Another look at amphetamine-induced stereotyped locomotor activity in rats using a new statistic to measure locomotor stereotypy

Rat open field behavior is often used as a tool to study the behavioral effects of drugs. In this report, drug-induced patterns of locomotion in an open field were studied with the aid of a simple new statistic. Briefly, the animal's path through the open field is converted into a series of trips. Gamma ( \(\hat \gamma\) ) estimates the probability that the animal will repeat the trip that it has just exhibited; thus \(\hat \gamma\) quantifies “locomotor stereotypy”. Trip lengths can also be compared across drug groups. Thus caffeine has no effect on \(\hat \gamma\) even though it produces a dose-related increase in locomotions. Caffeine does not produce amphetamine-like stereotypy. On the other hand, amphetamine produces a dose-related increase in \(\hat \gamma\) . Although \(\hat \gamma\) was designed to detect any pattern of locomotor behavior, rats treated with high doses of amphetamine almost always exhibited the same pattern of locomotor behavior — repetitive trips around the perimeter of the open field. Although further characterization of the statistic is necessary, these findings suggest that \(\hat \gamma\) has potential for quantifying “locomotor stereotypy” and for providing a more subtle description of locomotor behavior in general.