Speed and efficiency of information processing as a basis for working memory deficits in users of ‘ecstasy’ (MDMA)

Background: Ecstasy related cognitive impairments have been compared to age related impairments which are underpinned by a reduction in information processing speed. The present study predicted that if a common mechanism underlay both types of impairment, then controlling for the efficiency and speed of information processing should remove differences in working memory performance between ecstasy users and nonusers. Method: For all tasks group was a between-participants independent variable at three levels, namely current ecstasy users (n = 29), former ecstasy users (n = 10), and controls (n = 46). Two information processing speed tasks were performed requiring as many same/ different judgements of letters and patterns, respectively, in 30 s as possible. Each task presented three levels of stimulus complexity. Working memory performance was measured by the computation span task. Results: Both user groups performed significantly worse than controls on the computation span task when the speed and efficiency of information processing were controlled by covariates representing the numbers of correct responses and errors on both comparison tasks. No significant inter-group differences were found for the number of correct responses on the pattern task, although a trend was found on the letter task with controls performing better. Current users made more errors than controls on both comparison tasks. Conclusions: The failure of the covariates to remove inter-group differences on the computation span task suggests that these working memory differences are not mediated by the same mechanism which has been shown to underlie age related differences in performance. An alternative mechanism for ecstasy related deficits could be the premature termination of processing, related to elevated levels of impulsivity reported in this population.