Abnormal brain activity in prefrontal brain regions in abstinent marijuana users

Plasma Cannabinoid Pharmacokinetics After Controlled Smoking and Ad libitum Cannabis Smoking in Chronic Frequent Users

More Americans are dependent on cannabis than any other illicit drug. The main analytes for cannabis testing include the primary psychoactive constituent, Δ(9)-tetrahydrocannabinol (THC), equipotent 11-hydroxy-THC (11-OH-THC) and inactive 11-nor-9-carboxy-THC (THCCOOH). Eleven adult chronic frequent cannabis smokers resided on a closed research unit with unlimited access to 5.9% THC cannabis cigarettes from 12:00 to 23:00 during two ad libitum smoking phases, followed by a 5-day abstinence period in seven participants. A single cigarette was smoked under controlled topography on the last day of the smoking and abstinence phases. Plasma cannabinoids were quantified by two-dimensional gas chromatography-mass spectrometry. Median plasma maximum concentrations (Cmax) were 28.3 (THC), 3.9 (11-OH-THC) and 47.0 μg/L (THCCOOH) 0.5 h after controlled single cannabis smoking. Median Cmax 0.2-0.5 h after ad libitum smoking was higher for all analytes: 83.5 (THC), 14.2 (11-OH-THC) and 155 μg/L (THCCOOH). All 11 participants' plasma samples were THC and THCCOOH-positive, 58.3% had THC ≥5 μg/L and 79.2% were 11-OH-THC-positive 8.1-14 h after last cannabis smoking. Cannabinoid detection rates in seven participants 106-112 h (4-5 days) after last smoking were 92.9 (THC), 35.7 (11-OH-THC) and 100% (THCCOOH), with limits of quantification of 0.5 μg/L for THC and THCCOOH, and 1.0 μg/L for 11-OH-THC. These data greatly expand prior research findings on cannabinoid excretion profiles in chronic frequent cannabis smokers during ad libitum smoking. Smoking multiple cannabis cigarettes led to higher Cmax and AUC compared with smoking a single cigarette. The chronic frequent cannabis smokers exhibited extended detection windows for plasma cannabinoids, reflecting a large cannabinoid body burden.

Mismatch Negativity and P50 Sensory Gating in Abstinent Former Cannabis Users

Prolonged heavy exposure to cannabis is associated with impaired cognition and brain functional and structural alterations. We recently reported attenuated mismatch negativity (MMN) and altered P50 sensory gating in chronic cannabis users. This study investigated the extent of brain functional recovery (indexed by MMN and P50) in chronic users after cessation of use. Eighteen ex-users (median 13.5 years prior regular use; median 3.5 years abstinence) and 18 nonusers completed (1) a multifeature oddball task with duration, frequency, and intensity deviants and (2) a P50 paired-click paradigm. Trend level smaller duration MMN amplitude and larger P50 ratios (indicative of poorer sensory gating) were observed in ex-users compared to controls. Poorer P50 gating correlated with prior duration of cannabis use. Duration of abstinence was positively correlated with duration MMN amplitude, even after controlling for age and duration of cannabis use. Impaired sensory gating and attenuated MMN amplitude tended to persist in ex-users after prolonged cessation of use, suggesting a lack of full recovery. An association with prolonged duration of prior cannabis use may indicate persistent cannabis-related alterations to P50 sensory gating. Greater reductions in MMN amplitude with increasing abstinence (positive correlation) may be related to either self-medication or an accelerated aging process.

Psychosocial sequelae of cannabis use and implications for policy: findings from the Christchurch Health and Development Study

BACKGROUND

The Christchurch Health and Development Study is a longitudinal study of a birth cohort of 1265 children who were born in Christchurch, New Zealand, in 1977. This cohort has now been studied from birth to the age of 35.

SCOPE OF THIS REVIEW

This article examines a series of findings from the CHDS that address a range of issues relating to the use of cannabis amongst the cohort. These issues include: (a) patterns of cannabis use and cannabis dependence; (b) linkages between cannabis use and adverse educational and economic outcomes; (c) cannabis and other illicit drug use; (d) cannabis and psychotic symptoms; (e) other CHDS findings related to cannabis; and (f) the consequences of cannabis use for adults using cannabis regularly.

FINDINGS

In general, the findings of the CHDS suggest that individuals who use cannabis regularly, or who begin using cannabis at earlier ages, are at increased risk of a range of adverse outcomes, including: lower levels of educational attainment; welfare dependence and unemployment; using other, more dangerous illicit drugs; and psychotic symptomatology. It should also be noted, however, that there is a substantial proportion of regular adult users who do not experience harmful consequences as a result of cannabis use.

CONCLUSIONS

Collectively, these findings suggest that cannabis policy needs to be further developed and evaluated in order to find the best way to regulate a widely-used, and increasingly legal substance.

Persistent effects of chronic Δ9-THC exposure on motor impulsivity in rats

RATIONALE

In humans, long-term marijuana use is associated with impaired impulse control and attentional capacity, though it has been difficult to distinguish pre-existing cognitive deficits from possible consequences of prolonged marijuana exposure.

OBJECTIVE

To evaluate the effects of long-term exposure to Δ9-Tetrahydrocannabinol (Δ9-THC), the primary psychoactive constituent in marijuana, on indices of impulse control and attentional capacity using the rat 5-Choice Serial Reaction Time Task (5-CSRTT).

METHODS

Ten 14-day cycles of Δ9-THC dosing and 5-CSRTT testing were employed, each comprised of 5-day Δ9-THC dosing (0.3 or 3 mg/kg b.i.d.) and 5-CSRTT testing during the 9 days of drug abstinence. Subsequent 5-CSRTT testing continued during 5 weeks of protracted abstinence.

RESULTS

Dose-dependent increases in motor impulsivity (premature responses) and behavioral disinhibition (perseverative responses) emerged following 5 cycles of Δ9-THC exposure that persisted for the remaining dosing and testing cycles. Δ9-THC-related disruptions in motor impulsivity and behavioral inhibition were most pronounced during cognitively challenging 5-CSRTT sessions incorporating varying novel inter-trial intervals (ITIs), and these disruptions persisted for at least 5 weeks of Δ9-THC abstinence. Δ9-THC-related impairments in attentional capacity (response accuracy) were also evident during variable ITI challenge tests, though these attentional disruptions abated within 3 weeks of Δ9-THC abstinence.

CONCLUSIONS

These observations demonstrate that long-term intermittent exposure to clinically meaningful Δ9-THC doses induces persistent impairments in impulse control and attentional function. If present in humans, these disruptions may impact academic and professional performance.

Chronic cannabis use and ERP correlates of visual selective attention during the performance of a flanker go/nogo task

The aim of the study was to investigate the relationship between chronic cannabis use and visual selective attention by examining event-related potentials (ERPs) during the performance of a flanker go/nogo task. Male participants were 15 chronic cannabis users (minimum two years use, at least once per week) and 15 drug naive controls. Cannabis users showed longer reaction times compared to controls with equivalent accuracy. Cannabis users also showed a reduction in the N2 'nogo effect' at frontal sites, particularly for incongruent stimuli, and particularly in the right hemisphere. This suggests differences between chronic cannabis users and controls in terms of inhibitory processing within the executive control network, and may implicate the right inferior frontal cortex. There was also preliminary evidence for differences in early selective attention, with controls but not cannabis users showing modulation of N1 amplitude by flanker congruency. Further investigation is required to examine the potential reversibility of these residual effects after long-term abstinence and to examine the role of early selective attention mechanisms in more detail.

A longitudinal study of the association of adolescent polydrug use, alcohol use and high school non-completion

AIMS

Failure to complete high school predicts substantial economic and social disadvantage in adult life. The aim of this study was to determine the longitudinal association of mid-adolescent polydrug use and high school non-completion, relative to other drug use profiles.

DESIGN

A longitudinal analysis of the relationship between polydrug use in three cohorts at grade 9 (age 14-15 years) and school non-completion (reported post-high school).

SETTING

A State-representative sample of students across Victoria, Australia.

PARTICIPANTS

A total of 2287 secondary school students from 152 high schools. The retention rate was 85%.

MEASUREMENTS

The primary outcome was non-completion of grade 12 (assessed at age 19-23 years). At grade 9, predictors included 30-day use of eight drugs, school commitment, academic failure and peer drug use. Other controls included socio-economic status, family relationship quality, depressive symptoms, gender, age and cohort.

FINDINGS

Three distinct classes of drug use were identified-no drug use (31.7%), mainly alcohol use (61.8%) and polydrug use (6.5%). Polydrug users were characterized by high rates of alcohol, tobacco and cannabis use. In the full model, mainly alcohol users and polydrug users were less likely to complete school than non-drug users [odds ratio (OR) = 1.54, 95% confidence interval (CI) = 1.17-2.03) and OR = 2.51, 95% CI = 1.45-4.33), respectively, P < 0.001]. These effects were independent of school commitment, academic failure, peer drug use and other controls.

CONCLUSIONS

Mid-adolescent polydrug use in Australia predicts subsequent school non-completion after accounting for a range of potential confounding factors. Adolescents who mainly consume alcohol are also at elevated risk of school non-completion.

Effects of cannabis on impulsivity: a systematic review of neuroimaging findings

We conducted a systematic review to assess the evidence for specific effects of cannabis on impulsivity, disinhibition and motor control. The review had a specific focus on neuroimaging findings associated with acute and chronic use of the drug and covers literature published up until May 2012. Seventeen studies were identified, of which 13 met the inclusion criteria; three studies investigated acute effects of cannabis (1 fMRI, 2 PET), while six studies investigated non-acute functional effects (4 fMRI, 2 PET), and four studies investigated structural alterations. Functional imaging studies of impulsivity studies suggest that prefrontal blood flow is lower in chronic cannabis users than in controls. Studies of acute administration of THC or marijuana report increased brain metabolism in several brain regions during impulsivity tasks. Structural imaging studies of cannabis users found differences in reduced prefrontal volumes and white matter integrity that might mediate the abnormal impulsivity and mood observed in marijuana users. To address the question whether impulsivity as a trait precedes cannabis consumption or whether cannabis aggravates impulsivity and discontinuation of usage more longitudinal study designs are warranted.

Preliminary functional MRI results from a combined stop-signal alcohol-cue task

OBJECTIVE

Individuals suffering from alcohol use disorders tend to show impairments in inhibitory control, and these deficits may be exacerbated in the presence of craving-inducing alcohol cues. Imbalances between neural reward and control networks can influence the trajectory of alcohol use disorders such that individuals for whom the reward (craving) network strongly overpowers the control (inhibition) network tend to have worse outcomes. Brain activation related to inhibitory control can be examined using the stop-signal task (SST), which requires balancing speed and accuracy in the context of frequent go and infrequent stop stimuli. Further, brain areas related to cue-induced craving can be studied using visual cue tasks comparing neural responses to alcohol and control images. This study aims to explore the interaction of inhibitory control and cue-elicited craving using a single functional neuroimaging task.

METHOD

We developed a novel task involving presentation of alcohol and control cues concurrently with a standard SST paradigm and administered it to 53 heavy drinkers (29 women).

RESULTS

Successful response inhibition during alcohol compared to control picture trials was associated with significant activation in anterior cingulate, supplementary motor, and frontal inferior regions, and this activation was differentially related to alcohol use symptom severity across several self-report measures.

CONCLUSIONS

RESULTS suggest that recruitment of compensatory error detection and inhibitory control resources may be required for successful inhibition in the presence of alcohol cues among more severe drinkers. These preliminary findings support the construct validity of the task and indicate several methodological alterations to the task's design that should be implemented in future studies.

Impairment of inhibitory control processing related to acute psychotomimetic effects of cannabis

Cannabis use can induce acute psychotic symptoms and increase the risk of schizophrenia. Impairments in inhibitory control and processing are known to occur both under the influence of cannabis and in schizophrenia. Whether cannabis-induced impairment in inhibitory processing is related to the acute induction of psychotic symptoms under its influence is unclear. We investigated the effects of acute oral administration of 10mg of delta-9-tetrahydrocannabinol (delta-9-THC), the main psychoactive ingredient of cannabis, on inhibitory control and regional brain activation during inhibitory processing in humans and examined whether these effects are related to the induction of psychotic symptoms under its influence using a repeated-measures, placebo-controlled, double-blind, within-subject design. We studied thirty-six healthy, English-speaking, right-handed men with minimal previous exposure to cannabis and other illicit drugs twice using functional magnetic resonance imaging (fMRI) while they performed a response inhibition (Go/No-Go) task. Relative to placebo, delta-9-THC caused transient psychotic symptoms, anxiety, intoxication and sedation, inhibition errors and impaired inhibition efficiency. Severity of psychotic symptoms was directly correlated with inhibition error frequency and inversely with inhibition efficiency under the influence of delta-9-THC. Delta-9-THC attenuated left inferior frontal activation which was inversely correlated with the frequency of inhibition errors and severity of psychotic symptoms and positively with inhibition efficiency under its influence. These results provide experimental evidence that impairments in cognitive processes involved in the inhibitory control of thoughts and actions and inferior frontal function under the influence of cannabis may have a role in the emergence of transient psychotic symptoms under its influence.

Cannabis abstinence during treatment and one-year follow-up: relationship to neural activity in men

Cannabis is among the most frequently abused substances in the United States. Cognitive control is a contributory factor in the maintenance of substance-use disorders and may relate to treatment response. Therefore, we assessed whether cognitive-control-related neural activity before treatment differs between treatment-seeking cannabis-dependent and healthy individuals and relates to cannabis-abstinence measures during treatment and 1-year follow-up. Cannabis-dependent males (N=20) completed a functional magnetic resonance imaging (fMRI) cognitive-control (Stroop) task before a 12-week randomized controlled trial of cognitive-behavioral therapy and/or contingency management. A healthy-comparison group (N=20) also completed the fMRI task. Cannabis use was assessed by urine toxicology and self-report during treatment, and by self-report across a 1-year follow-up period (N=18). The cannabis-dependent group displayed diminished Stroop-related neural activity relative to the healthy-comparison group in multiple regions, including those strongly implicated in cognitive-control and addiction-related processes (eg, dorsolateral prefrontal cortex and ventral striatum). The groups did not differ significantly in response times (cannabis-dependent, N=12; healthy-comparison, N=14). Within the cannabis-dependent group, greater Stroop-related activity in regions including the dorsal anterior cingulate cortex was associated with less cannabis use during treatment. Greater activity in regions including the ventral striatum was associated with less cannabis use during 1-year posttreatment follow-up. These data suggest that lower cognitive-control-related neural activity in classic 'control' regions (eg, dorsolateral prefrontal cortex and dorsal anterior cingulate) and classic 'salience/reward/learning' regions (eg, ventral striatum) differentiates cannabis-dependent individuals from healthy individuals and relates to less abstinence within-treatment and during long-term follow-up. Clinically, results suggest that treatment development efforts that focus on enhancing cognitive control in addition to abstinence may improve treatment outcomes in cannabis dependence.

Who are those "risk-taking adolescents"? Individual differences in developmental neuroimaging research

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Rates of development differ across brain regions linked to reward and inhibition.

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Adolescent risk-taking has been attributed in part to normative neurodevelopment.

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Significant risky behavior in mid-adolescence is not characteristic of typical youth.

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Youth with behavior disorders show increased behavioral and brain responses to reward.

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Maturational theories of adolescent risk-taking can consider individual differences.

Functional magnetic resonance imaging (fMRI) has illuminated the development of human brain function. Some of this work in typically-developing youth has ostensibly captured neural underpinnings of adolescent behavior which is characterized by risk-seeking propensity, according to psychometric questionnaires and a wealth of anecdote. Notably, cross-sectional comparisons have revealed age-dependent differences between adolescents and other age groups in regional brain responsiveness to prospective or experienced rewards (usually greater in adolescents) or penalties (usually diminished in adolescents). These differences have been interpreted as reflecting an imbalance between motivational drive and behavioral control mechanisms, especially in mid-adolescence, thus promoting greater risk-taking. While intriguing, we caution here that researchers should be more circumspect in attributing clinically significant adolescent risky behavior to age-group differences in task-elicited fMRI responses from neurotypical subjects. This is because actual mortality and morbidity from behavioral causes (e.g. substance abuse, violence) by mid-adolescence is heavily concentrated in individuals who are not neurotypical, who rather have shown a lifelong history of behavioral disinhibition that frequently meets criteria for a disruptive behavior disorder, such as conduct disorder, oppositional-defiant disorder, or attention-deficit hyperactivity disorder. These young people are at extreme risk of poor psychosocial outcomes, and should be a focus of future neurodevelopmental research.

Cannabis dependence, cognitive control and attentional bias for cannabis words

One of the characteristics of people suffering from addictive behaviors is the tendency to be distracted by drug cues. This attentional bias for drug cues is thought to lead to increased craving and drug use, and may draw individuals into a vicious cycle of drug addiction. In the current study we developed a Dutch version of the cannabis Stroop task and measured attentional bias for cannabis words in a group of heavy cannabis users and matched controls. The classical Stroop task was used as a global measure of cognitive control and we examined the relationship between cognitive control, cannabis-related problems, cannabis craving and cannabis attentional bias. Using our version of the cannabis Stroop task, a group of heavy cannabis users showed attentional bias to cannabis words, whereas a control group of non-users did not. Furthermore, within the group of cannabis users, those who were clinically recognized as dependent showed a stronger attentional bias than the heavy, non-dependent users. Cannabis users who displayed reduced cognitive control (as measured with the classical Stroop task) showed increased session-induced craving. Contrary to expectations, however, cognitive control did not appear to modulate the relationship between attentional bias to cannabis words (cannabis Stroop task) and cannabis dependence. This study confirmed the relationship between cannabis dependence and attentional bias and extends this by highlighting a moderating role for cognitive control, which may make some more vulnerable to craving.

Neural mechanisms of risky decision-making and reward response in adolescent onset cannabis use disorder

BACKGROUND

Neural mechanisms of decision-making and reward response in adolescent cannabis use disorder (CUD) are underexplored.

METHODS

Three groups of male adolescents were studied: CUD in full remission (n=15); controls with psychopathology without substance use disorder history (n=23); and healthy controls (n=18). We investigated neural processing of decision-making and reward under conditions of varying risk and uncertainty with the Decision-Reward Uncertainty Task while participants were scanned using functional magnetic resonance imaging.

RESULTS

Abstinent adolescents with CUD compared to controls with psychopathology showed hyperactivation in one cluster that spanned left superior parietal lobule/left lateral occipital cortex/precuneus while making risky decisions that involved uncertainty, and hypoactivation in left orbitofrontal cortex to rewarded outcomes compared to no-reward after making risky decisions. Post hoc region of interest analyses revealed that both control groups significantly differed from the CUD group (but not from each other) during both the decision-making and reward outcome phase of the Decision-Reward Uncertainty Task. In the CUD group, orbitofrontal activations to reward significantly and negatively correlated with total number of individual drug classes the CUD patients experimented with prior to treatment. CUD duration significantly and negatively correlated with orbitofrontal activations to no-reward.

CONCLUSIONS

The adolescent CUD group demonstrated distinctly different activation patterns during risky decision-making and reward processing (after risky decision-making) compared to both the controls with psychopathology and healthy control groups. These findings suggest that neural differences in risky decision-making and reward processes are present in adolescent addiction, persist after remission from first CUD treatment, and may contribute to vulnerability for adolescent addiction.

Functional imaging of implicit marijuana associations during performance on an Implicit Association Test (IAT)

This research evaluated the neural correlates of implicit associative memory processes (habit-based processes) through the imaging (fMRI) of a marijuana Implicit Association Test. Drug-related associative memory effects have been shown to consistently predict level of drug use. To observe differences in neural activity of associative memory effects, this study compared 13 heavy marijuana users and 15 non-using controls, ranging in age from 18 to 25, during performance of a marijuana Implicit Association Test (IAT). Group by condition interactions in the putamen, caudate, and right inferior frontal gyrus were observed. Relative to non-users, marijuana users showed greater bilateral activity in the dorsal striatum (caudate and putamen) during compatible trials focused on perceived positive outcomes of use. Alternatively, relative to the marijuana-using group, the non-users showed greater activity in the right inferior frontal gyrus during incompatible trials, which require more effortful processing of information. Further, relative to fixation, heavy users showed bilateral activity in the caudate and putamen, hippocampus and some frontal regions during compatible trials and no significant activity during incompatible trials. The non-using group showed greater activity in frontal regions during incompatible trials relative to fixation and no significant activity during compatible trials. These findings are consistent with a dual process framework of appetitive behaviors proposing that (1) implicit associations underlying habit are mediated through neural circuitry dependent on the striatum, and (2) deliberative/controlled behaviors are mediated through circuitry more dependent on the prefrontal cortex.

Prefrontal hypoactivity associated with impaired inhibition in stimulant-dependent individuals but evidence for hyperactivation in their unaffected siblings

A neurocognitive endophenotype has been proposed for stimulant dependence, based on behavioral measures of inhibitory response control associated with white matter changes in the frontal cortex. This study investigated the functional neuroimaging correlates of inhibitory response control, as functional activity serves as a more dynamic measure than brain structure, allowing refinement of the suggested endophenotype. Stimulant-dependent individuals (SDIs), their unaffected siblings (SIBs), and healthy controls (CTs) performed the stop-signal task, including stop-signal reaction time (SSRT) as a measure of response inhibition, while undergoing functional magnetic resonance imaging. SDIs had impaired response inhibition accompanied by hypoactivation in the ventrolateral prefrontal cortex (PFC). In addition, they demonstrated hypoactivation in the anterior cingulate when failing to stop. In contrast, no hypoactivations were noted in their unaffected SIBs. Rather, they exhibited increased activation in the dorsomedial PFC relative to controls, together with inhibitory performance that was intermediate between that of the stimulant group and the healthy CT group. Such hyperactivations within the neurocircuitry underlying response inhibition and control are suggestive of compensatory mechanisms that could be protective in nature or could reflect coping with a pre-existing vulnerability, thus expressing potential aspects of resilience. The functional activation associated with response inhibition and error monitoring showed differential patterns of results between SDIs and their unaffected first-degree relatives, suggesting that the proposed endophenotype does not generalize to functional brain activity.

Modulation of the Endocannabinoids N-Arachidonoylethanolamine (AEA) and 2-Arachidonoylglycerol (2-AG) on Executive Functions in Humans

Animal studies point to an implication of the endocannabinoid system on executive functions. In humans, several studies have suggested an association between acute or chronic use of exogenous cannabinoids (Δ9-tetrahydrocannabinol) and executive impairments. However, to date, no published reports establish the relationship between endocannabinoids, as biomarkers of the cannabinoid neurotransmission system, and executive functioning in humans. The aim of the present study was to explore the association between circulating levels of plasma endocannabinoids N-arachidonoylethanolamine (AEA) and 2-Arachidonoylglycerol (2-AG) and executive functions (decision making, response inhibition and cognitive flexibility) in healthy subjects. One hundred and fifty seven subjects were included and assessed with the Wisconsin Card Sorting Test; Stroop Color and Word Test; and Iowa Gambling Task. All participants were female, aged between 18 and 60 years and spoke Spanish as their first language. Results showed a negative correlation between 2-AG and cognitive flexibility performance (r = −.37; p<.05). A positive correlation was found between AEA concentrations and both cognitive flexibility (r = .59; p<.05) and decision making performance (r = .23; P<.05). There was no significant correlation between either 2-AG (r = −.17) or AEA (r = −.08) concentrations and inhibition response. These results show, in humans, a relevant modulation of the endocannabinoid system on prefrontal-dependent cognitive functioning. The present study might have significant implications for the underlying executive alterations described in some psychiatric disorders currently associated with endocannabinoids deregulation (namely drug abuse/dependence, depression, obesity and eating disorders). Understanding the neurobiology of their dysexecutive profile might certainly contribute to the development of new treatments and pharmacological approaches.

Neural correlates of performance monitoring in chronic cannabis users and cannabis-naive controls

Chronic cannabis use is associated with residual negative effects on measures of executive functioning. However, little previous work has focused specifically on executive processes involved in performance monitoring in frequent cannabis users. The present study investigated event-related potential (ERP) correlates of performance monitoring in chronic cannabis users. The error-related negativity (ERN) and error positivity (Pe), ERPs sensitive to performance monitoring, were recorded from 30 frequent cannabis users (mean usage=5.52 days/week) and 32 cannabis-naïve control participants during a speeded stimulus discrimination task. The "oddball" P3 ERP was recorded as well. Users and controls did not differ on the amplitude or latency of the ERN; however, Pe amplitude was larger among users. Users also showed increased amplitude and reduced latency of the P3 in response to infrequent stimuli presented during the task. Among users, urinary cannabinoid metabolite levels at testing were unrelated to ERP outcomes. However, total years of cannabis use correlated negatively with P3 latency and positively with P3 amplitude, and age of first cannabis use correlated negatively with P3 amplitude. The results of this study suggest that chronic cannabis use is associated with alterations in neural activity related to the processing of motivationally-relevant stimuli (P3) and errors (Pe).

Impact of prolonged cannabinoid excretion in chronic daily cannabis smokers' blood on per se drugged driving laws

BACKGROUND

Cannabis is the illicit drug most frequently reported with impaired driving and motor vehicle accidents. Some "per se" laws make it illegal to drive with any amount of drug in the body, while others establish blood, saliva, or urine concentrations above which it is illegal to drive. The persistence of Δ(9)-tetrahydrocannabinol (THC) in chronic daily cannabis smokers' blood is unknown.

METHODS

Thirty male chronic daily cannabis smokers resided on a secure research unit for up to 33 days, with daily blood collection. Samples were processed in an ice bath during sample preparation to minimize cannabinoid adsorption onto precipitant material. We quantified THC by 2-dimensional GC-MS.

RESULTS

Of the 30 participants, 27 were THC-positive on admission, with a median (range) concentration of 1.4 μg/L (0.3-6.3). THC decreased gradually; only 1 of 11 participants was negative at 26 days, 2 of 5 remained THC-positive (0.3 μg/L) for 30 days, and 5.0% of participants had THC ≥ 1.0 μg/L for 12 days. Median 11-hydroxy-THC concentrations were 1.1 μg/L on admission, with no results ≥ 1.0 μg/L 24 h later. 11-Nor-9-carboxy-THC (THCCOOH) detection rates were 96.7% on admission, decreasing slowly to 95.7% and 85.7% on days 8 and 22, respectively; 4 of 5 participants remained THCCOOH positive (0.6-2.7 μg/L) after 30 days, and 1 remained positive on discharge at 33 days.

CONCLUSIONS

Cannabinoids can be detected in blood of chronic daily cannabis smokers during a month of sustained abstinence. This is consistent with the time course of persisting neurocognitive impairment reported in recent studies.

Impulsivity, attention, memory, and decision-making among adolescent marijuana users

RATIONALE

Marijuana is a popular drug of abuse among adolescents, and they may be uniquely vulnerable to resulting cognitive and behavioral impairments. Previous studies have found impairments among adolescent marijuana users. However, the majority of this research has examined measures individually rather than multiple domains in a single cohesive analysis. This study used a logistic regression model that combines performance on a range of tasks to identify which measures were most altered among adolescent marijuana users.

OBJECTIVES

The purpose of this research was to determine unique associations between adolescent marijuana use and performances on multiple cognitive and behavioral domains (attention, memory, decision-making, and impulsivity) in 14- to 17-year-olds while simultaneously controlling for performances across the measures to determine which measures most strongly distinguish marijuana users from nonusers.

METHODS

Marijuana-using adolescents (n = 45) and controls (n = 48) were tested. Logistic regression analyses were conducted to test for: (1) differences between marijuana users and nonusers on each measure, (2) associations between marijuana use and each measure after controlling for the other measures, and (3) the degree to which (1) and (2) together elucidated differences among marijuana users and nonusers.

RESULTS

Of all the cognitive and behavioral domains tested, impaired short-term recall memory and consequence sensitivity impulsivity were associated with marijuana use after controlling for performances across all measures.

CONCLUSIONS

This study extends previous findings by identifying cognitive and behavioral impairments most strongly associated with adolescent marijuana users. These specific deficits are potential targets of intervention for this at-risk population.

Structural and functional imaging studies in chronic cannabis users: a systematic review of adolescent and adult findings

Background

The growing concern about cannabis use, the most commonly used illicit drug worldwide, has led to a significant increase in the number of human studies using neuroimaging techniques to determine the effect of cannabis on brain structure and function. We conducted a systematic review to assess the evidence of the impact of chronic cannabis use on brain structure and function in adults and adolescents.

Methods

Papers published until August 2012 were included from EMBASE, Medline, PubMed and LILACS databases following a comprehensive search strategy and pre-determined set of criteria for article selection. Only neuroimaging studies involving chronic cannabis users with a matched control group were considered.

Results

One hundred and forty-two studies were identified, of which 43 met the established criteria. Eight studies were in adolescent population. Neuroimaging studies provide evidence of morphological brain alterations in both population groups, particularly in the medial temporal and frontal cortices, as well as the cerebellum. These effects may be related to the amount of cannabis exposure. Functional neuroimaging studies suggest different patterns of resting global and brain activity during the performance of several cognitive tasks both in adolescents and adults, which may indicate compensatory effects in response to chronic cannabis exposure.

Limitations

However, the results pointed out methodological limitations of the work conducted to date and considerable heterogeneity in the findings.

Conclusion

Chronic cannabis use may alter brain structure and function in adult and adolescent population. Further studies should consider the use of convergent methodology, prospective large samples involving adolescent to adulthood subjects, and data-sharing initiatives.

Memory-related hippocampal functioning in ecstasy and amphetamine users: a prospective fMRI study

RATIONALE

Recreational use of ecstasy (3,4-methylenedioxymethamphetamine [MDMA]) has been associated with memory impairments. Functional neuroimaging studies with cross-sectional designs reported altered memory-related hippocampal functioning in ecstasy-polydrug users. However, differences might be pre-existing or related to the concomitant use of amphetamine.

OBJECTIVE

To prospectively investigate the specific effects of ecstasy on memory-related hippocampal functioning.

METHODS

We used an associative memory task and functional magnetic resonance imaging (fMRI) in 40 ecstasy and/or amphetamine users at baseline (t1) and after 12 months (t2). At t1, all subjects had very limited amphetamine and/or ecstasy experience (less than 5 units lifetime dose). Based on the reported drug use at t2, subjects with continued ecstasy and/or amphetamine use (n = 17) were compared to subjects who stopped use after t1 (n = 12).

RESULTS

Analysis of repeated measures revealed that encoding-related activity in the left parahippocampal gyrus changed differentially between the groups. Activity in this region increased in abstinent subjects from t1 to t2, however, decreased in subjects with continued use. Decreases within the left parahippocampal gyrus were associated with the use of ecstasy, but not amphetamine, during the follow-up period. However, there were no significant differences in memory performance.

CONCLUSIONS

The current findings suggest specific effects of ecstasy use on memory-related hippocampal functioning. However, alternative explanations such as (sub-)acute cannabis effects are conceivable.

The effect of cannabis use on memory function: an update

Investigating the effects of cannabis use on memory function appears challenging. While early observational investigations aimed to elucidate the longer-term effects of cannabis use on memory function in humans, findings remained equivocal and pointed to a pattern of interacting factors impacting on the relationship between cannabis use and memory function, rather than a simple direct effect of cannabis. Only recently, a clearer picture of the chronic and acute effects of cannabis use on memory function has emerged once studies have controlled for potential confounding factors and started to investigate the acute effects of delta-9-tetrahydrocannabinol (Δ9-THC) and cannabidiol (CBD), the main ingredients in the extract of the cannabis plant in pharmacological challenge experiments. Relatively consistent findings have been reported regarding the acute impairments induced by a single dose of Δ9-THC on verbal and working memory. It is unclear whether they may persist beyond the intoxication state. In the long-term, these impairments seem particularly likely to manifest and may also persist following abstinence if regular and heavy use of cannabis strains high in Δ9-THC is started at an early age. Although still at an early stage, studies that employed advanced neuroimaging techniques have started to model the neural underpinnings of the effects of cannabis use and implicate a network of functional and morphological alterations that may moderate the effects of cannabis on memory function. Future experimental and epidemiological studies that take into consideration individual differences, particularly previous cannabis history and demographic characteristics, but also the precise mixture of the ingredients of the consumed cannabis are necessary to clarify the magnitude and the mechanisms by which cannabis-induced memory impairments occur and to elucidate underlying neurobiological mechanisms.

Cognitive enhancement as a treatment for drug addictions

Drug addiction continues to be an important public health problem, with an estimated 22.6 million current illicit drug users in the United States alone. For many addictions, including cocaine, methamphetamine, and marijuana addiction, there are no approved pharmacological treatments. Behavioral treatments are effective but effects vary widely across individuals. Treatments that are effective across multiple addictions are greatly needed, and accumulating evidence suggests that one such approach may be pharmacological or behavioral interventions that enhance executive inhibitory control in addicts. Current evidence indicates that most forms of chronic drug use may be associated with significant cognitive impairments, especially in attention, working memory, and response inhibition functions. In some studies, these impairments predict poor treatment retention and outcome. A number of cognitive enhancing agents, including galantamine, modafinil, atomoxetine, methylphenidate, and guanfacine, have shown promising findings in human studies. Specific behavioral interventions, including cognitive remediation, also show promise. However, whether improvement of selective cognitive functions reduces drug use behavior remains to be determined. Cognitive enhancement to improve treatment outcomes is a novel strategy worthy of future research, as are related questions such as whether these approaches may be broadly beneficial to most addicts or best reserved for substance users with specific demonstrated cognitive impairments. This article is part of a Special Issue entitled 'Cognitive Enhancers'.

Methylphenidate enhances executive function and optimizes prefrontal function in both health and cocaine addiction

Previous studies have suggested dopamine to be involved in error monitoring/processing, possibly through impact on reinforcement learning. The current study tested whether methylphenidate (MPH), an indirect dopamine agonist, modulates brain and behavioral responses to error, and whether such modulation is more pronounced in cocaine-addicted individuals, in whom dopamine neurotransmission is disrupted. After receiving oral MPH (20 mg) or placebo (counterbalanced), 15 healthy human volunteers and 16 cocaine-addicted individuals completed a task of executive function (the Stroop color word) during functional magnetic resonance imaging (fMRI). During MPH, despite not showing differences on percent accuracy and reaction time, all subjects committed fewer total errors and slowed down more after committing errors, suggestive of more careful responding. In parallel, during MPH all subjects showed reduced dorsal anterior cingulate cortex response to the fMRI contrast error>correct. In the cocaine subjects only, MPH also reduced error>correct activity in the dorsolateral prefrontal cortex (controls instead showed lower error>correct response in this region during placebo). Taken together, MPH modulated dopaminergically innervated prefrontal cortical areas involved in error-related processing, and such modulation was accentuated in the cocaine subjects. These results are consistent with a dopaminergic contribution to error-related processing during a cognitive control task.

Error processing and response inhibition in excessive computer game players: an event-related potential study

Excessive computer gaming has recently been proposed as a possible pathological illness. However, research on this topic is still in its infancy and underlying neurobiological mechanisms have not yet been identified. The determination of underlying mechanisms of excessive gaming might be useful for the identification of those at risk, a better understanding of the behavior and the development of interventions. Excessive gaming has been often compared with pathological gambling and substance use disorder. Both disorders are characterized by high levels of impulsivity, which incorporates deficits in error processing and response inhibition. The present study aimed to investigate error processing and response inhibition in excessive gamers and controls using a Go/NoGo paradigm combined with event-related potential recordings. Results indicated that excessive gamers show reduced error-related negativity amplitudes in response to incorrect trials relative to correct trials, implying poor error processing in this population. Furthermore, excessive gamers display higher levels of self-reported impulsivity as well as more impulsive responding as reflected by less behavioral inhibition on the Go/NoGo task. The present study indicates that excessive gaming partly parallels impulse control and substance use disorders regarding impulsivity measured on the self-reported, behavioral and electrophysiological level. Although the present study does not allow drawing firm conclusions on causality, it might be that trait impulsivity, poor error processing and diminished behavioral response inhibition underlie the excessive gaming patterns observed in certain individuals. They might be less sensitive to negative consequences of gaming and therefore continue their behavior despite adverse consequences.

Performance of young adult cannabis users on neurocognitive measures of impulsive behavior and their relationship to symptoms of cannabis use disorders

Recent studies suggest that abstinent cannabis users show deficits on neurocognitive laboratory tasks of impulsive behavior. But results are mixed, and less is known on the performance of non-treatment-seeking, young adult cannabis users. Importantly, relationships between performance on measures of impulsive behavior and symptoms of cannabis addiction remain relatively unexplored. We compared young adult current cannabis users (CU, n = 65) and nonusing controls (NU, n = 65) on several laboratory measures of impulsive behavior, as well as on a measure of episodic memory commonly impacted by cannabis use. The CU group performed more poorly than the NU group on the Hopkins Verbal Learning Test-Revised Total Immediate Recall and Delayed Recall. No significant differences were observed on the measures of impulsive behavior (i.e., Iowa Gambling Task, IGT; Go-Stop Task; Monetary Choice Questionnaire; Balloon Analogue Risk Task). We examined relationships between neurocognitive performance and symptoms of cannabis use disorder symptoms (Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition, DSM-IV CUD) among the CU group, which revealed that poorer IGT performance was associated with more symptoms of DSM-IV CUD. Our results show poorer memory performance among young adult cannabis users than among healthy controls, but no differences on measures of impulsive behavior. However, performance on a specific type of impulsive behavior (i.e., poorer decision making) was associated with more cannabis use disorder symptoms. These results provide preliminary evidence to suggest that decision-making deficits may be more strongly associated with problems experienced from cannabis use, rather than solely being a consequence of cannabis use, per se.

Neural correlates of hot and cold executive functions in polysubstance addiction: association between neuropsychological performance and resting brain metabolism as measured by positron emission tomography

The study of substance-abuse-related neuropsychological deficits and brain alterations may provide a better understanding of the neuroadaptations associated with addiction. In this study we investigated the association between performance on neuropsychological tests of cold and hot executive functions and regional brain metabolism. Measured with positron emission tomography (PET), in a sample of 49 substance-dependent individuals (SDI). Neuropsychological performance in the SDI group was compared to that of a non-drug-using control group of 30 participants, and associated with two sets of PET-derived dependent measures: one based on regions of interest (examining mean uptake in selected regions), and a second based on voxel uptake measures (using Statistical Parametric Mapping voxel-based whole-brain analyses). Behavioral analyses showed that SDI had poorer performance than controls across executive function and emotion processing measures. Regression models showed that SDI's performance in "cold" executive tests (i.e., updating, inhibition and flexibility) was associated with regional metabolism in the dorsolateral prefrontal cortex (DLPFC), mid-superior frontal gyrus, superior and inferior temporal gyrus and inferior parietal cortex, whereas performance in "hot" executive functions (i.e., self-regulation, decision-making and emotion perception) was associated with DLPFC, mid-superior frontal gyrus, anterior and mid-posterior cingulate, and temporal and fusiform gyrus. These results are discussed in terms of their relevance for the understanding of cognitive dysfunction and neuroadaptations linked to addiction.

Altered cerebral blood flow and neurocognitive correlates in adolescent cannabis users

RATIONALE

The effects of adolescent marijuana use on the developing brain remain unclear, despite its prevalence. Arterial spin labeling (ASL) is a noninvasive imaging technique that characterizes neurovascular status and cerebral blood flow (CBF), potentially revealing contributors to neuropathological alterations. No studies to date have looked at CBF in adolescent marijuana users.

OBJECTIVES

This study examined CBF in adolescent marijuana users and matched healthy controls at baseline and after 4 weeks of monitored abstinence.

METHODS

Heavy adolescent marijuana users (n = 23, >200 lifetime marijuana use days) and demographically matched controls (n = 23) with limited substance exposure underwent an ASL brain scan at an initial session and after 4 weeks of sequential urine toxicology to confirm abstinence.

RESULTS

Marijuana users showed reduced CBF in four cortical regions including the left superior and middle temporal gyri, left insula, left and right medial frontal gyrus, and left supramarginal gyrus at baseline; users showed increased CBF in the right precuneus at baseline, as compared to controls (corrected p values < 0.05). No between group differences were found at follow-up.

CONCLUSIONS

Marijuana use may influence CBF in otherwise healthy adolescents acutely; however, group differences were not observed after several weeks of abstinence. Neurovascular alterations may contribute to or underlie changes in brain activation, neuropsychological performance, and mood observed in young cannabis users with less than a month of abstinence.

Functional connectivity in brain networks underlying cognitive control in chronic cannabis users

The long-term effect of regular cannabis use on brain function underlying cognitive control remains equivocal. Cognitive control abilities are thought to have a major role in everyday functioning, and their dysfunction has been implicated in the maintenance of maladaptive drug-taking patterns. In this study, the Multi-Source Interference Task was employed alongside functional magnetic resonance imaging and psychophysiological interaction methods to investigate functional interactions between brain regions underlying cognitive control. Current cannabis users with a history of greater than 10 years of daily or near-daily cannabis smoking (n=21) were compared with age, gender, and IQ-matched non-using controls (n=21). No differences in behavioral performance or magnitude of task-related brain activations were evident between the groups. However, greater connectivity between the prefrontal cortex and the occipitoparietal cortex was evident in cannabis users, as compared with controls, as cognitive control demands increased. The magnitude of this connectivity was positively associated with age of onset and lifetime exposure to cannabis. These findings suggest that brain regions responsible for coordinating behavioral control have an increased influence on the direction and switching of attention in cannabis users, and that these changes may have a compensatory role in mitigating cannabis-related impairments in cognitive control or perceptual processes.

Cortico-cerebellar abnormalities in adolescents with heavy marijuana use

There are currently no studies that have evaluated the motor network, including the cerebellum, in adolescent marijuana (MJ) smokers. The current study aimed to evaluate whether there were activation differences in Brodmann's area 4 (BA4), Brodmann's area 6 (BA6), cingulate (CG) and cerebellum between MJ-using adolescents and healthy controls (HC) on a functional magnetic resonance imaging (fMRI) bilateral finger-tapping task. Twenty-four adolescents (aged 18.2 ± 0.7 years) with heavy MJ use and 24 HC (18.0 ± 1.9) had MRI scans on a 3T Siemens scanner, including a standard bilateral fMRI finger-tapping sequence. Imaging data were analyzed using SPM5 in Matlab. As regions of interest, BA4, BA6, cingulate (CG) and cerebellum were selected, and significant clusters of activity were thresholded at p<0.05, corrected. Healthy controls had significantly greater activation than MJ users for the CG and cerebellum. In addition, activation of the cerebellum and CG correlated with lifetime MJ smokes. This is one of the first studies to evaluate cortico-cerebellar circuits in adolescents with heavy MJ use. The study, which used a bilateral finger-tapping fMRI task, provides evidence for both CG and cerebellar dysfunction in MJ abuse and indicates that lifetime MJ use may impact the developing brain.

Examining the effects of former cannabis use on cerebellum-dependent eyeblink conditioning in humans

RATIONALE

Previous work in humans has shown that chronic cannabis users exhibit disruptions in classical eyeblink conditioning (EBC), a form of associative learning that is known to be dependent on the cerebellum. Based upon previous work in animals, it was hypothesized that these learning deficits were related to cannabinoid receptor (CB1R) downregulation. However, it remains unclear whether there is a recovery of cerebellum-dependent learning after the cessation of cannabis use.

METHODS

Therefore, former cannabis users (n=10), current cannabis users (n=10), and cannabis-naïve controls (n=10), all free of DSM-IV Axis-I or -II disorders, were evaluated. A standard delay EBC procedure was utilized in which paired presentations of a conditioned stimulus (CS; e.g., tone) and a co-terminating unconditioned stimulus (US; e.g., ocular airpuff) were administered, thus eliciting a conditioned eyeblink response (CR). The primary dependent measures were percentage of CRs and CR latency across conditioning blocks.

RESULTS

Similar to prior studies, current cannabis users exhibited marked impairments in both the acquisition and timing of CRs compared to controls. Although former cannabis users showed intact CR acquisition compared to controls, they exhibited significantly impaired (shorter) CR latencies. In both cannabis groups, UR amplitude did not differ from controls, indicating normal US processing.

CONCLUSIONS

These data suggest that a recovery of function has occurred for the learning of the CS-US association, while the accurate timing of the CR shows lasting impairments. Taken together, these results suggest that heavy cannabis use can disrupt timing-related synaptic plasticity within the cerebellum, even after the cessation of cannabis use.

The differential effect of illicit drug use on cognitive function in first-episode psychosis and healthy controls

OBJECTIVE

Illicit drug use can result in impairment in cognitive function in healthy individuals. Individuals with a psychotic disorder also show a deficit in cognitive function. Drug use may simply contribute to the characteristic cognitive deficit found in psychosis or alternatively result in a 'double deficit'. This study aims to investigate the association between drug use and cognitive function at the first-episode of psychosis and in community-matched controls.

METHOD

One hundred and seventy-seven patients at the first episode of psychosis completed a battery of neuropsychological tests. Those that had used drugs in the previous year (n = 80) were compared with those who had not used drugs in the previous year (n = 97). A subsample of the first-episode psychosis patients were compared with community-matched controls (n = 110) according to drug-use status.

RESULTS

Patients with a first episode of psychosis who had used drugs performed equally to those who had not used drugs on neuropsychological tests. In contrast, healthy controls who had used drugs in the previous year performed worse on tests of executive function and working memory compared with those controls that had not used drugs.

CONCLUSION

There are differential associations of illicit drug misuse with cognitive function for first-episode psychosis patients and healthy controls.

Orbitofrontal volumes in early adolescence predict initiation of cannabis use: a 4-year longitudinal and prospective study

BACKGROUND

There is growing evidence that long-term, heavy cannabis use is associated with alterations in regional brain volumes. Although these changes are frequently attributed to the neurotoxic effects of cannabis, it is possible that some abnormalities might predate use and represent markers of vulnerability. To date, no studies have examined whether structural brain abnormalities are present before the onset of cannabis use. This study aims to determine whether adolescents who have initiated cannabis use early (i.e., before age 17 years) show premorbid structural abnormalities in the amygdala, hippocampus, orbitofrontal cortex, and anterior cingulate cortex.

METHODS

Participants (n = 121) were recruited from primary schools in Melbourne, Australia, as part of a larger study examining adolescent emotional development. Participants underwent structural magnetic resonance imaging at age 12 years and were assessed for cannabis use 4 years later, at age 16 years. At the follow-up assessment, 28 participants had commenced using cannabis (16 female subjects [57%]), and 93 had not (43 female subjects [46%]).

RESULTS

Smaller orbitofrontal cortex volumes at age 12 years predicted initiation of cannabis use by age 16 years. The volumes of other regions (amygdala, hippocampus, and anterior cingulate cortex) did not predict later cannabis use.

CONCLUSIONS

These findings suggest that structural abnormalities in the orbitofrontal cortex might contribute to risk for cannabis exposure. Although the results have important implications for understanding neurobiological predictors of cannabis use, further research is needed to understand their relationship with heavier patterns of use in adulthood as well as later abuse of other substances.

Substance Abuse, Hepatitis C, and Aging in HIV: Common Cofactors that Contribute to Neurobehavioral Disturbances

Although the prevalence of neurocognitive disturbances among individuals with HIV has decreased in recent years, rates of impairment still remain high. This review presents findings from comorbid conditions that may contribute to further neurocognitive impairments in this already vulnerable population. We will focus on three co-factors that have received substantial attention in the neuroAIDS literature: drug use, hepatitis C co-infection (HCV), and aging. All three conditions commonly co-occur with HIV and likely interact with HIV in complex ways. Collectively, the extant literature suggests that drug use, HCV, and aging serve to worsen the neurocognitive profile of HIV through several overlapping mechanisms. A better understanding of how specific comorbidities interact with HIV may reveal specific phenotypes of HIV-associated neurocognitive disorder that may aid in the development of more targeted behavioral and pharmacological treatment efforts.

Similar hyporesponsiveness of the dorsomedial prefrontal cortex in problem gamblers and heavy smokers during an inhibitory control task

BACKGROUND

Behavioral addictions like pathological gambling share many clinical characteristics with substance dependence. In addition, both types of disorders are associated with impairments in inhibitory control. Studies in patients with substance use disorders point to hyporesponsiveness of the dorsomedial prefrontal cortex. However, no such data exist on behavioral addictions.

METHODS

Using functional magnetic resonance imaging, we investigated the neural circuitry associated with impaired response inhibition in a group of male problem gamblers (n=17) using a stop signal task. We included control conditions tailored to specifically isolate neural correlates of inhibitory control. To investigate the specificity of effects, a group of heavy smokers (n=18) and a group of healthy controls (n=17) were also included.

RESULTS

Groups did not differ in behavioral performance on the stop signal task. However, both problem gamblers and heavy smokers showed hyporesponsiveness of the dorsomedial prefrontal cortex compared to healthy controls, during successful as well as failed response inhibition. These effects were robust against adjustments for depression and adult attention deficit scores.

CONCLUSIONS

These findings suggest that hypoactivation of the inhibition circuit is a shared neural mechanism in substance use disorders and behavioral addictions. As such, they support the reclassification of pathological gambling as a behavioral addiction in DSM-V.

Age of onset of marijuana use impacts inhibitory processing

Difficulties in the ability to successfully inhibit impulsive behaviors have been reported in marijuana (MJ) smokers, yet few studies have made direct comparisons between early (prior to age 16) and late (age 16 or later) onset MJ smokers, specifically during behavioral inhibition tasks. The current study utilized the Multi-Source Interference Task (MSIT) during functional magnetic resonance imaging (fMRI) in chronic, heavy MJ smokers and healthy non-MJ smoking controls which revealed a more focal pattern of anterior cingulate activity in controls relative to smokers. Early onset smokers had more focal activation but tended to make more errors of commission relative to late onset smokers, suggesting a possible neural adaptation despite difficulty with behavioral inhibition. Further investigation is warranted, as early exposure to MJ may result in reorganization of critical brain regions.

Assessing topographical orientation skills in cannabis users

The long-term effects of cannabis on human cognition are still unclear, but, considering that cannabis is a widely used substance and, overall, its potential use in therapeutic interventions, it is important to evaluate them. We hypothesize that the discrepancies among studies could be attributed to the specific cognitive function investigated and that skills subserved by the hippocampus, such as the spatial orientation abilities and, specifically, the ability to form and use cognitive maps, should be more compromised than others. Indeed it has been showed that cannabis users have a reduced hippocampus and that the hippocampus is the brain region in which cannabis has the greatest effect since it contains the highest concentration of cannabinoid receptors. To test this hypothesis we asked 15 heavy cannabis users and 19 nonusers to perform a virtual navigational test, the CMT, that assesses the ability to form and use cognitive maps. We found that using cannabis has no effect on these hippocampus-dependent orientation skills. We discuss the implications of our findings and how they relate to evidence reported in the literature that the intervention of functional reorganization mechanisms in cannabis user allows them to cope with the cognitive demands of navigational tasks.

Reflection impulsivity in adolescent cannabis users: a comparison with alcohol-using and non-substance-using adolescents

RATIONALE

Reflection impulsivity-a failure to gather and evaluate information before making a decision-is a critical component of risk-taking and substance use behaviours, which are highly prevalent during adolescence.

OBJECTIVES AND METHODS

The Information Sampling Test was used to assess reflection impulsivity in 175 adolescents (mean age 18.3, range 16.5-20; 55% female)-48 cannabis users (2.3 years use, 10.8 days/month), 65 alcohol users, and 62 non-substance-using controls-recruited from a longitudinal cohort and from the general community and matched for education and IQ. Cannabis and alcohol users were matched on levels of alcohol consumption.

RESULTS

Cannabis users sampled to the lowest degree of certainty before making a decision on the task. Group differences remained significant after controlling for relevant substance use and clinical confounds (e.g., anxiety, depressive symptoms, alcohol, and ecstasy use). Poor performance on multiple IST indices was associated with an earlier age of onset of regular cannabis use and greater duration of exposure to cannabis, after controlling for recent use. Alcohol users did not differ from controls on any IST measure.

CONCLUSIONS

Exposure to cannabis during adolescence is associated with increased risky and impulsive decision making, with users adopting strategies with higher levels of uncertainty and inefficient utilisation of information. The young cannabis users did show sensitivity to losses, suggesting that greater impulsivity early in their drug using career is more evident when there is a lack of negative consequences. This provides a window of opportunity for intervention before the onset of cannabis dependence.

Neurocognitive effects of HIV, hepatitis C, and substance use history

HIV-associated neurocognitive dysfunction persists in the highly active antiretroviral therapy (HAART) era and may be exacerbated by comorbidities, including substance use and hepatitis C virus (HCV) infection. However, the neurocognitive impact of HIV, HCV, and substance use in the HAART era is still not well understood. In the current study, 115 HIV-infected and 72 HIV-seronegative individuals with significant rates of lifetime substance dependence and HCV infection received comprehensive neuropsychological assessment. We examined the effects of HIV serostatus, HCV infection, and substance use history on neurocognitive functioning. We also examined relationships between HIV disease measures (current and nadir CD4, HIV RNA, duration of infection) and cognitive functioning. Approximately half of HIV-infected participants exhibited neurocognitive impairment. Detectable HIV RNA but not HIV serostatus was significantly associated with cognitive functioning. HCV was among the factors most consistently associated with poorer neurocognitive performance across domains, while substance use was less strongly associated with cognitive performance. The results suggest that neurocognitive impairment continues to occur in HIV-infected individuals in association with poor virologic control and comorbid conditions, particularly HCV coinfection.

Neurophysiological functioning of occasional and heavy cannabis users during THC intoxication

RATIONALE

Experienced cannabis users demonstrate tolerance to some of the impairing acute effects of cannabis.

OBJECTIVES

The present study investigates whether event-related potentials (ERPs) differ between occasional and heavy cannabis users after acute Δ9-tetrahydrocannabinol (THC) administration, as a result of tolerance.

METHODS

Twelve occasional and 12 heavy cannabis users participated in a double-blind, placebo-controlled, crossover study. On two separate days, they smoked a joint containing 0 or 500 μg/kg body weight THC. ERPs were measured while subjects performed a divided attention task (DAT) and stop signal task (SST).

RESULTS

In the DAT, THC significantly decreased P100 amplitude in occasional but not in heavy cannabis users. P300 amplitude in the DAT was significantly decreased by THC in both groups. The N200 peak in the SST was not affected by treatment in neither of the groups. Performance in the SST was impaired in both groups after THC treatment, whereas performance in the DAT was impaired by THC only in the occasional users group.

CONCLUSIONS

The present study confirms that heavy cannabis users develop tolerance to some of the impairing behavioral effects of cannabis. This tolerance was also evident in the underlying ERPs, suggesting that tolerance demonstrated on performance level is not (completely) due to behavioral compensation.

Adolescent exposure to cannabis as a risk factor for psychiatric disorders

Adolescence represents a critical period for brain development and the endocannabinoid system plays a crucial role in the regulation of neuronal refinement during this period. Cannabis is the most consumed drug among adolescent people and its heavy use may affect maturational refinement by disrupting the regulatory role of the endocannabinoid system. In animals, adolescent cannabinoid exposure has been reported to cause long-term impairment in specific components of learning and memory and to differentially affect emotional reactivity with milder effects on anxiety behaviour and more pronounced effects on depression-like behaviour. Moreover, adolescent exposure to cannabinoids might represent a risk factor for developing psychotic-like symptoms at adulthood. Also epidemiological studies suggest that heavy adolescent cannabis use may increase the risk of cognitive abnormalities, psychotic illness, mood disorders and other illicit substance use later in life. In conclusion, the available data point to the hypothesis that heavy cannabis use in adolescence could increase the risk of developing psychiatric disorders, especially in people who already have a vulnerability to develop a psychiatric syndrome. Only few papers have investigated the neurobiological substrates of this vulnerability, thus further studies are needed to clarify the molecular mechanisms underlying the effect of cannabis on the adolescent brain.

Prefrontal hypoactivation during cognitive control in early abstinent methamphetamine-dependent subjects

Individuals who abuse methamphetamine (MA) perform at levels below those of healthy controls on tests that require cognitive control. As cognitive control deficits may influence the success of treatment for addiction, we sought to help clarify the neural correlates of this deficit. MA-dependent (n=10, abstinent 4-7 days) and control subjects (n=18) performed a color-word Stroop task, which requires cognitive control, during functional MRI (fMRI). The task included a condition in which participants were required to respond to one stimulus dimension while ignoring another conflicting dimension, and another condition without conflict. We compared the groups on performance and neural activation in the two conditions. MA-dependent subjects made more errors and responded more slowly than controls. Controlling for response times in the incongruent condition, voxel-wise mixed effects analyses (whole-brain corrected) demonstrated that MA-dependent subjects had less activation than control subjects in the right inferior frontal gyrus, supplementary motor cortex/anterior cingulate gyrus and the anterior insular cortex during the incongruent condition only. MA-dependent subjects did not exhibit greater activation in any brain region in either of the Stroop conditions. These preliminary findings suggest that hypofunction in cortical areas that are important for executive function underlies cognitive control deficits associated with MA dependence.

Age of onset of marijuana use and executive function

Marijuana (MJ) remains the most widely abused illicit substance in the United States, and in recent years, a decline in perceived risk of MJ use has been accompanied by a simultaneous increase in rates of use among adolescents. In this study, the authors hypothesized that chronic MJ smokers would perform cognitive tasks, specifically those that require executive function, more poorly than control subjects and that individuals who started smoking MJ regularly prior to age 16 (early onset) would have more difficulty than those who started after age 16 (late onset). Thirty-four chronic, heavy MJ smokers separated into early and late onset groups, and 28 non-MJ smoking controls completed a battery of neurocognitive measures. As hypothesized, MJ smokers performed more poorly than controls on several measures of executive function. Age of onset analyses revealed that these between-group differences were largely attributed to the early onset group, who were also shown to smoke twice as often and nearly 3 times as much MJ per week relative to the late onset smokers. Age of onset, frequency, and magnitude of MJ use were all shown to impact cognitive performance. Findings suggest that earlier MJ onset is related to poorer cognitive function and increased frequency and magnitude of MJ use relative to later MJ onset. Exposure to MJ during a period of neurodevelopmental vulnerability, such as adolescence, may result in altered brain development and enduring neuropsychological changes.

Dysfunction of the prefrontal cortex in addiction: neuroimaging findings and clinical implications

The loss of control over drug intake that occurs in addiction was initially believed to result from disruption of subcortical reward circuits. However, imaging studies in addictive behaviours have identified a key involvement of the prefrontal cortex (PFC) both through its regulation of limbic reward regions and its involvement in higher-order executive function (for example, self-control, salience attribution and awareness). This Review focuses on functional neuroimaging studies conducted in the past decade that have expanded our understanding of the involvement of the PFC in drug addiction. Disruption of the PFC in addiction underlies not only compulsive drug taking but also accounts for the disadvantageous behaviours that are associated with addiction and the erosion of free will.

delta(9)-Tetrahydrocannabinol-dependent mice undergoing withdrawal display impaired spatial memory

RATIONALE

Cannabis users display a constellation of withdrawal symptoms upon drug discontinuation, including sleep disturbances, irritability, and possibly memory deficits. In cannabinoid-dependent rodents, the CB(1) antagonist rimonabant precipitates somatic withdrawal and enhances forskolin-stimulated adenylyl cyclase activity in cerebellum, an effect opposite that of acutely administered ∆(9)-tetrahydrocannabinol (THC), the primary constituent in cannabis.

OBJECTIVES

Here, we tested whether THC-dependent mice undergoing rimonabant-precipitated withdrawal display short-term spatial memory deficits, as assessed in the Morris water maze. We also evaluated whether rimonabant would precipitate adenylyl cyclase superactivation in hippocampal and cerebellar tissue from THC-dependent mice.

RESULTS

Rimonabant significantly impaired spatial memory of THC-dependent mice at lower doses than those necessary to precipitate somatic withdrawal behavior. In contrast, maze performance was near perfect in the cued task, suggesting sensorimotor function and motivational factors were unperturbed by the withdrawal state. Finally, rimonabant increased adenylyl cyclase activity in cerebellar, but not in hippocampal, membranes.

CONCLUSIONS

The memory disruptive effects of THC undergo tolerance following repeated dosing, while the withdrawal state leads to a rebound deficit in memory. These results establish spatial memory impairment as a particularly sensitive component of cannabinoid withdrawal, an effect that may be mediated through compensatory changes in the cerebellum.

The relationships of 'ecstasy' (MDMA) and cannabis use to impaired executive inhibition and access to semantic long-term memory

This study aimed to examine the relationship between the consumption of ecstasy (3,4-methylenedioxymethamphetamine (MDMA)) and cannabis, and performance on the random letter generation task which generates dependent variables drawing upon executive inhibition and access to semantic long-term memory (LTM). The participant group was a between-participant independent variable with users of both ecstasy and cannabis (E/C group, n = 15), users of cannabis but not ecstasy (CA group, n = 13) and controls with no exposure to these drugs (CO group, n = 12). Dependent variables measured violations of randomness: number of repeat sequences, number of alphabetical sequences (both drawing upon inhibition) and redundancy (drawing upon access to semantic LTM). E/C participants showed significantly higher redundancy than CO participants but did not differ from CA participants. There were no significant effects for the other dependent variables. A regression model comprising intelligence measures and estimates of ecstasy and cannabis consumption predicted redundancy scores, but only cannabis consumption contributed significantly to this prediction. Impaired access to semantic LTM may be related to cannabis consumption, although the involvement of ecstasy and other stimulant drugs cannot be excluded here. Executive inhibitory functioning, as measured by the random letter generation task, is unrelated to ecstasy and cannabis consumption.