The time and space machine: continuous measurement of drug-induced behavior patterns in the rat

Because of the increasing demand for refined techniques to record drug-induced motoric changes, we designed and evaluated a computer monitoring system with continuous measurement of different parameters of rat motor activity. This system is particularly useful for chronic drug studies because it can characterize patterns of behavior and combines the residential and experimental environments, thus enabling automated behavioral measurement without experimenter intervention. Behavioral responses are detected by a capacitance-sensing device that generates bipolar analog voltages representing the location of the rat in its home cage. These voltages are first transduced, then amplified, and finally converted to digital signals in a computer that processes the input using algorithms to define specific responses. The technique pinpoints the exact location of the rat and identifies many kinds of responses simultaneously (e.g., rearing, circling) by tracking the path of movement or setting threshold limits. Some threshold values (representing rearing, gross movements, fine movements) were validated against stereotypy rating scales for amphetamine, apomorphine, and beta-phenylethylamine. Among these drugs, quantitatively distinct response profiles were obtained. The system has wide applications for studies of biological rhythms, sleep, aging, and drug toxicology.