Event related potential (ERP) evidence for selective impairment of verbal recollection in abstinent recreational methylenedioxymethamphetamine (“Ecstasy”)/polydrug users

Ecstasy is a recreational drug whose active ingredient, 3,4 Methylenedioxymethamphetamine (MDMA), acts predominantly on the serotonergic system. Although MDMA is known to be neurotoxic in animals, the long-term effects of recreational Ecstasy use in humans remain controversial but one commonly reported consequence is mild cognitive impairment particularly affecting verbal episodic memory. Although event-related potentials (ERPs) have made significant contributions to our understanding of human memory processes, until now they have not been applied to study the long term effects of Ecstasy. The aim of this study was to examine the effects of past Ecstasy use on recognition memory for both verbal and non-verbal stimuli using ERPs. We compared the ERPs of abstinent Ecstasy usersEcstasy/polydrug users with those of matched groups of cannabis users and non-drug using controls. Despite equivalent memory performance, Ecstasy usersEcstasy/polydrug users showed an attenuated late positivity over left-parietal scalp sites, a component associated with the specific memory process of recollection. This effect was only found in the word recognition task which is consistent with evidence that left hemisphere cognitive functions are disproportionately affected by Ecstasy, probably because the serotonergic system is laterally asymmetrical. Experimentally decreasing central serotonergic activity through acute tryptophan depletion also selectively impairs recollection, and this too suggests the importance of the serotonergic system. Overall, our results suggest that Ecstasy has a durable effect on a specific component of recognition memory, recollection, and that this is most probably caused by the serotonergic neurotoxicity of MDMA although the role of other drugs cannot be excluded