By Dan Ferber, Science Now, December 8, 2011
Brown rat |
Empathy lets us feel another person's pain and drives us
to help ease it. But is empathy a uniquely human trait? For decades researchers
have debated whether nonhuman animals possess this attribute. Now a new study
shows that rats will free a trapped cagemate in distress. The results mean that
these rodents can be used to help determine the genetic and physiological
underpinnings of empathy in people.
A few years ago, neuroscientist Jeffrey Mogil of McGill
University in Montreal, Canada, reported in Science that mice possess a simple kind of empathy called emotional contagion. They
sense what another mouse is feeling and feel it themselves. For example, when
one mouse receives a painful chemical injection into its paw, the mouse and its
cagemate lick their paw to ease the pain.
That's a necessary first step toward empathy, but it's
not sufficient, says neuroscientist Jean Decety of the University of Chicago in
Illinois, a co-author of the new study. To truly empathize, one needs to
understand on some level what the other individual is experiencing, as when a
mother senses what's upsetting her child. Only then can she help, Decety says.
To find out whether rats can feel true empathy and act
on it, Decety and his University of Chicago colleagues, neuroscientist Peggy
Mason and graduate student Inbal Bartal, placed pairs of unrelated rats in
plastic cages for 2 weeks so they became familiar with each other. They then
put one of the rodents into a small Plexiglas container inside the cage. Using
a commercial bat detector, the team showed that many of the trapped rats
emitted high-pitched squeaks, indicating that they were distressed. The small
container was outfitted with a door that was rigged to fall to the side when
the free rat bumped or nudged it.
After running rat pairs through a week of daily testing sessions,
the researchers found that three-quarters of the rats with trapped cagemates
had learned how to open the door (see video), whereas only one rat in six
without a trapped cagemate learned to do this. This difference showed that rats
with trapped cagemates were motivated to learn how to free them (to see the video click here).
But what motivated the rats in the first place? To find
out, the Chicago team kept up daily tests on the rodents that had learned how
to open the container. Each free rat kept liberating its trapped cagemate for a
month, which ruled out simple curiosity as a motivation. What's more, the free
rat would liberate its cagemate even when the trapped animal exited into a
separate cage, which showed that the free rat wasn't simply seeking the reward
of schmoozing with its friend. The rats also freed trapped cagemates even when
they had the option of bumping open an identical container and obtaining five
chocolate chips for themselves, which showed that their motivation to help was
on par with their desire for a tasty treat. In fact, half of the time they even
shared chips by leaving one or two for the trapped rat, the team reports online
today in Science.
The results are the first to demonstrate that rodents take action in response to
another's distress, Decety says. Similar behavior has been observed in monkeys and
chimpanzees. But unlike those animals, rats can be readily used in laboratory
studies to investigate which brain structures underlie empathy and helping
behavior and whether empathy is acquired through nature or nurture.
"The study ... is truly groundbreaking,"
ethologist Frans de Waal of Emory University in Atlanta, writes in an e-mail.
It "shows for the first time that rodents are not just affected by the
emotions of others, but that empathy motivates altruism."
Evolutionary anthropologist Joan Silk of the University of
California, Los Angeles, is not so sure, however. "I think experiments
like this are extremely important," she says. But she adds that if the
free rats are acting to relieve their own distress at their cagemate's
suffering—a possibility the authors admit—then that's very different from
acting altruistically to relieve the distress of others. Nevertheless, she
allows, "it's a step in the right direction."
No comments:
Post a Comment