Effects of drugs of abuse on response accuracy and bias under a delayed matching-to-sample procedure in squirrel monkeys

The effects on memory of drugs of abuse from several pharmacological classe s were examined in four adult male squirrel monkeys responding under a dela yed matching-to-sample schedule of food presentation. Subjects were require d to emit 20 responses on a sample key transilluminated by either a constan t white or a flashing blue light. The twentieth response initiated a 3-seco nd delay followed by presentation of two comparison stimuli. If a response was made to the key that matched the sample stimulus (correct match), a sin gle food pellet (97 mg) was delivered. Pentobarbital (0.32-10 mg/kg), diaze pam (0.1-5.6 mg/kg), phencyclidine (0.01-0.32 mg/kg) and cocaine (0.1-3.2 m g/kg) dose-dependently reduced accuracy of matching performance towards cha nce levels. Amphetamine (0.01-1.0 mg/kg) resulted in a small, but statistic ally significant, reduction in accuracy at a dose of 0.56 mg/kg, while 1.0 mg/kg completely suppressed responding. Analyses indicated that pentobarbit al, diazepam and cocaine produced either position or color biases in respon ding, and in some cases these biases in responding were associated with dec reases in accuracy. No such response biases were observed with phencyclidin e or D-amphetamine. These results suggest that drug effects on working memo ry performance can, in some cases, be the result of non-mnemonic processes. Thus, they illustrate the importance of examining behavioral endpoints in addition to task accuracy when interpreting drug effects on working memory in laboratory animals. (C) 2001 Lippincott Williams & Wilkins.