Rats, like humans, avoid actions that can cause pain to their fellow beings, scientists have found.
This trait, known as harm aversion, is seen as an important part of moral development in humans but is reduced in violent antisocial individuals.
Researchers believe their findings, published in the journal Current Biology, could help scientists develop new drug treatments to increase harm aversion in patients who show psychopathic behaviour.
Professor Christian Keysers, study group leader at the Netherlands Institute for Neuroscience (NIN), said: “We share a mechanism that prevents antisocial behaviour with rats, which is extremely exciting to me.
“We can now use all the powerful tools of brain science to explore how to increase harm aversion in antisocial patients.”
To investigate harm aversion in rats, the researchers gave them a choice between two levers they could press to receive sugary treats.
Once the animals developed a preference for one of the two levers, the scientists reconfigured the system so that pressing the favourite lever would also cause the rat in the next cage to receive an unpleasant shock while the treat was being dispensed.
When the fellow rodents reacted by squeaking their protest, the rats stopped using their preferred lever.
Dr Julen Hernandez-Lallement, first author of the study and a researcher at the NIN, said: “Much like humans, rats actually find it aversive to cause harm to others.”
The researchers then scanned the brains of rats and found a region of the brain, known as the anterior cingulate cortex, to become active.
This same brain region has also been found to light up in people empathising with the pain of others.
The team then reduced brain activity in the same brain region in the rodents by injecting a local anaesthetic and found the animals “stopped avoiding harming fellow rats for sweet treats”.
Dr Valeria Gazzola, one of the senior authors of the study and also group leader at the NIN, said: “That humans and rats use the same brain region to prevent harm to others is striking.
“It shows that the moral motivation that keeps us from harming our fellow humans is evolutionary old, deeply ingrained in the biology of our brain and shared with other animals.”