Differential effects of ecstasy, cocaine, and cannabis use on Executive Function Function

Although it is evident from the EF literature that ecstasy impairs the updating component and tasks that load on WM, the ecstasy-related deficits on inhibition and shifting are less evident. Recent neuropsychological studies have investigated the differential effects of ecstasy, cannabis and cocaine on executive components in order to determine whether these executive components are susceptible to other recreational drugs (Verdejo-Garcia & Perez-Garcia, 2007; Verdejo-Garcia et al., 2005; Fernandez-Serrano et al., 2010; Madoz-Gúrpide et al., 2011). For instance, Verdejo-Garcia et al. (2005) investigated the severity of consumption of different drugs and neuropsychological performance on tasks sensitive to executive components of working memory, response inhibition, cognitive flexibility, and abstract reasoning. Thirty-eight polysubstance abusers completed the different tasks along with a severity of drug consumption interview. Using multiple regression analyses the authors found that severity of ecstasy use had an impact on working memory and abstract reasoning indices whilst severity of cocaine use was associated with the inhibitory control index. Severity of cannabis use was associated with the cognitive flexibility index.

117 Verdejo-Garcia and Perez-Garcia (2007) also suggested that chronic use of cocaine has adverse effects on executive functioning. In their study two groups of participants were recruited i.e., abstinent polysubstance users and drug free controls. Polysubstance users were further subdivided based on their drug of choice (cocaine vs heroin). Tests of fluency, working memory, reasoning, inhibitory control, flexibility, and decision making were administered. It was found that abstinent polysubstance users had clinically significant impairments on all executive components. In fact, cocaine polysubstance users had more severe impairments than heroin users and controls on measures of inhibition (using the Stroop Task) and shifting (using the go/no go and category test). Indeed, greater severity of drug use predicted poorer performance on updating measures. These finding therefore suggest that chronic drug use is associated with widespread impairment on executive components, with cocaine use inducing more severe deficits on inhibition and shifting.

Further evidence for the involvement of cocaine in EF comes for a recent study that investigated the relationship between executive deficits and three measures of severity of cocaine use: years of use, quantity used, and frequency of use.

Twenty-four cocaine users were compared with twenty-seven community controls on several neuropsychological tests of EF. Chronic cocaine users in comparison to the drug naïve controls performed worse on measures of attention and working memory, set-shifting abilities, cognitive test of mental flexibility and response inhibition and the WCST. All three aspects of cocaine use were associated with most of the EF measures suggesting that increased cocaine use is associated with more EF problems (Madoz-Gúrpideet al., 2011).

118 Besides the aforementioned cocaine-related effect on several executive components, the use of cannabis can also affect adversely EF. For example, the use of cannabis was also implicated in deficits on the updating component.

Montgomery et al. (2005) showed that in relation to non-ecstasy users, ecstasy users demonstrated deficits on updating and access to long-term memory tasks.

The authors also found that cannabis use was negatively correlated with updating performance while cocaine use was associated with long-term memory access.

Also, chronic cannabis users have shown WM deficits on several measures from the Cambridge Neuropsychological Test Automated Battery (CANTAB) including Rapid Visual Information Processing, Pattern Recognition Memory, Spatial Recognition Memory, Spatial Span, Spatial Working Memory and Visuospatial Paired Associate Learning (Harvey et al., 2007; Solowij et al., 2008).

Furthermore, long-term cannabis users were found to be impaired on measures of inhibition (such as the Stroop task, Go/NoGo and a variety of decision-making and gambling tasks) (Solowij et al., 2002; Bolla et al., 2002; 2005; Smith et al., 2004; Hester et al., 2009).

It is therefore apparent that different drugs affect executive components in distinct ways. Although the recreational use of ecstasy only affects the updating component and tasks loading on WM, it leaves the inhibition and shifting components intact. Other recreational drugs such as cocaine and cannabis, however, have adverse effects on these components. It is therefore crucial to evaluate the contribution of these drugs when investigating executive functioning in ecstasy/polydrug users.

119 6.5 Chapter summary

In summary, it is evident from the existing literature that ecstasy-related deficits exist in laboratory measures of EF. Although, it seems that the updating component and in general tasks that load on WM are susceptible to the effects of ecstasy, there is little evidence to date to suggest that ecstasy use is associated with impairment on executive shifting or executive inhibition. It is therefore necessary to further investigate the effect of recreational drug use on these components using different laboratory or self-report measures that map on the construct components of executive shifting and executive inhibition. It is also evident from the ecstasy-related EF literature that assessment of EF is restricted to laboratory measures, that although offer strong internal validity, control over extraneous variables and the possibility of examining the component EF processes individually, laboratory measures are limited in terms of their ecological validity and in their ability to capture executive processes as they are manifested in the everyday environment (Gioia et al., 2008).

In order to further investigate the effect of recreational use of ecstasy on executive components and provide an alternative method of assessment, the present investigation will use a self-report measure of EF; the BRIEF-A. As previously discussed in chapter 3, the BRIEF-A is a self-report measure of executive functioning which consists of nine subscales each including questions which involve everyday activities and contain an executive component. The BRIEF-A has been developed to capture the behavioural manifestations of executive dysfunction in the various interrelated domains of the construct that have been commonly discussed in the literature. It is also argued that the BRIEF-A,

120 measures subtle individual differences in discrete real world processes and unlike many laboratory tests it is unrelated to, and not contaminated by overall differences in general ability measures such as IQ (Bodnar et al., 2007).

Having evaluated the current literature in ecstasy/polydrug use and its adverse effects on PM and EF, the following chapters will further investigate the ecstasy/polydrug-related effect on these processes. The present investigations will also address the identified grey areas in the literature of PM and EF in terms of assessing these multidimentional constructs. Consequently, chapters that follow will evaluate the impact of recreational use of ecstasy on prospective remembering and executive functioning by utilising different assessment approaches as opposed to the traditional measures adopted throughout the literature and assess components that have previously been neglected in the area of recreational drug use.

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