Mice can feel cagemate's pain
Canadian researchers observe empathy in mice.
by Lydia Fong -- July 12, 2006
If the world's smallest violin is tiny enough, perhaps a couple of mice
could play the world's saddest song on it.
A Canadian research team in the Pain Genetics Lab at McGill University
discovered that a mouse's response to pain is intensified in the
presence of another mouse that is also in pain. In addition, according
to a study published in the June 30th issue of Science, the mice appear
to synchronize their pain responses.
"Both of those things, ultimately, are suggestive of empathy," said
Jeffrey Mogil, a psychology professor and one of the study's lead
Previously, empathy was a behavior thought to exist only in higher
primates and humans.
To induce pain in their mouse subjects, the researchers used what is
known as the "acetic acid writhing test," which simulates a
In response, the mice displayed a subclass of empathy known as
"emotional contagion," where one mouse recognizes and adopts the
emotional state of another. Surprisingly, this only occurred if the
mice knew each other-that is, if they had been cagemates for at least
two weeks. This is the amount of time required for a mouse to
familiarize itself with the pheromones of another mouse, according to
Since pheromones play a big role in the interactions of mice,
researchers guessed the mice would communicate their pain via scent.
However, after using a zinc sulfate treatment to block the animals'
sense of smell, researchers found they could still sense one another's
pain. After disrupting other senses, the researchers determined that
communication was only interrupted when an opaque Plexiglas divider was
placed between the mice.
"The message 'I'm in pain' appears to be transmitted visually," Mogil
said. "Humans are very, very good at telling when another human is in
pain by looking at the face, and we think that probably mice can do it,
Frans de Waal, a psychology professor at Emory University who studies
primate behavior, speculates that empathy first evolved in mammals
because mothers needed to be able to respond immediately to the
distresses of their offspring. It then expanded beyond the
"Animals need to be in tune with each other, with alarm and fear," said
de Waal. "It's highly adaptive to be in tune with others."
According to Mogil, scientists may be able to use the mouse model to
more closely study the mechanism of empathy, particularly the genes,
neurochemicals, and brain areas involved. The finding could be useful
for studying human conditions such as autism, which is associated with
a reduced ability to empathize.
"Empathy is a very hot topic with humans, but the problem with humans
is that we can't really do any experiments on them," Mogil said. "You
can stick them under an imager and see what parts of the brain lights
up, and that's about it."