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THE STATE-DEPENDENT EFFECTS OF METHYLPHENIDATE AND DEXTROAMPHETAMINE

This study was designed to evaluate the effects of two stimulant drugs on both learning and retention. However, the fundamental purpose was to evaluate the transfer effects which might result when the critical independent variable was the maintenance or change of the drug condition from learning to retention sessions. The subjects were 18 hyperactive children who were randomly assigned to one of three acquisition groups: placebo, methylphenidate (Ritalin), or dextroamphetamine (Dexedrine). Testing was conducted in “sequences.” Each sequence consisted of training session and a subsequent retention session which occurred 48 hours later. There were four of these sequences allowing for one baseline sequence and three transfer sequences. Once assigned to an acquisition group, the subject always learned the tasks under that drug condition. However, each subject was tested for retention under each of the possible drug conditions. Three tasks were employed in this experiment: a recognition task, paired associate task, and a maze task. These tasks were selected with the rationale that they described a hierarchy of processes, any one of which might be critically affected if state dependency emerged as a significant factor. The results indicated that neither of the active drugs significantly improved learning or retention performance. Furthermore, although numerous dependent measures were used on each of the three tasks, all tests for statedependent effects were statistically nonsignificant. Many of the transfer data actually proceeded in directions contrary to what would be predicted from state-dependent theory. Several studies which employed similar tasks were discussed. It was emphasized that the majority of these had obtained results virtually identical with the present experiment. The two studies presenting major exceptions were shown to be procedurally inadequate in many respects. It was concluded that state dependency does not occur with these drugs when they are administered in reasonable clinical doses. Transfer appears to be as great when the drug conditions are changed as when they are maintained constant.