Three independent factors characterize spontaneous rat motor activity.

A scaling approach was introduced recently to assess sequential and geometrical aspects of animal behavior. This study describes the relationship between different measures of unconditioned motor activity of rats. Specifically, the amount of motor activity was assessed using both a traditional photobeam break measure, counts, and the temporal scaling exponent, alpha, which describes the ratio of fast to slow behavioral micro-events. The sequential characteristics of the behavior were assessed by the dynamical entropy, h, describing the degree of unpredictability of future movements. The geometrical characteristics of rat motor activity were quantified by the spatial scaling exponent, d. Exploratory activity was measured by counting rearings and holepoking responses. A factor analysis of these measures was conducted based on results from 137 drug-naive animals that were tested for 1 h in the Behavioral Pattern Monitor. Three independent factors account for 77% of the variance. These factors can be described as the 'amount of activity', 'sequential response organization', and 'exploratory activity'. The factor loadings support the initial hypothesis that the geometrical structure of rat motor activity, i.e. the spatial scaling exponent d, varies independently from the amount of activity, i.e. counts. In addition, the distribution of these measures did not deviate significantly from normality suggesting that the z-scores of these variables, which have been used previously in the d-alpha plane description, are able to indicate significant changes of behavior. These results suggest that unconditioned motor activity is influenced by at least three independent factors. The independent assessment of these factors may contribute significantly to the understanding of the neural substrates involved in the organization of unconditioned behavior.