Differences in prefrontal blood oxygenation during an acute multitasking stressor in ecstasy polydrug users.

BACKGROUND: Cognitive deficits are well documented in ecstasy (3,4-methylenedioxymethamphetamine; MDMA) users, with such deficits being taken as evidence of dysregulation of the serotonin (5-hydroxytryptamine; 5-HT) system. More recently neuroimaging has been used to corroborate these deficits. The present study aimed to assess multitasking performance in ecstasy polydrug users, polydrug users and drug-naive individuals. It was predicted that ecstasy polydrug users would perform worse than non-users on the behavioural measure and this would be supported by differences in cortical blood oxygenation. METHOD: In the study, 20 ecstasy-polydrug users, 17 polydrug users and 19 drug-naive individuals took part. On day 1, drug use history was taken and questionnaire measures were completed. On day 2, participants completed a 20-min multitasking stressor while brain blood oxygenation was measured using functional near infrared spectroscopy (fNIRS). RESULTS: There were no significant differences between the three groups on the subscales of the multitasking stressor. In addition, there were no significant differences on self-report measures of perceived workload (NASA Task Load Index). In terms of mood, ecstasy users were significantly less calm and less relaxed compared with drug-naive controls. There were also significant differences at three voxels on the fNIRS, indicating decreased blood oxygenation in ecstasy users compared with drug-naive controls at voxel 2 (left dorsolateral prefrontal cortex), voxel 14 and voxel 16 (right dorsolateral prefrontal cortex), and compared with polydrug controls at V14. CONCLUSIONS: The results of the present study provide support for changes in brain activation during performance of demanding tasks in ecstasy polydrug users, which could be related to cerebral vasoconstriction.

Electrophysiological indices of response inhibition in human polydrug users.

Previous research in ecstasy users suggests impairment of various executive functions. In general, the executive function of response inhibition appears unaffected by ecstasy use. Nonetheless, it remains a possibility that cognitive tasks alone are not sensitive enough to pick up subtle changes in function. The current study sought to investigate behavioural measures of response inhibition and their electrophysiological correlates in drug users. Twenty ecstasy polydrug users, 20 non-ecstasy polydrug users and 20 drug naïve controls were recruited. Participants completed questionnaires about their background drug use, sleep quality, fluid intelligence and mood state. Each individual also completed a Go/NoGo response inhibition task whilst electroencephalography (EEG) measures were recorded. Analysis of variance (ANOVA) revealed that there were no between-group differences on the behavioural measure of response inhibition. Multivariate analysis of variance (MANOVA) revealed no main effect of group across midline electrodes for the P3, N2 and P2 components. Univariate ANOVA revealed significant between-group differences in the P2 component with the ecstasy user group having a significantly higher mean amplitude than drug naïve controls at two midline frontal electrodes: at Fz and significantly higher mean amplitude than both control groups at FCz. The present study provides evidence of atypical early processing in ecstasy users that is suggestive of compensatory mechanisms ameliorating any behavioural differences.

ERP evidence suggests executive dysfunction in ecstasy polydrug users.

BACKGROUND: Deficits in executive functions such as access to semantic/long-term memory have been shown in ecstasy users in previous research. Equally, there have been many reports of equivocal findings in this area. The current study sought to further investigate behavioural and electro-physiological measures of this executive function in ecstasy users. METHOD: Twenty ecstasy-polydrug users, 20 non-ecstasy-polydrug users and 20 drug-naïve controls were recruited. Participants completed background questionnaires about their drug use, sleep quality, fluid intelligence and mood state. Each individual also completed a semantic retrieval task whilst 64 channel Electroencephalography (EEG) measures were recorded. RESULTS: Analysis of Variance (ANOVA) revealed no between-group differences in behavioural performance on the task. Mixed ANOVA on event-related potential (ERP) components P2, N2 and P3 revealed significant between-group differences in the N2 component. Subsequent exploratory univariate ANOVAs on the N2 component revealed marginally significant between-group differences, generally showing greater negativity at occipito-parietal electrodes in ecstasy users compared to drug-naïve controls. Despite absence of behavioural differences, differences in N2 magnitude are evidence of abnormal executive functioning in ecstasy-polydrug users.

Cannabis-related deficits in real-world memory.

BACKGROUND: 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. METHOD: Twenty cannabis-only users and 20 non-illicit drug users were recruited. Participants completed a substance use inventory and a mood scale, followed by a non-immersive virtual reality task assessing PM and executive functioning. The task involved the participant playing the role of an office worker for the day and performing routine office duties. A number of subscales were used to assess facets of executive function (planning, adaptive thinking, creative thinking, selection, prioritisation) and PM (time-based, event-based and action-based PM). RESULTS: Multivariate analysis of variance revealed cannabis users performed worse overall on the task, with poor performance on the planning, time-based PM and event-based PM subscales. In addition, indices of cannabis (length, dose, frequency, total use) were correlated with performance on these three subscales. CONCLUSIONS: The present study expands on previously established research, providing support for the cannabis-related deficits in PM and executive functioning, and the role of different aspects of cannabis use in these deficits.

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.

Is emotional intelligence impaired in ecstasy-polydrug users?

Previous findings report use of the drug ecstasy (MDMA) to be associated with lower emotional intelligence (EI), and compromised functioning in brain areas responsible for emotion. This study explored the relationship between ecstasy use, EI, mood and parenting styles. Questionnaire measures of drug use, lifestyle, parenting style and EI were obtained, with separate IQ measures for fluid intelligence (Ravens matrices) and pre-morbid intelligence [National Adult Reading Test (NART)]. Current mood measures were obtained from an adjective checklist. The sample comprised 78 ecstasy/polydrug users, 38 cannabis only users and 34 non-drug users. Drug use was categorised at three levels (non-user, cannabis-only user and ecstasy-polydrug user). Factorial ANOVA using drug use as an independent variable showed no significant group effects in EI. EI showed significant correlations with current mood that were positive for arousal and negative for both anxiety and depression. EI was also significantly and positively correlated with the perceived degree of parental control. Regression analyses showed that these relationships remained significant after controlling for differences in IQ, age, gender, and ecstasy use. Adverse mood effects specifically associated with ecstasy use were significantly related to lower EI, and were independent of IQ, age and gender. Higher EI was significantly associated with ecstasy-related precautions used when taking this drug. Contrary to earlier findings, ecstasy-polydrug users did not differ from non-users on EI. However, self-reported ecstasy-related mood disturbances were related to lower EI, with the compromising of orbitofrontal cortical functioning being possible here.

Evidence for selective executive function deficits in ecstasy/polydrug users.

Previous research has suggested that the separate aspects of executive functioning are differentially affected by ecstasy use. Although the inhibition process appears to be unaffected by ecstasy use, it is unclear whether this is true of heavy users under conditions of high demand. Tasks loading on the updating process have been shown to be adversely affected by ecstasy use. However, it remains unclear whether the deficits observed reflect the executive aspects of the tasks or whether they are domain general in nature affecting both verbal and visuo-spatial updating. Fourteen heavy ecstasy users (mean total lifetime use 1000 tablets), 39 light ecstasy users (mean total lifetime use 150 tablets) and 28 non-users were tested on tasks loading on the inhibition executive process (random letter generation) and the updating component process (letter updating, visuo-spatial updating and computation span). Heavy users were not impaired in random letter generation even under conditions designed to be more demanding. Ecstasy-related deficits were observed on all updating measures and were statistically significant for two of the three measures. Following controls for various aspects of cannabis use, statistically significant ecstasy-related deficits were obtained on all three updating measures. It was concluded that the inhibition process is unaffected by ecstasy use even among heavy users. By way of contrast, the updating process appears to be impaired in ecstasy users with the deficit apparently domain general in nature.

Real-world memory and executive processes in cannabis users and non-users.

The relationships between executive processes, associative learning and different aspects of real world memory functioning were explored in a sample of cannabis users and nonusers. Measures of executive component processes, associative learning, everyday memory, prospective memory, and cognitive failures were administered. Relative to nonusers, cannabis users were found to be impaired in several aspects of real world memory functioning. No other group differences were apparent. The absence of cannabis related deficits in those executive component processes and aspects of learning that are believed to support real world memory processes is surprising given that cannabis related deficits were obtained in real world memory. The present results are discussed within the context of neuroimaging evidence which suggests that cannabis users may exhibit different patterns of neural activation when performing executive tasks while not always exhibiting deficits on these tasks.

Working memory deficits in current and previous users of MDMA ('ecstasy').

Current and previous users of the drug MDMA ('ecstasy') were tested on measures of central executive functioning, information processing speed, and on self-report measures of arousal and anxiety. The results were compared with those for a control group who did not use MDMA. Relative to the control group, both user groups were found to be impaired in some aspects of central executive functioning. Also, there were significant group differences on the measures of anxiety (users were more anxious) and on arousal (previous users scoring higher on the arousal measure relative to current users). Users processed information as quickly as non-users but less accurately. Some possible mediators of the above group differences are discussed.

Associative learning and short-term forgetting as a function of age, perceptual speed, and central executive functioning.

In a study of two components of associative learning, it was found that during acquisition older people were more likely to forget material on which they were previously correct, but only for associations which were not well learned. Older people also formed fewer correct associations in the course of the task. Differences in learners' perceptual speed were found to account for some of the age deficit in the number of learning attempts, but speed was less relevant in accounting for age differences in forgetting and in the ability to generate new responses. Measured central executive functioning was less important in accounting for age differences on all measures. It is argued that forgetting is less important as a source of learning performance than has been suggested elsewhere (e.g., Salthouse, 1994). Rather, it is the inability of older persons to form associations as rapidly as younger ones which accounts for most of the age effect.

Age and working memory: the role of perceptual speed, the central executive, and the phonological loop.

In a study (N = 61) comparing older (age range = 60-80 years, M = 67) and younger (age range = 20-33 years, M = 25) people, age deficits were observed in working memory, perceptual speed, and central executive functioning but not in phonological loop functioning. Controlling for age differences in central executive performance removed over 50% of the age-related variance in working memory span. However, controlling for perceptual speed removed all of the age-related variance in working memory span. In addition, age differences in central executive functioning were largely eliminated after controlling for age deficits in perceptual speed. These findings suggest that age differences in central executive functioning are primarily attributable to a general slowdown in the rate at which information is activated within the working memory system and that no specific deficits in the central executive occur as a consequence of aging.