Development of Exploration and Investigation in the Norway Rat (Rattus norvegicus)

A cross-sectional study of the development of spontaneous exploratory behavior in the laboratory rat was conducted. Long-Evans hooded rat pups aged 11 to 28 days (n = 158, from 25 litters) were placed into a dimly illuminated arena for 10 min on 2 consecutive days. Analysis of videotaped records from the second session for each rat pup showed a relatively sudden emergence of locomotor exploration between 12 and 16 days of age. The behavioral topography of interactions with objects developed less uniformly, with some features (e.g., bout length) relatively unchanging and other features (e.g., number of bouts, number of different behaviors displayed) increasing with age. The data for locomotor exploration are consistent with an explanation that depends on maturation-driven emergence of species-typical behavior, but that explanation cannot account for the pattern of development for object investigation. These results provide further evidence that some important aspects of the character of exploratory behavior depend, at least partially, on experience, and that exploration is not in fact a single behavior system. In addition, they provide important baseline information for further studies of the structure and function of exploratory behavior.