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

To study how drugs may disrupt short-term memory function, squirrel monkeys were trained to respond under a titrating de-layed 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 time