Empathy and Pro-Social Behavior in Rats
To test for empathically motivated pro-social behavior in rodents
After several sessions, the free rat learned to intentionally and quickly open the restrainer and free the cagemate. Rats did not open empty or object-containing restrainers. They freed cagemates even when social contact was prevented. When liberating a cagemate was pitted against chocolate contained within a second restrainer, rats opened both restrainers and typically shared the chocolate. Thus, rats behave pro-socially in response to a conspecific’s distress, providing strong evidence for biological roots of empathically motivated helping behavior.
Insights, lessons learnt:
Rats show clear signs of empathy (presumably helps survival, like for us). Likely the same for other animals, ie. the suffering of an animal can cause suffering for observing animals.
we sought to determine whether rats are capable of empathically motivated helping behavior. We tested whether the presence of a trapped cagemate induces a pro-social motivational state in rats, leading them to open the restrainer door and liberate the cagemate.
he start of testing. In each session, a rat (the free rat) was placed in an arena with a centrally located restrainer in which a cagemate was trapped (trapped condition, n = 30 rats, 6 females). The free rat could liberate the trapped rat by applying enough force to tip over the restrainer door (Fig. 1A). If a free rat failed to open the door, the experimenter opened it halfway, allowing the trapped rat to escape and preventing learned helplessness. Rats remained in the arena together for the final third of the session. Door-opening only counted as such if the free rat opened the door before the experimenter opened it halfway. Sessions were repeated for 12 days. Control conditions included testing a free rat with an empty restrainer (empty condition, n = 20 rats, 6 females) or toy rat鈥揷ontaining restrainer (object condition, n = 8 males). As an additional control, for the number of rats present, we tested a free rat with an empty restrainer and an unrestrained cagemate located across a perforated divide (2+empty condition, n = 12 males)
rats were motivated to move and act specifically in the presence of a trapped cagemate
A sharp increase in the free rat’s activity was observed at the time of door-opening (Fig. 2C), suggesting that the liberation of a trapped cagemate is a salient event.
Initially, rats in the trapped condition opened the door in any of three ways: tipping the door over from the side or top or pushing it up with their heads. However, on days 6 to 12, they consistently opened the door with their heads (Fig. 2D). Furthermore, whereas rats initially froze after the door fell over, later on they did not freeze (Fig. 2E), demonstrating that door-opening was the expected outcome of a deliberate, goaldirected action
Significantly more alarm calls were recorded during the trapped condition (13%) than during the empty and object conditions [3 to 5%, P < 0.05
A greater proportion of female rats (6⁄6) than male rats (17⁄24) in the trapped condition became door-openers (P < 0.05, c-square), which is consistent with suggestions that females are more empathic than males (7, 12, 13).
Animals who became openers had lower approach latencies than nonopeners (P < 0.01, t test), suggesting that successful opening behavior correlates with boldness scores (fig. S1). This demonstrates that individual trait differences may factor into the expression of pro-social behavior.
In order to examine the relative value of liberating a trapped cagemate, we tested a cohort of rats in a cagemate versus chocolate paradigm. When given a choice, these non鈥揻ood-deprived rats ate an average of >7 chocolate chips and no rat chow, indicating that they found chocolate highly palatable. The free rat was placed in an arena with two restrainers, one containing the trapped cagemate and the other containing five chocolate chips (chocolate cagemate condition, Fig. 4, C and D). As a control, one restrainer was empty while the other contained chocolate (chocolate empty condition). For rats in the chocolate cagemate condition, there was no difference in the door-opening latencies for the two restrainers during days 6 to 12 (Fig. 4C). In contrast, rats in the chocolate empty condition opened the chocolate-containing restrainer more quickly than the empty one (P < 0.01, t test, Fig. 4D). These results show that the value of freeing a trapped cagemate is on par with that of accessing chocolate chips. Like rats in the trapped condition, rats needed several days (5.8 T 2.1) to learn to open the chocolate restrainer, which is evidence that door-opening was neither easy nor instinctual
Rats in the chocolate empty condition ate virtually all the chips (4.8 T 0.7), whereas free rats in the chocolate cagemate condition ate fewer chips (3.5 T 1.5, P < 0.01, t test), which allowed trapped rats to eat the remaining chips (1.5 T 1.4).
Our study demonstrates that rats behave pro-socially when they perceive a conspecific experiencing nonpainful psychological restraint stress (14, 15), acting to end that distress through deliberate action. In contrast to previous work (5, 9, 16, 17), the present study shows pro-social behavior accomplished by the deliberate action of a rat. Moreover, this behavior occurred in the absence of training or social reward, and even when in competition with highly palatable food.
To determine whether anticipation of social interaction is necessary to motivate door-opening, we tested rats in a modified setup in which the trapped animal could only exit into a separate arena
Thus, rats opened the door of a cagemate-containing restrainer but not of an empty restrainer, indicating that the expectation of social contact is not necessary for eliciting pro-social behavior