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This week:
Do Animals Feel Empathy?
A young chimp comforts an elder who has just lost a fight with a rival.
Photo by Frans B.M. de Waal, copyright Frans B.M. de Waal, all rights reserved. Used by permission.
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Introduction
by David Dobbs
Editor, Mind Matters
Do animals feel empathy? This question could draw scoffing dismissal from many scientists only a few decades ago. Now it receives marvelously productive attention in neuroscience, psychology, and the burgeoning field of
neuroethology. Below, two leaders in these fields, Emory University primatologist
Frans de Waal and University of Chicago neurobiologist
Peggy Mason, review both the history of animal studies of empathy and a particularly thought-provoking recent mouse study from the McGill University lab of Jeffrey Mogil. As de Waal and Mason note, this clever study holds surprises about both the baseline and the limitations of empathy in these small, "simple" rodents. One can't read these reviews without seeing one's own empathetic capacities and limitations in a new light.
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Commiserating Mice
Frans B. M. de Waal
Living Links, Yerkes Primate Center
Emory University
Atlanta, GA 30322
Apart from a few rear-guard
behaviorists, few people hesitate to ascribe empathy to their dogs. But then dog is man's best friend, freely credited with lots of human sentiments. You wouldn't expect a hard-nosed scientist to make similar claims about, say, rodents, would you? Yet a significant line of research, freshened most recently with the paper under review, demonstrates not just empathy's existence in rodents and other animals but its subtleties and exceptions as well.
A Tentative Start
An early, seminal study was a 1959 paper by psychologist
Russell Church in the
Journal of Comparative & Physiological Psychology , provocatively titled "
Emotional reactions of rats to the pain of others." Having trained rats to obtain food by pressing a lever, Church found that if a rat pressing the lever saw another rat in a neighboring cage get a shock from an electrified cage floor, the first rat would interrupt its activity  a remarkable result. Why should the rat not continue to get food and ignore the other animal's flinching? The bigger question is whether the rats that stopped pressing the lever were worried about their companions or just afraid that something bad might happen to themselves.
Church's work inspired a brief flurry of research during the 1960s that investigated concepts like "empathy," "sympathy," and "altruism" in animals. To avoid trouble, the investigators would place the topics of their research in quotation marks, for the prevailing behaviorist atmosphere made mention of animals' emotions taboo. Combined with the traditional emphasis on nature's nasty side, this taboo ensured that these studies went largely ignored.
In the meantime, however, human empathy became a respectable study topic. First, in the 1970s came studies of empathy in young children, then in the 1980s in human adults, and finally, beginning in the 1990s, studies in which humans placed in a brain scanner are asked to watch others in pain or distress or who have a disgusted facial expression. This field now produces new articles every week. Animal studies, however, have lagged.
An Old Sorrow
This is changing, however. Slowly but steadily - half a century after Church's rat study - the evolutionary origin of empathy is becoming a hot topic, reviving interest in animal studies of empathy. For instance, University of Michigan psychologist
Stephanie Preston and I
have argued [warning: large pdf download] that a basic neural process, first developed in our animal ancestors, underlies even the fancy kinds of empathy that only we humans are capable of. Seeing another person in a certain situation re-activates neural representations of when we were in similar situations ourselves; this brain activity in turn generates a bodily state resembling that of the object of our attention. Thus to see another's pain may lead us to share it. You can see this empathic capacity even in a newborn, who will start crying if it hears another baby crying. Such state-matching, or emotional contagion, may underlie all empathic responses.
Now comes a study by Dale J. Langford and co-workers at McGill University entitled "
Social modulation of pain as evidence for empathy in mice". This study was inspired by a puzzle that intrigued Langford and the lab's director, Jeffrey Mogil: When testing mice from the same home cage, the order in which the mice were used seemed to affect their pain response. The first mouse would always show fewer signs of pain than the last. Was the last mouse being sensitized to pain by seeing others in pain? Or was something else at work? Langford and her colleagues determined to find out.
The Writhe Test
The experiment involved putting pairs of mice through a so-called "writhing test." In each trial, two mice were placed in two transparent Plexiglas tubes so that they could see one another. Either one or both mice were injected with diluted acetic acid, which is known to cause a mild stomach ache. Mice respond to this discomfort with characteristic stretching movements. The researchers found that an injected mouse would show more of this movement if its partner displayed it than it would if its partner had not been injected.
Significantly, this increased display occurred only in mouse pairs who were cage mates.
Male (and not female) mice showed an interesting additional phenomenon when witnessing a strange male mouse in pain: its own pain sensitivity actually dropped. The counter-empathic reaction occurred only in male pairs that didn't know each other, which are probably the pairs with the greatest degree of rivalry. Was that rivalry suppressing their reaction, or did they actually feel less empathy for a strange rival?
This gender effect reminds me of a
wonderful 2006 study of human
Schadenfreude by Tania Singer and colleagues. They found that in both men and women, seeing the pain of a person we have just cooperated with activates pain-related brain areas. But if a man felt he had been treated unfairly by another man, his brain's pleasure centers would light up at seeing the other's pain. Such male antipathy towards rivals may be a mammalian universal.
Finally, Langford and colleagues also exposed pairs of mice to different sources of pain -- the acetic acid as before and a radiant heat source that would cause pain if a mouse didn't move away. Mice observing a cage mate suffering stomachache withdrew more quickly from the heat source. In other words, the reactions of mice cannot be attributed to mere imitation, because a mouse seeing a companion in pain seems sensitized to
any pain.
A Foundation of Empathy
I admire this study greatly. It is not the sort of manipulation we would nowadays apply to primates, but goes a long way towards confirming the tentative conclusions of the 1960s, only with more subjects and more rigorous controls. While it doesn't prove that the mice feel vicarious emotions, it demonstrates they experience a vicarious intensification of their own experience.
This demonstration justifies speaking of "empathy" -- at least for some. Here we find an interesting division between psychologists, who tend to think top-down, and biologists, who tend to think bottom-up. The top-down view considers the most advanced forms of empathy, such as putting yourself into another's "shoes" and imagining her situation, and wonders how this ability arises; the inevitable answer is advanced cognition, perhaps even language. Yet merely imagining someone else's situation is not empathy. Such imagination can be a cold affair, not unlike understanding how airplanes fly. Empathy requires emotional involvement.
Here the bottom-up view offers a better perspective. When we react to seeing someone display emotion and construct an advanced understanding of the other's situation, this process indeed involves -- in humans and some other large-brained animals -- a great deal of cognition. But the emotional connection comes first; understanding and imagination follow. This mouse experiment suggests that the emotional component of this process is at least as old as the mammals and runs deep within us.
Frans de Waal is director of the Living Links Center at Emory University, where he studies the behavior and evolution of humans and primates. His book describing this growing field, Our Inner Ape (Riverside), was chosen as a New York Times Notable Book of the Year in 2005.
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Empathy is a Pain. So Why Bother?
Peggy Mason
Department of Neurobiology
University of Chicago
Chicago, Ill.
As Frans de Waal notes, the principles of biological continuity should make it unsurprising that mice act in empathetic ways similar to those seen in primates, including humans. This study bolsters that view in striking ways.
For instance, it's tempting to explain empathetic behavior in animals that we believe to have only rudimentary cognition, such as mice, by arguing that the sight of a suffering fellow mouse simply evokes an automatic fear reaction. This study undermines that explanation by showing that mice showed empathetic reactions only with cage mates; the mice seem to go far beyond being frightened by injury to accounting for whom the injured party is -- friend, family, foe, stranger. This response is a significant step toward human-like social feeling -- toward caring for acquaintances more than for strangers, just as our empathy for someone who is hurt differs depending on whether the person is a foreigner, a national compatriot, a school chum or an immediate family member.
A Reflection of Pain
So how can the brain accomplish empathy in general, and empathy for pain in particular? The answer is likely to involve mirror neurons, discovered more than a decade ago by Giacomo Rizzolatti and colleagues. In Rizzolatti's original study, he and his colleagues found that premotor neurons in a monkey's prefrontal cortex -- neurons that routinely fire as the monkey prepares a particular movement, such as reaching out to grasp something -- fire in a similar pattern when the monkey merely watched a human perform the same task. Rizzolatti's group also demonstrated that mirror neurons fire not just in response to an observed action but also in response to the action's apparent intent. For example, a monkey may have a premotor neuron that fires when the monkey grabs a peanut to eat but not when she grabs a peanut for other reasons, such as to place it in a cup. This 'grab-to-eat' neuron will fire when the monkey watches a human grab a peanut to eat it but not when the human picks up the peanut for other reasons; the neuron responds to the action's intent. Finally, mirror neurons are activated by a perception of purpose, rather than of detecting specific muscle movements: cells that discharge when the monkey watches a human reach for an object will continue to respond even if much of the movement is hidden by an opaque screen.
A Critical Mass of Empathy
Other findings suggest that mirror functionality may not be restricted just to neurons in prefrontal cortex; some portion of "regular" cortical neurons in numerous areas may have mirror functionality. Functional imaging experiments in humans support this possibility and suggest a potential substrate for pain empathy. Consider, for instance, the insula and anterior cingulate, two brain regions that contain neurons that fire in relation to pain's affective component (the "I care" portion of pain as opposed to the discriminative, or "where, when, what type of pain?" component). When an experimenter applies a painful stimulus to a volunteer, cells in the subject's insula and anterior cingulate are activated, presumably giving rise to the negative affect associated with pain sensation. If in fact these affect-relevant neurons have mirror functionality, then when the volunteer watches a loved one experience pain, these affect-relevant neurons will discharge and create an affective state much like the volunteer would feel if she were receiving the painful stimulus.
Viewing mirror functionality as a substrate for empathetic behavior provides specific explanations for two of the findings in the Langford paper. First, pain behavior -- the actions that we and other animals take when feeling pain -- occurred simultaneously when two cage mates in pain could see each other. If mirror neurons underlie pain empathy, then the sight of one mouse acting in pain will elicit mirror discharge in its cage mate. When this mirror discharge is added to the activation due to the pain received directly, it may bring activity in the insula and anterior cingulate to a perceptual threshold, resulting in an emotion of "I care" -- and therefore "I move." Mirror neurons thus provide a mechanism for synchronizing behavior within a group.
Mirror functionality also helps explain why mice showed empathetic reactions even if they suffered from a different type of pain than the fellow sufferers they observed, as when a mouse showed more sensitivity to heat if it saw a cage mate suffering a stomachache. Mirror functionality accounts for meaning rather than specific muscle activations. The meaning of pain is pain, even if the motor reactions to different pains differ substantially.
From Empathy to Action
Finally (as if the above is not sufficiently conjectural) it's intriguing to speculate further about the role of pain empathy in socialization. Severe injuries -- deep gashes, broken bones -- and chronic pains isolate and incapacitate the sufferer. Humans survive such damage because other humans take care of them. Animals such as rodents typically do not survive, however, because other rodents do not feed and protect them from predation. Empathetic behavior for others in pain would seem a natural first step in developing the social feeling necessary to care for sick and injured con-specifics. Although I suspect that mice are not ready for nursing duty yet, they may have taken the first step toward socialized medicine.
Peggy Mason is in the Department of Neurobiology and chairs the Committee on Neurobiology, a leading graduate program, at the University of Chicago, where she studies the role of the brainstem in pain modulation and homeostasis.
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