Emotional contagion in nonhuman animals: A review

Anxiolytic treatment of a trapped rat reduces helping and anxiogenic treatment increases helping: Evidence for emotional contagion in altruism

The present experiment used the trapped rat model to explore whether pharmacological manipulation of distress affects the likelihood of helping behavior. 120 Sprague-Dawley rats (30 male pairs and 30 female pairs) completed 12 consecutive, daily trials assessing helping behavior. During an individual trial, a trapped rat was placed in a restrainer in the center of an open field, while its cagemate could move around freely and possibly open the restrainer by lifting a door. Trapped rats received an intraperitoneal injection of either 1) physiological saline, 2) the anxiolytic midazolam (1.5 mg/kg), or 3) the anxiogenic yohimbine (2.5 mg/kg) 30 min prior to the start of each trial. Dependent variables measured were: 1) door opening latency (sec), 2) percentage of trials in which a door opening occurred, and 3) the number of free rats classified as "openers." Based on emotional contagion theory, we predicted that 1) free rats paired with midazolam-subjects would show attenuated helping behavior (e.g., higher door opening latency) compared to controls, and conversely 2) free rats paired with yohimbine-subjects would show enhanced helping behavior. First, a significant sex-difference was observed, in that more females were classified as openers than males. This supports previous evidence that females express higher altruistic motivation and experience stronger emotional contagion than males. Second, midazolam-treatment significantly attenuated helping behavior. From trials 4-12, free rats paired with midazolam-subjects expressed slower door opening latencies compared to controls. Third, yohimbine-treatment significantly increased helping behavior (e.g., reduced door opening latencies) - but only on trials 1-3; by trials 9-12, this pattern was reversed. These results are consistent with emotional contagion theory and indicate that intensity of distress directly modulates altruistic motivation through vicarious state-matching.

Prosocial behaviors in rodents

Prosocial behaviors (i.e., actions that benefit others) are central for social interactions in humans and other animals, by fostering social bonding and cohesion. To study prosociality in rodents, scientists have developed behavioral paradigms where animals can display actions that benefit conspecifics in distress or need. These paradigms have provided insights into the role of social interactions and transfer of emotional states in the expression of prosociality, and increased knowledge of its neural bases. However, prosociality levels are variable: not all tested animals are prosocial. Such variation has been linked to differences in animals' ability to process another's state as well as to contextual factors. Moreover, evidence suggests that prosocial behaviors involve the orchestrated activity of multiple brain regions and neuromodulators. This review aims to synthesize findings across paradigms both at the level of behavior and neural mechanisms. Growing evidence confirms that these processes can be studied in rodents, and intense research in the past years is rapidly advancing our knowledge. We discuss a strong bias in the field towards the study of these processes in negative valence contexts (e.g., pain, fear, stress), which should be taken as an opportunity to open new venues for future research.

Environmental complexity impacts anxiety in broiler chickens depending on genetic strain and body weight

The objective was to assess the impact of environmental complexity on affective state (anxiety) in fast- and slow-growing broilers (Gallus gallus domesticus) as they gain weight. Six hundred fast-growing broilers (Ross 708; "fast-growers") and 600 slow-growing broilers (Hubbard Redbro Mini; "slow-growers") were raised in 24 pens with simple (standard; SE) or complex (permanent and temporary enrichments; CE) environments. Six birds/pen underwent the attention bias test on day 23 (fast-growers only), 28-29, 35-36, 42-43, and 56-57 (slow-growers only), with individuals only tested once (n = 576). Proportion of birds feeding, time spent vigilant and latencies to eat and step were recorded. Greater vigilance and longer latencies indicate more anxiety. Slow-growers fed more (p = 0.001), were less vigilant (p = 0.003), and stepped sooner than fast-growers (p = 0.007). For both strains, likelihood of feeding was unrelated to weight in SE, but decreased with increasing weight in CE (p = 0.048). Birds in CE stepped sooner than birds in SE (p = 0.030). Vigilance increased with body weight (p = 0.024). These results indicate that affective state (anxiety) can change as birds gain weight, depending on environmental complexity and genetic strain. Overall, slow-growers showed reduced anxiety compared to fast-growers, across housing treatments or weights.

Do sheep (Ovis aries) discriminate human emotional odors?

While sheep can detect and discriminate human emotions through visual and vocal cues, their reaction to human body odors remains unknown. The present study aimed to determine whether sheep (Ovis aries) can detect human odors, olfactorily discriminate stressed from non-stressed individuals, and behave accordingly based on the emotional valence of the odors. Axillary secretions from 34 students were collected following an oral examination (stress odor) or a regular class (non-stress odor). Fourteen female and 15 male lambs were then exposed to these odors through a habituation-dishabituation procedure. The habituation stimulus was presented four times for one minute, followed by the dishabituation stimulus presented once for one minute. Behavioral variables included spatiality relative to target odors, approach/withdrawal, ear positioning, sniffing, ingestion, and vocalization. Both female and male lambs more often positioned their ears backwards/forwards, and asymmetrically when exposed to the dishabituation stimulus, but regardless of their stress or non-stress value. They also changed their approach behavior when exposed to the dishabituation stimuli. Lambs displayed some behavioral signs of discrimination between the habituation and dishabituation odors, but regardless of their relation to stress or non-stress of human donors. In sum, this exploratory study suggests that young sheep respond negatively to the odor of unfamiliar humans, without showing any specific emotional contagion related to the stress odor. This exploratory study suggests young ovines can detect human body odor, a further step toward understanding the human-sheep relationship.

Physiological state matching in a pair bonded poison frog

More than a century ago, Charles Darwin hypothesized that the empathy-like phenotype is a phylogenetically widespread phenomenon. This idea remains contentious, due to the challenges of empirically examining emotions, and few investigations among non-mammalian vertebrates. We provide support for Darwin's hypothesis by discovering partial evidence for the most ancestral form of empathy, emotional contagion (i.e. matching another individual's emotional state), in the pair bonding mimetic poison frog, Ranitomeya imitator. We found that male corticosterone, a physiological biomarker of stress, positively correlates with female partners in experimental and semi-natural conditions. This does not appear to coincide with behavioural state-matching. However, it is specific to female partners relative to familiar female non-partners, and is independent of effects that commonly confound studies on emotional contagion. Furthermore, this physiological state-matching is irrespective of partnership longevity or lifetime reproductive output. These results physiologically indicate socially selective emotional contagion in a monogamous amphibian, and paradigms that elicit coinciding neural and behavioural indicators and morphogenic co-variation are needed for further corroboration. Further studies on ancestral forms of empathy in non-mammalian vertebrates are warranted.

Emotional contagion in a collective ritual

Collective gatherings are often associated with the alignment of psychophysiological states between members of a crowd. While the process of emotional contagion has been studied extensively in dyads as well as at the population level, our understanding of its operation and dynamics as they unfold in real time in real-world group contexts remains limited. Employing a naturalistic design, we investigated emotional contagion in a public religious ritual by examining the relationship between interpersonal distance and autonomic arousal. We found that proximity in space was associated with heightened affective synchrony between participants in the context of the emotionally laden ritual (a Hindu procession) compared with an unstructured walk along the same route performed by the same group. Our findings contribute to the understanding of collective emotions and their underlying psychophysiological mechanisms, emphasizing the role of cultural practices in shaping collective emotional experiences.

How and Why People Synchronize: An Integrated Perspective

Academic AbstractInterpersonal synchrony, the alignment of behavior and/or physiology during interactions, is a pervasive phenomenon observed in diverse social contexts. Here we synthesize across contexts and behaviors to classify the different forms and functions of synchrony. We provide a concise framework for classifying the manifold forms of synchrony along six dimensions: periodicity, discreteness, spatial similarity, directionality, leader-follower dynamics, and observability. We also distill the various proposed functions of interpersonal synchrony into four interconnected functions: reducing complexity and improving understanding, accomplishing joint tasks, strengthening social connection, and influencing partners' behavior. These functions derive from first principles, emerge from each other, and are accomplished by some forms of synchrony more than others. Effective synchrony flexibly adapts to social goals and more synchrony is not always better. Our synthesis offers a shared framework and language for the field, allowing for better cross-context and cross-behavior comparisons, generating new hypotheses, and highlighting future research directions.

Calls of the little auk (Alle alle) chicks reflect their behavioural contexts

Animal vocalisations can often inform conspecifics about the behavioural context of production and the underlying affective states, hence revealing whether a situation should be approached or avoided. While this is particularly important for socially complex species, little is known about affective expression in wild colonial animals, and even less to about their young. We studied vocalisations of the little auk (Alle alle) chicks in the Hornsund breeding colony, Svalbard. Little auks are highly colonial seabirds, and adults convey complex behavioural contexts through their calls. We recorded chick calls during two contexts of opposite affective valence: handing by a human, and while they interact with their parents inside the nest. Using permuted discriminant function analysis and a series of linear mixed models, we examined the effect of the production context/associated affective valence on the acoustic parameters of those calls. Calls were reliably classified to their context, with over 97% accuracy. Calls uttered during handling had higher mean entropy, fundamental frequency, as well as lower spectral centre of gravity and a less steep spectral slope compared to calls produced during interactions with a parent inside the nest. The individuality of handling calls, assessed by information content, was lower than the individuality of calls uttered in the nest. These findings suggest that seabird chicks can effectively communicate behavioural/affective contexts through calls, conveying socially important messages early in development. Our results are mostly in line with emotional expression patterns observed across taxa, supporting their evolutionary continuity.

Audible pain squeaks can mediate emotional contagion across pre-exposed rats with a potential effect of auto-conditioning

Footshock self-experience enhances rodents' reactions to the distress of others. Here, we tested one potential mechanism supporting this phenomenon, namely that animals auto-condition to their own pain squeaks during shock pre-exposure. In Experiment 1, shock pre-exposure increased freezing and 22 kHz distress vocalizations while animals listened to the audible pain-squeaks of others. In Experiment 2 and 3, to test the auto-conditioning theory, we weakened the noxious pre-exposure stimulus not to trigger pain squeaks, and compared pre-exposure protocols in which we paired it with squeak playback against unpaired control conditions. Although all animals later showed fear responses to squeak playbacks, these were weaker than following typical pre-exposure (Experiment 1) and not stronger following paired than unpaired pre-exposure. Experiment 1 thus demonstrates the relevance of audible pain squeaks in the transmission of distress but Experiment 2 and 3 highlight the difficulty to test auto-conditioning: stimuli weak enough to decouple pain experience from hearing self-emitted squeaks are too weak to trigger the experience-dependent increase in fear transmission that we aimed to study. Although our results do not contradict the auto-conditioning hypothesis, they fail to disentangle it from sensitization effects. Future studies could temporarily deafen animals during pre-exposure to further test this hypothesis.

Horses discriminate between human facial and vocal expressions of sadness and joy

Communication of emotions plays a key role in intraspecific social interactions and likely in interspecific interactions. Several studies have shown that animals perceive human joy and anger, but few studies have examined other human emotions, such as sadness. In this study, we conducted a cross-modal experiment, in which we showed 28 horses two soundless videos simultaneously, one showing a sad, and one a joyful human face. These were accompanied by either a sad or joyful voice. The number of horses whose first look to the video that was incongruent with the voice was longer than their first look to the congruent video was higher than chance, suggesting that horses could form cross-modal representations of human joy and sadness. Moreover, horses were more attentive to the videos of joy and looked at them for longer, more frequently, and more rapidly than the videos of sadness. Their heart rates tended to increase when they heard joy and to decrease when they heard sadness. These results show that horses are able to discriminate facial and vocal expressions of joy and sadness and may form cross-modal representations of these emotions; they also are more attracted to joyful faces than to sad faces and seem to be more aroused by a joyful voice than a sad voice. Further studies are needed to better understand how horses perceive the range of human emotions, and we propose that future experiments include neutral stimuli as well as emotions with different arousal levels but a same valence.

Social zebrafish: Danio rerio as an emerging model in social neuroendocrinology

The fitness benefits of social life depend on the ability of animals to affiliate with others and form groups, on dominance hierarchies within groups that determine resource distribution, and on cognitive capacities for recognition, learning and information transfer. The evolution of these phenotypes is coupled with that of neuroendocrine mechanisms, but the causal link between the two remains underexplored. Growing evidence from our research group and others demonstrates that the tools available in zebrafish, Danio rerio, can markedly facilitate progress in this field. Here, we review this evidence and provide a synthesis of the state-of-the-art in this model system. We discuss the involvement of generalized motivation and cognitive components, neuroplasticity and functional connectivity across social decision-making brain areas, and how these are modulated chiefly by the oxytocin-vasopressin neuroendocrine system, but also by reward-pathway monoamine signaling and the effects of sex-hormones and stress physiology.

Autism-associated gene shank3 is necessary for social contagion in zebrafish

BACKGROUND

Animal models enable targeting autism-associated genes, such as the shank3 gene, to assess their impact on behavioural phenotypes. However, this is often limited to simple behaviours relevant for social interaction. Social contagion is a complex phenotype forming the basis of human empathic behaviour and involves attention to the behaviour of others for recognizing and sharing their emotional or affective state. Thus, it is a form of social communication, which constitutes the most common developmental impairment across autism spectrum disorders (ASD).

METHODS

Here we describe the development of a zebrafish model that identifies the neurocognitive mechanisms by which shank3 mutation drives deficits in social contagion. We used a CRISPR-Cas9 technique to generate mutations to the shank3a gene, a zebrafish paralogue found to present greater orthology and functional conservation relative to the human gene. Mutants were first compared to wild types during a two-phase protocol that involves the observation of two conflicting states, distress and neutral, and the later recall and discrimination of others when no longer presenting such differences. Then, the whole-brain expression of different neuroplasticity markers was compared between genotypes and their contribution to cluster-specific phenotypic variation was assessed.

RESULTS

The shank3 mutation markedly reduced social contagion via deficits in attention contributing to difficulties in recognising affective states. Also, the mutation changed the expression of neuronal plasticity genes. However, only downregulated neuroligins clustered with shank3a expression under a combined synaptogenesis component that contributed specifically to variation in attention.

LIMITATIONS

While zebrafish are extremely useful in identifying the role of shank3 mutations to composite social behaviour, they are unlikely to represent the full complexity of socio-cognitive and communication deficits presented by human ASD pathology. Moreover, zebrafish cannot represent the scaling up of these deficits to higher-order empathic and prosocial phenotypes seen in humans.

CONCLUSIONS

We demonstrate a causal link between the zebrafish orthologue of an ASD-associated gene and the attentional control of affect recognition and consequent social contagion. This models autistic affect-communication pathology in zebrafish and reveals a genetic attention-deficit mechanism, addressing the ongoing debate for such mechanisms accounting for emotion recognition difficulties in autistic individuals.

Effects of stress contagion on anxiogenic- and orofacial inflammatory pain-like behaviors with brain activation in mice

The conditions of stress contagion are induced in bystanders without direct experiences of stressful events. This study determined the effects of stress contagion on masseter muscle nociception in mice. Stress contagion was developed in the bystanders after cohabitating with a conspecific mouse subjected to social defeat stress for 10 days. On Day 11, stress contagion increased anxiety- and orofacial inflammatory pain-like behaviors. The c-Fos and FosB immunoreactivities evoked by masseter muscle stimulation were increased in the upper cervical spinal cord, while c-Fos expressions were increased in the rostral ventromedial medulla, including the lateral paragigantocellular reticular nucleus and nucleus raphe magnus in stress contagion mice. The level of serotonin in the rostral ventromedial medulla was increased under stress contagion, while the number of serotonin positive cells was increased in the lateral paragigantocellular reticular nucleus. Stress contagion increased c-Fos and FosB expressions in the anterior cingulate cortex and insular cortex, both of which were positively correlated with orofacial inflammatory pain-like behaviors. The level of brain-derived neurotrophic factor was increased in the insular cortex under stress contagion. These results indicate that stress contagion can cause neural changes in the brain, resulting in increased masseter muscle nociception, as seen in social defeat stress mice.

The spread of fear in an empathetic fish

An evolutionarily ancient signaling pathway mediates emotional contagion.

Evolutionarily conserved role of oxytocin in social fear contagion in zebrafish

Emotional contagion is the most ancestral form of empathy. We tested to what extent the proximate mechanisms of emotional contagion are evolutionarily conserved by assessing the role of oxytocin, known to regulate empathic behaviors in mammals, in social fear contagion in zebrafish. Using oxytocin and oxytocin receptor mutants, we show that oxytocin is both necessary and sufficient for observer zebrafish to imitate the distressed behavior of conspecific demonstrators. The brain regions associated with emotional contagion in zebrafish are homologous to those involved in the same process in rodents (e.g., striatum, lateral septum), receiving direct projections from oxytocinergic neurons located in the pre-optic area. Together, our results support an evolutionary conserved role for oxytocin as a key regulator of basic empathic behaviors across vertebrates.

"It Almost Makes Her Human": How Female Animal Guardians Construct Experiences of Cat and Dog Empathy

Understanding how humans perceive and construct experiences of non-human animal empathy (hereafter, 'animal/s') can provide important information to aid our understanding of how companion animals contribute to social support. This study investigates the phenomenology of animal empathy by examining how humans construct sense-making narratives of these experiences, with the hypothesis that anthropomorphic attributions would play a key role in these constructions. Comprehensive, semi-structured interviews were conducted with six participants, using established interpretative phenomenological analysis methodology to facilitate deep examination of how they interpreted and reacted emotionally. Participants were consistent in reporting changes to their companion animals' normal behaviour as the key to the identification of animal empathy experiences, yet they were highly paradoxical in their constructions of perceived internal drivers within their dogs and cats. Explanations were highly dichotomous, from highly anthropomorphic to highly anthropocentric, and these extremes were combined both within individual participant narratives and within some thematic constructs. This research demonstrates that experiences of companion animal empathy can be powerful and meaningful for humans, but the inconsistent mixture of anthropomorphic and anthropocentric reasoning illustrates the confused nature of human understanding of animals' internal states. Insight into how humans construct animal empathy has implications for the moral status of these animals and an application for companion animals used explicitly for social support, such as in animal-assisted therapy and emotional support animals.

Imitative and contagious behaviors in animals and their potential roles in the study of neurodevelopmental disorders

Social learning in the forms of imitative and contagious behaviors are essential for learning abilities and social interaction. However, children with neurodevelopmental disorders and intellectual disabilities show impairments in these behaviors, which profoundly affect their communication skills and cognitive functions. Although these deficits are well studied in humans, pre-clinical animal model assessments of imitative and contagious behavioral deficits are limited. Here, we first define various forms of social learning as well as their developmental and evolutionary significance in humans. We also explore the impact of imitative and contagious behavioral deficits in several neurodevelopmental disorders associated with autistic-like symptoms. Second, we highlight imitative and contagious behaviors observed in nonhuman primates and other social animals commonly used as models for neurodevelopmental disorders. Lastly, we conceptualize these behaviors in the contexts of mirror neuron activity, learning, and empathy, which are highly debated topics. Taken together, this review furthers the understanding of imitative and contagious behaviors. We hope to prompt and guide future behavioral studies in animal models of neurodevelopmental disorders.

Collective Emotional Contagion in Zebrafish

Seeking to match our emotional state with one of those around us is known as emotional contagion-a fundamental biological process that underlies social behavior across several species and taxa. While emotional contagion has been traditionally considered to be a prerogative of mammals and birds, recent findings are demonstrating otherwise. Here, we investigate emotional contagion in groups of zebrafish, a freshwater model species which is gaining momentum in preclinical studies. Zebrafish have high genetic homology to humans, and they exhibit a complex behavioral repertoire amenable to study social behavior. To investigate whether individual emotional states can be transmitted to group members, we pharmacologically modulated anxiety-related behaviors of a single fish through Citalopram administration and we assessed whether the altered emotional state spread to a group of four untreated conspecifics. By capitalizing upon our in-house developed tracking algorithm, we successfully preserved the identity of all the subjects and thoroughly described their individual and social behavioral phenotypes. In accordance with our predictions, we observed that Citalopram administration consistently reduced behavioral anxiety of the treated individual, in the form of reduced geotaxis, and that such a behavioral pattern readily generalized to the untreated subjects. A transfer entropy analysis of causal interactions within the group revealed that emotional contagion was directional, whereby the treated individual influenced untreated subjects, but not vice-versa. This study offers additional evidence that emotional contagion is biologically preserved in simpler living organisms amenable to preclinical investigations.

Mastering the scientific peer review process: tips for young authors from a young senior editor

Are you a student at a higher institution or an early-career researcher who is striving to understand and master the peer review process so to increase the odds of getting a paper published in the Journal of Forestry Research or another reputable, peer-reviewed, scientific journal? In this paper, a young, senior editor provides a handbook of the peer review process based on his decadal experience in scientific publishing. He covers major information you need to know during the entire process, from selecting journals to completing the proofing of your accepted paper. He introduces key points for consideration, such as avoidance of predatory journals, dubious research practices and ethics, interaction with peers, reviewers, and editors, and the pursuit of aretê. Finally, he points out some common statistical errors and misconceptions, such as P hacking and incorrect effect size inference. He hopes that this paper will enhance your understanding and knowledge of the peer-review process.