Catharine Montgomery

The differential effects of ecstasy/polydrug use on executive components: shifting, inhibition, updating and access to semantic memory

Rationale/ObjectivesRecent theoretical models suggest that the central executive may not be a unified structure. The present study explored the nature of central executive deficits in ecstasy users.MethodsIn study 1, 27 ecstasy users and 34 non-users were assessed using tasks to tap memory updating (computation span; letter updating) and access to long-term memory (a semantic fluency test and the Chicago Word Fluency Test). In study 2, 51 ecstasy users and 42 non-users completed tasks that assess mental set switching (number/letter and plus/minus) and inhibition (random letter generation).ResultsMANOVA revealed that ecstasy users performed worse on both tasks used to assess memory updating and on tasks to assess access to long-term memory (C- and S-letter fluency). However, notwithstanding the significant ecstasy group-related effects, indices of cocaine and cannabis use were also significantly correlated with most of the executive measures. Unexpectedly, in study 2, ecstasy users performed significantly better on the inhibition task, producing more letters than non-users. No group differences were observed on the switching tasks. Correlations between indices of ecstasy use and number of letters produced were significant.ConclusionsThe present study provides further support for ecstasy/polydrug-related deficits in memory updating and in access to long-term memory. The surplus evident on the inhibition task should be treated with some caution, as this was limited to a single measure and has not been supported by our previous work.

Executive Working Memory Deficits in Abstinent Ecstasy/MDMA Users: A Critical Review

Aims: This review examined studies of executive functioning in abstinent ecstasy (3,4-methylenedioxymethamphetamine, MDMA) users on tasks which had been empirically mapped onto updating, shifting, inhibition and accessing long-term memory executive processes. Studies of some aspects of visuospatial memory performance were also included because of the investment of executive resources in such tasks. Methods:Thirty-three studies were identified for the review following searches of the Psychinfo and Medline databases. Inclusion criteria were the reporting of new empirical findings from participants drug free at the time of testing, in peer-reviewed journals in the English language. Results:Evidence for ecstasy-related performance deficits was strongest for the updating of verbal material, and for visuospatial memory tasks requiring additional processing beyond storage and retrieval. Such processing suggested that the overall level of executive demand was an important consideration. Executive shifting showed little evidence of ecstasy-related impairment, whilst examination of inhibition and long-term memory access presented an unclear picture. Conclusions: All but one of the studies had a cross-sectional design. Although this is a potential weakness with regard to confounds, the necessity of such designs was acknowledged. Studies were generally aware of the need to control for potential confounds, especially the effects of other drugs, through a mixture of group designs and statistical techniques. It was recommended that future studies of executive functioning in ecstasy users should detail the relationship of the tasks and dependent variables reported to specific executive processes and consider the level of executive demand imposed by such tasks.

Assessing the functional significance of ecstasy-related memory deficits using a virtual paradigm.

Previous research shows that the use of ecstasy results in working memory and executive impairments in some users. The present study sought to assess the functional significance of such deficits using a virtual reality task.

Evidence for executive deficits among users of MDMA (Ecstasy).

Random letter generation and computation span are tasks known to load on executive, prefrontal resources. Previous research suggests that Ecstasy users are impaired on random letter generation. The current study, employing a larger sample (44 current Ecstasy users, and 59 non-Ecstasy users), together with more effective statistical controls for other drug use, failed to replicate previous findings. Ecstasy users were unimpaired on all measures of random generation performance. A significant difference was obtained on the computation span measure, with Ecstasy users scoring significantly lower than non-Ecstasy users. This difference remained statistically significant following control for various indicators of the use of other drugs including cannabis. The results are discussed in terms of the potential effects that Ecstasy might have on different component executive processes.

The effects of heavy social drinking on executive function: a systematic review and meta-analytic study of existing literature and new empirical findings.

Previous investigations of executive function in alcohol dependent and in social drinkers have not always produced consistent results and have not utilised key indicators of recent theoretical models of Executive Function (EF). The present paper reports the results of two studies that seek to address these limitations.

Reasoning deficits in ecstasy (MDMA) polydrug users

Rationale/objectivesPrevious research has shown that ecstasy users are impaired in thinking and reasoning. The present study sought to explore the possibility that syllogistic reasoning errors in ecstasy users were due to an inability to construct a model of the premises due to working memory limitations.MethodsTwenty-nine ecstasy users and 25 nonecstasy user controls completed abstract syllogistic reasoning problems varying in difficulty. Pairs of premises were provided, and participants were required to generate conclusions that followed necessarily from them.ResultsOn the easier problems, both groups performed at well above chance although nonusers achieved significantly more correct responses. Consistent with existing research, on the more difficult problems, errors by nonusers were characterised by incorrect conclusions suggesting that while nonusers have the working memory capacity to construct a single model of the premises, this is not an exhaustive representation and usually results in an erroneous conclusion. On the other hand, for all problem types, ecstasy users, rather than produce incorrect responses, were more likely to fail to generate a conclusion.ConclusionsThe present results are consistent with the possibility that ecstasy users with their reduced working memory capacity may experience difficulty in constructing even a single model of the premises. While this might be attributable to the effects of 3,4-methlylenedioxymethamphetamine neurotoxicity, many of the ecstasy users in the present study were polydrug users. Thus, the possibility that other drugs including cannabis and cocaine might contribute to the present results cannot be excluded.

The role of executive functions in human prospective interval timing

Human timing is thought to be based on the output of an internal clock. Whilst the functioning of this clock is well documented, it is unclear which other cognitive resources may moderate timing. Brown (2006) and Rattat (2010) suggest that the central executive of working memory may be recruited during timing. However it seems likely that the fractionated executive component processes identified by Miyake et al. (2000) and Fisk and Sharp (2004) may differentially contribute to timing performance; further exploration of this was the aim of the present study. An interference paradigm was employed in which participants completed an interval production task, and tasks which have been shown to tap the four key executive component processes (shifting, inhibition, updating and access) under single and dual-task conditions. Comparison of single and dual-task performance indicated that timing always became more variable when concurrently performing a second task. Bidirectional interference only occurred between the interval production task and the memory updating task, implying that both tasks are competing for the same executive resource of updating. There was no evidence in the current study to suggest that switching, inhibition or access was involved in timing, however they may be recruited under more difficult task conditions.

The effects of a modest dose of alcohol on executive functioning and prospective memory

Acute alcohol intoxication selectively impairs executive functioning and prospective memory (PM). Much previous researches in this area have used laboratory‐based tasks that may not mimic functions that individuals with dysexecutive syndrome have problems with in their everyday life. The present study aimed to assess the effects of a modest dose of alcohol on executive functioning and PM using a virtual reality task and investigate the role of executive planning in PM performance.

The nature of ecstasy-group related deficits in associative learning

Rationale/objectivesResearch has revealed associative learning deficits among users of ecstasy; the present study explored the component processes underlying these deficits.MethodsThirty-five ecstasy users and 62 non-ecstasy users completed a computer-based, verbal paired-associates learning task. Participants attempted to learn eight sequentially presented word pairs. After all eight had been presented, the first member of each pair was displayed and participants attempted to recall the second. Eight trials were administered. Correct responses on each trial, forgetting at various levels of learning, perseveration errors and the rate at which the associations were learned (trials to completion) were all recorded.ResultsMANOVA revealed that ecstasy users performed worse overall and subsequent ANOVAs showed that users performed significantly worse on virtually all measures. Regression analysis revealed that over half of the ecstasy-group related variance in trials to completion was attributable to group differences in initial learning and forgetting. In relation to forgetting, it appears that cannabis use may be an important determinant. In relation to rate of learning (trials to completion) and initial learning, both ecstasy and cannabis may be implicated.ConclusionsThere appears to be abundant evidence of associative learning deficits among ecstasy users. However, it appears that a range of illicit drugs including cannabis and ecstasy may contribute to these deficits.

Cannabis-related deficits in real-world memory

Research shows that cannabis users exhibit deficits in prospective memory (PM) and executive function, which persist beyond acute intoxication. However, many studies rely on self‐reports of memory failures or use laboratory‐based measures that may not mimic functional deficits in the real world. The present study aimed to assess real‐world memory functioning.