MDMA affects both error-rate dependent and independent aspects of decision-making in a two-choice prediction task

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Abstract
Decision-making, i.e. selecting an action from a number of alternatives when the outcome is uncertain, is a complex process that is important for everyday life. 3,4-Methylenedioxymethamphetamine (MDMA), also known as ‘Ecstasy’, is a widely used recreational drug that is known to increase serotonin (5-HT) and, to a lesser extent, dopamine (DA) in animals. This study examined whether MDMA alters decision-making in a way that depends on the degree of success and outcome. Forty-two normal, healthy volunteers were given placebo or 1.5mg/kg p.o. MDMA in a randomized crossover design. Subjects completed the two-choice prediction task 120min after administration of the drug. Decision-making characteristics were obtained at 20% error rate, 50% error rate or 80% error rate. MDMA affected decision-making via a process that is dependent on success or failure. Administration of MDMA increased the degree to which the previous response predicted the current response (mutual information) and the average response sequence predictability (average dynamical entropy) at low error rates. MDMA increased the degree to which the previous stimulus influenced the selection of the current response at 20%, 50% or 80% error rate. MDMA did not significantly alter basic response characteristics such as response latency or switching. Self-assessment of the psychological state induced by MDMA did not predict the MDMA induced decision-making patterns. These results support the hypothesis that acute administration of MDMA affects success-related response selection during decision-making.