Effects of drugs on concurrent variable-interval variable-interval schedule performance

According to the generalized matching law the ratio of responses between tw o alternatives matches the ratio of reinforcers produced by these responses . In these experiments using concurrent variable-interval variable-interval schedules in pigeons, responding occurred more frequently on the key assoc iated with the lower reinforcement density (undermatching) than would be pr edicted by perfect matching. Under control conditions, there was no bias to ward responding on either key. Pentobarbital, methamphetamine, morphine and phencylidine all increased bias toward responding on the left key with the exception of one 10 mg/kg dose of pentobarbital that increased bias toward responding on the right key. Higher doses of methamphetamine and morphine, and most doses of phencyclidine increased matching, but high doses of pent obarbital further decreased matching. Morphine increased bias toward respon ding on the left key at much lower doses than those that affected matching, while phencyclidine increased matching at lower doses than those that incr eased bias. Pentobarbital produced small increases in response rates that w ere sometimes accompanied by small increases in key switching. All other dr ugs only decreased response rate and decreased the number of key switches. These data suggest that drugs disrupt responding under concurrent schedules both by increasing bias and by changing baseline matching functions. Behav Pharmacol 1998; 9:663-670 (C) 1998 Lippincott Williams & Wilkins.