Operant conditioning of response variability in male and female Wistar rats.

It has previously been suggested that some of the behavioral differences between the sexes in food motivated operant procedures may be a function of the fact that males are more likely than females to exhibit stereotyped behavior. If such is the case, then it might be expected that behavioral variability is more easily conditioned in females than in males. The present experiment was designed to investigate this notion. Male and female Wistar rats were trained to respond in a procedure in which response variability was explicitly reinforced. In this procedure subjects had continuous access to two response levers in the experimental chamber. In the first experimental condition, each sequence of four responses was followed by the presentation of a food pellet, if the sequence differed from the two sequences which preceded it (Lag 2). Time-out was presented when such was not the case. During time-out the levers were retracted from the chamber and all stimulus lights were extinguished for 4 sec. In subsequent experimental conditions, subjects had to produce four-response sequences which differed from the preceding four, eight and sixteen sequences respectively (Lag 4, 8, 16). Response sequences were classified by the number of switches between levers. Behavioral variability increased as the lag requirement was increased, showing that variability is a conditionable dimension of behavior. Differences between males and females were however not observed. These results thus contradict the previously reported finding that males exhibit more behavioral stereotypy than females. It is suggested that procedural variables may account for these seemingly contradictory findings.