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Rats Show Empathy, By Freeing Trapped Companions

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Reporting in Science, researchers write of an experiment in which rats worked to open the cages of trapped rats, but not empty or dummy-filled cages. Author Peggy Mason discusses empathy in non-primates, and the value rats place on freeing a companion—about equal to that of a stash of chocolate chips.


This is SCIENCE FRIDAY. I'm Joe Palca, filling in for Ira Flatow. Rats aren't the most well-loved creatures out there. You've got sewer rats, subway rats, the evil rat in "The Nutcracker." Or how about someone calling you a rat?

Well, not something most of us aspire to, but this next story might burnish rats' reputations just a little bit. A new study found that rats are actually quite willing to come to another rat's aid, freeing a rat trapped in a container. And they're not just doing it for a dose of sugar water or some other reward; they're doing it out of empathy of the other rat's plight, or so the researchers write in their study out this week in the journal Science.

It makes you wonder if empathy really is a uniquely human capacity. Maybe the roots of empathy go back a lot farther than we thought. What do you think? Give us a call. Our number is 800-989-8255. That's 1-800-989-TALK. If you're on Twitter, you can tweet us your questions by writing the @ sign followed by scifri. And if you want more information about what we're talking about this hour, go to our website at, where you'll find links to our topic.

And now let me introduce my guest. Peggy Mason is a professor of neurobiology at the University of Chicago. She's the senior author on the rat study, and she joins us from a studio on campus. Welcome to SCIENCE FRIDAY, Dr. Mason.

DR. PEGGY MASON: Thanks so much for having me.

PALCA: So how did you come to do this research? What was the thinking that made you wonder if rats felt empathy?

MASON: We knew that rats feel very - or show a very rudimentary form of empathy called emotional contagion. That had been shown. Well, it had been shown that rodents show this about five years ago by Jeff Mogil at McGill University. And we wanted to take it a step further and examine...

PALCA: So I'm sorry, what is emotional contagion? I'm sorry, I don't recognize that term?

MASON: So emotional contagion is one individual mimicking the emotional state of another individual, and an example of that is when one baby cries, all the babies cry.

PALCA: Mm-hmm. I got it, OK. So you took this a step further. Why don't you describe the experimental setup so that we have a sense of what was happening?

MASON: Absolutely. So we had an arena, and in the center of an arena - of the arena was a restrainer. And in the restrainer was one of the rats. And outside of the restrainer, free to roam around, was his cage mate, the free rat. And the restrainer had a door, which can only be opened from the outside. So only the free rat can open the door.

And when we put the two rats into this situation, the free rat immediately goes to the restrainer, climbs all over the restrainer, bites the restrainer, tries to figure out why the cage mate is stuck in there and just focuses all of his activity on this restrainer.

Eventually, these sessions occurred for about an hour a day for 12 days, and by about day six, they figured out how to open the door.

PALCA: So the rat outside was never shown how to do it but eventually stumbled on how to open the door for the trapped rat?

MASON: Exactly, and it was typically an - well, it was accidental. It's not like the rat can look at the door and say: Gee, I see that counterweight, I know if I push here...

PALCA: Right.

MASON: So it's just because the rat is spending so much time at the restrainer because it's so concerned that he accidentally opens it. And that would be one thing, but the important feature is that the next day, he says oh, OK, I remember the door is the place to be. So he goes right for the door, fiddles with it, now instead of taking him 25 minutes to open the door, the next day it takes him 10 minutes.

Moreover, when the door falls over, now the rat, the free rat expects the sound. The first time it falls over, it makes a sound, the rat freezes because oh my God, something unusual has happened. I didn't expect that. I'm afraid. But the second time or the third time, certainly by the third time no longer surprised. So that tells us that by the third time, the rat is intentionally and deliberately opening the door to liberate the trapped cage mate.

PALCA: Right, and you say empathy. Let's play devil's advocate and say if you had to challenge your own study, what other explanation could you give for this?

MASON: Well, we thought the most simple - when all we had was what I've just told you, we thought the most simple explanation was simply that the free rat wanted to play with the trapped rat. That seems like a straightforward reason to open the door. And so we were very worried about that or concerned that that might be the case. So what we did was we put two arenas together, and then instead of putting the restrainer in the middle of one arena, we put the restrainer right up against the divide.

And the door was at the divide. Now the free rat, when he opened the door, the trapped rat was liberated but only into an adjacent arena, and they were not allowed - they couldn't play together. And we did this for almost 30 days, and day after day, the free rat would open the door to liberate the trapped cage mate, even though they never got to play.

PALCA: Right, OK, and the other explanation that occurred to me, and I heard Nell Greenfield-Boyce's story on NPR this morning, she played this ultrasonic sound that the rats - I don't think it was the right frequency, but, I mean, she played it at a frequency we could hear.

MASON: That's right.

PALCA: But the rats hear this, I mean, isn't it like, you know, shut that bloody racket up, and I'll let you out so that you'll stop making that screeching noise?

MASON: It's an entirely reasonable concern. The reason we don't think that that's what's going on is that we only reported ultrasonic vocalizations in 13 percent of the sessions. So it was very unusual, and certainly rats would open the door in sessions where there were no alarm calls.

PALCA: OK, well, empathy, that's certainly something that people would tend to believe, but let's see what our callers think. Let's go to Logan(ph) in Moultrie, Georgia. Logan, welcome to SCIENCE FRIDAY. You're on the air.

LOGAN: Great, good afternoon. Real quick, I was just thinking about a YouTube video that I saw of a dog, I believe it was in Columbia, come to the rescue of another dog that had been hit by a car on the interstate. And that sure seemed like empathy to me.

PALCA: Well, let's see what Dr. Mason...

MASON: Yeah, I agree with you, and I think that the reality is that there are lots of anecdotes - and we see empathy in our pets all the time. But these anecdotes are - probably have a large kernel of truth to them. And yet they don't allow us to understand anything more about empathy. And this is the first time that we've really controlled a situation, and we can prove that this is empathic, helping behavior.

And moreover, now we can use this model to examine what are the neurological, behavioral, genetic, pharmacological mechanisms that give rise to helping behavior.

PALCA: Hey, Logan, thanks for the call.

LOGAN: (unintelligible).

PALCA: Appreciate it. So what other emotional states do you think rats might be capable of, I mean, emotional senses that sort of mimic things that we tend to think of mostly as human?

MASON: Well, I think they certainly show fear. And...

PALCA: Well, I would think that most animals - I mean, fear seems pretty...

MASON: Fear is very useful. But the empathy is probably derived from the maternal relationship to her offspring. And it's very important for a mother to know how her babies feel, particularly if that mother is a mammal. In the case of mammals, the babies get born, and they're basically helpless. And so if mom doesn't know when the baby is hungry or cold or in some way distressed, then the baby is less likely to grow, develop, survive and thrive.

PALCA: Interesting. Let's take another call from Max(ph), who's in your same city of Chicago, Illinois. Max, welcome to SCIENCE FRIDAY. You're on the air.

MAX: Hello. Yeah, she just actually touched on my point, which was that - you know, I've studied evolutionary psychology and behavioral genetics, and it seems to me that any creature that cares for its offspring is capable of empathy. Anything that has a limbic system has to, like, as you said, be sensitive to the needs of their offspring and, you know, its fears, its wants, its desires and its needs.

So yeah, I mean, is there any way that you're differentiating the sort of rat empathy from, you know, basic maternal or, you know, parenting empathy?

MASON: Well, yes. These are unrelated male adults. And so the idea is that although empathic helping may have started with the mother-offspring relationship, it has generalized to relationships that go beyond that, to relationships between two adults, between two unrelated individuals and so on.

And I think that the potential benefit of this generalization is that social groups are more cohesive if the members of those social groups are willing to help each other, are sensitive to each other's distress and willing to help.

PALCA: And you had a condition in the experiment where you tried to get at this, you know, where the animal had a choice between something tasty and being helpful.

MASON: That's right.

PALCA: Maybe you could describe that.

MASON: So we really wanted to understand what the value of helping behavior was to the rat. So we did what we called in the lab the chocolate-versus-pal experiment. And this was one arena, two restrainers. In one restrainer was five chocolate chips, and in the other restrainer was the trapped cage mate.

Now, these rats had been eating chocolate for weeks, and they ate, on average, more than seven chocolate chips. When the free rat is placed into this arena, we didn't know what would happen. But what did happen was that the free rat opened both restrainers in no consistent order. So on one day, he might open the chocolate restrainer first, and on another day, he might open the trapped cage mate restrainer first.

So the result was that there was no difference in the opening times for the restrainers of the two types. And what this told us was that liberating a trapped cage mate is on a par with very yummy chocolate, which was really quite striking.

But even more amazing, and this was the thing that shocked me the most in the entire study, is that the free rat, although there were multiple ways that he could hog all the chocolate chips, he did not. He shared, on average, one and a half chocolate chips with the liberated cage mate.

PALCA: Well, all I can say is I wouldn't try that experiment on humans because I'm sure they'd leave me trapped. Most of my colleagues would leave me trapped and go for the chocolate and then let me out. But anyway, it's an interesting set of experiments. Thanks for sharing them with us today.

MASON: Hey, thanks so much for having me.

PALCA: Peggy Mason is a professor of neurobiology at the University of Chicago. After the break, we'll be talking about Asia's space race and whether this competition between China, Japan and India could lead to war in space. Stay with us.



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