Opioid receptor blockade inhibits self-disclosure during a closeness-building social interaction

Endogenous mu-opioid modulation of social connection in humans: a systematic review and meta-analysis

Social bonding, essential for health and survival in all social species, depends on mu-opioid signalling in non-human mammals. A growing neuroimaging and psychopharmacology literature also implicates mu-opioids in human social connectedness. To determine the role of mu-opioids for social connectedness in healthy humans, we conducted a preregistered ( https://osf.io/x5wmq ) multilevel random-effects meta-analysis of randomised double-blind placebo-controlled opioid antagonist studies. We included data from 8 publications and 2 unpublished projects, totalling 17 outcomes (N = 455) sourced from a final literature search in Web of Science, Scopus, PubMed and EMBASE on October 12, 2023, and through community contributions. All studies used naltrexone (25-100 mg) to block the mu-opioid system and measured social connectedness by self-report. Opioid antagonism slightly reduced feelings of social connectedness (Hedges' g [95% CI) = -0.20] [-0.32, -0.07]. Results were highly consistent within and between studies (I2 = 23%). However, there was some indication of bias in favour of larger effects among smaller studies (Egger's test: B = -2.16, SE = 0.93, z = -2.33, p = 0.02), and publication bias analysis indicated that the effect of naltrexone might be overestimated. The results clearly demonstrate that intact mu-opioid signalling is not essential for experiencing social connectedness, as robust feelings of connectedness are evident even during full pharmacological mu-opioid blockade. Nevertheless, antagonism reduced measures of social connection, consistent with a modulatory role of mu-opioids for human social connectedness. The modest effect size relative to findings in non-human animals, could be related to differences in measurement (subjective human responses versus behavioural/motivation indices in animals), species specific neural mechanisms, or naltrexone effects on other opioid receptor subtypes. In sum, these results help explain how mu-opioid dysregulation and social disconnection can contribute to disability, and conversely-how social connection can buffer risk of ill health.

Social homeostasis and psychoactive drugs: What can we learn from opioid and amphetamine drug challenge studies in humans?

BACKGROUND

Social disequilibrium, or disrupted social homeostasis, underlies many behavioral disorders, including problematic drug use. One way to study the relationship between drug use and social homeostasis is to determine whether single doses of psychoactive drugs relieve some of the discomfort of social isolation and promote social connection.

METHODS

In this narrative review, we discuss challenges and opportunities in studying the relationship between psychoactive drugs and social homeostasis. Using the examples of opioids and amphetamines, we discuss the evidence that drugs alleviate dysphoria related to lack of social connection or produce pro-social effects that improve connection.

RESULTS

With regard to opioid drugs, we report that mu opioid agonists and kappa opioid antagonists reduce distress from social isolation, and mu opioid agonists enhance social reward. Amphetamine-like stimulant drugs, including MDMA, do not seem to act by reducing the distress of social isolation, but they have notable prosocial effects that increase both motivation for social contact and the pleasure derived from interacting socially.

CONCLUSIONS

Many questions remain in understanding interactions between drugs and social equilibrium, including whether these effects contribute to problematic drug use. We identify gaps in knowledge, including the effects of drug withdrawal or dependence on social function, or the responses of individuals with psychiatric symptomatology. Understanding these actions on social processes will help to develop novel pharmacologic treatments for clinical problems related to social disequilibrium.

Social Psychopharmacology: Novel Approaches to Treat Deficits in Social Motivation in Schizophrenia

BACKGROUND AND HYPOTHESIS

Diminished social motivation is a negative symptom of schizophrenia and leads to severe functional consequences for many patients suffering from the illness. However, there are no effective medications available to treat this symptom. Despite the lack of approved treatments for patients, there is a growing body of literature on the effects of several classes of drugs on social motivation in healthy volunteers that may be relevant to patients. The aim of this review is to synthesize these results in an effort to identify novel directions for the development of medications to treat reduced social motivation in schizophrenia.

STUDY DESIGN

In this article, we review pharmacologic challenge studies addressing the acute effects of psychoactive drugs on social motivation in healthy volunteers and consider how these findings may be applied to deficits in social motivation in schizophrenia. We include studies testing amphetamines and 3,4-methylenedioxymethamphetamine (MDMA), opioids, cannabis, serotonergic psychedelics, antidepressants, benzodiazepines, and neuropeptides.

STUDY RESULTS

We report that amphetamines, MDMA, and some opioid medications enhance social motivation in healthy adults and may represent promising avenues of investigation in schizophrenia.

CONCLUSIONS

Given the acute effects of these drugs on behavioral and performance-based measures of social motivation in healthy volunteers, they may be particularly beneficial as an adjunct to psychosocial training programs in patient populations. It remains to be determined how these medications affect patients with deficits in social motivation, and in which contexts they may be most effectively administered.

Opioid-blunted cortisol response to stress is associated with increased negative mood and wanting of social reward

Animal research suggests a central role of the μ-opioid receptor (MOR) system in regulating affiliative behaviors and in mediating the stress-buffering function of social contact. However, the neurochemistry of stress-related social contact seeking in humans is still poorly understood. In a randomized, double-blind, between-subjects design, healthy female volunteers (N = 80) received either 10 mg of the µ-opioid agonist morphine sulfate, or a placebo. Following a standardized psychosocial stress induction, participants engaged in a social reward task, in which the motivation to obtain skin-to-skin social touch and the hedonic reactions elicited by such touch were assessed. Morphine prevented the increase of salivary cortisol typically observed following acute stress exposure. Notably, this altered HPA axis responsivity was associated with increased negative affect in response to psychosocial stress, and with enhanced subjective wanting of highly rewarding social contact. These findings provide novel evidence on the effect of exogenous opioids administration on the reactions to psychosocial stress and point to a state-dependent regulation of social motivation.

We're Not That Choosy: Emerging Evidence of a Progression Bias in Romantic Relationships

Dating is widely thought of as a test phase for romantic relationships, during which new romantic partners carefully evaluate each other for long-term fit. However, this cultural narrative assumes that people are well equipped to reject poorly suited partners. In this article, we argue that humans are biased toward pro-relationship decisions-decisions that favor the initiation, advancement, and maintenance of romantic relationships. We first review evidence for a progression bias in the context of relationship initiation, investment, and breakup decisions. We next consider possible theoretical underpinnings-both evolutionary and cultural-that may explain why getting into a relationship is often easier than getting out of one, and why being in a less desirable relationship is often preferred over being in no relationship at all. We discuss potential boundary conditions that the phenomenon may have, as well as its implications for existing theoretical models of mate selection and relationship development.

Blocking mu-opioid receptors inhibits social bonding in rituals

Religious rituals are universal human practices that play a seminal role in community bonding. In two experiments, we tested the role of mu-opioids as the active factor fostering social bonding. We used a mu-opioid blocker (naltrexone) in two double-blind studies of rituals from different religious traditions. We found the same effect across both studies, with naltrexone leading to significantly lower social bonding compared with placebo. These studies suggest that mu-opioids play a significant role in experiences of social bonding within ritual contexts.

Music as a coevolved system for social bonding

Why do humans make music? Theories of the evolution of musicality have focused mainly on the value of music for specific adaptive contexts such as mate selection, parental care, coalition signaling, and group cohesion. Synthesizing and extending previous proposals, we argue that social bonding is an overarching function that unifies all of these theories, and that musicality enabled social bonding at larger scales than grooming and other bonding mechanisms available in ancestral primate societies. We combine cross-disciplinary evidence from archaeology, anthropology, biology, musicology, psychology, and neuroscience into a unified framework that accounts for the biological and cultural evolution of music. We argue that the evolution of musicality involves gene-culture coevolution, through which proto-musical behaviors that initially arose and spread as cultural inventions had feedback effects on biological evolution due to their impact on social bonding. We emphasize the deep links between production, perception, prediction, and social reward arising from repetition, synchronization, and harmonization of rhythms and pitches, and summarize empirical evidence for these links at the levels of brain networks, physiological mechanisms, and behaviors across cultures and across species. Finally, we address potential criticisms and make testable predictions for future research, including neurobiological bases of musicality and relationships between human music, language, animal song, and other domains. The music and social bonding (MSB) hypothesis provides the most comprehensive theory to date of the biological and cultural evolution of music.

Lack of Intimacy Prospectively Predicts Breakup

In this prospective longitudinal study, we examined whether and how lack of intimacy or meaningful connection to a romantic partner (i.e., low social reward) and concerns over negative evaluation by the partner (i.e., high social threat) each predict dissolution of a relationship as well as adjustment when a breakup occurs. Our results showed that those who perceived lower levels of reward during the relationship were more likely to experience a breakup. This effect remained significant controlling for global relationship satisfaction and individual differences in attachment insecurity. The degree of reward also predicted experiencing less emotional attachment to the partner (now an ex-partner) postbreakup, but this effect diminished when controlling for satisfaction. In contrast, threat perceptions during the relationship did not predict breakup or emotional attachment to the ex. Our findings suggest that reward perceptions during the relationship have important consequences for relationship dissolution. Implications for breakup recovery are discussed.