Emotional contagion: Improving survival by preparing for socially sensed threats

Serotonin release in the habenula during emotional contagion promotes resilience

Negative emotional contagion-witnessing others in distress-affects an individual's emotional responsivity. However, whether it shapes coping strategies when facing future threats remains unknown. We found that mice that briefly observe a conspecific being harmed become resilient, withstanding behavioral despair after an adverse experience. Photometric recordings during negative emotional contagion revealed increased serotonin (5-HT) release in the lateral habenula. Whereas 5-HT and emotional contagion reduced habenular burst firing, limiting 5-HT synthesis prevented burst plasticity. Enhancing raphe-to-habenula 5-HT was sufficient to recapitulate resilience. In contrast, reducing 5-HT release in the habenula made witnessing a conspecific in distress ineffective to promote the resilient phenotype after adversity. These findings reveal that 5-HT supports vicarious emotions and leads to resilience by tuning definite patterns of habenular neuronal activity.

Individual Differences in Volitional Social Self-Administration and Motivation in Male and Female Mice Following Social Stress

BACKGROUND

A key challenge in developing treatments for neuropsychiatric illness is the disconnect between preclinical models and the complexity of human social behavior. We integrate voluntary social self-administration into a rodent model of social stress as a platform for the identification of fundamental brain and behavior mechanisms underlying stress-induced individual differences in social motivation.

METHODS

Here, we introduced an operant social stress procedure in male and female mice composed of 3 phases: 1) social self-administration training, 2) social stress exposure concurrent with reinforced self-administration testing, and 3) poststress operant testing under nonreinforced and reinforced conditions. We used social-defeat and witness-defeat stress in male and female mice.

RESULTS

Social defeat attenuated social reward seeking in males but not females, whereas witness defeat had no effect in males but promoted seeking behavior in females. We resolved social stress-induced changes to social motivation by aggregating z-scored operant metrics into a cumulative social index score to describe the spectrum of individual differences exhibited during operant social stress. Clustering does not adequately describe the relative distributions of social motivation following stress and is better described as a nonbinary behavioral distribution defined by the social index score, capturing a dynamic range of stress-related alterations in social motivation inclusive of sex as a biological variable.

CONCLUSIONS

We demonstrated that operant social stress can detect stable individual differences in stress-induced changes to social motivation. The inclusion of volitional behavior in social procedures may enhance the understanding of behavioral adaptations that promote stress resiliency and their mechanisms under more naturalistic conditions.

Psychopathy and gaze cueing

BACKGROUND AND OBJECTIVES

Psychopathic traits - and especially callous affective features - have been linked to altered processing of others' emotional expressions, and to reduced attention to the eyes. Despite the importance of gaze cueing (i.e., the tendency to orient attention toward where someone else is looking) for social functioning, few studies have investigated relationships between psychopathic traits and gaze cueing, and whether facial emotional expression influence these relationships, obtaining mixed results. To address this gap, the present study aimed to evaluate associations between psychopathic traits and gaze cueing for emotional and neutral expressions.

METHODS

65 non-clinical male participants (Mage = 27.3 years) completed two self-report measures of psychopathy and performed laboratory tasks to assess gaze-cueing for emotional vs. neutral faces and an arrow-cueing task as a comparison.

RESULTS

Linear mixed models showed no significant associations of emotional (versus neutral) expressions, or psychopathy trait dimensions, with either gaze cueing or arrow cueing.

LIMITATIONS

Reliance on a convenience sample of non-clinical men, assessed with self-reports measures of psychopathy, and using static emotional stimuli limit the generalizability of our findings.

CONCLUSIONS

Findings suggest that psychopathic traits are not associated with individual differences in following others' gaze to direct attention, and that there was no advantage for affective relative to neutral expressions.

Interpersonal physiological and psychological synchrony predict the social transmission of nocebo hyperalgesia between individuals

Witnessing another's pain can heighten pain in the observer. However, research has focused on the observer's intrapersonal experience. Here, a social transmission-chain explored the spread of socially-acquired nocebo hyperalgesia. Dyads of genuine participants were randomised to 'Generations' (G1-G3). G1-Demonstrators, observed by G2-Observers, experienced high/low thermal pain contingent on supposed activity/inactivity of a sham-treatment. G2 became Demonstrators, witnessed by G3-Observers. They experienced fixed low-temperature stimuli irrespective of sham-treatment 'activity'. G3 then Demonstrated for G4-Observers (a confederate), also experiencing low-temperature stimuli only. Pain ratings, electrodermal activity, and facial action units were measured. G1's treatment-related pain propagated throughout the chain. G2 and G3 participants showed heightened subjective and physiological response to sham-treatment, despite equivalent stimulus temperatures, and G3 never witnessing the initial pain-event. Dyadic interpersonal physiological synchrony (electrodermal activity) and psychological synchrony (Observer's ability to predict the Demonstrator's pain), predicted subsequent socially-acquired pain. Implications relate to the interpersonal spread of maladaptive pain experiences.

Emotion contagion and physiological synchrony: The more intimate relationships, the more contagion of positive emotions

The study aimed to explore how interpersonal closeness (friends vs. strangers) and emotion type (positive vs. negative) influenced emotion contagion and physiological synchrony between interacting partners. Twenty-eight friend dyads (n = 56) and 29 stranger dyads (n = 58) participated in an emotion contagion laboratory task. In each dyad, one participant, the 'sender', was randomly asked to watch a film clip (neutral, positive, or negative), while their partner, the 'observer' passively observed the sender's facial expressions. Participants' electrocardiograms (ECG) and facial electromyography (EMG) signals were recorded using the BIOPAC system. Results revealed that observing the sender's facial expressions led to the observer's spontaneous mimicry and emotional contagion, accompanied by enhanced physiological synchrony between interacting partners. In the positive emotion condition, the observers reported more positive emotions and displayed stronger zygomaticus major activity in friend dyads than in stranger dyads. Greater physiological synchrony (heart rate and heart rate variability) between interacting partners was also observed in friend dyads than in stranger dyads in the positive emotion condition. These results indicate that positive emotion contagion is more likely to occur between close partners than negative emotion contagion.

Vicarious Emotions of Fear and Pain in Rodents

Affective empathy, the ability to share the emotions of others, is an important contributor to the richness of our emotional experiences. Here, we review evidence that rodents show signs of fear and pain when they witness the fear and pain of others. This emotional contagion creates a vicarious emotion in the witness that mirrors some level of detail of the emotion of the demonstrator, including its valence and the vicinity of threats, and depends on brain regions such as the cingulate, amygdala, and insula that are also at the core of human empathy. Although it remains impossible to directly know how witnessing the distress of others feels for rodents, and whether this feeling is similar to the empathy humans experience, the similarity in neural structures suggests some analogies in emotional experience across rodents and humans. These neural homologies also reveal that feeling distress while others are distressed must serve an evolutionary purpose strong enough to warrant its stability across ~ 100 millions of years. We propose that it does so by allowing observers to set in motion the very emotions that have evolved to prepare them to deal with threats - with the benefit of triggering them socially, by harnessing conspecifics as sentinels, before the witness personally faces that threat. Finally, we discuss evidence that rodents can engage in prosocial behaviors that may be motivated by vicarious distress or reward.

Sharing Positive Affective States Amongst Rodents

Group living is thought to benefit from the ability to empathize with others. Much attention has been paid to empathy for the pain of others as an inhibitor of aggression. Empathizing with the positive affect of others has received less attention although it could promote helping by making it vicariously rewarding. Here, we review this latter, nascent literature to show that three components of the ability to empathize with positive emotions are already present in rodents, namely, the ability to perceive, share, and prefer actions that promote positive emotional states of conspecifics. While it has often been argued that empathy evolved as a motivation to care for others, we argue that these tendencies may have selfish benefits that could have stabilized their evolution: approaching others in a positive state can provide information about the source of valuable resources; becoming calmer and optimistic around animals in a calm or positive mood can help adapt to the socially sensed safety level in the environment; and preferring actions also benefiting others can optimize foraging, reduce aggression, and trigger reciprocity. Together, these findings illustrate an emerging field shedding light on the emotional world of rodents and on the biology and evolution of our ability to cooperate in groups.

Anterior cingulate cortex, but not amygdala, modulates the anxiogenesis induced by living with conspecifics subjected to chronic restraint stress in male mice

Cohabitation with a partner undergoing chronic restraint stress (CRE) induces anxiogenic-like behaviors through emotional contagion. We hypothesized that the anterior cingulate cortex (ACC) and the amygdala would be involved in the modulation of this emotional process. This study investigated the role of the ACC and amygdala in empathy-like behavior (e.g., anxiety-like responses) induced by living with a mouse subjected to CRE. Male Swiss mice were housed in pairs for 14 days and then allocated into two groups: cagemate stress (one animal of the pair was subjected to 14 days of restraint stress) and cagemate control (no animal experienced stress). Twenty-four hours after the last stress session, cagemates had their brains removed for recording FosB labeling in the ACC and amygdala (Exp.1). In experiments 2 and 3, 24 h after the last stress session, the cagemates received 0.1 μL of saline or cobalt chloride (CoCl₂ 1 mM) into the ACC or amygdala, and then exposed to the elevated plus-maze (EPM) for recording anxiety. Results showed a decrease of FosB labeling in the ACC without changing immunofluorescence in the amygdala of stress cagemate mice. Cohabitation with mice subjected to CRE provoked anxiogenic-like behaviors. Local inactivation of ACC (but not the amygdala) reversed the anxiogenic-like effects induced by cohabitation with a partner undergoing CRE. These results suggest the involvement of ACC, but not the amygdala, in anxiety induced by emotional contagion.

Why help others? Insights from rodent to human early childhood research

Helping behavior are actions aiming at assisting another individual in need or to relieve their distress. The occurrence of this behavior not only depends on automated physiological mechanisms, such as imitation or emotional contagion, that is, the individual's emotion and physiological state matching with others, but also needs motivation to sustain. From a comparative and developmental perspective, we discover that the motivation for helping behavior has a deep foundation both phylogenetically and ontogenetically. For example, empathic concern for others, relieving personal distress and the desire for social contact are universal motivations across rodents, non-human primates and human early childhoods. Therefore, a circle-layered model integrating evidences for motivation for helping behavior from rodent to human early childhood research is proposed: the inner circle contains the emotional-behavioral system and the outer circle contains the affective-cognitive system. The application of this model has significance for both behavioral neuroscience research and cultivating prosocial behavior in human society.

Tickle contagion in the rat somatosensory cortex

The cellular mechanisms of emotional contagion are unknown. We investigated tickle contagion and the underlying neuronal representations in playful rats. We recorded trunk somatosensory cortex activity of observer rats while they received tickling and audiovisual playback of tickling footage and while they witnessed tickling of demonstrator rats. Observers vocalized and showed "Freudensprünge" ("joy jumps") during witnessing live tickling, while they showed little behavioral responses to playbacks. Deep layers in the trunk somatosensory neurons showed a larger correlation between direct and witnessed tickling responses compared to superficial layers. Trunk somatosensory neurons discharged upon emission of own and demonstrator's vocalizations and might drive contagious "laughter". We conclude that trunk somatosensory cortex might represent ticklishness contagion.

What's familiarity got to do with it? Neural mechanisms of observational fear in siblings and strangers

Social modulation of pain sensitivity is considered part of the empathic response. In this issue of Neuron, Zhang at al. (2022) uncover the neurobiological basis of observational pain in mice. They report increased synaptic transmission from the insular cortex to the basolateral amygdala and explore genes mediating this effect.

Emotional contagion and prosocial behavior in rodents

Empathy is critical to adjusting our behavior to the state of others. The past decade dramatically deepened our understanding of the biological origin of this capacity. We now understand that rodents robustly show emotional contagion for the distress of others via neural structures homologous to those involved in human empathy. Their propensity to approach others in distress strengthens this effect. Although rodents can also learn to favor behaviors that benefit others via structures overlapping with those of emotional contagion, they do so less reliably and more selectively. Together, this suggests evolution selected mechanisms for emotional contagion to prepare animals for dangers by using others as sentinels. Such shared emotions additionally can, under certain circumstances, promote prosocial behavior.