Psychopharmacology (1991) 104: 6-16 0033315891000714 Psychophannacology 0 Springer-Verlag 1991 A temporal and spatial scaling hypothesis for the behavioral effects of psychostimulants Martin P. Paulus' and Mark A. Geyer2 Biological Dynamics and Theoretical Medicine, and Department of Psychiatry, School of Medicine, University of California, San Diego (M-003), La Jolla, CA 92093, USA Received January 2, 1990 / Final version October 20, 1990 Abstract. A variety of psychoactive substances (am- phetamine, nicotine, scopolamine, apomorphine, lis- uride, and MDMA) were tested to examine whether a proposed scaling hypothesis is appropriate for the de- scription of the amount and the structure of rat loco- motor paths recorded in the Behavioral Pattern Monitor (BPM). The analytical approach was based on the assumption that the scaling behavior of a few collective variables may characterize sufficiently changes in the animal's behavior induced by different drugs. The tem- poral scaling exponent a, describing the ratio of fast to slow responses in the BPM, sensitively reflected the dif- ferent stimulant properties of the substances. The spatial scaling exponent d, which relates the average pathlength to the resolution used to measure consecutive responses, was found to discriminate substances that had been separated previously via qualitative descriptions. Several behavioral response categories emerged from com- parisons of the locations of different drugs on a two- dimensional d-a plane. Scopolamine, MDMA, lisuride, and high doses of apomorphine increased a while de- creasing d, whereas amphetamine, nicotine, and caffeine produced an increased a with no change or an increase in d. Stereotypies could be identified on the opposite ends of the spatial scaling exponent scale and were interpreted as reflecting two kinds of perseveration. These results suggest that scaling approaches can be used to assess quantitatively the state of the animal based on its loco- motor behavior and that the exponents can serve as collective variables providing a macroscopic description based on the microscopic elements of behavior. Key words: Psychostimulants - Amphetamine - Dopa- mine - Locomotor activity - Behavioral pattern monitor - SpatiaI scaling exponent - Temporal scaling exponent The assessment of locomotor behavior using measures of activity allows one to characterize the unconditioned Offprint requests to: M.P. Paulus behavioral effects of acute drug treatments and to deter- mine whether substances have stimulant properties (Robbins 1977; Robbins and Sahakian 1983; Geyer et al. 1986; Harvey 1987). Locomotor behavior, however, consists of a variety of responses presumably purpose- fully organized in sequences to allow a successful adapta- tion of the animal to the test environment. Therefore, the assessment of patterns of motor activity has prompted several investigators to develop measures capturing this information (Lat 1965; Schiorring 1971 ; Ljungberg and Ungerstedt 1976). This effort to extract more informa- tion from experiments using the unconditioned locomo- tion paradigm has intensified during the last decade (Nickolson 1981 ; Adams and Geyer 1982; Flicker and Geyer 1982; Stoff et al. 1983; Geyer et al. 1986; Sanberg et al. 1987; Kernan et a1 1988). In some cases, explicit measures of investigatory behavior, such as rearings, holepokes or object contacts, have been added to mea- sures of locomotion in order to determine the contribu- tion of stimulus-directed behavior to the frequently ob- served qualitative differences in the effects of various stimulant drugs (Ljungberg and Ungerstedt 1977; Geyer et al. 1986). Similarly, attempts have been made to quan- tify differences in drug-induced changes in the patterns of the locomotion per se, using measures such as the coefficient of variation, the spatial correlation function, and the dynamical description based on ergodic theory (Geyer et al. 1986; Kernan et al. 1988; Paulus et al. 1990). Some groups have followed a different approach by la- beling different sequences of motions as behavioral cat- egories and describing sequences of categories and the changes within these sequences (Teitelbaum 1982; Ber- ridge et al. 1987). Others (Stahle 1987) have computed latent variables underlying the linear relationship be- tween linear factors to detect and describe subtle drug effects. Most of these approaches are based on assump- tions about the discrete nature of behavioral response categories (Norton 1968), operational measures of hypothetical constructs such as conflict, novelty, or un- certainty (Berlyne 1960), analyses of the range of re- sponse categories as influenced by specific drug treatments (Lyon and Robbins 1975), and/or multivariate charac-