Individually distinctive odours represent individual conspecifics in rats

Abstract

Individual recognition implies that a subject has the ability to discriminate between familiar conspecifics on the basis of their idiosyncratic characteristics. In this sense it is likely to be a more complex process than other forms of social recognition which involve classification of conspecifics into broad categories such as group, sex, age, kinship and familiarity. Using a go/no-go discrimination procedure, this study showed that rats,Rattus norvegicus, are indeed able to recognize conspecifics as individuals. Once rats had learned to discriminate a pair of conspecifics, they showed positive transfer on a series of discrimination problems involving novel conspecifics as stimuli. Furthermore, on a reversal test, rats were able to retain the memory of the individual identity of conspecifics to which they were exposed for the first time for at least 24h. Finally, using the individually distinctive odours of previously discriminated conspecifics in tests clearly demonstrated that rats perceive olfactory sig-natures as representations of known individuals. Taken together, these results provide evidence for true individual recognition in rats and invite further investigations to gain deeper insight into the cognitive processes used by rats to build up a representation of individual conspecifics.