Short-term social memory in the laboratory rat: its susceptibility to disturbance.

Adult rats presented with a juvenile conspecific for 5 min on two occasions, separated by a 15-min inter-exposure interval (IEI), investigated the reintroduced juvenile significantly less in the second encounter. It is suggested that this was because the adult rats remembered the identity of the juvenile, because when a novel juvenile was introduced for the second encounter, no such reduction in investigation was observed. When the rats were either handled, placed in a smaller, novel, cage, or introduced to a new juvenile midway through the IEI, investigation of the reintroduced juvenile did not decrease. This indicated that memory of that juvenile had been disrupted. However, a simple change of cage during the IEI had no disruptive effect on memory. These results suggest that routine husbandry procedures can disrupt short-term social memory, which may lead to an increase in aggression due to a failure of recognition. This has implications for the welfare of captive social animals.

The effects of environmental context on laboratory rat social recognition.

Moving an animal from the environmental context in which it has learned a particular task to an entirely different context can reduce performance. We investigated the effect of switching environmental contexts on the ability of adult laboratory rats, Rattus norvegicus, to recognize and habituate to repeated presentations of juvenile conspecifics. Adults were exposed to juveniles for four periods of 5 min, separated by a 15-min interval. Rats either received all four exposures in the same context, or the first three in one context and the fourth in a different context. Half the rats in this latter group were familiarized with both contexts prior to testing, the other half had no experience of either. In all groups, the adults reduced their investigation of the juveniles over the three initial exposures. Mild aggression increased over the same period for the context-unfamiliar rats. A significant reduction in investigation by these rats between the third and fourth exposures, when the context was changed, suggested that the context switch further increased habituation to the juveniles. However, the context-familiar rats showed no such change, indicating that the changes observed for the context-unfamiliar rats were due to the effect of context novelty. This was supported by the finding that, during the first exposure, context-familiar adults investigated juveniles more and were more aggressive than those for which the contexts were novel. These results suggest that familiar contextual cues play only a minor role in the short-term social memory of laboratory rats. Copyright 1999 The Association for the Study of Animal Behaviour.