Recreational cocaine polydrug use impairs cognitive flexibility but not working memory

Control dilemma: Evidence of the stability-flexibility trade-off

Cognitive control can be applied flexibly when task goals or environments change (i.e., cognitive flexibility), or stably to pursue a goal in the face of distraction (i.e., cognitive stability). Whether these seemingly contradictory characteristics have an inverse relationship has been controversial, as some studies have suggested a trade-off mechanism between cognitive flexibility and cognitive stability, while others have not found such reciprocal associations. This study investigated the possible antagonistic correlation between cognitive flexibility and stability using a novel version of the flexibility-stability paradigm and the classic cued task switching paradigm. In Experiment 1, we showed that cognitive flexibility was inversely correlated with cognitive stability, as increased distractor proportions were associated with decreased cognitive flexibility and greater cognitive stability. Moreover, cognitive flexibility and stability were regulated by a single control system instead of two independent control mechanisms, as the model selection results indicated that the reciprocally regulated model with one integration parameter outperformed all other models, and the model parameter was inversely linked to cognitive flexibility and stability. We found similar results using the classic cued task switching paradigm in Experiment 2. Therefore, a trade-off between cognitive flexibility and stability was observed from the paradigms used in this study.

Is Flexibility More than Fluency and Originality?

Flexibility (i.e., the number of categorically different ideas), fluency (i.e., the answer quantity), and originality (i.e., the quality of ideas) are essential aspects of the ability to think divergently. Theoretically, fluency and ideational flexibility tasks are akin to one another. However, flexibility was also considered to be uniquely related to working memory capacity due to the task requirements involved in generating diverse answers (e.g., self-monitoring, suppression, and category generation). Given that the role of working memory is strengthened in flexibility tasks relative to fluency and originality tasks, flexibility should be more strongly related with working memory. Additionally, mental speed should show a similar pattern of results because mental speed has been previously related to task complexity. Based on a sample of N = 409 adults (M_age = 24.01 years), we found in latent variable models that fluency/originality strongly predicts flexibility and accounts for 61% of its variance. Creative flexibility was unrelated to working memory and mental speed after controlling for fluency/originality. Additionally, the residual of a latent flexibility factor was unrelated to self-reported creative activities. We concluded that flexibility, as measured here, can be deemed primarily a method factor that did not show value over and above fluency/originality as assessed in traditional fluency and originality tasks. We discussed perspectives for disentangling trait and method variance in flexibility tasks.

Spontaneous Eye Blinks Predict Executive Functioning in Seniors

As the world’s population is aging rapidly, cognitive training is an extensively used approach to attempt improvement of age-related cognitive functioning. With increasing numbers of older adults required to remain in the workforce, it is important to be able to reliably predict future functional decline, as well as the individual advantages of cognitive training. Given the correlation between age-related decline and striatal dopaminergic function, we investigated whether eye blink rate (EBR), a non-invasive, indirect indicator of dopaminergic activity, could predict executive functioning (response inhibition, switching and working memory updating) as well as trainability of executive functioning in older adults. EBR was collected before and after a cognitive flexibility training, cognitive training without flexibility, or a mock training. EBR predicted working memory updating performance on two measures of updating, as well as trainability of working memory updating, whereas performance and trainability in inhibition and switching tasks could not be predicted by EBR. Our findings tentatively indicate that EBR permits prediction of working memory performance in older adults. To fully interpret the relationship with executive functioning, we suggest future research should assess both EBR and dopamine receptor availability among seniors.

Single Exposure to Cocaine Impairs Reinforcement Learning by Potentiating the Activity of Neurons in the Direct Striatal Pathway in Mice

Plasticity in the glutamatergic synapses on striatal medium spiny neurons (MSNs) is not only essential for behavioral adaptation but also extremely vulnerable to drugs of abuse. Modulation on these synapses by even a single exposure to an addictive drug may interfere with the plasticity required by behavioral learning and thus produce impairment. In the present work, we found that the negative reinforcement learning, escaping mild foot-shocks by correct nose-poking, was impaired by a single in vivo exposure to 20 mg/kg cocaine 24 h before the learning in mice. Either a single exposure to cocaine or reinforcement learning potentiates the glutamatergic synapses on MSNs expressing the striatal dopamine 1 (D1) receptor (D1-MSNs). However, 24 h after the cocaine exposure, the potentiation required for reinforcement learning was disrupted. Specific manipulation of the activity of striatal D1-MSNs in D1-cre mice demonstrated that activation of these MSNs impaired reinforcement learning in normal D1-cre mice, but inhibition of these neurons reversed the reinforcement learning impairment induced by cocaine. The results suggest that cocaine potentiates the activity of direct pathway neurons in the dorsomedial striatum and this potentiation might disrupt the potentiation produced during and required for reinforcement learning.

Dopaminergic modulation of working memory and cognitive flexibility in a zebrafish model of aging-related cognitive decline

Healthy aging is associated with a decline in memory and executive function, which have both been linked with aberrant dopaminergic signaling. We examined the relationship between cognitive performance and dopamine function of young and aging zebrafish (Danio rerio). We revealed age-related decreases in working memory and cognitive flexibility in the Free-Movement Pattern (FMP) Y-maze. An increase in drd5 gene expression in aging adults coincided with a decrease in cognitive performance. Treatment with a D1/D5 receptor agonist (SKF-38393, 35 µM) 30 minutes prior to behavioral assessment resulted in improved working memory in aging zebrafish, but no effect in younger adults. However, an "overdosing" effect caused by agonist treatment resulted in downregulation of dat expression in 6-month old, treated zebrafish. The translational relevance of these findings was tested in humans by analyzing exploratory behavior in young-adult, 18-35-year olds, and aged adults, 70+ year olds, in a virtual FMP Y-maze. Our findings revealed similar age-related decline in working memory. Thus, strongly supporting zebrafish as a translational model of aging and cognitive decline.

A promiscuous coenzyme A ligase provides benzoyl-coenzyme A for xanthone biosynthesis in Hypericum

Benzoic acid-derived compounds, such as polyprenylated benzophenones and xanthones, attract the interest of scientists due to challenging chemical structures and diverse biological activities. The genus Hypericum is of high medicinal value, as exemplified by H. perforatum. It is rich in benzophenone and xanthone derivatives, the biosynthesis of which requires the catalytic activity of benzoate-coenzyme A (benzoate-CoA) ligase (BZL), which activates benzoic acid to benzoyl-CoA. Despite remarkable research so far done on benzoic acid biosynthesis in planta, all previous structural studies of BZL genes and proteins are exclusively related to benzoate-degrading microorganisms. Here, a transcript for a plant acyl-activating enzyme (AAE) was cloned from xanthone-producing Hypericum calycinum cell cultures using transcriptomic resources. An increase in the HcAAE1 transcript level preceded xanthone accumulation after elicitor treatment, as previously observed with other pathway-related genes. Subcellular localization of reporter fusions revealed the dual localization of HcAAE1 to cytosol and peroxisomes owing to a type 2 peroxisomal targeting signal. This result suggests the generation of benzoyl-CoA in Hypericum by the CoA-dependent non-β-oxidative route. A luciferase-based substrate specificity assay and the kinetic characterization indicated that HcAAE1 exhibits promiscuous substrate preference, with benzoic acid being the sole aromatic substrate accepted. Unlike 4-coumarate-CoA ligase and cinnamate-CoA ligase enzymes, HcAAE1 did not accept 4-coumaric and cinnamic acids, respectively. The substrate preference was corroborated by in silico modeling, which indicated valid docking of both benzoic acid and its adenosine monophosphate intermediate in the HcAAE1/BZL active site cavity.

Risky decision-making in individuals with substance use disorder: A meta-analysis and meta-regression review

BACKGROUND

This review aims to identify whether risky decision-making is increased in substance users, and the impact of substance type, polysubstance use status, abstinence period, and treatment status on risky decision-making.

METHODS

A literature search with no date restrictions was conducted to identify case-control studies or cross-sectional studies that used behavioral tasks to measure risky decision-making in substance users. A random-effects model was performed. GRADE criteria was used to assess the quality of evidence.

RESULTS

52 studies were enrolled. The result showed that the difference in risky decision-making performance between user groups and control groups was significant (SMD = - 0.590; 95%CI = - 0.849 to - 0.330; p < 0.001; I² = 93.4%; P_{heterogeneity} < 0.001). Subgroup analysis showed that users in the subgroups of alcohol (p < 0.001), tobacco (p < 0.01), cocaine (p < 0.001), opioid (p < 0.001), mixed group (p < 0.01), adult users (p < 0.001), small sample size (p < 0.001), large sample size (p < 0.01), low education (p < 0.001), high education (p < 0.001), short-abstinence period (p < 0.001), long-abstinence period (p < 0.001), without current polysubstance dependence (p < 0.001), and with treatment (p < 0.001) had increased risky decision-making when compared to the controls. On the other hand, elderly substance users with short-abstinence period showed increased risky decision-making. Moreover, current treatment status and polysubstance use may not influence the level of decision-making in substance users.

CONCLUSIONS

The results show that substance use is associated with impaired risky decision-making, indicating that interventions targeting risky decision-making in substance users should be developed for relapse prevention and rehabilitation.

Identifying cognitive deficits in cocaine dependence using standard tests and machine learning

There is a growing need to address the variability in detecting cognitive deficits with standard tests in cocaine dependence (CD). The aim of the current study was to identify cognitive deficits by means of Machine Learning (ML) algorithms: Generalized Linear Model (Glm), Random forest (Rf) and Elastic Net (GlmNet), to allow more effective categorization of CD and Non-dependent controls (NDC and to address common methodological problems. For our validation, we used two independent datasets, the first consisted of 87 participants (53 CD and 34 NDC) and the second of 40 participants (20 CD and 20 NDC). All participants were evaluated with neuropsychological tests that included 40 variables assessing cognitive domains. Using results from the cognitive evaluation, the three ML algorithms were trained in the first dataset and tested on the second to classify participants into CD and NDC. While the three algorithms had a receiver operating curve (ROC) performance over 50%, the GlmNet was superior in both the training (ROC = 0.71) and testing datasets (ROC = 0.85) compared to Rf and Glm. Furthermore, GlmNet was capable of identifying the eight main predictors of group assignment (CD or NCD) from all the cognitive domains assessed. Specific variables from each cognitive test resulted in robust predictors for accurate classification of new cases, such as those from cognitive flexibility and inhibition domains. These findings provide evidence of the effectiveness of ML as an approach to highlight relevant sections of standard cognitive tests in CD, and for the identification of generalizable cognitive markers.

Tonic exploration governs both flexibility and lapses

In many cognitive tasks, lapses (spontaneous errors) are tacitly dismissed as the result of nuisance processes like sensorimotor noise, fatigue, or disengagement. However, some lapses could also be caused by exploratory noise: randomness in behavior that facilitates learning in changing environments. If so, then strategic processes would need only up-regulate (rather than generate) exploration to adapt to a changing environment. This view predicts that more frequent lapses should be associated with greater flexibility because these behaviors share a common cause. Here, we report that when rhesus macaques performed a set-shifting task, lapse rates were negatively correlated with perseverative error frequency across sessions, consistent with a common basis in exploration. The results could not be explained by local failures to learn. Furthermore, chronic exposure to cocaine, which is known to impair cognitive flexibility, did increase perseverative errors, but, surprisingly, also improved overall set-shifting task performance by reducing lapse rates. We reconcile these results with a state-switching model in which cocaine decreases exploration by deepening attractor basins corresponding to rule states. These results support the idea that exploratory noise contributes to lapses, affecting rule-based decision-making even when it has no strategic value, and suggest that one key mechanism for regulating exploration may be the depth of rule states.

Blunted Frontostriatal Blood Oxygen Level-Dependent Signals Predict Stimulant and Marijuana Use

BACKGROUND

Occasional recreational stimulant (amphetamine and cocaine) use is an important public health problem among young adults because 16% of those who experiment develop stimulant use disorder. This study aimed to determine whether behavioral and/or neural processing measures can forecast the transition from occasional to problematic stimulant use.

METHODS

Occasional stimulant users completed a Risky Gains Task during functional magnetic resonance imaging and were followed up 3 years later. Categorical analyses tested whether blood oxygen level-dependent (BOLD) responses differentiated occasional stimulant users who became problem stimulant users (n = 35) from those who desisted from stimulant use (n = 75) at follow-up. Dimensional analyses (regardless of problem stimulant user or desisted stimulant use status; n = 144) tested whether BOLD responses predicted baseline and follow-up stimulant and marijuana use.

RESULTS

Categorical results indicated that relative to those who desisted from stimulant use, problem stimulant users 1) made riskier decisions after winning feedback; 2) exhibited lower frontal, insular, and striatal BOLD responses to win/loss feedback after making risky decisions; and 3) displayed lower thalamic but greater temporo-occipital BOLD responses to risky losses than to risky wins. In comparison, dimensional results indicated that lower BOLD signals to risky choices than to safe choices in frontal, striatal, and additional regions predicted greater marijuana use at follow-up.

CONCLUSIONS

Taken together, blunted frontostriatal signals during risky choices may quantify vulnerability to future marijuana consumption, whereas blunted frontostriatal signals to risky outcomes mark risk for future stimulant use disorder. These behavioral and neural processing measures may prove to be useful for identifying ultra-high risk individuals prior to onset of problem drug use.

Why Is Working Memory Performance Unstable? A Review of 21 Factors

In this paper, we systematically reviewed twenty-one factors that have been shown to either vary with or influence performance on working memory (WM) tasks. Specifically, we review previous work on the influence of intelligence, gender, age, personality, mental illnesses/medical conditions, dieting, craving, stress/anxiety, emotion/motivation, stereotype threat, temperature, mindfulness training, practice, bilingualism, musical training, altitude/hypoxia, sleep, exercise, diet, psychoactive substances, and brain stimulation on WM performance. In addition to a review of the literature, we suggest several frameworks for classifying these factors, identify shared mechanisms between several variables, and suggest areas requiring further investigation. This review critically examines the breadth of research investigating WM while synthesizing the results across related subfields in psychology.

Assessing cognitive functioning in individuals with cocaine use disorder

INTRODUCTION

There have been mixed findings assessing the impact of regular cocaine use on cognitive functioning. This study employed a comprehensive cognitive battery to compare the performance of individuals diagnosed with a cocaine use disorder (N = 3 abusers, N = 17 dependent) against the performance of two control groups: (a) non-drug-users, and (b) marijuana users who report no cocaine use (N = 7 marijuana abusers, N = 0 dependent, N = 13 marijuana users with no Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition, DSM-IV, diagnosis).

METHOD

This one-session, between-participants, outpatient study was conducted at the New York State Psychiatric Institute. Sixty research volunteers completed the study. Drug users in both groups had no signs of current intoxication, but had a positive urine toxicology-which indicated use within 72 hours in the cocaine use disorder group and within the past 30 days (depending on frequency of use) for the marijuana-using control group. The National Institutes of Health (NIH) Toolbox Cognition Battery was used to assess cognitive functioning across six domains: executive function, attention, episodic memory, working memory, processing speed, and language. Each participant's score was also compared against a normative database adjusted for age.

RESULTS

Although the mean cognitive scores for all groups fell within the normal range for all tests, marijuana-using control participants outperformed those with a cocaine use disorder on a cognitive flexibility and language measure.

CONCLUSIONS

Cognitive functioning of individuals diagnosed with cocaine use disorder was observed to be similar to that of control group participants on the majority of tasks and fell within the normal range when compared against normative data.

Attention and memory deficits in crack-cocaine users persist over four weeks of abstinence

BACKGROUND

Crack-cocaine addiction is an important public health problem worldwide. Although there is not a consensus, preliminary evidence has suggested that cognitive impairments in patients with crack-cocaine dependence persist during abstinence, affecting different neuropsychological domains. However, few studies have prospectively evaluated those deficits in different phases of abstinence.

OBJECTIVES

The main aim of present study was to examine neuropsychological performance of patients with crack-cocaine dependence during early abstinence and after four weeks, comparing with matched controls.

METHODS

Thirty-five males with crack-cocaine dependence, aged 18 to 50years, who met DSM-IV criteria for cocaine dependence and a control group of 33 healthy men were enrolled. They were assessed through Block Design, Digit Span and Vocabulary of Wechsler Adult Intelligence Scale (WAIS-III), the Rey Auditory Learning Test (RAVLT) and the Verbal Fluency (FAS) between 3 and 10days (mean of 6.1±2.0days) and after 4weeks of abstinence.

RESULTS

Compared to controls, the crack-cocaine dependent group exhibited deficits in cognitive performance affecting attention, verbal memory and learning tasks in early withdrawal. Most of the cognitive deficits persisted after four weeks of abstinence.

CONCLUSION

Present results observed that the group of patients with crack-cocaine dependence presented persistent deficits affecting memory and attention even after four weeks of abstinence, confirming previous studies that had disclosed such cognitive impairments.

Developmental Exposure to Cocaine Dynamically Dysregulates Cortical Arc/Arg3.1 Modulation in Response to a Challenge

During adolescence, the medial prefrontal cortex (mPFC) is still developing. We have previously shown that developmental cocaine exposure alters mPFC's ability to cope with challenging events. In this manuscript, we exposed rats developmentally treated with cocaine to a novelty task and analyzed the molecular changes of mPFC. Rats were exposed to cocaine from post-natal day (PND) 28 to PND 42 and sacrificed at PND 43, immediately after the novel object recognition (NOR) test. Cocaine-treated rats spent more time exploring the novel object than saline-treated counterparts, suggesting an increased response to novelty. The messenger RNA (mRNA) and protein levels of the immediate early gene Arc/Arg3.1 were reduced in both infralimbic (IL) and prelimbic (PL) cortices highlighting a baseline reduction of mPFC neuronal activity as a consequence of developmental exposure to cocaine. Intriguingly, significant molecular changes were observed in the IL, but not PL, cortex in response to the combination of cocaine exposure and test such as a marked upregulation of both Arc/Arg3.1 mRNA and protein levels only in cocaine-treated rats. As for proteins, such increase was observed only in the post-synaptic density and not in the whole homogenate, suggesting psychostimulant-induced changes in trafficking of Arc/Arg3.1 or an increased local translation. Notably, the same profile of Arc/Arg3.1 was observed for post-synaptic density (PSD)-95 leading to the possibility that Arc/Arg3.1 and PSD-95 bridge together to promote aberrant synaptic connectivity in IL cortex following repeated exposure to cocaine during brain development.

Recreational cocaine use is associated with attenuated latent inhibition

INTRODUCTION

Evidence has linked chronic cocaine use with various cognitive deficits; however few studies have investigated the effects of recreational (non-dependent) use. The present study aimed to assess whether recreational users show deficits in latent inhibition (LI: a measure of delayed learning of an association between 2 stimuli, one of which has been previously exposed (PE) without consequence and thus deemed irrelevant).

METHODS

Using a quasi-experimental between groups design, recreational cocaine users (n = 21), poly-drug users (n = 17) and drug-naive controls (n = 18) were compared on a LI task. Questionnaires assessing psychological health and drug use were also completed.

RESULTS

There was a statistically significant interaction between condition (PE vs non PE) and group (cocaine, polydrug and control); cocaine users scored lower in the PE condition compared to polydrug users and controls, indicating quicker learning.

CONCLUSIONS

Recreational cocaine users show attenuated LI reflecting reduced ability to filter out irrelevant stimuli enabling faster learning of a PE irrelevant and novel stimuli association. This does not appear to be a result of schizotypy and/or other drug use. Thus even at recreational levels, cocaine use may be sufficient to affect inhibitory attentional processes.

Take it or leave it: prefrontal control in recreational cocaine users

Though stimulant drugs such as cocaine are considered highly addictive, some individuals report recreational use over long periods without developing dependence. Difficulties in response inhibition have been hypothesized to contribute to dependence, but previous studies investigating response inhibition in recreational cocaine users have reported conflicting results. Performance on a stop-signal task was examined in 24 recreational cocaine users and 32 healthy non-drug using control participants matched for age, gender and verbal intelligence during functional magnetic resonance imaging scanning. The two groups were further matched on traumatic childhood histories and the absence of family histories of addiction. Results revealed that recreational cocaine users did not significantly differ from controls on any index of task performance, including response execution and stop-signal reaction time, with the latter averaging 198 ms in both groups. Functional magnetic resonance imaging analyses indicated that, compared with controls, stopping in the recreational users was associated with increased activation in the pre-supplementary motor area but not the right inferior frontal cortex. Thus, findings imply intact response inhibition abilities in recreational cocaine users, though the distinct pattern of accompanying activation suggests increased recruitment of brain areas implicated in response inhibition. This increased recruitment could be attributed to compensatory mechanisms that enable preserved cognitive control in this group, possibly relating to their hypothetical resilience to stimulant drug dependence. Such overactivation, alternatively, may be attributable to prolonged cocaine use leading to neuroplastic adaptations.

Guanfacine enhances inhibitory control and attentional shifting in early abstinent cocaine-dependent individuals

OBJECTIVES

Attenuation of adrenergic drive and cognitive enhancement, via stimulation of alpha2 pre- and post-synaptic receptors, may selectively enhance executive performance in early abstinent cocaine-dependent individuals. As these cognitive processes underpin important treatment-related behaviors, the alpha2 agonist, guanfacine HCl, may represent an effective pharmaco-therapeutic intervention.

METHODS

Twenty-five early abstinent cocaine-dependent individuals were administered a battery of neurocognitive tasks on entry into treatment (baseline) and again following 3 weeks of either placebo or guanfacine treatment (up to 3 mg). Tasks included: Stop Signal, Stroop, 3-Dimentional Intra-dimensional/Extra-dimensional (IDED) task, Spatial Working Memory (SWM), Paired Associates Learning (PAL), Verbal Fluency and the Rey Auditory Verbal Learning Test (RAVLT).

RESULTS

Compared with placebo, the guanfacine group demonstrated attenuated anxiety and negative affect as well as improved performance on selective executive tests. This included fewer directional errors on the stop signal task, fewer errors on the extra-dimensional shift component of the IDED task and better attentional switching during verbal fluency. Guanfacine did not improve strategic working memory or peripheral memory.

CONCLUSION

Guanfacine improves selective cognitive processes which may underlie salient treatment-related regulatory behaviors. Alpha2 agonists may therefore represent important agents for cocaine dependence.

Neuropsychological Consequences of Chronic Drug Use: Relevance to Treatment Approaches

Heavy use of drugs impacts of the daily activities of individuals in these activities. Several groups of investigators have indeed documented changes in cognitive performance by individuals who have a long history of chronic drug use. In the case of marijuana, a wealth of information suggests that heavy long-term use of the drug may have neurobehavioral consequences in some individuals. In humans, heavy cocaine use is accompanied by neuropathological changes that might serve as substrates for cognitive dysfunctions. Similarly, methamphetamine users suffer from cognitive abnormalities that may be consequent to alterations in structures and functions. Here, we detail the evidence for these neuropsychological consequences. The review suggests that improving the care of our patients will necessarily depend on the better characterization of drug-induced cognitive phenotypes because they might inform the development of better pharmacological and behavioral interventions, with the goal of improving cognitive functions in these subsets of drug users.

Cognitive impairment in cocaine users is drug-induced but partially reversible: evidence from a longitudinal study

Cocaine users consistently display cognitive impairments. However, it is still unknown whether these impairments are cocaine-induced and if they are reversible. Therefore, we examined the relation between changing intensity of cocaine use and the development of cognitive functioning within 1 year. The present data were collected as part of the longitudinal Zurich Cocaine Cognition Study (ZuCo(2)St). Forty-eight psychostimulant-naive controls and 57 cocaine users (19 with increased, 19 with decreased, and 19 with unchanged cocaine use) were eligible for analysis. At baseline and after a 1-year follow-up, cognitive performance was measured by a global cognitive index and four neuropsychological domains (attention, working memory, declarative memory, and executive functions), calculated from 13 parameters of a broad neuropsychological test battery. Intensity of cocaine use was objectively determined by quantitative 6-month hair toxicology at both test sessions. Substantially increased cocaine use within 1 year (mean +297%) was associated with reduced cognitive performance primarily in working memory. By contrast, decreased cocaine use (-72%) was linked to small cognitive improvements in all four domains. Importantly, users who ceased taking cocaine seemed to recover completely, attaining a cognitive performance level similar to that of the control group. However, recovery of working memory was correlated with age of onset of cocaine use-early-onset users showed hampered recovery. These longitudinal data suggest that cognitive impairment might be partially cocaine-induced but also reversible within 1 year, at least after moderate exposure. The reversibility indicates that neuroplastic adaptations underlie cognitive changes in cocaine users, which are potentially modifiable in psychotherapeutical or pharmacological interventions.

Using a drug-word Stroop task to differentiate recreational from dependent drug use

Distinguishing dependent from recreational drug use can be a surprisingly difficult task, and the current means for identifying substance abuse can be inadequate or even misleading. In subjective self-reports, those who are most at risk may down play their consumption, not admitting to the full extent of their habit, and measures purely of quantity of use rarely capture the true nature of an individual's relationship to the drug, such as a psychological dependence on the substance. This trend is particularly true for heavy stimulant use, which is absent of the physical withdrawal symptoms that can help identify opiate or alcohol dependence. As such, a simple objective measure to help identify substance abuse, particularly in individuals who might not otherwise raise suspicion, would be a valuable tool in both clinical and experimental settings. We propose that the drug-word Stroop task, an objective assessment of attentional bias and distraction to salient drug-related stimuli, would be a valuable tool in helping to make these categorizations. This measure has been shown to correlate with drug craving, as well as to successfully distinguish dependent from recreational stimulant users and to help to predict outcomes in treatment-seeking individuals. Here, we survey prior literature on the drug-word Stroop task and provide a perspective on using the assessment as a potential diagnostic for drug use severity.

Altered social and non-social decision-making in recreational and dependent cocaine users

BACKGROUND

Maladaptive decision-making is assumed to be a core feature of cocaine addiction. Indeed, numerous studies have reported deficits in non-social decision-making tasks and reward-related impulsivity in dependent cocaine users. However, social decision-making has not been examined in cocaine users yet. Moreover, it is unknown if even recreational and non-dependent cocaine use is linked to decision-making deficits. Therefore, we investigated whether recreational and dependent cocaine users exhibit alterations in social and non-social decision-making.

METHOD

The performance of healthy controls (n = 68), recreational cocaine users (n = 68) and dependent cocaine users (n = 30) in classical decision-making paradigms (Iowa Gambling Task, Delay Discounting) and in social interaction paradigms (Distribution Game, Dictator Game) was assessed.

RESULTS

Decisions in the social interaction tasks of both cocaine user groups were more self-serving compared with controls as cocaine users preferred higher monetary payoffs for themselves. In the Iowa Gambling Task, only dependent cocaine users were more likely to choose disadvantageous card decks, reflecting worse decision-making. They were also more likely to choose immediate smaller rewards over larger delayed rewards in the Delay Discounting task.

CONCLUSIONS

Our results imply that both recreational and dependent cocaine users are more concerned with their own monetary gain when interacting with another person. Furthermore, primarily dependent cocaine users are less foresighted and more impulsive regarding immediate reward. Overall, social interaction deficits are already present in recreational users, while non-social decision-making deficits occur predominantly in dependent cocaine users. Thus, social interaction training and cognitive remediation strategies may improve treatment success and quality of life in cocaine dependence.

Enhanced orbitofrontal cortex function and lack of attentional bias to cocaine cues in recreational stimulant users

BACKGROUND

Although cocaine is known to be a highly addictive drug, there appears to be a select subset of individuals who are able to use the substance recreationally without developing dependence. These individuals do not report experiencing feelings of craving for cocaine, an important distinction from dependent users. However, no prior studies have compared attentional bias with cocaine cues between these groups to confirm this difference. Additionally, previous investigations into cognitive abilities in these individuals have been conflicting, and no research has been conducted on the neurobiological processes underlying cognitive functioning in this group.

METHODS

This study administered the emotional cocaine-word Stroop to 27 recreational cocaine users, 50 stimulant-dependent individuals, and 52 healthy control participants during functional magnetic resonance imaging scanning. Behavioral and functional imaging results were compared between groups to assess attentional bias and cognitive effort to resist salient cocaine stimuli.

RESULTS

Recreational users did not exhibit attentional bias to the cocaine words and did not differ from control subjects on task performance. Conversely, stimulant-dependent individuals were significantly more impaired on the task. Recreational participants also displayed a unique pattern of activation during performance, with significant underactivation in the orbitofrontal and anterior cingulate cortices compared with both dependent users and control subjects.

CONCLUSIONS

The absence of bias to cocaine-related stimuli in recreational users indicates they do not share attentional preference for these words with dependent users. Their distinct pattern of activation suggests a decreased need for cognitive control due to diminished desire for the drug, potentially serving as a resilience factor against dependence.

Persistent cocaine-induced reversal learning deficits are associated with altered limbic cortico-striatal local field potential synchronization

Repeated exposure to cocaine is known to produce persistent deficits in behavioral flexibility. Evidence suggests that these deficits are mediated in part by a circuit involving the medial prefrontal and orbitofrontal cortices (PFC and OFC), nucleus accumbens (NAC), and basolateral amygdala (BLA). To assess the effects of cocaine on this circuit, we treated rats with cocaine daily for 14 d, followed by 4 weeks of abstinence. Animals were then tested on a cross-maze-based reversal learning and set-shifting task, after which they were anesthetized to allow for recording of spontaneous local field potential (LFP) activity simultaneously from all four regions, in addition to activity evoked from acute BLA stimulation. Cocaine-treated (COC) animals showed specific deficits in reversal learning; furthermore, spontaneous LFP oscillation power was reduced and BLA-induced oscillation power was increased in all regions compared with saline-treated (SAL) rats. Theta-burst stimulation of BLA potentiated BLA-evoked responses in all regions and cocaine challenge reduced spontaneous oscillation power and evoked response amplitude, with no COC/SAL group differences. Notably, cocaine challenge produced differential changes in coherence between OFC-BLA, BLA-NAC, and OFC-NAC in COC and SAL groups. These data indicate that repeated exposure to cocaine can produce changes in oscillatory LFP synchronization along limbic cortico-striatal circuits that persist long into abstinence. Furthermore, the regional specificity of these changes strongly correlates with the observed behavioral deficits. Aberrant synchronization within and between regions and consequent dysregulation of the neurocircuitry involved in executive control may contribute to the long-lasting maladaptive decision making seen in cocaine abusers.

Working memory reloaded: tyrosine repletes updating in the N-back task

In this study we tested the idea that the food supplement l-Tyrosine (TYR) repletes resources required for cognitive-control operations. We investigated whether the “updating” (and monitoring) of working memory (WM) representations, a key cognitive-control function, can be promoted by administering TYR, the biochemical precursor of dopamine. Participants performed an N-back task where we compared the WM-demanding 2-back condition with the WM-undemanding 1-back condition. As expected, TYR promoted performance in the more demanding (2-back) but not in the easier (1-back) condition, suggesting that TYR selectively targets cognitive-control operations. This result suggests that TYR can replete cognitive resources when more control is needed and, more generally, that food can act as a cognitive enhancer.

Cognitive impairments in poly-drug ketamine users

RATIONALE

Cognitive impairment has been found to be reversible in people with substance abuse, particularly those using ketamine. Ketamine users are often poly-substance users. This study compared the cognitive functions of current and former ketamine users who were also abusing other psychoactive substances with those of non-users of illicit drugs as controls.

METHODS

One hundred ketamine poly-drug users and 100 controls were recruited. Drug users were divided into current (n = 32) and ex-users (n = 64) according to the duration of abstinence from ketamine (>30 days). The Beck Depression Inventory (BDI), the Hospital Anxiety Depression Scale (HADSA) and the Severity of Dependence Scale (SDS) were used to evaluate depression and anxiety symptoms and the severity of drug use, respectively. The cognitive test battery comprised verbal memory (Wechsler Memory Scale III: Logic Memory and Word List), visual memory (Rey-Osterrieth Complex Figure, ROCF), executive function (Stroop, Wisconsin Card Sorting Test, and Modified Verbal Fluency Test), working memory (Digit Span Backward), and general intelligence (Information, Arithmetic and Digit-Symbol Coding) tests.

RESULTS

Current users had higher BDI and HADSA scores than ex-users (p < 0.001 for BDI and p = 0.022 for HADSA) and controls (p < 0.001 for BDI and p = 0.002 for HADSA). Ex-users had higher BDI (p = 0.006) but equal HADSA scores (p = 1.000) compared to controls. Both current and ex-users had lower scores on Logical Memory delayed recall (p = 0.038 for current users and p = 0.032 for ex-users) and ROCF delayed recall (p = 0.033 for current users and p = 0.014 for ex-users) than controls. Current users also performed worse on ROCF recognition than controls (p = 0.002). No difference was found between the cognitive functions of current and ex-users.

CONCLUSIONS

Ketamine poly-drug users displayed predominantly verbal and visual memory impairments, which persisted in ex-users. The interactive effect of ketamine and poly-drug use on memory needs further investigation.

Latent class analysis of polysubstance use, sexual risk behaviors, and infectious disease among South African drug users

BACKGROUND

HIV transmission risk among non-injection drug users is high due to the co-occurrence of drug use and sexual risk behaviors. The purpose of the current study was to identify patterns of drug use among polysubstance users within a high HIV prevalence population.

METHODS

The study sample included 409 substance users from the Pretoria region of South Africa. Substances used by 20% or more the sample included: cigarettes, alcohol, marijuana and heroin in combination, marijuana and cigarettes in combination, and crack cocaine. Latent class analysis was used to identify patterns of polysubstance use based on types of drugs used. Multivariate logistic regression analyses compared classes on demographics, sexual risk behavior, and disease status.

RESULTS

Four classes of substance use were found: MJ+Cig (40.8%), MJ+Her (30.8%), Crack (24.7%), and Low Use (3.7%). The MJ+Cig class was 6.7 times more likely to use alcohol and 3 times more likely to use drugs before/during sex with steady partners than the Crack class. The MJ+Cig class was 16 times more likely to use alcohol before/during sex with steady partners than the MJ+Her class. The Crack class was 6.1 times more likely to engage in transactional sex and less likely to use drugs before/during steady sex than the MJ+Her class.

CONCLUSIONS

Findings illustrate patterns of drug use among a polysubstance using population that differ in sexual risk behavior. Intervention strategies should address substance use, particularly smoking as a route of administration (ROA), and sexual risk behaviors that best fit this high-risk population.

Characterizing the cognitive effects of cocaine: a comprehensive review

Understanding the cognitive sequela of repeated cocaine use is a growing area of research and is crucial to the development of cognitive models of addiction. We systematically reviewed all available placebo-controlled and case-controlled studies on the acute and long-term effects of cocaine on cognitive functioning. In order to compare the magnitude of cognitive effects across cognitive domains we conducted several meta-analyses on a subset of data from long-term effect studies. Studies on acute cocaine administration suggest enhancement of response inhibition and psychomotor speed, while all other domains appear to be unaffected or not investigated adequately. Long-term effects of cocaine show a wide array of deteriorated cognitive functions, indicating that long term cocaine use is characterized by a general cognitive impairment across functions, rather than by specific cognitive deficits. Literature on long-term cocaine effects is more substantial than literature on acute effects. This comprehensive review outlines possible dissociations and similarities of acute vs. long-term cocaine effects in the human brain. Atherosclerosis after cocaine exposure may underlie cognitive dysfunction, suggesting involvement of multiple brain areas. Acute drug studies are important to the future development of addiction models.

Cognitive dysfunctions in recreational and dependent cocaine users: role of attention-deficit hyperactivity disorder, craving and early age at onset

BACKGROUND

Dependent cocaine users consistently display cognitive deficits but cognitive performance of recreational cocaine users has rarely been investigated.

AIMS

To examine whether cognitive performance is impaired in relatively pure recreational and dependent cocaine users.

METHOD

The cognitive performance of recreational (n = 68) and dependent cocaine users (n = 30) was compared with the performance of stimulant-naive controls (n = 68) employing an extensive neuropsychological test battery. Moreover, the impact of attention-deficit hyperactivity disorder (ADHD) symptoms, craving and early age at onset was analysed.

RESULTS

Dependent cocaine users display broad cognitive impairments in the domains of attention, working memory, declarative memory and executive functions. The performance of recreational cocaine users in all four domains was intermediate between that of controls and dependent users and they displayed significant deficits foremost in the domains of attention and working memory. In addition, ADHD symptoms, craving and age at onset were important modulators of cognitive function in cocaine users.

CONCLUSIONS

Cognitive deficits occur at a recreational and non-dependent level of cocaine use. Cocaine use and ADHD seem to have mutually aggravating effects on cognitive impairment.

Acute khat use reduces response conflict in habitual users

Khat consumption has become a worldwide phenomenon broadening from Eastern Africa and the south west of the Arabian Peninsula to ethnic communities in the rest of the world. So far, the cognitive effects of khat use are poorly understood and no studies have looked into the relation between acute khat use and cognitive control functions, the way we control our thoughts and goal directed behavior. We studied how acute khat use affects the emergence and the resolution of response conflict, a central cognitive control function. Khat users (n = 11) and khat-free controls (n = 18) were matched in terms of education, sex, alcohol, and cannabis consumption. Groups were tested on response conflict, as measured by the Simon task. In one single session, participants worked through two task blocks: the khat group chewed exclusively khat whereas the khat-free group chewed solely a gum. Results showed that in the second block, which reflects the acute impact of khat, the khat group was better than controls in resolving stimulus-induced response conflict as indexed by a smaller Simon effect. These results suggest that the acute intake of khat may improve participants' ability of handling response conflict.

Comparison of impulsivity and working memory in cocaine addiction and pathological gambling: Implications for cocaine-induced neurotoxicity

BACKGROUND

The aim of this study was to compare the cognitive performance of cocaine dependent individuals (CDI) with that of pathological gamblers (PG). Cocaine dependence and pathological gambling share neurobiological vulnerabilities related to addiction, but PG are relatively free of the toxic consequences, such that any additional deficits observed in CDI may be interpreted as pertaining to specific drug effects.

METHODS

We used a case-control observational design contrasting multiple measures of impulsivity (UPPS-P trait impulsivity, delay discounting) and executive measures of response inhibition (Stroop) and working memory performance (N-back) between groups of CDI (n=29), PG (n=23), and healthy controls (n=20). We conducted one-way ANOVAs, followed by planned pairwise tests and calculations of Cohen's d to estimate significant differences between the groups.

RESULTS

CDI, as compared to PG, had elevated scores on UPPS-P Negative Urgency and poorer performance on working memory (2-back). PG had steeper delay-discounting rates. Both groups had elevated Positive Urgency and poorer Stroop inhibition compared to controls. Peak amount of cocaine use was negatively correlated with working memory and response inhibition performance.

CONCLUSION

We found cocaine-related specific elevations in Negative Urgency and working memory deficits, putatively identified as cocaine neurotoxicity effects. Other aspects of impulsivity (Positive Urgency, Stroop inhibition) were increased across CDI and PG groups and may reflect vulnerability factors for addiction.

Effects of chronic low- and high-dose nicotine on cognitive flexibility in C57BL/6J mice

The addictive nature of nicotine remains a global health problem. Despite the availability of treatments for smoking cessation, relapse to smoking after quit attempts still remains very high. Here, we evaluated the effects of chronic nicotine in male C57BL/6J mice in an operant cognitive flexibility task that required the animals to progress sequentially through multiple phases including visual discrimination, strategy shifting and response reversal. As frontostriatal circuits involving discrete regions of dorsal striatum contribute directly to decision-making processes, and BDNF modulates synaptic plasticity and learning, we also assessed the effects of nicotine on striatal BDNF expression. Osmotic minipumps containing either of the two doses of nicotine (low: 6.3 mg/kg/day; high: 18 mg/kg/day) or saline (control) were implanted for chronic delivery that lasted 4 weeks. Nicotine-treated mice exhibited greater response accuracy during visual discrimination. Neither dose of nicotine affected learning of new egocentric response strategy during set-shifting. However, higher but not lower dose of nicotine impaired reversal learning by increasing perseverative responding to the previously non-reinforced stimulus. Furthermore, this effect was associated with reduced BDNF levels in the dorsal striatum. Collectively, these findings suggest that higher relapse rates often observed in high nicotine-dependent smokers may be attributed to impairments in inhibitory control processes. Moreover, striatal BDNF may play a critical role in nicotine-induced alterations in cognitive flexibility.

Personality, psychopathology, life attitudes and neuropsychological performance among ritual users of Ayahuasca: a longitudinal study

Ayahuasca is an Amazonian psychoactive plant beverage containing the serotonergic 5-HT_2A agonist N,N-dimethyltryptamine (DMT) and monoamine oxidase-inhibiting alkaloids (harmine, harmaline and tetrahydroharmine) that render it orally active. Ayahuasca ingestion is a central feature in several Brazilian syncretic churches that have expanded their activities to urban Brazil, Europe and North America. Members of these groups typically ingest ayahuasca at least twice per month. Prior research has shown that acute ayahuasca increases blood flow in prefrontal and temporal brain regions and that it elicits intense modifications in thought processes, perception and emotion. However, regular ayahuasca use does not seem to induce the pattern of addiction-related problems that characterize drugs of abuse. To study the impact of repeated ayahuasca use on general psychological well-being, mental health and cognition, here we assessed personality, psychopathology, life attitudes and neuropsychological performance in regular ayahuasca users (n = 127) and controls (n = 115) at baseline and 1 year later. Controls were actively participating in non-ayahuasca religions. Users showed higher Reward Dependence and Self-Transcendence and lower Harm Avoidance and Self-Directedness. They scored significantly lower on all psychopathology measures, showed better performance on the Stroop test, the Wisconsin Card Sorting Test and the Letter-Number Sequencing task from the WAIS-III, and better scores on the Frontal Systems Behavior Scale. Analysis of life attitudes showed higher scores on the Spiritual Orientation Inventory, the Purpose in Life Test and the Psychosocial Well-Being test. Despite the lower number of participants available at follow-up, overall differences with controls were maintained one year later. In conclusion, we found no evidence of psychological maladjustment, mental health deterioration or cognitive impairment in the ayahuasca-using group.

Neuropsychological effects associated with recreational cocaine use

RATIONALE

Recent evidence suggests that recreational cocaine use is on the increase, with the UK reporting one of the highest levels of use in the EU (EMCDDA 2010). Nevertheless, very few studies have addressed the neuropsychological effects associated with non-dependent recreational cocaine use.

OBJECTIVES

The current study aimed to assess whether recreational cocaine users show neuropsychological deficits on a battery of tests, previously shown to be sensitive to cocaine-dependent and psychosis-prone individuals. Schizotypal traits were also measured.

METHODS

Recreational cocaine users (n = 17) were compared with controls (n = 24) on drug use patterns, the General Health Questionnaire, the Brief Schizotypal Personality Questionnaire (SPQ-B) and four neuropsychological tasks: spatial working memory, intra/extra-dimensional set shifting, the Stocking of Cambridge and the rapid visual processing.

RESULTS

Relative to controls, recreational cocaine users produced significantly more errors on the intra/extra-dimensional set shift task and completed fewer stages, made significantly more six box stage errors on the spatial working memory task, and made significantly more errors and fewer hits, with overall poorer detection rates on the rapid visual processing task. Recreational cocaine users reported significantly higher scores on the cognitive perceptual and disorganised thinking SPQ-B subscales and total SPQ-B scores compared to controls.

CONCLUSIONS

Recreational cocaine users displayed impairments on tasks tapping sustained attention, attentional shifting and spatial memory and reported higher schizotypal trait expression. These findings are consistent with the emerging literature suggesting subtle cognitive deficits, putatively reflecting underlying dopaminergic dysfunction, in non-dependent, recreational cocaine users.

Substrates of neuropsychological functioning in stimulant dependence: a review of functional neuroimaging research

Stimulant dependence is associated with neuropsychological impairments. Here, we summarize and integrate the existing neuroimaging literature on the neural substrates of neuropsychological (dys)function in stimulant dependence, including cocaine, (meth-)amphetamine, ecstasy and nicotine dependence, and excessive caffeine use, comparing stimulant abusers (SAs) to nondrug using healthy controls (HCs). Despite some inconsistencies, most studies indicated altered brain activation in prefrontal cortex (PFC) and insula in response to reward and punishment, and higher limbic and anterior cingulate cortex (ACC)/PFC activation during craving and attentional bias paradigms in SAs compared with HCs. Impulsivity in SAs was associated with lower ACC and presupplementary motor area activity compared with HCs, and related to both ventral (amygdala, ventrolateral PFC, insula) and dorsal (dorsolateral PFC, dorsal ACC, posterior parietal cortex) systems. Decision making in SAs was associated with low dorsolateral PFC activity and high orbitofrontal activity. Finally, executive function in SAs was associated with lower activation in frontotemporal regions and higher activation in premotor cortex compared with HCs. It is concluded that the lower activations compared with HCs are likely to reflect the neural substrate of impaired neurocognitive functions, whereas higher activations in SAs compared with HCs are likely to reflect compensatory cognitive control mechanisms to keep behavioral task performance to a similar level as in HCs. However, before final conclusions can be drawn, additional research is needed using neuroimaging in SAs and HCs using larger and more homogeneous samples as well as more comparable task paradigms, study designs, and statistical analyses.

Khat use is associated with increased response conflict in humans

OBJECTIVE

Khat consumption has become a worldwide phenomenon broadening from Eastern Africa and the south west of the Arabian Peninsula to ethnic communities in the rest of the world. Only few studies have systematically looked into cognitive impairments in khat users. We studied whether khat use is associated with changes in the emergence and resolution of response conflict, a central cognitive control function.

METHOD

Khat users (n = 16) and khat-free controls (n = 16) were matched in terms of sex, ethnicity, socio-economical situation, age, alcohol and cannabis consumption, and IQ (Raven's Progressive Matrices). Groups were tested on response conflict, as measured by the Simon task.

RESULTS

Khat users performed significantly slower than controls and were more strongly affected by stimulus-induced response conflict.

CONCLUSIONS

Khat use is associated with specific impairments in behavioral control: general slowing and less efficient resolution of response conflicts, which is likely to impair decision making in everyday life.

Action video gaming and cognitive control: playing first person shooter games is associated with improvement in working memory but not action inhibition

The interest in the influence of videogame experience in our daily life is constantly growing. "First Person Shooter" (FPS) games require players to develop a flexible mindset to rapidly react and monitor fast moving visual and auditory stimuli, and to inhibit erroneous actions. This study investigated whether and to which degree experience with such videogames generalizes to other cognitive control tasks. Experienced video game players (VGPs) and individuals with little to no videogame experience (NVGPs) performed on a N-back task and a stop-signal paradigm that provide a relatively well-established diagnostic measure of the monitoring and updating of working memory (WM) and response inhibition (an index of behavioral impulsivity), respectively. VGPs were faster and more accurate in the monitoring and updating of WM than NVGPs, which were faster in reacting to go signals, but showed comparable stopping performance. Our findings support the idea that playing FPS games is associated with enhanced flexible updating of task-relevant information without affecting impulsivity.

Avaliação da memória operacional fonológica e impulsividade de usuários de drogas atendidos em um Centro de Atenção Integrada à Saúde Mental

OBJETIVO: avaliar a memória operacional fonológica e relacionar com a impulsividade de pacientes em tratamento no Centro de Atenção Integrada à Saúde Mental. MÉTODO: 29 usuários: 21 do gênero masculino e 8 do feminino, usuários de substâncias psicoativas, com 37,9±10,5 anos de idade e 10,59±3,53 anos de escolaridade; e 30 voluntários: 19 do gênero masculino e 11 do feminino, com 32,4±11,9 anos de idade e 11,07±3,29 anos de escolaridade, sem histórico psiquiátrico ou de dependência química foram convocados à avaliação de: 1) memória operacional para palavras e pseudo-palavras; 2) impulsividade em seus fatores de segunda ordem (impulsividade atencional, motora e de não planejamento). RESULTADOS: o desempenho dos usuários de substâncias psicoativas na avaliação da memória em comparação ao grupo controle foi pior tanto no span auditivo de palavras e pseudo-palavras como também no número total de recordação de palavras e pseudo-palavras. Na avaliação da impulsividade, os usuários apresentaram escores elevados em contraposição aos sujeitos controle em todos os subtipos de impulsividade, inclusive no total. Na análise de correlação dos dados não foram encontradas relações entre os escores de impulsividade e memória. CONCLUSÃO: : este padrão de respostas indica comprometimento da memória operacional fonológica provavelmente independente do alto nível de impulsividade apresentado pelos usuários de drogas. Estas análises contribuem para propor estratégias de tratamento direcionadas às alterações detectadas.

Khat use is associated with impaired working memory and cognitive flexibility

Rationale

Khat consumption has increased during the last decades in Eastern Africa and has become a global phenomenon spreading to ethnic communities in the rest of the world, such as The Netherlands, United Kingdom, Canada, and the United States. Very little is known, however, about the relation between khat use and cognitive control functions in khat users.

Objective

We studied whether khat use is associated with changes in working memory (WM) and cognitive flexibility, two central cognitive control functions.

Methods

Khat users and khat-free controls were matched in terms of sex, ethnicity, age, alcohol and cannabis consumption, and IQ (Raven's progressive matrices). Groups were tested on cognitive flexibility, as measured by a Global-Local task, and on WM using an N-back task.

Result

Khat users performed significantly worse than controls on tasks tapping into cognitive flexibility as well as monitoring of information in WM.

Conclusions

The present findings suggest that khat use impairs both cognitive flexibility and the updating of information in WM. The inability to monitor information in WM and to adjust behavior rapidly and flexibly may have repercussions for daily life activities.

Differential effects of cocaine and MDMA self-administration on cortical serotonin transporter availability in monkeys

Cocaine self-administration alters brain dopaminergic and serotonergic function primarily in mesolimbic and prefrontal brain regions whereas 3,4-methylenedioxymethamphetamine (MDMA) self-administration predominately alters brain serotonergic function in a more widespread distribution across cortical regions. We previously reported that, compared to drug-naïve rhesus monkeys, self-administration of cocaine but not MDMA was associated with increased serotonin transporter (SERT) availability in two mesolimbic regions, the caudate nucleus and putamen, as measured by positron emission tomography (PET) using the SERT-specific ligand [(11)C]-3-amino-4(2-dimethylamino-methyl-phenylsulfanyl)-benzonitrile ([(11)C]DASB). The goal of the present study was to extend this comparison between cocaine and MDMA self-administration to SERT availability in cortical regions, which have been shown previously to be affected in human drug abusers and are associated with executive function. PET studies using [(11)C]DASB were conducted in adult male rhesus monkeys with a history of cocaine (mean intake = 742.6 mg/kg) or MDMA (mean intake = 121.0 mg/kg) self-administration, and drug-naïve controls (n = 4/group). Regions of interest were drawn for several cortical (prefrontal, temporal, parietal, occipital and midcingulate) and subcortical (thalamus, amygdala and hippocampus) areas. Cortical SERT availability was significantly higher in monkeys with a cocaine self-administration history compared to controls whereas MDMA self-administration resulted in lower levels of SERT availability. These data extend our previous findings indicating that cocaine and MDMA self-administration differentially alter SERT availability in subcortical and cortical regions, which may have implications for development of treatment drugs.

Long-term effects of chronic khat use: impaired inhibitory control

So far no studies have systematically looked into the cognitive consequences of khat use. This study compared the ability to inhibit and execute behavioral responses in adult khat users and khat-free controls, matched in terms of age, race, gender distribution, level of intelligence, alcohol and cannabis consumption. Response inhibition and response execution were measured by a stop-signal paradigm. Results show that users and non-users are comparable in terms of response execution but users need significantly more time to inhibit responses to stop signals than non-users.