes after knee replacement surgery (KR) for knee osteoarthritis (KOA). We aimed to evaluate the association between pre-operative central and peripheral pain sensitization measured using a digital pressure algometer and KR outcomes.

METHODS

Consecutive patients with severe KOA listed for KR were recruited. Sociodemographic and symptoms data were collected prior to surgery. Pre-operative pressure pain thresholds (PPTs) were measured using a digital pressure algometer at the index knee and forearm. Patient satisfaction at 6 and 12 months after KR was assessed using a 4-point Likert scale, and dichotomized to satisfied and dissatisfied to KR. Western Ontario and McMaster Universities Index (WOMAC) Pain and function was assessed. The associations between pre-operative PPTs with KR outcomes at 6 and 12 months were evaluated.

RESULTS

Of the 243 patients recruited, response rate at 6 and 12 months were 95.5% and 96.7%. The dissatisfaction rates were 8.2% and 5.1% at 6 and 12 months. There was no statistically significant association between pre-operative index knee or forearm PPTs and patient satisfaction. PPTs measured at the knee, but not the forearm, were weakly associated with change in the WOMAC pain score at 12 months, after adjustment for confounding factors.

CONCLUSION

Pre-operative central sensitization, measured by handheld digital algometry, was not statistically significantly associated with satisfaction or change in pain after KR. Pre-operative peripheral sensitization was associated with change in pain symptoms after KR; however, this association was weak and unlikely to be a meaningful predictor of KR outcome in clinical practice.

The Anatomy of Friendship

Friendship is the single most important factor influencing our health, well-being, and happiness. Creating and maintaining friendships is, however, extremely costly, in terms of both the time that has to be invested and the cognitive mechanisms that underpin them. Nonetheless, personal social networks exhibit many constancies, notably in their size and their hierarchical structuring. Understanding the processes that give rise to these patterns and their evolutionary origins requires a multidisciplinary approach that combines social and neuropsychology as well as evolutionary biology.

The Influence of Endogenous Opioids on the Relationship between Testosterone and Romantic Bonding

The endogenous opioid system has received attention and extensive research for its effects on reward, pleasure, and pain. However, relative to other neurochemicals, such as oxytocin, vasopressin and dopamine, the function of opioids in regulating human attachment, sociosexuality, and other aspects of human sociality has not received much consideration. For example, nonapeptides (oxytocin and vasopressin) have been extensively studied in animals and humans for their possible roles in mother-offspring attachment, romantic attachment, fatherhood, and social cognition. Likewise, others have proposed models wherein oxytocin and vasopressin are moderators of the relationship between steroid hormones and human social behaviors. Recently, opioids have generated renewed interest in relation to social pain, and importantly, the brain opioid hypothesis of social attachment (BOTSA), which suggests that endogenous opioids are a key implementer in primate and human bonding, has received some support. Here we focus on romantic bonds by proposing that endogenous opioids are an important mechanism mediating reproductive trade-offs through their inhibitory effects on testosterone production.

[Social pain at the core of suicidal behavior]

BACKGROUND

Intolerable pain is often reported in suicide notes. Moreover, the frequency of life events preceding a suicidal act is high, especially interpersonal difficulties. Such adversity is the source of psychological or social pain.

METHODS

We propose a narrative review to discuss the role of pain in the suicidal process while having a focus on social ties.

RESULTS

Using Ecological Momentary Assessment in suicide attempters it has been shown that being alone increased suicidal ideation while being with close others significantly reduced this risk. At a neuroanatomical level, suicidal vulnerability is associated with dysfunctional insula activation during social exclusion, a region involved in social and physical pain processing. Social pain elicited by social exclusion or devaluation shares common neurobiological patterns with physical pain. It is also an exemplar of psychological pain. Despite the complexity of its definition, higher psychological pain levels are associated with suicidal ideation and acts. Finally, intense physical pain or chronic pain are strong risk factors of suicidal ideation and act. Interestingly, suicide notes often report the existence of an intolerable pain. Presence of psychological pain and difficulties in communication predict the lethality and seriousness of suicide attempts. Moreover, presence of psychological pain is associated with more impulsive choices in suicidal patients, suggesting that a suicidal act is a means to escape intolerable suffering despite negative long-term consequences (i.e. death). Analgesics are usually used to get relief from pain but are also frequently involved in suicidal overdoses. It has been shown that opioid analgesics are associated with an increased risk of suicide. Higher consumption of opioid analgesics has been shown in suicidal patients in comparison to patients with history of depression but no suicidal act and healthy controls whereas non-suicidal patients were those reporting higher presence of pain in comparison to healthy controls. It may suggest that opioids are being used by suicidal patients to get relief from psychological/social pain rather than from physical pain. Involvement of opioidergic system in suicidal process opens new therapeutic strategies. Recently, the time-limited, short-term use of very low dosages of sublingual buprenorphine (vs. placebo) was associated with decreased suicidal ideation and mental pain in severely suicidal patients without substance abuse. In a randomized controlled trial comparing a 7-week acceptance and commitment therapy (ACT) versus relaxation group, as adjunct to treatment as usual for adult outpatients suffering from a current suicidal behavior disorder, ACT has shown its effectiveness in reducing suicidal ideation and psychological pain. Evidence indicates that maintaining contact either via letter, postcard or telephone with at-risk adults following discharge from care services after a suicide attempt can reduce reattempt risk. Based on these results, a preventive program of recontact for suicide attempters, VIGILANS, has been developed in France in usual care.

CONCLUSION

The approach of the suicidal issue by the angle of pain and social disconnection offers new advances to improve clinical assessment, to identify new biological pathways involved in suicidal risk, and to propose innovative therapeutic and preventive actions.

Endogenous Opiates and Behavior: 2016

This paper is the thirty-ninth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2016 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

Evolutionary dynamics of group formation

Group formation is a quite ubiquitous phenomenon across different animal species, whose individuals cluster together forming communities of diverse size. Previous investigations suggest that, in general, this phenomenon might have similar underlying reasons across the interested species, despite genetic and behavioral differences. For instance improving the individual safety (e.g. from predators), and increasing the probability to get food resources. Remarkably, the group size might strongly vary from species to species, e.g. shoals of fishes and herds of lions, and sometimes even within the same species, e.g. tribes and families in human societies. Here we build on previous theories stating that the dynamics of group formation may have evolutionary roots, and we explore this fascinating hypothesis from a purely theoretical perspective, with a model using the framework of Evolutionary Game Theory. In our model we hypothesize that homogeneity constitutes a fundamental ingredient in these dynamics. Accordingly, we study a population that tries to form homogeneous groups, i.e. composed of similar agents. The formation of a group can be interpreted as a strategy. Notably, agents can form a group (receiving a ‘group payoff’), or can act individually (receiving an ‘individual payoff’). The phase diagram of the modeled population shows a sharp transition between the ‘group phase’ and the ‘individual phase’, characterized by a critical ‘individual payoff’. Our results then support the hypothesis that the phenomenon of group formation has evolutionary roots.

Social interaction and pain: An arctic expedition

Complex human behaviour can only be understood within its social environment. However, disentangling the causal links between individual outcomes and social network position is empirically challenging. We present a research design in a closed real-world setting with high-resolution temporal data to understand this interplay within a fundamental human experience - physical pain. Study participants completed an isolated 3-week hiking expedition in the Arctic Circle during which they were subject to the same variation in environmental conditions and only interacted amongst themselves. Adolescents provided daily ratings of pain and social interaction partners. Using longitudinal network models, we analyze the interplay between social network position and the experience of pain. Specifically, we test whether experiencing pain is linked to decreasing popularity (increasing isolation), whether adolescents prefer to interact with others experiencing similar pain (homophily), and whether participants are increasingly likely to report similar pain as their interaction partners (contagion). We find that reporting pain is associated with decreasing popularity - interestingly, this effect holds for males only. Further exploratory analyses suggest this is at least partly driven by males withdrawing from contact with females when in pain, enhancing our understanding of pain and masculinity. Contrary to recent experimental and clinical studies, we found no evidence of pain homophily or contagion in the expedition group.

The association between Act-Belong-Commit indicators and problem drinking among older Irish adults: Findings from a prospective analysis of the Irish Longitudinal Study on Ageing (TILDA)

The Act-Belong-Commit campaign is the world's first comprehensive, population-wide, community-based program to promote mental health. However, its potential for preventing substance use disorders is unknown. Further, a literature gap is evident concerning behavioral modification strategies to prevent such disorders. The aim of this study was to prospectively assess the association between indicators of the Act-Belong-Commit behavioral domains and the development of problem drinking. Data from two waves of the Irish Longitudinal Study on Ageing (TILDA) were analyzed. The sample consisted of 3950 adults aged ≥50years. A validated scale for problem drinking was used. The number of social/recreational activities engaged in was used as an indicator of Act, social network integration as an indicator of Belong, and frequency of participation in these social/recreational activities as an indicator of Commit. Multivariable logistic regression analyses were conducted to assess associations between baseline indicators of Act-Belong-Commit and the development of problem drinking at two-year follow-up. Each increase in the number of social/recreational activities (Act) inversely predicted the onset of problem drinking. Similarly, being well integrated into social networks (Belong) was negatively associated with the development of problem drinking. Finally, frequency of participation in social/recreational activities (Commit) also inversely predicted the onset of problem drinking. These associations were apparent regardless of the presence of baseline common mental disorders. Act-Belong-Commit indicators are shown to be associated with a reduced risk for problem drinking. This lends further support to the Act-Belong-Commit domains and has wide-ranging implications for preventing substance use disorders in the aging community.

Sync to link: Endorphin-mediated synchrony effects on cooperation

Behavioural synchronization has been shown to facilitate social bonding and cooperation but the mechanisms through which such effects are attained are poorly understood. In the current study, participants interacted with a pre-recorded confederate who exhibited different rates of synchrony, and we investigated three mechanisms for the effects of synchrony on likeability and trusting behaviour: self-other overlap, perceived cooperation, and opioid system activation measured via pain threshold. We show that engaging in highly synchronous behaviour activates all three mechanisms, and that these mechanisms mediate the effects of synchrony on liking and investment in a Trust Game. Specifically, self-other overlap and perceived cooperation mediated the effects of synchrony on interpersonal liking, while behavioural trust was mediated only by change in pain threshold. These results suggest that there are multiple compatible pathways through which synchrony influences social attitudes, but endogenous opioid system activation, such as β-endorphin release, might be important in facilitating economic cooperation.

Variation in the β-endorphin, oxytocin, and dopamine receptor genes is associated with different dimensions of human sociality

There is growing evidence that the number and quality of social relationships have substantial impacts on health, well-being, and longevity, and, at least in animals, on reproductive fitness. Although it is widely recognized that these outcomes are mediated by a number of neuropeptides, the roles these play remain debated. We suggest that an overemphasis on one neuropeptide (oxytocin), combined with a failure to distinguish between different social domains, has obscured the complexity involved. We use variation in 33 SNPs for the receptor genes for six well-known social neuropeptides in relation to three separate domains of sociality (social disposition, dyadic relationships, and social networks) to show that three neuropeptides (β-endorphin, oxytocin, and dopamine) play particularly important roles, with each being associated predominantly with a different social domain. However, endorphins and dopamine have a much wider compass than oxytocin (whose effects are confined to romantic/reproductive relationships and often do not survive control for other neuropeptides). In contrast, vasopressin, serotonin, and testosterone play only limited roles.

The Company You Keep

Studies on personality and friendship have focused on similarities between friends, while differences in friendship patterns have received less attention. We used data from the British Household Panel Survey data ( N = 12,098) to investigate how people’s personalities are related to various characteristics of their three closest friends. All personality traits of the five-factor model were associated with several friendship characteristics with effect sizes corresponding to correlations between −.06 and .09. Openness was especially prominent and idiosyncratic; individuals with high (vs. low) openness were about 3% more likely to have friends who live further away, are of the opposite sex and another ethnicity, and whom they meet less often. Agreeableness and extroversion were related to more traditional friendship ties. Individuals with high agreeableness had known their friends for a longer time, lived close to them, and had more “stay-at-homes” among their friends.