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The Scientist: Evidence for empathy in mice

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  • Kim Bartlett
    ... Mice show evidence of empathy Adults become more sensitive to pain after watching other mice in pain, the first sign of empathy in non-primate mammals
    Message 1 of 1 , Jun 30, 2006
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      Mice show evidence of empathy
      Adults become more sensitive to pain after
      watching other mice in pain, the first sign of
      empathy in non-primate mammals

      [Published 30th June 2006 05:01 PM GMT]

      Mice who watch their peers in pain are more
      sensitive to it themselves, Canadian researchers
      report this week in Science -- the first evidence
      of empathy between adult, non-primate mammals.

      There is an "increasingly popular" view that this
      kind of basic, pre-cognitive response to social
      cues may be present in all mammals, said Frans de
      Waal at Emory University and the Yerkes National
      Primate Research Center, who did not participate
      in the study. "This "highly significant
      [paper]Šconfirms that empathy is an ancient
      capacity," he told The Scientist in an Email.

      The response mice showed to their peers in pain
      is an example of emotional contagion, according
      to senior author Jeffrey Mogil. (The best known
      example found in both humans and chimpanzees is
      the contagious yawn.) In higher primates,
      emotional contagion can progress to the more
      complex behaviors commonly associated with the
      term empathy, such as when a human identifies
      with a friend's pain and is driven to help.

      Mogil and his team at McGill University became
      interested in looking at empathy in mice after
      they stumbled onto an interesting pattern in a
      large data set suggesting that a mouse's
      sensitivity to a pain test depends on its
      exposure to others that have been through the
      test. The pattern suggested that mice "might be
      talking to each other" about their pain in ways
      that changed their response to it, he said.

      In this study, the scientists injected acetic
      acid into one or both of each pair of same-sex
      adult mice they were studying, causing them to
      writhe in pain, and allowed them to observe each
      other. An injected mouse writhed more if its
      partner was also writhing, but only if the mouse
      had previously shared a cage with its partner for
      more than 14 days.

      Observing another mouse also reduced a mouse's
      response to pain. When the researchers injected
      the paws of familiar mice pairs with varying
      doses of inflammation-causing formalin, mice
      whose partners experienced less pain tended to
      show less pain sensitivity (indicated by how long
      a mouse licked its paw).

      The researchers also found that a writhing mouse
      became more sensitive to the acetic acid while
      watching its cagemate deal with a different
      painful stimulus -- heat. These findings suggest
      that mice experience a general increased
      sensitivity to pain, and don't simply imitate
      what they see.

      To figure out what the mice were using to
      communicate pain to their similarly distressed
      peers, the researchers systematically blocked
      each of their senses, using physical barriers or
      rendering the animals deaf or unable to smell.
      They found that mice appeared to depend primarily
      on visual cues to generate an empathic response
      -- a surprise, since mice are known to be reliant
      on smell, along with ultrasonic vocalizations to
      care for their offspring. "Given that rodents
      don't use visual senses muchŠthat was our last
      guess," said Mogil. However, it's "almost
      impossible" to knock out pheromone circuits,
      which mice use to identify their acquaintances in
      the first place, so pheromones may also be a
      significant mediator of empathy, he said.

      There's a practical lesson here for mouse
      researchers, according to Mogil -- mice who
      observe each other during experiments may be
      "contaminating" the data. He added that he and
      his colleagues now routinely put up an opaque
      barrier between mice being tested simultaneously.

      Empathy is "an evolutionary mechanism to maintain
      social cohesion. If you're evolving and you're in
      a group, you're more sensitive to the pain of
      other members in a group," explained James Harris
      at Johns Hopkins University, who did not
      participate in this study.

      Greater empathy between individuals who are
      familiar goes back to the early evolution of
      maternal care in mammals, according to de Waal.
      "This may have driven initial evolution of being
      in tune with the emotions of others, after which
      all the fancy stuff that we associate with
      empathy came into play."

      However, these findings in mice hinge on how one
      defines empathy, which is still under debate, de
      Waal noted. "Lots of psychologists think
      top-down, hence equate empathy with complex
      cognitionŠ which requires introspection," he
      said. "In this view, mice shouldn't have empathy."

      In 2004, British researchers used brain imaging
      to pinpoint the empathy center in humans. The
      next step here will be to find the mechanisms
      behind the phenomenon in mice, according to Mogil
      and Harris. Researchers "may have avoided looking
      at altruism [in rodents] because it seemed too
      ridiculous," Mogil said, but these findings have
      "opened our eyes [about the] abilities of rodents
      in terms of social interactions."

      "If it turns out that the 'empathetic' effect in
      mice is mediated by the same brain mechanisms as
      human empathy," Jaak Panksepp at Washington State
      University, not a co-author, told The Scientist
      in an Email, "then the evidence would be truly
      compelling that their model actually reflects
      evolutionary continuity in a pro-social mechanism
      among many different mammalian species."

      Ishani Ganguli

      Links within this article

      D.L. Langford, et al, "Social modulation of pain
      as evidence for empathy in mice," Science, June
      30, 2006.

      E. Russo, "New views on mind-body connection:
      Studies into placebo effect and empathy suggest
      how the brain encodes subjective experience," The
      Scientist, August 2, 2004.

      S.D. Preston and F.B. de Waal, "Empathy: Its
      ultimate and proximate bases," Behav Brain Sci,
      February 2002.
      PM_ID: 12625087

      Frans de Waal

      Jeffrey Mogil

      James Harris

      T. Singer et al, "Empathy for pain involves the
      affective but not sensory components of pain,"
      Science, February 20, 2004
      PM_ID: 14976305

      Panksepp, J. "Brief social isolation, pain
      responsivity, and morphine analgesia in young
      rats," Psychopharmacology, 1980.
      PM_ID: 6781002

      Jaak Panksepp

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