Cooperation increases bottlenose dolphins' (Tursiops truncatus) social affiliation

Dolphins live in a fission-fusion society, where strong social bonds and alliances can last for decades. However, the mechanism that allows dolphins to form such strong social bonds is still unclear. Here, we hypothesized the existence of a positive feedback mechanism in which social affiliation promotes dolphins' cooperation, which in turn promotes their social affiliation. To test it, we stimulated the cooperation of the 11 dolphins studied by providing a cooperative enrichment tool based on a rope-pulling task to access a resource. Then we measured the social affiliation [simple ratio index (SRI)] of each possible pair of dolphins and evaluated whether it increased after cooperation. We also evaluated whether, before cooperation, pairs that cooperated had a higher SRI than those that did not cooperate. Our findings showed that the 11 cooperating pairs had significantly stronger social affiliation before cooperation than the 15 non-cooperating pairs. Furthermore, cooperating pairs significantly increased their social affiliation after cooperation, while non-cooperating pairs did not. As a result, our findings provide support to our hypothesis, and suggest that the previous social affiliation between dolphins facilitates cooperation, which in turn promotes their social affiliation.

Effects of the mu-opioid receptor agonist morphine on facial mimicry and emotion recognition

Facial mimicry and emotion recognition are two socio-cognitive abilities involved in adaptive socio-emotional behavior, promoting affiliation and the establishment of social bonds. The mu-opioid receptor (MOR) system plays a key role in affiliation and social bonding. However, it remains unclear whether MORs are involved in the categorization and spontaneous mimicry of emotional facial expressions. Using a randomized, placebo-controlled, double-blind, between-subjects design, we investigated in 82 healthy female volunteers the effects of the specific MOR agonist morphine on the recognition accuracy of emotional faces (happiness, anger, fear), and on their facial mimicry (measured with electromyography). Frequentist statistics did not reveal any significant effects of drug administration on facial mimicry or emotion recognition abilities. However, post hoc Bayesian analyses provided support for an effect of morphine on facial mimicry of fearful facial expressions. Specifically, compared to placebo, morphine reduced mimicry of fear, as shown by lower activity of the frontalis muscle. Bayesian analyses also provided support for the absence of a drug effect on mimicry of happy and angry facial expressions, which were assessed with the zygomaticus major and corrugator supercilii muscles, as well as on emotion recognition accuracy. These findings suggest that MOR activity is involved in automatic facial responses to fearful stimuli, but not in their identification. Overall, the current results, together with the previously reported small effects of opioid compounds, suggest a relatively marginal role of the MOR system in emotion simulation and perception.

The neuroscience of social feelings: mechanisms of adaptive social functioning

Social feelings have conceptual and empirical connections with affect and emotion. In this review, we discuss how they relate to cognition, emotion, behavior and well-being. We examine the functional neuroanatomy and neurobiology of social feelings and their role in adaptive social functioning. Existing neuroscience literature is reviewed to identify concepts, methods and challenges that might be addressed by social feelings research. Specific topic areas highlight the influence and modulation of social feelings on interpersonal affiliation, parent-child attachments, moral sentiments, interpersonal stressors, and emotional communication. Brain regions involved in social feelings were confirmed by meta-analysis using the Neurosynth platform for large-scale, automated synthesis of functional magnetic resonance imaging data. Words that relate specifically to social feelings were identfied as potential research variables. Topical inquiries into social media behaviors, loneliness, trauma, and social sensitivity, especially with recent physical distancing for guarding public and personal health, underscored the increasing importance of social feelings for affective and second person neuroscience research with implications for brain development, physical and mental health, and lifelong adaptive functioning.

Negative symptoms and the formation of social affiliative bonds in schizophrenia

Negative symptoms in schizophrenia are characterized by deficits in normative experiences and expression of emotion, and they are associated with poor social functioning. Negative symptoms relating to deficits in motivation and pleasure may hinder the development of affiliative bonds. The current study used a novel procedure to examine the relation between negative symptoms and the development of social affiliation within a laboratory setting. Fifty-five men (35 controls; 20 with a schizophrenia spectrum disorder) completed three Social Affiliation Enhancement Tasks with an experimenter partner. Self-reported affiliation and affect ratings were assessed before and after the affiliative interaction. Across groups, social affiliation and positive affect increased following the interactive tasks. However, the schizophrenia group reported less positive and more negative affect than controls. Within individuals with schizophrenia, negative symptoms reflecting motivation and pleasure deficits and self-reported social anhedonia were associated with less affiliative feelings of interpersonal closeness and less willingness to interact. Additionally, these self-reported reactions to the interaction partner were significantly related to social functioning in the community. These findings indicate that though individuals with schizophrenia can form affiliative bonds, the extent to which this is possible may be limited by negative symptoms relating to motivation and pleasure. Additional research will be necessary to examine just how these negative symptoms interfere with social affiliation.

Interacting effect of two social factors on 18-month-old infants' imitative behavior: Communicative cues and demonstrator presence

Certain aspects of a demonstration have been shown to influence infants' interpretation of an observational situation and result in selective imitation. Studying social factors that trigger selective imitation may improve our understanding of how infants encode certain situations. However, only a few studies have investigated the possible interactions among these factors. In our study, 18-month-old infants (N=54) observed an adult demonstrator retrieve a toy from under an opaque ("baited") container by manipulating another transparent empty one. Infants were assigned to one of four conditions representing all combinations of two social factors: ostensive communication during demonstration (Communicative vs. Non-communicative) and presence of the demonstrator during reenactment (D-present vs. D-not present). Results suggest that infants' choice behavior was formed in two steps: during the demonstration and during the test phase. Furthermore, an interaction between the effects of the two levels was observed. Communication during the demonstration triggered imitative learning. Infants tended to copy the observed manipulation to learn the communicatively assigned way to reach the goal. This choice behavior was not influenced later by the presence or absence of the demonstrator. The non-communicative demonstration, however, did not elicit a particular learning mechanism. Therefore, in this situation, infants' choice behavior was affected by the demonstrator's presence or absence. Infants developed an individual solution and chose the baited container in the D-not present condition, indicative of emulation. In the D-present situation, they were more likely to reproduce the observed manipulation, which can be interpreted as a tendency to communicate with or conform to the demonstrator.

An evaluation of behavioural endpoints: The pharmaceutical pollutant fluoxetine decreases aggression across multiple contexts in round goby (Neogobius melanostomus)

Fluoxetine (Prozac™) is designed to alter human behaviour; however, because many physiological pathways are conserved across vertebrates, this drug may affect the behaviour of fish living in fluoxetine-polluted environments. Although a number of studies have used behaviour to document the sub-lethal effects of fluoxetine, the repeatability of these effects across experiments, across behavioural contexts, and over different exposure durations are rarely considered. Here, we conducted two experiments and assessed how fluoxetine exposure affected a range of fitness-related behaviours in wild round goby (Neogobius melanostomus). We found that fluoxetine impacts round goby behaviour at high (40 μg/l) doses, but not at environmentally relevant low doses (1 μg/l). In both experiments, an acute 3-day exposure to fluoxetine reduced round goby aggression in multiple behavioural contexts, but had no detectable effect on overall activity or social affiliative behaviour. While a chronic 28-day exposure to fluoxetine exposure still reduced aggression, this reduction was only detectable in one behavioural context. Our findings demonstrate the importance of repeated behavioural testing (both between and within experiments) and contribute to a growing body of literature evaluating the effects of fluoxetine and other pharmaceuticals on animal behaviour.

Naltrexone increases negatively-valenced facial responses to happy faces in female participants

Positive social cues, like happy facial expressions, activate the brain's reward system and indicate interest in social affiliation. Facial mimicry of emotions, which is the predominantly automatic and unconscious imitation of another person's facial expression, has been shown to promote social affiliation. It has been demonstrated repeatedly that the opioid system is vital to social affiliation in rodents, but there is less evidence in humans. We investigated whether a 50mg administration of naltrexone, an opioid antagonist with highest affinity for the mu-opioid system, modulates emotional mimicry. A passive viewing task with dynamic facial expressions was used in a randomized placebo controlled between-subjects design. Mimicry was measured with electromyography (EMG) on three facial muscles, the corrugator supercilii and the depressor jaw muscle, associated with negatively-valenced emotions, and the zygomaticus major, which is activated during smiling. The results demonstrate an increase of negatively-valenced facial responses (corrugator and depressor) to happy facial expressions after naltrexone compared to placebo, consistent with lowered interest in social interaction or affiliation. Our findings provide evidence for a role of the opioid system in modulating automatic behavioral responses to cues of reward and social interaction, and translate to rodent models of the mu-opioid system and social affiliation.