A new study reveals that prairie voles console loved ones who are feeling stressed -- and it appears that the infamous "love hormone," oxytocin, is the underlying mechanism. Until now, consolation behavior has only been documented in a few nonhuman species with high levels of sociality and cognition, such as elephants, dolphins and dogs.

Prairie voles are particularly social rodents, causing them to be the focus of many studies. This led James Burkett and colleagues to explore their potential for empathy-motivated behaviors.

The researchers created an experiment where relatives and known individuals were temporarily isolated from each other, while one was exposed to mild shocks. Upon reunion, the non-stressed prairie voles proceeded to lick the stressed voles sooner and for longer durations, compared to a control scenario where individuals were separated but neither was exposed to a stressor.

Measurements of hormone levels revealed that the family members and friends were distressed when they could not comfort their loved one.

The fact that consoling behavior occurred only between those who were familiar with each other -- including non-kin members -- but not strangers, demonstrates that the behavior is not simply a reaction to aversive cues, the authors note.

Since the oxytocin receptor is associated with empathy in humans, Burkett et al. blocked this neurotransmitter in prairie voles in a series of similar consolation experiments. Blocking oxytocin did not cause family members and friends to alter their self-grooming behavior, yet they did cease consoling each other.

These findings provide new insights into the mechanisms of empathy and the evolution of complex empathy-motivated behaviors.