In an Oct 19 post, I discussed some fascinating published and unpublished studies on rodent empathy. This week, a new article on the topic appeared in Science, which evoked a commentary in the Washington Post, as well as comments in the Society of Neuroscience blogosphere. Inbal Ben-Ami Bartal and colleagues at the U of Chicago established a paradigm in which a freely moving rat is placed in a cage with another rat that is trapped in a transparent plastic restrainer. The restrainer has a lever that opens a door, allowing the restrained rat to escape into the cage with the free rat. After several sessions moving around the restrainer, the free rat accidentally opens the door, allowing the trapped rat to come out. In subsequent sessions, the freely moving rat opens the door to liberate the trapped rat very quickly. A video of this test can be found here. The freely moving rat does not open the container when it is empty or when it contains a novel object rather than a rat. The free rat also opens the restrainer even when it is prevented from subsequent contact with the trapped rat. Interestingly, all 6 of the female rats tested learned to open the captive’s cage, but 7 of the 26 males tested never did. Does this mean that the males are less empathetic, or that they learn the task less well? Or that they did not bump into the lever in the first place? The senior author on the paper, Peggy Mason, thinks that the males may not have the ability to down-regulate their own stress in order to act on their empathetic impulses.
In a further test, a second container was placed in the cage, and the freely moving rat was given the opportunity to open one containing chocolate chips and/or the one containing the trapped rat. Perhaps surprisingly, the free rat opens both containers and even shares some of the chocolate with the newly freed rat.
Regarding the interpretation of the results, some neuroscientists disagree with the idea of empathy here, preferring the notion that the free rat lets the trapped rat out in order to end its own stress rather than the stress experienced by the trapped rat. My own opinion is that this is a false dichotomy. Humans feel stress when they see someone else in stress, and they probably try to release the stress in both parties.