Response acquisition with fixed and variable resetting delays of reinforcement in male and female Wistar rats.

Experimentally naive, food-deprived male and female Wistar rats were exposed to different experimental procedures in which response-independent food pellets were delivered as long as the rats did not press either one of the two levers in the experimental chamber. Once a lever was pressed, the presentation of response-independent food was suspended for the remainder of that session and food pellets were delivered only after an unsignalled, resetting period of time from each lever press had elapsed. For five different groups of subjects there was either no delay between a lever press and food presentation, a fixed delay of 10 s or 30 s, or a variable delay of 10 s or 30 s. Response acquisition occurred most rapidly when a lever press was immediately followed by food presentation. Responding was also acquired when variable resetting delays of 10 s or 30 s or a fixed resetting delay of 10 s was inserted between a lever press and food presentation. When a fixed resetting delay of 30 s followed a lever press before food presentation some responding was observed, but not as much as in the other experimental conditions. The present results show that naive male and female Wistar rats will acquire a lever-press response when food presentation is contingent upon, but not immediately contiguous with a lever press. Consistent differences between the sexes were not observed.