Why Do Animals Engage in Pro-Social Behavior

Lisa Hiura ’14 is working with rats to determine social tendencies and animal motivation. By giving rats the choice of two levers — one for access to banana pellets and the other for access to social contact — she can determine the relative value of each stimulus. 

She also tests rats that are deprived of food, social contact, or both, to determine the effect of environmental history on motivation for each reward. In the environmental factors test, Lisa is basically asking two questions: Does a food-deprived rat respond differently from a non-deprived rat in the social contact/banana pellet test? Does a socially-deprived rat respond differently from a non-deprived rat given the same test? More data is to come, but so far it seems that tasty food is more reinforcing than social contact across deprivation conditions (although social contact elicits lever pressing, too).

The test is simple: a rat sees its buddy trapped in a restraint and can choose to release him (via a lever, nose poke, etc.). The restraint is meant to cause psychological but not physical stress. In the first treatment, the trapped rat is released into the free rat’s chamber and they are free to play. In a second treatment, the rat is released into a separate chamber which bars social contact. 

One research group allowed rats to experience the first treatment (correct response followed by playing) for several trials, and then tested them in the second. Free (non-restrained) rats respond correctly by releasing their buddies whether or not they were allowed to play afterward. By this group’s logic, the free rat showed empathy; he didn’t just want to play, he wanted to relieve the distress of the trapped rat!

According to some, it’s not so simple. An alternate hypothesis, termed the “neophobia plus social contact hypothesis,” posits that there are two major motivations at play here: fear of new environments (neophobia), and want of social contact. Trapped rats may have left their restraints out of fear of this novel environment, in favor of a more familiar second cage. Consistent with the “social contact” piece of the hypothesis, rats actually returned to the restraint after it became more familiar, thereby moving closer to the other rat. Furthermore, free rats did not release the trapped rat if they were never trained in the “play” condition. Rather than being explained by empathy, operant responding may instead be explained by desire for social contact.

Through her work, Hiura seeks to add depth to these theories and find a “parsimonious explanation… with a critical eye to all potential variables.” Her results may also reflect trends in human motivation, and address the effect of environment on relative reward.