Abstract
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.
Highlights
Interacting with individuals displaying certain emotional states can elicit similar states in other group members
When we compared the effect of the social context on the behavior of the treated subject, we observed that swimming alone or in a group remarkably altered the average distance from the bottom of vehicle-treated individuals but not of Citalopram-treated ones as indicated by the significant social context x Citalopram administration interaction (F(2,64) = 5.535; p < 0.050) and further confirmed by post hoc analyses
Post hoc analyses revealed that vehicle-treated subjects swam closer to the bottom when they were in groups rather than alone (p < 0.001; Figure 2). This effect was absent for 30 mg/L (p = 0.931) indicating that the presence of a shoal did not alter the behavior of the focal fish when treated with Citalopram for this concentration
Summary
Interacting with individuals displaying certain emotional states can elicit similar states in other group members This phenomenon is known as emotional contagion and is known to be of paramount importance to understand the underpinnings of cognition, emotion, and behavior (Hatfield et al, 1994; Von Scheve and Salmella, 2014). In early experiments with Rhesus macaques (Mirsky et al, 1958; Miller et al, 1963), it was found that fear induced by a conspecific can be transmitted to observer monkeys in a separate cage These early findings were mechanistically backed by the discovery of mirror neurons, a set of neurons that fire when a monkey observes an action performed by another individual (Ferrari et al, 2003)
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