Rats (Rattus norvegicus) find occupancy of a restraint tube rewarding

Abstract

Two experiments evaluated whether rats' occupancy of a restraint tube is reinforcing. In Experiment 1, each rat in the 0‐min group moved freely in a chamber where a wall blocked access to a restraint tube. After 10 min the wall was removed, permitting 15 min of chamber access and tube entry. The other 2 groups were locked in the tube for 10 and 20 min respectively before release into the chamber for 15 min. Across sessions, rats locked up for 10 and 20 min entered the tube more frequently than rats in the 0‐min group, and during the first 2 sessions rats in the 20‐min group stayed in the tube longer than the other groups. Over sessions this difference disappeared. However, for all groups and sessions the mean percentage of session time in the tube exceeded chance expectations. This result suggests tube occupation was reinforcing. In Experiment 2’s Phase 1, rats could enter an open tube. On exiting, the tube door closed. A lever press opened the door for the rest of the 1‐hr session. In Phase 2, these rats were locked in the tube for 10 min before the door opened. Upon exiting, the door closed. As in Phase 1, a lever press opened the door for the rest of the session. The latency between pressing and tube entry decreased over sessions, indicating that tube entry reinforced lever pressing. These results are difficult to reconcile with accounts of rat empathy based on the thesis that tube restraint distresses occupants.

Social preference in rats

“…Although the rats allocated more responding to the social than the nonsocial option, the preferences were at times small, and most sessions included choices of both types. Thus, just as the opportunity to explore an empty tube restraint holds some reinforcing value (Hachiga et al 2020), so too does the opportunity to explore an empty chamber in the present study. This finding underscores the need to include such nonsocial options as controls when assessing social reinforcement.…”

“…In point of fact, however, evidence does not support an aversive function of the restraint (or accompanying distress in the restrained rats), as required by an empathy‐based account. First, ultrasonic vocalizations, as markers of distress, do not correlate with social release (Bartal et al, 2011); and second, rats freely enter the restraint, suggesting a reinforcing rather than an aversive function (Hachiga et al, 2020). Nevertheless, the social release procedures in general bear the mark of these questions they were originally designed to address, and it may therefore be useful to explore methods that do not rely on the restraint as a potential motivating variable.…”

Observation of rescue behaviour in wild boar (Sus scrofa)

“…Underlying motivations of rescue behaviour are difficult to reliably study due to experimental design or because several motivators can act simultaneously. Most of the studies do not provide data on motivations and, thus, the discussion on the underlying mechanism of rescue behaviour is ongoing [8][9][10][11][12] .Experiments with laboratory rodents emphasized the importance of experimental design to verify empirically the empathic motivators. In the first condition of the experiment of Ben-Ami Bartal et al (2011) 3 , rats opened a front door of a restraint tube and released their trapped cage mates into the same chamber.…”

“…Underlying motivations of rescue behaviour are difficult to reliably study due to experimental design or because several motivators can act simultaneously. Most of the studies do not provide data on motivations and, thus, the discussion on the underlying mechanism of rescue behaviour is ongoing [8][9][10][11][12] .…”

“…Furthermore, a recent study on mice suggested that rescue behaviour might be motivated by general interest in the restraining apparatus 16 . Finally, Hachiga et al (2020) 12 proved that the stay in the restraint tube was not stressful for the trapped rats but rather rewarding. Therefore, the design of experimental paradigm, measuring physiological or emotional responses to restraint, and the succession of rescuer actions are crucial in disentangling the motivators of rescue behaviour 1,8,[16][17][18] .…”