Social memory of the male laboratory rat.

Abstract

Duration of social-investigatory behavior by mature male Long-Evans rats was used as a measure of individual recognition in a series of five experiments to assess social memory. In Experiment 1, the duration of social investigation during a second exposure to the same juvenile was directly related \o the length of the interexposure interval. In Experiment 2, males were exposed to the same or to a different juvenile 10 min after an initial 5-min exposure to a novel juvenile; reexposure to the same juvenile elicited significantly less social investigation than an exposure to a different juvenile. Experiments 3 and 4 demonstrated that following a 5-min introductory exposure, social memory of the juvenile male or female is relatively brief in comparison with that of mature males. Experiment 5 revealed a retroactive interference effect on recently acquired memory for an individual: Male subjects exposed to interpolated social experience engaged in significantly longer investigation of a juvenile stimulus than those with no interpolated social experience. The combined results suggest that the rat normally engages in spontaneous learning of individual identity and that social memory may be a significant aspect of complex social interactions.

The effects of environmental context on laboratory rat social recognition

“…We used the social recognition test (Thor & Holloway 1982), which is based upon a comparison of behaviour, particularly investigation, between two exposures of the same individual to a subject animal. A reduction in investigation in the second exposure implies recognition of the individual, whereas no change suggests that the subject's social memory of that individual has decayed over the interval between exposures.…”

“…Social memory after short term exposures appears to be relatively brief, with no apparent recognition by a male adult rat of a juvenile previously introduced for 5 min, after an interval of 120 min (e.g. Thor & Holloway 1982;Dantzer et al 1987). We exposed juveniles to adults for four consecutive 5-min exposures each separated by a 15-min interval, during which the juveniles were returned to their home cages.…”

“…Observations were made of the total amount of investigation and mildly aggressive behaviour during the introductions. Investigation of the juvenile included sniffing, grooming and following within a distance of 1cm (Thor & Holloway 1982), and mild aggression consisted of rolling/standing over the juvenile, and/or pushing it away. Any overtly aggressive behaviour, such as biting, resulted in the session being abandoned immediately.…”

The influence of preexperimental experience on social discrimination in rats (Rattus norvegicus).

“…Whilst very short-term social memory does appear to be interfered with retroactively by the introduction of a novel conspecific (e.g. Thor & Holloway 1982;Dantzer et al 1987, Burman & Mendl 2000, it is unlikely that long-term social memory is affected in the same way.…”

“…the social recognition test: e.g. Thor & Holloway 1982, Dantzer et al 1987; the habituation/discrimination technique: e.g. Johnston & Bullock 2001; the social discrimination procedure: e.g.…”