Calling someone a "rat" is no compliment, but a new study shows that rats actually are empathetic and will altruistically lend a helping paw to a cage mate who is stuck in a trap.
Not only will rats frantically work to free their trapped cage mate; they will do so even when there's a tempting little pile of chocolate chips nearby, the study reveals. Instead of leaving their pal in the trap and selfishly gobbling the candy all by themselves, rats will free their cage mate and share the chocolate.
"To me that's absolutely stunning," says neurobiologist Peggy Mason of the University of Chicago. "The fact that the rat does that is really amazing."
Mason and her colleagues designed a series of experiments, described in the journal Science, to explore the evolutionary roots of empathy.
They wanted to look at rats because they already knew, from previous work, that rodents can be emotionally affected by the emotions of their cage mates. For example, during lab procedures, mice seem to experience more pain when they see another mouse in pain.
This is called "emotional contagion," and humans have it too — just think of how one crying baby can make other babies cry. "But in the end, emotional contagion doesn't take you very far," says Mason. "It's an internal experience. It doesn't actually do anything for another individual."
Helping A Fellow Rat
So Mason and her colleagues devised a test to see if rats would take the next step and actually try to help out a fellow rat in distress. They took two cage mates, who knew each other, and trapped one of them in a narrow Plexiglas tube. That's a mild stressor and one the trapped rat doesn't like — it would sometimes make an alarm call.
The free rat outside of this tube seemed to immediately "get" the problem and would work to liberate its pal, says Mason.
The free rat would focus its activity on this plastic tube, crawling all over it and biting it, and interact with the trapped rat through little holes in the tube. "And if the trapped rat has a tail poking out, the free rat will actually grab that tail and kind of pull on it," says Mason.
Eventually, all this activity would lead to the free rat accidentally triggering a door that opened, releasing the trapped animal. The rats quickly learned to purposefully open the door, and during repeated experiments they would do so faster and faster — but only for a trapped rat. They didn't act this way when the plastic trap was empty or contained a toy rat.
Rats would free their pals even if the experiment was set up so that the other rat was released into a different cage, so that the two rats did not get to interact after the door was opened. This suggests that the door-opener was really trying to aid its fellow rat, and not just working to get a playmate.
A Helping Behavior
The researchers had a question for the rats: What is it worth to you, to free your fellow rat? "Obviously we can't ask that question verbally, so we wanted to ask it in terms that a rat can communicate to us," says Mason.
So the scientists used chocolate. They put rats into a cage that held two different clear plastic traps. One contained chocolate chips. The other contained the trapped cage mate.
What they found is that the free rats quickly opened both cages, in no particular order. And they did not eat all the chocolate — instead, they shared it with their fellow rat.
While the rats clearly engage in pro-social helping behavior, Mason says it's impossible to know the rats' internal experience of all this. "I think it's extremely unlikely that the rat has the same conscious experience that we do," says Mason.
Still, this study shows that the roots of empathy extend all the way back to rodents and aren't something that's unique to primates, she says.
A minority of rats never opened the trap's door, says Mason. They tended to freeze, suggesting that they felt their partner's distress but could not shake it off and calm down enough to take action.
A 'Pro-Social' Behavior
Jeffrey Mogil of McGill University in Montreal, who has studied empathetic behavior in mice, says this is a surprising study.
"You know, it's one thing to free the trapped rat that might be making alarm calls. It's quite another thing to share the chocolate chips," Mogil says.
Previous work in Mogil's lab has shown that when mice are given a temporary stomach pain, their female cage mates will go spend more time near them. And the more time their cage mates spend with them, the less pain behavior the mice will show — suggesting that the extra companionship is in response to the pain and that it actually helps in alleviating it.
Mogil says the new experiment on cage-opening rats is "a lot more robust, a lot less subtle" than that earlier mouse study.
"What's impressive about the current study is that it's an active response," says Mogil. "We can argue about why they're doing it, but there's absolutely no doubt in my mind that they're doing something that can really only be called pro-social behavior."
What's more, he says, the experimental setup in this study is so simple that he expects lots of labs, including his own, to repeat the rat study and start expanding on it.
He says it could be used to explore the neurobiology of helping behavior and allow scientists to find genes that are involved in empathy. He also wonders if rats would be as quick to help strange rats that weren't known to them, as opposed to their familiar cage mates.
Even though, in the past, many scientists have assumed that altruistic behavior is something uniquely human, Mogil says we really should not be so surprised to see it in the lowly rat.
"Behaviors have to come from somewhere," he notes. "And so it would be almost absurd to expect not to see some sort of simpler form of human sociabilities in other animals."
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LINDA WERTHEIMER, HOST:
Calling someone a rat means you think they're a scoundrel, the kind of person who would abandon others in their time of need. A new study shows actual rats are not like that. NPR's Nell Greenfieldboyce reports rats will actually lend a helping paw to a cage mate in distress.
NELL GREENFIELDBOYCE, BYLINE: Pretend you're a rat. For a couple of weeks, you've lived with a cage mate. You've gotten to know each other. One day, your cage mate disappears. A human picks you up and puts you in a plastic box. There, before you, is your cage mate - trapped in a narrow, plastic tube, clearly unhappy, maybe even making ultrasonic distress calls that you can hear because remember, you are a rat.
(SOUNDBITE OF DISTRESS CALL)
GREENFIELDBOYCE: What would you do? Peggy Mason is a neurobiologist at the University of Chicago. She and her colleagues recently put rats in this situation. And, she says, it's as if the free rat immediately sizes things up and takes action. The rat will go to the tube where its pal is imprisoned, stand on the tube, bite it, paw at it.
DR. PEGGY MASON: So the free rat wants the trapped rat to be free.
GREENFIELDBOYCE: The free rat tries everything to get its friend out. Mason says the trap has little air holes in it.
MASON: And if the trapped rat has a tail poking out, the free rat will actually grab that tail and kind of pull on it.
GREENFIELDBOYCE: Eventually, the free rat will accidentally trigger a door that opens, releasing its buddy.
The researchers repeated this experiment many times. The animals quickly learned to open the door on purpose. But they only did so for a pal, not when the trap was empty or contained a toy rat. And they did this even when opening the door released their pal into a separate cage. So it wasn't just that the free rat wanted a playmate. They seemed to just want to help.
The results are reported in the journal Science. Mason says she wanted to find some way of understanding what this helping action meant to the rats.
MASON: What is this worth to you, to open the door for a trapped cage mate? And obviously, we can't ask that question verbally. So we wanted to ask it in terms that a rat can communicate to us.
GREENFIELDBOYCE: Rats really care about food, and they love chocolate. So Mason's team tried putting two traps inside the plastic box: inside one, yummy chocolate chips; inside the other, the distressed friend. What they found is that the free rats would quickly open both traps, and in no particular order.
MASON: So what that tells us is that liberating a trapped cage mate has a value that is on a par with chocolate.
GREENFIELDBOYCE: What's more, even though the free rats could've just gobbled all the chocolate and then released their friend, they instead chose to share the candy with their fellow rat.
DR. JEFFREY MOGIL: You know, its one thing to free the trapped rat that might be making alarm calls. It's quite another thing to share the chocolate chips. I was actually really, really surprised by that point.
GREENFIELDBOYCE: Jeffrey Mogil, of McGill University in Montréal, has previously shown how mice seem to pick up on the distress of their cage mates. He says this new study is a dramatic confirmation; that it's not just primates who can feel a friend's pain and try to help.
MOGIL: It's always been strange to me that people think that these social abilities that humans have are human-specific, as if they'd just arrived out of nowhere with no evolutionary antecedents.
GREENFIELDBOYCE: He says it looks like the roots of empathy and altruism go way back, and the rat experiment gives scientists a new tool for studying the biology of this behavior in the lab.
Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright NPR.