Rat pairs cooperate only to defend individual water homeostasis

Ben-Ami Bartal, Decety and Mason (2011) demonstrated that a rat free to move in an open chamber would open a door blocking a second rat’s egress from a restraint tube. They theorized that the free rat behaved empathically by opening the door to the restraint tube, permitting the trapped rat to escape. Silberberg, Allouch, Sandfort, Kearns, Karpel and Slotnick(2014) reinterpreted their result. They attributed the free-rat’s door-opening response not to empathy, but to the free rat’s pursuit of social contact with the trapped rat. I investigated cooperative responding for water rewards in a procedure that did not allow for physical contact between pairs of rats, but did allow them to observe one another through a transparent barrier. Pairs of rats learned to cooperate for water rewards by climbing ladders and inserting their heads into respective reward ports synchronously. Thirst states of rats within each pair were then systematically manipulated. Results were consistent with the notion that absent social contact, rats are unmotivated by the need states of others. Sated rats with thirsty partners initially responded at a significantly higher rate than when their partners were also sated—a result compatible with empathic action in the sated rats. However, these response rates decreased over experimental conditions. By the end of the study, rats that were sated cooperated no more frequently with thirsty rats than they did when all rats were sated. While these results evidence cooperation between rats, they do not provide evidence of rat empathy.