۱- Introduction

۲- Traditional rodent models of emotional contagion

۳- Vicarious social defeat

۴- Social defeat stress crossover

۵- Conclusion

References

Abstract

Stressful experiences can be transmitted among individuals through social interactions. Like humans, rodents are social creatures whose behavior and physiology can be influenced by the emotional state of fellow rodents. This paper will review rodent studies which have explored two conditions of potential social stress contagion using the social defeat paradigm. In the vicarious social defeat model, mice and rats that witness a conspecific being socially defeated exhibit physiological stress responses and develop a host of depressive- and anxiety-like behavioral deficits. Likewise, social interaction with a stressed partner in the aftermath of social defeat stress results in physiological stress responses and social avoidance behavior. After summarizing the existing literature on this newly emerging area of social defeat stress contagion in rodents, we will discuss the potential utility of these rodent models for investigating the neurobiological processes and sensory channels of information that allow for the spread of psychophysiological effects of stress across individuals.

Introduction

Emotional contagion, a term coined by psychology professor Elaine Hatfield (Hatfield et al., 1993), has been construed as a simple or automatic process in which one simply “catches” aspects of another person’s emotional state, producing similar affective and physiological responses that result directly from the observation (Hatfield et al., 1993; Hoffman, 2000). Findings of brain regions with mirror properties that are active when individuals perform an action as well as when they observe others perform the same or similar actions have fueled speculations about neural mechanisms underlying the social sharing of emotions (Ferrari and Rizzolatti, 2014; Iacoboni et al., 1999). Specifically, within the social domain, mirroring would occur when the same neurons are activated by emotions experienced directly and by observing/interacting with others who are experiencing emotions (Carr et al., 2003; Rizzolatti et al., 2001; Wicker et al., 2001). Emotional contagion, also known as the “resonance” of emotions among individuals, may form the basis – together with more complex processes – for a full capacity for empathy (Preston and de Waal, 2002). Such capacity has been long considered uniquely human. However, studies in nonhuman primates (e.g., Palagi et al., 2014), pigs (e.g., Reimert et al., 2013), dogs (e.g., Huber et al., 2017) and rodents (e.g., Atsak et al., 2011) have shown that emotional contagion exists across species, does not require advanced cognitive capabilities, and is crucial to successfully navigate the social environment (Decety and Lamm, 2009; Panksepp and Panksepp, 2013). Recent years have witnessed growing interest in the study of “empathic stress” or “stress contagion” or “stress resonance”, as it has been variably called in human studies (Engert et al., 2019; White and Buchanan, 2016). Indeed, stress often occurs in social settings and can be transmitted among individuals as a consequence of social interactions in dyads and groups. Such “contagious stress” may induce emotional and physiological responses also in those who are not directly exposed to the stressor and may ultimately represent an additional pathway to the deleterious mental and physical consequences associated with stress exposure, beyond the daily stressors experienced firsthand.