Natural segmentation of the locomotor behavior of drug-induced rats in a photobeam cage

Recently, Drai et al. (J Neurosci Methods 96 (2000) 119) have introduced an algorithm that segments rodent locomotor behavior into natural units of 's taying in place' (lingering) behavior versus going between places (progress ion segments). This categorization, based on the maximum speed attained wit hin the segment, was shown to be intrinsic to the data, using the statistic al method of Gaussian Mixture Model. These results were obtained in normal rats and mice using very large (650 or 320 cm) circular arenas and a video tracking system. In the present study, we reproduce these results with amph etamine, phencyclidine and saline injected rats, using data measured by a s tandard photobeam tracking system in square 45 cm cages. An intrinsic disti nction between two or three 'gears' could be shown in all animals. The spat ial distribution of these gears indicates that. as in the large arena behav ior, they correspond to the difference between 'staying in place' behavior and 'going between places'. The robustness of this segmentation over arena size, different measurement system and dose of two psychostimulant drugs in dicates that this is an intrinsic, natural segmentation of rodent locomotor behavior. Analysis of photobeam data that is based on this segmentation ha s thus a potential use in psychopharmacology research. (C) 2001 Elsevier Sc ience B.V. All rights reserved.