The (Un)surprising Empathic Abilities of Rodents

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Regrettably, it has taken a very long time for psychologists and neuroscientists to take the leap towards investigating empathy in non-primate mammals. Of course, why should sociobiology get in the way of politics and religion?

The study that had perhaps the biggest impact in this field, was conducted by Langford et al. (2006), entitled "Social modulation of pain as evidence of empathy in mice". The simple yet ingenious design included placing two mice, which were either strangers or cage mates, into transparent Plexiglas cylinders, such that they could see one another. Either one or both mice received an injection of 0.9% acetic acid into the stomach cavity and their pain response (writhing behavior) was measured. Remarkably, mice appeared to be in more pain when they saw another mouse also in pain, but only when that mouse was their cage mate or sibling, not when it was a stranger. Their pain was amplified by seeing familiar individuals in pain.

More recently, Ben-Ami Bartal and his colleagues (2011) developed a rodent pro-sociality  test resembling those typically used in primate studies. In their setup, one rat was free to roam an arena, while a second rat was trapped in a see-through tube with a door, which could be opened from the outside. It took rats that had been housed together about a week to learn how to open the door and free their comrade. Rats did this much more often than when the "restrainer" was empty or had a toy rat in it. The researchers also recorded ultrasonic alarm calls and found those to be more frequent in the early days of the experiment, when the free-roamers had not yet learned how to open the door.

Ben-Ami Bartal et al. built on this by presenting the free rats with a choice between opening a door that would free their restrained cage mate and a door behind which there were chocolate chips. Rats were equally likely to open either one of the two doors (whereas they only opened the door to the treats when there was no trapped mate to be freed) and shared the food with the freed rat.

Both experiments demonstrate that uncovering empathy and pro-social behavior in rodents requires some clever experimentation and a healthy aversion to what Mogil (2012) dubbed "anthropodenial" (as opposed to anthropomorphism). Mogil, incidentally, in his admirable short review, asked something of an awkward question about the rats in Ben-Ami Bartal et al.'s experiment:

"are they performing this behavior to end the distress of the

trapped rat or to mitigate their own aversive vicarious

arousal?" (p.143)

Mogil was interested in the motivation of the rodents for this behavior, almost implying that ending the distress of the trapped rat should be considered selfless and/or truly pro-social, whereas doing it to stop one's own distress is somehow less impressive. I have to point out a logical flaw in this supposition: for the latter to be true, the rats must be experiencing distress in response to the distress of their cage mate in an example of the familiar emotional contagion. However, this type of distress is not likely to be an accident - it is probably there to elicit pro-social behavior, making the former necessarily true as well. So, the rats are ending their own distress by ending the distress of their cage mates. One is bound to wonder, what type of emotional/cognitive processes would satisfy just the former. And are those to be found in any species?

Let's hope that many more scientists will be heading in this direction soon.

References

Ben-Ami Bartal, I., Decety, J., & Mason, P. (2011). Empathy and pro-social behavior in rats. Science (New York, N.Y.), 334(6061), 1427–30. doi:10.1126/science.1210789

Langford, D. J., Crager, S. E., Shehzad, Z., Smith, S. B., Sotocinal, S. G., Levenstadt, J. S., … Mogil, J. S. (2006). Social modulation of pain as evidence for empathy in mice. Science (New York, N.Y.), 312(5782), 1967–70. doi:10.1126/science.1128322

Mogil, J. S. (2012). The surprising empathic abilities of rodents. Trends in Cognitive Sciences, 16(3), 143–4. doi:10.1016/j.tics.2011.12.012