Desire for social contact, not empathy, may explain "rescue" behavior in rats.

Ben-Ami Bartal et al. (Science 334:1427-1430, 2011) showed that a rat in an open space (free rat) would touch the front door of a restraining tube to open its rear door, thereby enabling a rat trapped within (trapped rat) to enter a larger space that was farther away from the free rat. Since opening the rear door distanced the trapped rat from the free rat, Ben-Ami Bartal et al. argued free-rat behavior could not be motivated by the pursuit of social contact. Instead, this rat was empathically motivated, its goal being to reduce the presumed distress of the rat trapped in the restraining tube. In two experiments, we show that (a) a free rat will not learn to touch the front door to open the rear door when it is the first condition of the experiment; (b) over time, a trapped rat will often return to a restraining tube despite its presumed aversiveness; and (c) a free rat experienced in touching the front door will continue to touch it even if touching does not free the trapped rat. We explain these results and Ben-Ami Bartal et al.'s in terms of two processes, neophobia and the pursuit of social contact. When first placed in a restraining tube, neophobia causes the trapped rat to escape the tube when the rear door is opened. Across sessions, neophobia diminishes, permitting the rats' pursuit of social contact to emerge and dominate free- and trapped-rat behavior.

Time preferences in long-tailed macaques (Macaca fascicularis) and humans (Homo sapiens).

Rosati et al. (Curr Biol 17(19):1663-1668, 2007) found in a self-control test in which choice was between a smaller, immediately delivered food and a larger, delayed food, that chimpanzees preferred the larger reward (self-control); humans, however, preferred the smaller reward (impulsivity). They attributed their results to a species difference in self-control. In Experiment 1, monkeys (long-tailed macaques) were exposed to a self-control task in two conditions: where the food was hidden under differently colored bowls and where it was visible. When these two conditions were compared, choice shifted from greater preference for the impulsive alternative in the hidden condition to greater preference for the self-control alternative in the visible condition. Additionally, in both conditions, preference shifted from self-control to impulsivity over sessions. These results were explained in terms of the reversed-contingency effect (a propensity to reach for more over less when rewards are visible) and not to a capacity for self-control. In Experiment 2, humans that demonstrated preference for more over less in choice preferred the impulsive alternative when choice to either alternative was followed by the same intertrial interval-a preference that accelerates trial rates relative to preference of the self-control alternative. When trial rates were equated so that neither choice accelerated session's end, humans demonstrated self-control. These results suggest that Rosati et al.'s demonstration of impulsivity in humans was due to participants' desire to minimize session time.