Prairie voles are fuzzy little critters that live in and around the Great Plains of the United States. If you own a garden in Kansas, it's not improbable that you despise them, and you may even have commissioned a hawk - or other predator - to scare them away.

Luckily for the vole, if such measures are taken and a predator is set after them, they'll always have someone to console them at home, provided they survive the attack in question.

Researchers at Emory University say prairie voles show empathy with their mates, especially when they are aware that their partner has gone through a rough patch.

If you separate two mates and subject one of them to electric shocks, the other consoles its shocked partner when they reunite, the researchers claimed in study published Thursday in Science.

Two kinds of empathy

That animals can display empathy is nothing new; this has been well documented in crows, dolphins, elephants, dogs, and certain kinds of apes. However, these are all intelligent species compared to the prairie vole, and this could be why this study is so groundbreaking, says co-author Frans de Waal, who specializes in primate behavior at Emory.

"Previous explanations of empathy have been quite cognitive and complex. The new study shows that reactions to the distress of others are very basic... and rest on a matching mechanism known as emotional contagion, whereby the observer is stressed by seeing stress in the other."

"But this doesn't suggest that voles experience empathy in the same was as us," Larry Young, head of the Emory laboratory, where the study was conducted, said.

The two different types of empathy are distinguished by varying levels of cognition. The empathy displayed by elephants or apes, for instance, suggests an ability to understand or identify cognitively with another's state.

With voles, the empathy is of an emotional nature: It is felt - and not understood.

When the voles were separated, the same level of the stress hormone corticosterone was found in the blood of the observing vole as its stressed partner. This strongly suggests the presence of what behavioral neuroscientists call emotional contagion, and which de Waal called the "very driver" of empathy.

"Empathy without being sensitive to the emotional state of others does not exist. The voles reacted to the stress of the other by being stressed themselves, but then instead of acting on their own stress, they groom the partner, hence showing an other-directed response - typical of empathy."

Oxytocin - the missing link?

De Waal, a Dutch scientist who claims to have discovered empathy in chimpanzees in the 1970s, said the present study provided solid neuroscience to back up his observations based on behavioral data.

The team at Emory said it could control the consoling of the voles by manipulating oxytocin, which is a neurotransmitter in humans known as the "cuddling hormone." When the researchers injected the observing vole with a drug that blocked oxytocin secretion, there was no consolation - no licking, grooming or petting - of the stressed partner.

And it's this aspect of the study, de Waal concluded, namely that rodents depend on the same neurotransmitter to induce empathy and consolation as primates and humans, which could have far-reaching consequences for future research.

"Neuroscience on rodents is much easier and less ethically controversial than on primates or humans, so this step is important."