Impulsivity, inhibition and negative priming in ecstasy users

A modified Stroop color-word interference paradigm was used to investigate the effects of recreational ecstasy (MDMA) use on central executive inhibitory processes. Ecstasy users who also used cannabis were compared with non-users matched for cannabis consumption and with non-drug users on a Stroop task in which standard color-word interference trials were interspersed with trials in which the target color was the same as the distractor word on the immediately preceding trial. Ecstasy's effects on standard inhibition (conscious suppression of a prepotent response pattern—responsible for Stroop interference) could thus be contrasted with its effect on the short-term, unconscious, inhibitory process responsible for suppression of the preceding distractor word (negative priming). Neither drug group differed from the non-drug users in level of Stroop interference but ecstasy users showed reduced negative priming compared to the cannabis users and non-drug users. The loss of inhibition in the ecstasy users was not related to impulsivity assessed by two standard scales since these were similar in both drug-user groups and raised relative to the non-drug users. It is argued that previous failures to demonstrate loss of inhibition could be partly due to the fact that standard executive function tests, such as the Stroop, are unable to differentiate between sub-types of inhibition, only some of which may be affected by ecstasy use.