Effects of drugs of abuse and cholinergic agents on delayed matching-to-sample responding in the squirrel monkey.

To study how drugs may disrupt short-term memory function, squirrel monkeys were trained to respond under a titrating delayed matching-to-sample schedule of reinforcement. Monkeys could respond on each of three keys in an operant chamber. At the start of each trial, the 30th response on the center key illuminated each of the side keys, one of which matched the stimulus presented on the center key (simultaneous matching). A response to the correct (matching) side key turned off all stimuli and initiated a delay, the length of which varied as a function of ongoing performance. After the delay, stimuli were randomly presented on two of the three keys. A response to the key which matched the color on the center key before the delay resulted in delivery of a food pellet (delayed matching). Incorrect simultaneous or delayed matching responses initiated a timeout. Under this procedure, diazepam and scopolamine decreased delayed matching accuracy at one or more doses that did not significantly decrease mean delay values, but only scopolamine decreased matching accuracy at a dose that did not significantly decrease response rates. Cocaine decreased mean delay values after the highest dose without affecting matching accuracy. Pentobarbital and methylscopolamine decreased matching accuracy and mean and maximum delay values after the highest doses. Nicotine and phencyclidine produced small decreases in delayed matching accuracy without affecting mean and maximum delay values. Caffeine, morphine, physostigmine and neostigmine did not alter matching performance even after doses that markedly decreased rates of responding.(ABSTRACT TRUNCATED AT 250 WORDS)