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 mo nkeys were trained to respond under a titrating delayed matching-to-sa mple schedule of reinforcement. Monkeys could respond on each of three keys in an operant chamber. At the start of each trial, the 30th resp onse on the center key illuminated each of the side keys, one of which matched the stimulus presented on the center key (simultaneous matchi ng). A response to the correct (matching) side key turned off all stim uli 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 col or on the center key before the delay resulted in delivery of a food p ellet (delayed matching). Incorrect simultaneous or delayed matching r esponses initiated a time-out. Under this procedure, diazepam and scop olamine 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 decr ease response rates. Cocaine decreased mean delay values after the hig hest dose without affecting matching accuracy. Pentobarbital and methy lscopolamine decreased matching accuracy and mean and maximum delay va lues after the highest doses. Nicotine and phencyclidine produced smal l decreases in delayed matching accuracy without affecting mean and ma ximum delay values. Caffeine, morphine, physostigmine and neostigmine did not alter matching performance even after doses that markedly decr eased rates of responding. This study shows that the effects of drugs of abuse on matching-to-sample performance may differ from each other as well as from those of the cholinergic antagonist scopolamine.