Introduction

The Anterior cingulate cortex (ACC) is a collar-like structure that wraps around the corpus callosum, in the middle portion of the brain. It is associated with control over empathy, pain, and witnessing pain in other beings (Lockwood 2016). Oxytocin (OT), a hormone produced in the pituitary gland, is an important regulator of social bonding in animals that have complex social structure, like the prairie vole (Bosch & Young 2018). OT receptors in the ACC will bind in a diverse range of social situations: pair-bonding, parental-child bonding, and when witnessing group members in pain or in distress (Preckel et al. 2015). When prairie voles witness members of their social group subjected to stressors, Burkett and their team observed a distinct display of consoling-like behavior. These findings represent a commonality between humans and less cognitively advanced animals, contrasting with the notion that only highly intelligent animals experience empathy. The process of feeling empathy may be an evolutionarily conserved neurological pathway shared by animals that live socially in groups. Studying empathy in non-human species may grant insight into the evolution of social behavior in humans.

Empathy, as defined by humans, is the ability for an animal to understand the pain and suffering of others based on their own experiences—something thought to be absent in rodents (Chen 2018). For Burkett’s team, empathy for most rodents was determined to be licking and grooming directed at the stressed individual (Burkett et al. 2016). Disruptions in the release of oxytocin, or the use of drugs that block the binding of oxytocin in the ACC, often results in ambivalence towards other members of the social group (Preckel et al. 2015). Therefore, a healthy social life requires the input of OT into the ACC to form, maintain and strengthen social connections between individuals and express empathy for the suffering of others (Panksepp & Panksepp 2013).

Methods

In the experiment, twenty-four pairs of unstressed male and female voles were assigned observers or demonstrators of stress. Kept in separate parts of the cage by a clear plastic wall, one demonstrator vole was simply left alone in confinement as a control. The other was given stressors in the form of noise paired with light foot shocks given over twenty-four minutes. On reuniting with the observer vole, the behavior between the two animals was observed for displays of consolation and natural responses—quantitatively, consolation was measured as periods of time spent licking and grooming the demonstrator vole. A second experiment with twelve pairs of voles tested responses to thirty-second conditioned stimulus. The observer voles  and demonstrator voles were not separated. Freezing responses by the demonstrators to the conditioned stimulus was measured alongside similar responses from the observers (Burkett et al. 2016).

Results

Prairie voles demonstrated an increased amount of consolation behavior towards the individuals that received the stressor than those that were simply left in isolation. This behavior was cross-examined with a similar species, the meadow vole. Meadow vole observers did not express any changes in behavior based on the stress of the demonstrator, unlike prairie voles. Burkett’s team established that the act of grooming from the observer voles after the application of stressors reduced anxiety in the demonstrator voles. Stressed voles that did not undergo consolation grooming from observer voles remained in a higher state of anxiety when compared to the control group. Stressed demonstrator individuals showed no changes in the amount of social grooming given to others, suggesting this is not a stress-coping, generalized behavior for this species. Animals separated with a clear barrier able to witness the demonstrator’s stress evoked a stronger response measured in the plasma corticosterone, a stress marker in the blood, than with no barrier or an opaque barrier. Voles given an Oxytocin-receptor antagonist injected into the cerebral ventricles of observers prior to the experiment demonstrated no consolation-based grooming to stressed, familiar demonstrators. (Burkett et al. 2016). 

Emotion contagion, the idea that emotional states of individuals can affect others, was examined in the second experiment. When conditioned to the stimulus, stressed demonstrator individuals’ freezing responses inspired similar, but lesser in severity, freezing responses in observer social members. Prairie voles also demonstrated specificity towards reacting to familiar voles’ stress rather than to an unfamiliar stranger’s stress. Heightened stress responses were present in the observer voles and showed that prairie voles are not ambivalent towards the demonstrator’s stress—when a conditioned stimulus was received, both the observer and demonstrator froze in a coordinated fear response. When paired with unfamiliar stranger demonstrators, there was no response to the demonstrator’s reaction to the stimulus (Burkett et al. 2016).

Discussion

Prairie voles, as demonstrated in Burkett’s experiments, are capable of complex social behavior that clearly distinguishes the suffering of familiar individuals from strangers. These animals are more than capable of engaging in empathy in response to other’s suffering—a behavior long assumed to be present in mainly in humans (Riess 2017). Blocking the binding of OT in the ACC, reduced the vole’s ability to display pro-social behaviors like consolation (Burkett et al. 2016). The significance of this finding is important: humans with psychiatric conditions that display inability to form healthy social bonds, or those with conditions like Autism Spectrum Disorder, benefit from the administration of OT (Andari et al. 2010). When taken intranasally, OT improves the subject’s ability to read emotions in others better (Domes et al. 2007). Empathy is clearly identifiable based on activity in the ACC (Lamm et al. 2011). This region of the brain contains a high density of OT-receptors, linking the concept of empathy and emotion to the presence of OT—with OT-receptors being a big driver of complex social behaviors ranging from empathy, trust, and maternal instinct (Jurek and Neumann 2018). Since the prairie vole is capable of empathy, it is a valuable model to test the intricacies of the behavior and the development of empathy in more complex organisms.

[+] References

[+] Other Work By Kelly Stewart