Differential effects of midazolam and pentylenetetrazole on behavioral repetition and variation.

The present study investigated the effects of midazolam and pentylenetetrazole upon repeating and varying sequences of responses. Rats were exposed to a multiple schedule with two components. Under the VARY component, water was provided if the current sequence of four responses differed from each of the five previous ones; under the REPEAT component, water delivery was contingent upon a particular four-response sequence. Each component was signaled by specific exteroceptive stimuli. Overall, sequence variability was affected by midazolam, and to a lesser degree, by pentylenetetrazole. With the REPEAT contingency, drug administration increased behavior variation, thus reducing accuracy; with the VARY contingency, behavior variation and accuracy were not altered. These results were explained on the basis of the disruptive effects of both drugs upon the discriminative control exerted by previous responses within a sequence and by exteroceptive stimuli.