Those Empathic Rats: Take Two

I jumped the gun the other day by trying to comment on a research report as it was described on an NPR interview and in the Science Times. As a result, I missed an important factor (although I stand by my remarks about the role of empathy and altruism in rats’ daily lives). Now my copy of Science has come and I can comment more constructively on the article by Bartal, Decety, and Mason, “ Empathy and pro-social behavior in rats”, Science, 9 December 2011, pp 1427-1430.

The basic study involved observing laboratory rats (the usual little Sprague-Dawley guys with the white fur and beady red eyes) to see whether they would work to open a door and release a familiar cagemate from a container. To be able to claim that rats were motivated to release a trapped rat, the authors also needed to show that the door releasing a trapped rat was opened more often than the door to an empty container or the door to a container with a toy rat in it. The rats were tested daily over several weeks, and on the average managed to open the door and let the trapped rat out after about a week. Twenty-three of 30 rats eventually opened the door for a trapped rat, and 5 out of 40 opened the door when there was no trapped rat. All 6 of the female rats who saw a trapped rat opened the door, but only 17 of 24 males did so. The authors concluded that the rats showed motivation by empathy when they released the trapped cage mate.

In an additional study, where the free rats could choose between opening a container that held chocolate chips and releasing a trapped cage mate, they did the two things about equally. In addition, they ate fewer of the chocolate chips when they had released another rat than they did when they were alone with the chips (these animals had free access to food and water and were not especially hungry). The authors referred to this as “sharing” with the other rat.

The general conclusion of the article was that the free rats were “not simply empathically sensitive to another rat’s distress but acted intentionally to liberate a trapped conspecific”. I believe this conclusion raises many questions, as does the use of the term “share” with respect to eating fewer chocolate chips. I don’t reject the idea that empathy might be part of rat psychology, but I consider the study to suggest as many questions as it answers.

One of my questions comes from watching the video of one of the rats at work, to be seen at www.sciencemag.org/cgi/content/full/334/6061/1427/DC1. As the free rat succeeds in opening the door to the container, it does not step aside and let the trapped rat out. Instead, it squeezes past the trapped rat into the container so they are both briefly inside; when the trapped rat emerges, the free rat explores the container for a moment, then finally comes out and follows the formerly-trapped rat closely, sometimes appearing to mount it briefly (not an unusual thing for a rat to do). My question is, what was the exploration of the container about? Did rats other than the one selected for the video also show this activity? To what extent would it be appropriate to say that a more parsimonious explanation--- that the container and the other rat are interesting-- may be more appropriate than the “empathy” conclusion?

A second set of questions has to do with the role of the trapped rat in triggering its “rescue”. The authors refer to the possibility that high-pitched distress cries were annoying to the free rat, who might have released the cagemate in order to stop all that crying. However, they used a bat-cry detector to record the calls, and reported that such calls were infrequent. This assumes that the pitch of the cries was the disturbing part, whereas human infants’ cries differ in many ways other than pitch during different emotional states, and the same may be true of rats. Although the report alluded in a note to the role of smell in rat emotional contagion, and although the container and “arena” were carefully washed between observations, there seems to have been no attention paid to the role of airborne pheromones in possible distress of the free rat. Finally, although the researchers reported the sexes of the free rats, they did not specifically state this about the trapped rats. Because the trapped rats were said to be cagemates of the free rats, and because normal procedure would be to cage males and females separately, it seems likely that male free rats were with male trapped rats, and females with females. This raises the question whether the “unhelpful” 7 out of 24 males would have been helpful to trapped females, and conversely whether the helpful females would not have helped trapped males. Again, it may be more parsimonious to consider environmental factors that led to the door-opening rather than assuming that some form of empathy was in operation.

A curious thing about empathy is that it may be just as important in negotiating hostility as it is in causing prosocial, helping behavior. Empathic responses are a matter of identifying and even experiencing another individual’s emotions, and are easy to recognize when we are sorry for a sad person and want to help him or her. But what about situations where someone may be angry at us, or frightened and ready for self-defense? To recognize those feelings before the other acts on them allows us to escape, to placate the other, or even to attack first--- all possibly related to survival of the individual and of the group, but not prosocial in the usual sense. And a mixed picture is surely possible. What if the rats had been confronted with a human hand restraining their cagemate? Would biting the hand be prosocial or hostile behavior? Like oxytocin, which can be involved in both maternal care and fighting, empathy has a complex function. We may reach some wrong conclusions when we assume that behavior must be empathically motivated.