Poor decision-making by chronic marijuana users is associated with decreased functional responsiveness to negative consequences

Cocaine dependence and thalamic functional connectivity: a multivariate pattern analysis

Cocaine dependence is associated with deficits in cognitive control. Previous studies demonstrated that chronic cocaine use affects the activity and functional connectivity of the thalamus, a subcortical structure critical for cognitive functioning. However, the thalamus contains nuclei heterogeneous in functions, and it is not known how thalamic subregions contribute to cognitive dysfunctions in cocaine dependence. To address this issue, we used multivariate pattern analysis (MVPA) to examine how functional connectivity of the thalamus distinguishes 100 cocaine-dependent participants (CD) from 100 demographically matched healthy control individuals (HC). We characterized six task-related networks with independent component analysis of fMRI data of a stop signal task and employed MVPA to distinguish CD from HC on the basis of voxel-wise thalamic connectivity to the six independent components. In an unbiased model of distinct training and testing data, the analysis correctly classified 72% of subjects with leave-one-out cross-validation (p < 0.001), superior to comparison brain regions with similar voxel counts (p < 0.004, two-sample t test). Thalamic voxels that form the basis of classification aggregate in distinct subclusters, suggesting that connectivities of thalamic subnuclei distinguish CD from HC. Further, linear regressions provided suggestive evidence for a correlation of the thalamic connectivities with clinical variables and performance measures on the stop signal task. Together, these findings support thalamic circuit dysfunction in cognitive control as an important neural marker of cocaine dependence.

Effects of Marijuana Use on Brain Structure and Function: Neuroimaging Findings from a Neurodevelopmental Perspective

Marijuana, behind only tobacco and alcohol, is the most popular recreational drug in America with prevalence rates of use rising over the past decade. A wide range of research has highlighted neurocognitive deficits associated with marijuana use, particularly when initiated during childhood or adolescence. Neuroimaging, describing alterations to brain structure and function, has begun to provide a picture of possible mechanisms associated with the deleterious effects of marijuana use. This chapter provides a neurodevelopmental framework from which recent data on brain structural and functional abnormalities associated with marijuana use is reviewed. Based on the current data, we provide aims for future studies to more clearly delineate the effects of marijuana on the developing brain and to define underlying mechanisms of the potential long-term negative consequences of marijuana use.

Marijuana dependence: not just smoke and mirrors

Marijuana (Cannabis sativa) is the most commonly used illicit drug worldwide as well as in the Unites States. Prolonged use of marijuana or repeated administration of its primary psychoactive constituent, Δ9-tetrahydrocannabinol (THC), can lead to physical dependence in humans and laboratory animals. The changes that occur with repeated cannabis use include alterations in behavioral, physiological, and biochemical responses. A variety of withdrawal responses occur in cannabis-dependent individuals: anger, aggression, irritability, anxiety and nervousness, decreased appetite or weight loss, restlessness, and sleep difficulties with strange dreams. But the long half-life and other pharmacokinetic properties of THC result in delayed expression of withdrawal symptoms, and because of the lack of contiguity between drug cessation and withdrawal responses the latter are not readily recognized as a clinically relevant syndrome. Over the past 30 years, a substantial body of clinical and laboratory animal research has emerged supporting the assertion that chronic exposure to cannabinoids produces physical dependence and may contribute to drug maintenance in cannabis-dependent individuals. However, no medications are approved to treat cannabis dependence and withdrawal. In this review, we describe preclinical and clinical research that supports the existence of a cannabinoid withdrawal syndrome. In addition, we review research evaluating potential pharmacotherapies (e.g., THC, a variety of antidepressant drugs, and lithium) to reduce cannabis withdrawal responses and examine how expanded knowledge about the regulatory mechanisms in the endocannabinoid system may lead to promising new therapeutic targets.

Abnormal medial prefrontal cortex activity in heavy cannabis users during conscious emotional evaluation

RATIONALE

Long-term heavy cannabis users (cannabis users) who are not acutely intoxicated have diminished subconscious neural responsiveness to affective stimuli.

OBJECTIVE

This study sought to determine if abnormal processing extends to the conscious evaluation of emotional stimuli.

METHODS

Functional magnetic resonance imaging (fMRI) was used to examine brain activity as cannabis users (N = 16) and non-cannabis-using controls (N = 17) evaluated and categorized standardized International Affective Picture System (IAPS) stimuli. Individual judgments were used to isolate activity during the evaluation of emotional (i.e., emotional evaluation) or neutral (i.e., neutral evaluation) stimuli. Within- and between-group analyses were performed.

RESULTS

Both groups judged the same stimuli as emotional and had activations in visual, midbrain, and middle cingulate cortices during emotional evaluation, relative to neutral. Within-group analyses also revealed amygdalar and inferior frontal gyrus activations in controls, but not cannabis users, and medial prefrontal cortex (mPFC) deactivations in cannabis users, but not controls, during emotional evaluation, relative to neutral. Between-group comparisons found that mPFC activity during positive and negative evaluation was significantly hypoactive in cannabis users, relative to controls.

CONCLUSIONS

Abnormal neural processing of affective content extends to the level of consciousness in cannabis users. The hypoactive mPFC responses observed resembles the attenuated mPFC responses found during increased non-affective cognitive load in prior research. These findings suggest that abnormal mPFC singling in cannabis users during emotional evaluation might be associated with increased non-affective cognitive load.

Altered subjective reward valuation among drug-deprived heavy marijuana users: Aversion to uncertainty

Marijuana is the most commonly used illicit drug in the United States and its use is rising. Nonetheless, scientific efforts to clarify the risk for addiction and other harm associated with marijuana use have been lacking. Maladaptive decision-making is a cardinal feature of addiction that is likely to emerge in heavy users. In particular, distorted subjective reward valuation related to homeostatic or allostatic processes has been implicated for many drugs of abuse. Selective changes in responses to uncertainty have been observed in response to intoxication and deprivation from various drugs of abuse. To assess for these potential neuroadaptive changes in reward valuation associated with marijuana deprivation, we examined the subjective value of uncertain and certain rewards among deprived and nondeprived heavy marijuana users in a behavioral economics decision-making task. Deprived users displayed reduced valuation of uncertain rewards, particularly when these rewards were more objectively valuable. This uncertainty aversion increased with increasing quantity of marijuana use. These results suggest comparable decision-making vulnerability from marijuana use as other drugs of abuse, and highlights targets for intervention.

An fMRI-Based Neural Signature of Decisions to Smoke Cannabis

Drug dependence may be at its core a pathology of choice, defined by continued decisions to use drugs irrespective of negative consequences. Despite evidence of dysregulated decision making in addiction, little is known about the neural processes underlying the most clinically relevant decisions drug users make: decisions to use drugs. Here, we combined functional magnetic resonance imaging (fMRI), machine learning, and human laboratory drug administration to investigate neural activation underlying decisions to smoke cannabis. Nontreatment-seeking daily cannabis smokers completed an fMRI choice task, making repeated decisions to purchase or decline 1-12 placebo or active cannabis 'puffs' ($0.25-$5/puff). One randomly selected decision was implemented. If the selected choice had been bought, the cost was deducted from study earnings and the purchased cannabis smoked in the laboratory; alternatively, the participant remained in the laboratory without cannabis. Machine learning with leave-one-subject-out cross-validation identified distributed neural activation patterns discriminating decisions to buy cannabis from declined offers. A total of 21 participants were included in behavioral analyses; 17 purchased cannabis and were thus included in fMRI analyses. Purchasing varied lawfully with dose and cost. The classifier discriminated with 100% accuracy between fMRI activation patterns for purchased vs declined cannabis at the level of the individual. Dorsal striatum, insula, posterior parietal regions, anterior and posterior cingulate, and dorsolateral prefrontal cortex all contributed reliably to this neural signature of decisions to smoke cannabis. These findings provide the basis for a brain-based characterization of drug-related decision making in drug abuse, including effects of psychological and pharmacological interventions on these processes.

Impaired learning from errors in cannabis users: Dorsal anterior cingulate cortex and hippocampus hypoactivity

BACKGROUND

The chronic use of cannabis has been associated with error processing dysfunction, in particular, hypoactivity in the dorsal anterior cingulate cortex (dACC) during the processing of cognitive errors. Given the role of such activity in influencing post-error adaptive behaviour, we hypothesised that chronic cannabis users would have significantly poorer learning from errors.

METHODS

Fifteen chronic cannabis users (four females, mean age=22.40 years, SD=4.29) and 15 control participants (two females, mean age=23.27 years, SD=3.67) were administered a paired associate learning task that enabled participants to learn from their errors, during fMRI data collection.

RESULTS

Compared with controls, chronic cannabis users showed (i) a lower recall error-correction rate and (ii) hypoactivity in the dACC and left hippocampus during the processing of error-related feedback and re-encoding of the correct response. The difference in error-related dACC activation between cannabis users and healthy controls varied as a function of error type, with the control group showing a significantly greater difference between corrected and repeated errors than the cannabis group.

CONCLUSIONS

The present results suggest that chronic cannabis users have poorer learning from errors, with the failure to adapt performance associated with hypoactivity in error-related dACC and hippocampal regions. The findings highlight a consequence of performance monitoring dysfunction in drug abuse and the potential consequence this cognitive impairment has for the symptom of failing to learn from negative feedback seen in cannabis and other forms of dependence.

Aberrant orbitofrontal connectivity in marijuana smoking adolescents

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Increased OFC functional connectivity was observed in heavy MJ users compared to HC.

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Greater MJ use correlated with increased OFC functional connectivity in MJ users.

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Motor impulsivity correlated with increased OFC functional connectivity in MJ users.

Introduction

Orbitofrontal (OFC) circuits have been implicated in the pathophysiology of substance use disorders. The current study examined OFC functional connectivity differences in marijuana-using adolescents (MJ) and non-using healthy controls (HC).

Methods

Functional magnetic resonance imaging (fMRI) resting-state data were obtained on a 3 T MRI scanner on 31 HC and 43 heavy MJ smokers. Image analyses were performed between groups (MJ, HC) for the left and right OFC separately. Regression analyses between OFC functional connectivity and lifetime MJ use, age of first MJ use and impulsivity also were performed.

Results

Increased OFC functional connectivity to frontal and motor regions was observed in heavy MJ users compared to HC. Earlier age of first MJ use was associated with increased functional connectivity of the right OFC to motor regions. High lifetime MJ use was associated with increased OFC functional connectivity to posterior brain regions in MJ youth.

Discussion

Findings indicate atypical OFC functional connectivity patterns in attentional/executive, motor and reward networks in adolescents with heavy MJ use. These anomalies may be related to suboptimal decision making capacities and increased impulsivity. Results also suggest different OFC connectivity patterns may be present in adolescents with early onset of MJ use and high lifetime exposure to MJ.

Balanced modulation of striatal activation from D2 /D3 receptors in caudate and ventral striatum: Disruption in cannabis abusers

Proper communication between dorsal caudate (CD) and ventral striatum (VS) is likely to be crucial for on-time responses and its disruption might result in impulsivity. Here, we used functional magnetic resonance imaging (fMRI) with a sensorimotor reaction time task and positron emission tomography (PET) with [(11)C]raclopride in 14 healthy controls and 18 cannabis abusers to contrast the modulation of striatal fMRI responses by dopamine receptors (D2 /D3 R) in CD and VS. In controls, we show that the fMRI signals in VS that occurs concomitantly with on-time responses showed opposite modulation from D2 /D3 R in CD (inhibitory) and D2 /D3 R in VS (stimulatory). In contrast, this modulation was not significant in cannabis abusers. Findings suggest that action speed requires balanced VS-inhibition from D2 /D3 R in CD and VS-facilitation from D2 /D3 R in VS.

Cannabis, Cigarettes, and Their Co-Occurring Use: Disentangling Differences in Gray Matter Volume

BACKGROUND

Structural magnetic resonance imaging techniques are powerful tools for examining the effects of drug use on the brain. The nicotine and cannabis literature has demonstrated differences between nicotine cigarette smokers and cannabis users compared to controls in brain structure; however, less is known about the effects of co-occurring cannabis and tobacco use.

METHODS

We used voxel-based morphometry to examine gray matter volume differences between four groups: (1) cannabis-dependent individuals who do not smoke tobacco (Cs); (2) cannabis-dependent individuals who smoke tobacco (CTs); (3) cannabis-naïve, nicotine-dependent individuals who smoke tobacco (Ts); and (4) healthy controls (HCs). We also explored associations between gray matter volume and measures of cannabis and tobacco use.

RESULTS

A significant group effect was observed in the left putamen, thalamus, right precentral gyrus, and left cerebellum. Compared to HCs, the Cs, CTs, and Ts exhibited larger gray matter volumes in the left putamen. Cs also had larger gray matter volume than HCs in the right precentral gyrus. Cs and CTs exhibited smaller gray matter volume than HCs in the thalamus, and CTs and Ts had smaller left cerebellar gray matter volume than HCs.

CONCLUSIONS

This study extends previous research that independently examined the effects of cannabis or tobacco use on brain structure by including an examination of co-occurring cannabis and tobacco use, and provides evidence that cannabis and tobacco exposure are associated with alterations in brain regions associated with addiction.

Functional activation and effective connectivity differences in adolescent marijuana users performing a simulated gambling task

Background. Adolescent marijuana use is associated with structural and functional differences in forebrain regions while performing memory and attention tasks. In the present study, we investigated neural processing in adolescent marijuana users experiencing rewards and losses. Fourteen adolescents with frequent marijuana use (>5 uses per week) and 14 nonuser controls performed a computer task where they were required to guess the outcome of a simulated coin flip while undergoing magnetic resonance imaging. Results. Across all participants, “Wins” and “Losses” were associated with activations including cingulate, middle frontal, superior frontal, and inferior frontal gyri and declive activations. Relative to controls, users had greater activity in the middle and inferior frontal gyri, caudate, and claustrum during “Wins” and greater activity in the anterior and posterior cingulate, middle frontal gyrus, insula, claustrum, and declive during “Losses.” Effective connectivity analyses revealed similar overall network interactions among these regions for users and controls during both “Wins” and “Losses.” However, users and controls had significantly different causal interactions for 10 out of 28 individual paths during the “Losses” condition. Conclusions. Collectively, these results indicate adolescent marijuana users have enhanced neural responses to simulated monetary rewards and losses and relatively subtle differences in effective connectivity.

Decision-making for risky gains and losses among college students with Internet gaming disorder

Individuals with Internet gaming disorder (IGD) tend to exhibit disadvantageous risky decision-making not only in their real life but also in laboratory tasks. Decision-making is a complex multifaceted function and different cognitive processes are involved in decision-making for gains and losses. However, the relationship between impaired decision-making and gain versus loss processing in the context of IGD is poorly understood. The main aim of the present study was to separately evaluate decision-making for risky gains and losses among college students with IGD using the Cups task. Additionally, we further examined the effects of outcome magnitude and probability level on decision-making related to risky gains and losses respectively. Sixty college students with IGD and 42 matched healthy controls (HCs) participated. Results indicated that IGD subjects exhibited generally greater risk taking tendencies than HCs. In comparison to HCs, IGD subjects made more disadvantageous risky choices in the loss domain (but not in the gain domain). Follow-up analyses indicated that the impairment was associated to insensitivity to changes in outcome magnitude and probability level for risky losses among IGD subjects. In addition, higher Internet addiction severity scores were associated with percentage of disadvantageous risky options in the loss domain. These findings emphasize the effect of insensitivity to losses on disadvantageous decisions under risk in the context of IGD, which has implications for future intervention studies.

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.

Executive-affective connectivity in smokers viewing anti-smoking images: an fMRI study

Despite knowledge of the harmful consequences of smoking on health, tobacco users continue to smoke. Neuroimaging studies have begun to provide insight into the mechanisms underlying this response. Regions involved in executive control and affective processing/persuasion are activated when viewing the negative value of smoking, but these systems can interact in ways that promote or hinder its impact on behavior. The goal of this functional magnetic resonance imaging (fMRI) study was to examine the dynamics between these systems during the processing of images designed to elicit a negative emotional response regarding tobacco smoking in a group of current smokers. Thirty chronic smokers passively viewed aversive smoking-related, aversive nonsmoking-related and neutral images presented in a block design while being scanned. Functional connectivity analyses showed that the left inferior frontal gyrus (IFG) is negatively associated to activity in medial frontal, cingulate, limbic, subcortical and parietal regions in chronic smokers during the processing of aversive smoking-related material, a pattern that was significantly greater when stimuli were drug-related compared with when they were nondrug-related. Our results suggest that individuals with tobacco dependence present different patterns of functional connectivity depending on whether the aversive stimuli are smoking- or nonsmoking-related. Activity in the left inferior frontal gyrus may act to down-regulate corresponding activity in regions key to an affective and persuasive response during the processing of anti-smoking material. This mechanism may reduce the extent to which "feeling bad" brings about a change in behavior.

Impaired self-awareness in human addiction: deficient attribution of personal relevance

Compromised self-awareness of illness-related deficits and behaviors in psychopathology (e.g., schizophrenia) has been associated with deficient functioning of cortical midline regions including the ventromedial prefrontal cortex (vmPFC), implicated in personal relevance. Here, we review and critically analyze recent evidence to suggest that vmPFC abnormalities could similarly underlie deficient tagging of personal relevance in drug addiction, evidenced by a constellation of behaviors encompassing drug-biased attention, negative outcome insensitivity, self-report/behavior dissociation, and social inappropriateness. This novel framework might clarify, for example, why drug-addicted individuals often ruin long-standing relationships or forego important job opportunities while continuing to engage in uncontrolled drug-taking. Therapeutic interventions targeting personal relevance and associated vmPFC functioning could enhance self-awareness and facilitate more adaptive behavior in this chronically relapsing psychopathology.

Reward processing in obesity, substance addiction and non-substance addiction

Similarities and differences between obesity and addiction are a prominent topic of ongoing research. We conducted an activation likelihood estimation meta-analysis on 87 studies in order to map the functional magnetic resonance imaging (fMRI) response to reward in participants with obesity, substance addiction and non-substance (or behavioural) addiction, and to identify commonalities and differences between them. Our study confirms the existence of alterations during reward processing in obesity, non-substance addiction and substance addiction. Specifically, participants with obesity or with addictions differed from controls in several brain regions including prefrontal areas, subcortical structures and sensory areas. Additionally, participants with obesity and substance addictions exhibited similar blood-oxygen-level-dependent fMRI hyperactivity in the amygdala and striatum when processing either general rewarding stimuli or the problematic stimuli (food and drug-related stimuli, respectively). We propose that these similarities may be associated with an enhanced focus on reward--especially with regard to food or drug-related stimuli--in obesity and substance addiction. Ultimately, this enhancement of reward processes may facilitate the presence of compulsive-like behaviour in some individuals or under some specific circumstances. We hope that increasing knowledge about the neurobehavioural correlates of obesity and addictions will lead to practical strategies that target the high prevalence of these central public health challenges.

Resting state functional magnetic resonance imaging reveals distinct brain activity in heavy cannabis users - a multi-voxel pattern analysis

Chronic cannabis use can cause cognitive, perceptual and personality alterations, which are believed to be associated with regional brain changes and possible changes in connectivity between functional regions. This study aims to identify the changes from resting state functional magnetic resonance imaging scans. A two-level multi-voxel pattern analysis was proposed to classify male cannabis users from normal controls. The first level analysis works on a voxel basis and identifies clusters for the input of a second level analysis, which works on the functional connectivity between these regions. We found distinct clusters for male cannabis users in the middle frontal gyrus, precentral gyrus, superior frontal gyrus, posterior cingulate cortex, cerebellum and some other regions. Based on the functional connectivity of these clusters, a high overall accuracy rate of 84-88% in classification accuracy was achieved. High correlations were also found between the overall classification accuracy and Barrett Barrett Impulsiveness Scale factor scores of attention and motor. Our result suggests regional differences in the brains of male cannabis users that span from the cerebellum to the prefrontal cortex, which are associated with differences in functional connectivity.

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.

Choosing Money over Drugs: The Neural Underpinnings of Difficult Choice in Chronic Cocaine Users

Addiction is considered a disorder that drives individuals to choose drugs at the expense of healthier alternatives. However, chronic cocaine users (CCUs) who meet addiction criteria retain the ability to choose money in the presence of the opportunity to choose cocaine. The neural mechanisms that differentiate CCUs from non-cocaine using controls (Controls) while executing these preferred choices remain unknown. Thus, therapeutic strategies aimed at shifting preferences towards healthier alternatives remain somewhat uninformed. This study used BOLD neuroimaging to examine brain activity as fifty CCUs and Controls performed single- and cross-commodity intertemporal choice tasks for money and/or cocaine. Behavioral analyses revealed preferences for each commodity type. Imaging analyses revealed the brain activity that differentiated CCUs from Controls while choosing money over cocaine. We observed that CCUs devalued future commodities more than Controls. Choices for money as opposed to cocaine correlated with greater activity in dorsal striatum of CCUs, compared to Controls. In addition, choices for future money as opposed to immediate cocaine engaged the left dorsolateral prefrontal cortex (DLPFC) of CCUs more than Controls. These data suggest that the ability of CCUs to execute choices away from cocaine relies on activity in the dorsal striatum and left DLPFC.

Age-related differences in advantageous decision making are associated with distinct differences in functional community structure

Human decision making is dependent on not only the function of several brain regions but also their synergistic interaction. The specific function of brain areas within the ventromedial prefrontal cortex has long been studied in an effort to understand choice evaluation and decision making. These data specifically focus on whole-brain functional interconnectivity using the principles of network science. The Iowa Gambling Task (IGT) was the first neuropsychological task used to model real-life decisions in a way that factors reward, punishment, and uncertainty. Clinically, it has been used to detect decision-making impairments characteristic of patients with prefrontal cortex lesions. Here, we used performance on repeated blocks of the IGT as a behavioral measure of advantageous and disadvantageous decision making in young and mature adults. Both adult groups performed poorly by predominately making disadvantageous selections in the beginning stages of the task. In later phases of the task, young adults shifted to more advantageous selections and outperformed mature adults. Modularity analysis revealed stark underlying differences in visual, sensorimotor and medial prefrontal cortex community structure. In addition, changes in orbitofrontal cortex connectivity predicted behavioral deficits in IGT performance. Contrasts were driven by a difference in age but may also prove relevant to neuropsychiatric disorders associated with poor decision making, including the vulnerability to alcohol and/or drug addiction.

Temporal profile of fronto-striatal-limbic activity during implicit decisions in drug dependence

BACKGROUND

Substance dependence is associated with impaired decision-making and altered fronto-striatal-limbic activity. Both greater and lesser brain activity have been reported in drug users compared to controls during decision-making. Inconsistent results might be explained by group differences in the temporal profile of the functional magnetic resonance imaging (fMRI) response. While most previous studies model a canonical hemodynamic response, a finite impulse response (FIR) model measures fMRI signal at discrete time points without assuming a temporal profile. We compared brain activity during decision-making and feedback in substance users and controls using two models: a canonical hemodynamic response function (HRF) and a FIR model.

METHODS

37 substance-dependent individuals (SDI) and 43 controls performed event-related decision-making during fMRI scanning. Brain activity was compared across group using canonical HRF and FIR models.

RESULTS

Compared to controls, SDI were impaired at decision-making. The canonical HRF model showed that SDI had significantly greater fronto-striatal-limbic activity during decisions and less activity during feedback than controls. The FIR model confirmed greater activity in SDI during decisions. However, lower activity in SDI during feedback corresponded to a lower post-stimulus undershoot of the hemodynamic response.

CONCLUSIONS

Greater activity in fronto-striatal-limbic pathways in SDI compared to controls is consistent with prior work, further supporting the hypothesis that abnormalities in these circuits underlie impaired decision-making. We demonstrate for the first time using FIR analysis that lower activity during feedback may simply reflect the tail end of the hemodynamic response to decision, the post-stimulus undershoot, rather than an actual difference in feedback response.

Neuroimaging in Alcohol and Drug Dependence

Neuroimaging, including PET, MRI, and MRS, is a powerful approach to the study of brain function. This article reviews neuroimaging findings related to alcohol and other drugs of abuse that have been published since 2011. Uses of neuroimaging are to characterize patients to determine who will fare better in treatment and to investigate the reasons underlying the effect on outcomes. Neuroimaging is also used to characterize the acute and chronic effects of substances on the brain and how those effects are related to dependence, relapse, and other drug effects. The data can be used to provide encouraging information for patients, as several studies have shown that long-term abstinence is associated with at least partial normalization of neurological abnormalities.

Unique functional abnormalities in youth with combined marijuana use and depression: an FMRI study

Prior research has shown a relationship between early onset marijuana (MJ) use and depression; however, this relationship is complex and poorly understood. Here, we utilized passive music listening and fMRI to examine functional brain activation to a rewarding stimulus in 75 participants [healthy controls (HC), patients with major depressive disorder (MDD), frequent MJ users, and the combination of MDD and MJ (MDD + MJ)]. For each participant, a preferred and neutral piece of instrumental music was determined (utilizing ratings on a standardized scale), and each completed two 6-min fMRI scans of a passive music listening task. Data underwent pre-processing and 61 participants were carried forward for analysis (17 HC, 15 MDD, 15 MJ, 14 MDD + MJ). Two statistical analyses were performed using SPM8, an analysis of covariance with two factors (group × music type) and a whole brain, multiple regression analysis incorporating two predictors of interest [MJ use in past 28 days; and Beck Depression Inventory (BDI) score]. We identified a significant group × music type interaction. Post hoc comparisons showed that the preferred music had significantly greater activation in the MDD + MJ group in areas including the right middle and inferior frontal gyri extending into the claustrum and putamen and the anterior cingulate. No significant differences were identified in MDD, MJ, or HC groups. Multiple regression analysis showed that activation in medial frontal cortex was positively correlated with amount of MJ use, and activation in areas including the insula was negatively correlated with BDI score. Results showed modulation in brain activation during passive music listening specific to MDD, frequent MJ users. This supports the suggestion that frequent MJ use, when combined with MDD, is associated with changes in neurocircuitry involved in reward processing in ways that are absent with either frequent MJ use or MDD alone. This could help inform clinical recommendations for youth with MDD.

Reduced neural tracking of prediction error in substance-dependent individuals

OBJECTIVE

Substance-dependent individuals make poor decisions on the Iowa Gambling Task, a reward-related decision-making task that involves risk and uncertainty. Task performance depends on several factors, including how sensitive individuals are to feedback and how well they learn based on such feedback. A physiological signal that guides decision making based on feedback is prediction error. The authors investigated whether disruptions in the neural systems underlying prediction error processing in substance-dependent individuals could account for decision-making performance on a modified Iowa Gambling Task.

METHODS

Thirty-two substance-dependent individuals and 30 healthy comparison subjects played a modified version of the Iowa Gambling Task during MR scanning. Trial-to-trial behavior and functional MRI (fMRI) blood-oxygen-level-dependent (BOLD) signal were analyzed using a computational model of prediction error based on internal expectancies. The authors investigated how well BOLD signal tracked prediction error in the striatum and the orbitofrontal cortex as well as over the whole brain in patients relative to comparison subjects.

RESULTS

Compared with healthy subjects, substance-dependent patients were less sensitive to loss compared with gain, made less consistent choices, and performed worse on the modified Iowa Gambling Task. The ventral striatum and medial orbitofrontal cortex did not track prediction error as strongly in patients as in healthy subjects.

CONCLUSIONS

Weaker tracking of prediction error in substance-dependent relative to healthy individuals suggests that altered frontal-striatal error learning signals may underlie decision-making impairments in drug abusers. Computational fMRI may help bridge the knowledge gap between physiology and behavior to inform research aimed at substance abuse treatment.

Individual differences in decision making and reward processing predict changes in cannabis use: a prospective functional magnetic resonance imaging study

Decision-making deficits are thought to play an important role in the development and persistence of substance use disorders. Individual differences in decision-making abilities and their underlying neurocircuitry may, therefore, constitute an important predictor for the course of substance use and the development of substance use disorders. Here, we investigate the predictive value of decision making and neural mechanisms underlying decision making for future cannabis use and problem severity in a sample of heavy cannabis users. Brain activity during a monetary decision-making task (Iowa gambling task) was compared between 32 heavy cannabis users and 41 matched non-using controls using functional magnetic resonance imaging. In addition, within the group of heavy cannabis users, associations were examined between task-related brain activations, cannabis use and cannabis use-related problems at baseline, and change in cannabis use and problem severity after a 6-month follow-up. Despite normal task performance, heavy cannabis users compared with controls showed higher activation during wins in core areas associated with decision making. Moreover, within the group of heavy cannabis users, win-related activity and activity anticipating loss outcomes in areas generally involved in executive functions predicted change in cannabis use after 6 months. These findings are consistent with previous studies and point to abnormal processing of motivational information in heavy cannabis users. A new finding is that individuals who are biased toward immediate rewards have a higher probability of increasing drug use, highlighting the importance of the relative balance between motivational processes and regulatory executive processes in the development of substance use disorders.

Effects of a novel CB1 agonist on visual attention in male rats: role of strategy and expectancy in task accuracy

The effects of cannabinoid CB1 agonists (including Δ9-tetrahydrocannabinol, the main psychoactive component of marijuana) on attention are uncertain, with reports of impairments, no effects, and occasionally performance enhancements. To better understand these effects, we sought to uncover a role of changing online (within-session) strategy as a possible mediator of the effects of the novel, potent CB1 agonist AM 4054, on a model of sustained attention in male Sprague-Dawley rats. In this operant, two-choice reaction time (RT) task, AM 4054 decreased accuracy in an asymmetric manner; that is, performance was spared on one lever but impaired on the other. Furthermore, this pattern was enhanced by the outcome of the previous trial such that AM 4054 strengthened a win-stay strategy on the "preferred" lever and a lose-shift strategy on the "nonpreferred" lever. This pattern is often found in tests of expectancy; therefore, in a second experiment AM 4054 enhanced expectancy that we engendered by altering the probability of the two stimulus cues. Accuracy was impaired in reporting the less frequent cue, but only after two or more presentations of the more frequent cue. Taking the results of the experiments together, AM 4054 engendered expectancy by increasing the role of previous trial location and outcome on performance of future trials, diminishing stimulus control (and therefore, accuracy). This novel effect of CB1 receptor agonism may contribute to the deleterious effects of cannabinoids on attention.

Preliminary evidence for a sex-specific relationship between amount of cannabis use and neurocognitive performance in young adult cannabis users

Accumulating evidence suggests neuropsychological deficits from cannabis use, with a burgeoning area of preclinical research indicating possible sex-differences. However, few studies have examined how cannabis use may differentially impact neurocognition in male and female cannabis users. As such, we examined potential sex-differences in associations between amount of cannabis use (across several time frames) and neurocognitive performance among young adult regular cannabis users. Consistent with previous studies, more cannabis use was generally associated with poorer episodic memory and decision-making, but not other measures of inhibitory control. However, patterns of results suggested sex-specific dissociations. In particular, more cannabis use was more consistently associated with poorer episodic memory performance in females than males. Conversely, more cannabis use was associated with poorer decision-making performance for males, but not females. These results provide further evidence for residual cannabis-associated neurocognitive deficits and suggest the importance of examining the impact of cannabis on neurocognition separately for males and females.

Relationships between marijuana dependence and condom use intentions and behavior among justice-involved adolescents

The current study examined the relationships among marijuana dependence, a theoretical model of condom use intentions, and subsequent condom use behavior in justice-involved adolescents. Participants completed baseline measures of prior sexual and substance use behavior. Of the original 720 participants, 649 (90.13 %) completed follow-up measures 6 months later. There were high levels of marijuana use (58.7 % met criteria for dependence) and risky sexual behavior among participants. Baseline model constructs were associated with condom use intentions, and intentions were a significant predictor of condom use at follow-up. Marijuana dependence did not significantly influence the relationships between model constructs, nor did it moderate the relationship of model constructs with subsequent condom use. Findings suggest that the theoretical model of condom use intentions is equally valid regardless of marijuana dependence status, suggesting that interventions to reduce sexual risk behavior among both marijuana dependent and non-dependent justice-involved adolescents can be appropriately based on the model.

Altered risk-related processing in substance users: imbalance of pain and gain

BACKGROUND

Substance use disorders (SUDs) can be conceptualized as a form of risk-taking behavior with the potential for highly aversive outcomes such as health or legal problems. Risky decision-making likely draws upon several related brain processes involved in estimations of value and risk, executive control, and emotional processing. SUDs may result from a dysfunction in one or more of these cognitive processes.

METHODS

We performed a systematic literature review of functional neuroimaging studies examining risk-related decision making in individuals with SUDs. A quantitative meta-analysis tool (GingerALE) and qualitative approach was used to summarize the imaging results.

RESULTS

Meta-analysis findings indicate that individuals with SUDs exhibit differences in neural activity relative to healthy controls during risk-taking in the anterior cingulate cortex, orbitofrontal cortex, dorsolateral prefrontal cortex, striatum, insula, and somatosensory cortex. In addition, a qualitative review of the literature suggests that individuals with SUDs may have altered function in the amygdala and ventromedial prefrontal cortex.

CONCLUSIONS

The neuroimaging literature reveals that several neural substrates involved in the computation of risk may function suboptimally in SUDs. Future research is warranted to elucidate which computational processes are affected, whether dysfunctional risk-related processing recovers with sobriety, and whether different drugs of abuse have specific effects on risk-taking.

Effects of cannabis on neurocognitive functioning: recent advances, neurodevelopmental influences, and sex differences

Decades of research have examined the effects of cannabis on neurocognition. Recent advances in this field provide us with a better understanding of how cannabis use influences neurocognition both acutely (during intoxication) and non-acutely (after acute effects subside). Evidence of problems with episodic memory is one of the most consistent findings reported; however, several other neurocognitive domains appear to be adversely affected by cannabis use under various conditions. There is significant variability in findings across studies, thus a discussion of potential moderators is increasingly relevant. The purpose of this review was to 1) provide an update on research of cannabis' acute and non-acute effects on neurocognition, with a focus on findings since 2007 and 2) suggest and discuss how neurodevelopmental issues and sex differences may influence cannabis effects on neurocognition. Finally we discuss how future investigations may lead to better understanding of the complex interplay among cannabis, stages of neurodevelopment, and sex on neurocognitive functioning.

A Review of Magnetic Resonance Spectroscopy Studies in Marijuana using Adolescents and Adults

Marijuana (MJ) remains the most widely used illicit drug of abuse, and accordingly, is associated with adverse effects on mental and physical health, and neurocognitive decline. Studies investigating the neurobiology of underlying MJ effects have demonstrated structural and functional alterations in brain areas that contain moderate to high concentrations of cannabinoid (CB1) receptors and that are implicated in MJ-related cognitive decrements. Proton magnetic resonance spectroscopy (1H MRS), a non-invasive imaging technique used to assess neurochemistry, has been widely applied to probe a variety of substance-abusing populations. To date, however, there is a relative paucity of MRS published studies characterizing changes in neurometabolite concentrations in MJ users. Thus, the current review provides a summary of data from the eight existing MRS studies of MJ use in adolescents and adults, as well as interpretations and implications of study findings. Future MRS studies that address additional factors such as sex differences, onset and duration of use, abstinence and age, are warranted, and would lead to a more thorough characterization of potential neurochemical correlates of chronic MJ use, which would fill critical gaps in the existing literature.

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.

Lower Left Thalamic Myo-Inositol Levels Associated with Greater Cognitive Impulsivity in Marijuana-Dependent Young Men: Preliminary Spectroscopic Evidence at 4T

The effects of chronic marijuana (MRJ) use on neurochemistry are not well characterized. Previously, altered global myo-Inositol (mI) concentrations and distribution in white matter were associated with impulsivity and mood symptoms in young MRJ-dependent men. The objective of this study was to retrospectively examine previously collected data, to investigate the potential regional specificity of metabolite levels in brain regions densely packed with cannabinoid receptors. Spectra were acquired at 4.0 Tesla using 2D J-resolved proton magnetic resonance spectroscopic imaging (MRSI) to quantify the entire J-coupled spectral surface of metabolites from voxels in regions of interest. For the current regional spectral analyses, a 2D-JMRSI grid was positioned over the central axial slice and shifted in the x and y dimensions to optimally position voxels over regions containing thalamus, temporal lobe, and parieto-occipital cortex. MRJ users exhibited significantly reduced mI levels in the left thalamus (lThal), relative to non-using participants, which were associated with elevated cognitive impulsivity. Other regional analyses did not reveal any significant group differences. The current findings indicate that reduced mI levels are regionally specific to the lThal in MRJ users. Furthermore, findings suggest that mI and the lThal uniquely contribute to elevated impulsivity.

Cannabinoids and value-based decision making: implications for neurodegenerative disorders

In recent years, disturbances in cognitive function have been increasingly recognized as important symptomatic phenomena in neurodegenerative diseases, including Parkinson's Disease (PD). Value-based decision making in particular is an important executive cognitive function that is not only impaired in patients with PD, but also shares neural substrates with PD in basal ganglia structures and the dopamine system. Interestingly, the endogenous cannabinoid system modulates dopamine function and subsequently value-based decision making. This review will provide an overview of the interdisciplinary research that has influenced our understanding of value-based decision making and the role of dopamine, particularly in the context of reinforcement learning theories, as well as recent animal and human studies that demonstrate the modulatory role of activation of cannabinoid receptors by exogenous agonists or their naturally occurring ligands. The implications of this research for the symptomatology of and potential treatments for PD are also discussed.

Effects of chronic marijuana use on brain activity during monetary decision-making

Marijuana (MJ) acutely acts on cannabinoid receptors that are found in numerous brain regions, including those involved in reward processing and decision-making. However, it remains unclear how long-term, chronic MJ use alters reward-based decision-making. In the present study, using [(15)O]water PET imaging, we measured brain activity in chronic MJ users, who underwent monitored abstinence from MJ for approximately 24 h before imaging, and control participants, while they took part in the Iowa Gambling Task (IGT), a monetary decision making task that strongly relies on the ventromedial prefrontal cortex (vmPFC). During PET imaging, participants took part in the standard and a variant version of the IGT as well as a control task. Chronic MJ users performed equally well on the standard IGT, but significantly worse than controls on the variant IGT. Chronic MJ users and control subjects showed increased regional cerebral blood flow (rCBF) in the vmPFC on both versions of the IGT compared to the control task. In the two-group comparison, chronic MJ users showed significantly greater rCBF than controls in the vmPFC on the standard IGT and greater activity in the cerebellum on both versions of the IGT. Furthermore, duration of use, but not age of first use, was associated with greater activity in the vmPFC. Thus, chronic MJ users tend to strongly recruit neural circuitry involved in decision-making and reward processing (vmPFC), and probabilistic learning (cerebellum) when performing the IGT.

Neuropsychological deficits associated with cannabis use in young adults

BACKGROUND

Cannabis is the most widely used illicit substance and has been associated with cognitive impairment. It is unclear whether such impairment can occur in the absence of potential confounding influences of co-morbid axis-I disorders and use of other illicit substances.

METHOD

Young adult volunteers (18-29 years) were recruited from the general community on the basis of having no axis-I disorders or history of illicit substance use other than cannabis use. Subjects were then grouped according to presence or absence of cannabis use (>1 time/week over past 12 months). Cognition was compared between groups using selected paradigms from the CANTAB.

RESULTS

Cannabis users (N=16) and controls (N=214) did not differ significantly on salient demographic characteristics. Compared to controls, cannabis users showed significant impairments on quality of decision-making (Cambridge Gamble task), and executive planning (One Touch Stockings of Cambridge task). Response inhibition, spatial working memory, and sustained attention were intact.

CONCLUSIONS

This study identified cognitive deficits in cannabis users even in the absence of axis-I disorders and a history of using other illicit drugs. Future work should use longitudinal designs to track whether these deficits predate cannabis use or are due to its consumption.

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.

Deficits in default mode network activity preceding error in cocaine dependent individuals

BACKGROUND

Cocaine dependence is associated with cognitive deficits and altered task-related cerebral activation in cognitive performance (see Li and Sinha, 2008, for a review). Relatively little is known whether these individuals are also impaired in regional brain activation of the default mode network (DMN). We demonstrated previously that greater activation of the default brain regions precedes errors in a stop signal task performed by healthy controls (SST, Li et al., 2007). We seek to determine whether individuals with cocaine dependence are impaired in DMN activity, specifically activity preceding error, as compared to the healthy people. We also examine the relation to years of cocaine use.

METHODS

Individuals with cocaine dependence (CD, n=23) and demographics-matched healthy controls (HC, n=27) performed a SST that employed a tracking procedure to adjust the difficulty of stop trials and elicit errors approximately half of the time. Blood oxygenation level dependent (BOLD) signals of go trials preceding stop error as compared to those preceding stop success trials were extracted with generalized linear models using statistical parametric mapping.

RESULTS

HC showed activation of bilateral precuneus and posterior cingulate cortices and ventromedial prefrontal cortex (vmPFC) preceding errors during the SST. In contrast, despite indistinguishable stop signal performance, CD did not show these error predicting activations. Furthermore, the effect size of error-preceding vmPFC activation was inversely correlated with years of cocaine use.

CONCLUSIONS

These findings indicate DMN deficits and could potentially add to our understanding of the effects of chronic cocaine use on cerebral functions in cocaine dependence. Work to further clarify potential changes in functional connectivity and gray matter volume is warranted to understand the relevance of DMN to the pathology of cocaine misuse.