Working memory fMRI activation in cocaine-dependent subjects: association with treatment response

Lower Dorsal Putamen D2/3 Receptor Availability and Amphetamine-Induced Dopamine Release are Related to Poorer Cognitive Function in Recently Abstinent People Who Smoke and Healthy Controls

INTRODUCTION

In the dopamine system, the mesolimbic pathway, including the dorsal striatum, underlies the reinforcing properties of tobacco smoking, and the mesocortical pathway, including the dorsolateral prefrontal cortex (dlPFC), is critical for cognitive functioning. Dysregulated dopamine signaling has been linked to drug-seeking behaviors and cognitive deficits. The dorsal striatum and dlPFC are structurally and functionally connected and are key regions for cognitive functioning. We recently showed that people who smoke have lower dlPFC dopamine (D2/3R) receptor availability than people who do not, which is related to poorer cognitive function.

AIMS AND METHODS

The goal of this study was to examine the same brain-behavior relationship in the dorsal striatum. Twenty-nine (18 males) recently abstinent people who smoke and 29 sex-matched healthy controls participated in 2 same-day [11C]-(+)-PHNO positron emission tomography scans before and after amphetamine administration to provoke dopamine release. D2/3R availability (binding potential; BPND) and amphetamine-induced dopamine release (%ΔBPND) were calculated. Cognition (verbal learning and memory) was assessed with the CogState computerized battery.

RESULTS

There were no group differences in baseline BPND. People who smoke have a smaller magnitude %ΔBPND in dorsal putamen than healthy controls (p = .022). People who smoke perform worse on immediate (p = .035) and delayed (p = .011) recall than healthy controls. In all people, lower dorsal putamen BPND was associated with worse immediate (p = .006) and delayed recall (p = .049), and lower %ΔBPND was related to worse delayed recall (p = .022).

CONCLUSIONS

Lower dorsal putamen D2/3R availability and function are associated with disruptions in cognitive function that may underlie difficulty with resisting smoking.

IMPLICATIONS

This study directly relates dopamine imaging outcomes in the dorsal striatum to cognitive function in recently abstinent people who smoke cigarettes and healthy controls. The current work included a well-characterized subject sample in terms of demographics, smoking characteristics, and a validated neurocognitive test of verbal learning and memory. The findings of this study extend previous literature relating dopamine imaging outcomes to cognition in recently abstinent people who smoke and people who do not smoke, expanding our understanding of brain-behavior relationships.

Attentional ERPs in consumers of smoked and insufflated cocaine associated with neuropsychological performance

BACKGROUND

Cocaine consumption is associated with reduced attentional event-related potentials (ERPs), namely P3a and P3b, indicating bottom-up and top-down deficits respectively. At cognitive level, these impairments are larger for faster routes of administration (e.g., smoked cocaine [SC]) than slower routes (e.g., insufflated cocaine [IC]). Here we assess these ERPs considering the route of cocaine administration. We hypothesized that SC dependent (SCD) would exhibit reduced amplitude of the P3a, while both SCD and IC dependent (ICD) would show reduced amplitude of the P3b.

METHODS

We examined 25 SCD, 22 ICD matched by poly-consumption profiles, and 25 controls matched by demographic variables. We combined EEG data from the Global-Local task with behavioral data from attentional cognitive tasks.

RESULTS

At the behavioral level, SCD exhibited attentional deficits in both bottom-up and top-down processes, while ICD only showed a tendency for top-down deficits. The amplitude of P3a and P3b was lower in Users groups. We observed subtle route-based differences, with larger differences in the P3a for SCD and in the P3b for ICD. Neurophysiological and behavioral data converged, with the P3a associated to bottom-up performance and P3b to top-down.

CONCLUSIONS

Different routes of administration lead to distinct attentional neurocognitive profiles. Specifically, SCD showed greater attentional impairment, mainly at bottom-up/P3a, while ICD showed a trend of top-down/P3b deficits. These findings emphasize the crucial role of considering the route of administration in both clinical and research settings and support the use of attentional ERPs as valid measures for assessing attentional deficits in substance Dependence.

Biomarkers of Relapse in Cocaine Use Disorder: A Narrative Review

Introduction: Cocaine use disorder is a chronic disease with severe consequences and a high relapse rate. There is a critical need to explore the factors influencing relapse in order to achieve more efficient treatment outcomes. Furthermore, there is a great need for easy-to-measure, repeatable, and valid biomarkers that can predict treatment response or relapse. Methods: We reviewed the available literature on the Pubmed database concerning the biomarkers associated with relapse in CUD, including central nervous system-derived, genetic, immune, oxidative stress, and “other” biomarkers. Results: Fifty-one articles were included in our analysis. Twenty-five imaging brain anatomic and function assessment studies, mostly using fMRI, examined the role of several structures such as the striatum activity in abstinence prediction. There were fewer studies assessing the use of neuropsychological factors, neurotrophins, or genetic/genomic factors, immune system, or oxidative stress measures to predict abstinence. Conclusion: Several biomarkers have been shown to have predictive value. Prospective studies using combined multimodal assessments are now warranted.

Strengthened and posterior-shifted structural rich-club organization in people who use cocaine

BACKGROUND

People with cocaine use disorder (CUD) often have abnormal cognitive function and brain structure. Cognition is supported by brain networks that typically have characteristics like rich-club organization, which is a group of regions that are highly connected across the brain and to each other, and small worldness, which is a balance between local and long-distance connections. However, it is unknown whether there are abnormalities in structural brain network connectivity of CUD.

METHODS

Using diffusion-weighted imaging, we measured structural connectivity in 37 people with CUD and 38 age-matched controls. We identified differences in rich-club organization and whether such differences related to small worldness and behavior. We also tested whether rich-club reorganization was associated with caudate and putamen structural connectivity due to the relevance of the dopamine system to cocaine use.

RESULTS

People with CUD had a higher normalized rich-club coefficient than controls, more edges connecting rich-club nodes to each other and to non-rich-club nodes, and fewer edges connecting non-rich-club nodes. Rich-club nodes were shifted posterior and lateral. Rich-club reorganization was related to lower clustered connectivity around individual nodes found in CUD, to increased impulsivity, and to a decrease in caudate connectivity.

CONCLUSIONS

These findings are consistent with previous work showing increased rich-club connectivity in conditions associated with a hypofunctional dopamine system. The posterior shift in rich-club nodes in CUD suggests that the structural connectivity of posterior regions may be more impacted than previously recognized in models based on brain function and morphology.

A transcranial magnetic stimulation protocol for decreasing the craving of methamphetamine-dependent patients

Transcranial magnetic stimulation (TMS) is a non-invasive brain stimulation technique. Many substance use disorders lack effective treatments, and TMS is expected to reduce cravings and risk of relapse by regulating brain function. Here, we introduce three alternative TMS settings and specific operations to interfere with methamphetamine use disorders. Theoretically, this protocol can also be applied to diseases with similar brain damage characteristics. For complete details on the use and execution of this protocol, please refer to Chen et al. (2020).

Targeting white matter neuroprotection as a relapse prevention strategy for treatment of cocaine use disorder: Design of a mechanism-focused randomized clinical trial

Cocaine use continues to be a significant public health problem with limited treatment options and no approved pharmacotherapies. Cognitive-behavioral therapy (CBT) remains the mainstay treatment for preventing relapse, however, people with chronic cocaine use display cognitive impairments that are associated with poor response to CBT. Emerging evidence in animal and human studies suggests that the peroxisome proliferator-activated receptor-gamma (PPAR- γ) agonist, pioglitazone, improves white matter integrity that is essential for cognitive function. This project will determine whether adjunctive use of pioglitazone enhances the effect of CBT in preventing relapse during the early phase of recovery from cocaine use disorder. This paper describes the design of a mechanism-focused phase 2 randomized clinical trial that aims first to evaluate the effects of pioglitazone on targeted mechanisms related to white matter integrity, cognitive function, and cocaine craving; and second, to evaluate the extent to which improvements on target mechanisms predict CBT response. Positive results will support pioglitazone as a potential cognitive enhancing agent to advance to later stage medication development research.

Reduced Working Memory is Associated with Heavier Alcohol Consumption History, Role Impairment and Executive Function Difficulties

Both HIV status and heavy alcohol use have been associated with reduced cognitive function, particularly in the domains of working memory and executive function. It is unclear what aspects of working memory and executive function are associated with HIV status and heavy alcohol use and whether performance on these measures are associated with functional impairment. We examined the relationship between HIV, history of heavy alcohol consumption, and HIV/alcohol interaction on speeded tests of frontal inhibitory abilities, a working memory task related to mental manipulation of letters and numbers, cognitive flexibility, and measures of functional impairment. Study participants included 284 individuals (151 HIV +) recruited from two different studies focusing on HIV associated brain dysfunction, one specific to the effects of alcohol, the other specific to the effects of aging. HIV status was not independently associated with working memory and executive function measures. Higher level of alcohol consumption was associated with reduced performance on Letter Number Sequencing. Poorer Letter Number Sequencing performance was associated with role impairment (an inability to do certain kinds of work, housework, or schoolwork) and executive function difficulties. Future studies should examine causal associations and interventions targeting working memory abilities.

Sex-dependent prefrontal cortex activation in regular cocaine users: A working memory functional magnetic resonance imaging study

Although two thirds of patients with a cocaine use disorder (CUD) are female, little is known about sex differences in the (neuro)pathology of CUD. The aim of this explorative study was to investigate sex‐dependent differences in prefrontal cortex (PFC) functioning during a working memory (WM) functional magnetic resonance imaging (fMRI) task in regular cocaine users (CUs), as PFC deficits are implicated in the shift from recreational cocaine use to CUD. Neural activation was measured using fMRI during a standard WM task (n‐back task) in 27 male and 28 female CUs and in 26 male and 28 female non‐cocaine users (non‐CUs). Although there were no main or interaction effects of sex and group on n‐back task performance, WM‐related (2‐back > 0‐back) PFC functioning was significantly moderated by sex and group: female compared with male CUs displayed higher WM‐related activation of the middle frontal gyrus (MFG), whereas female compared with male non‐CUs displayed lower WM‐related MFG activation. Additionally, WM‐related activation of the inferior frontal gyrus, insula, and putamen was negatively associated with cocaine use severity in female but not male CUs. These data support the hypothesis of sex‐dependent PFC differences in CUs and speculatively suggest that PFC deficits may be more strongly implicated in the development, continuation, and possibly treatment of CUD in females. Most importantly, the current data stress the importance of studying both males and females in psychiatry research as not doing so could greatly bias our knowledge of CUD and other psychiatric disorders.

Effect of chronic cocaine use on fine motor coordination tested during ophthalmic vitreoretinal simulated performance

We conducted a case-control study using the Eyesi simulator to assess the surgical performance of 24 chronic cocaine users (CCUs) and 24 sex-/age-matched controls to numerically quantify ophthalmic microsurgical simulator performance and fine motor deficiencies. The inclusion criteria were no exposure to illicit drugs other than cocaine, marijuana, or alcohol within the previous month and no health conditions that could impact manual task performance. The outcomes included surgical scores (0-100, worst-best) and task completion time (minutes). Fisher's exact test, analysis of variance, Mann-Whitney U test, and Kruskal-Wallis test followed by Dunn-Bonferroni post-hoc were conducted for statistical analysis. The Eyesi scores were lower among CCUs compared to controls for bimanual tasks (4.50 ± 14.30 vs. 18.46 ± 26.64, p = 0.012), for exercises demanding upper and lower limb coordination (both hands and two foot pedals, respectively) (74.13 ± 35.01 vs. 85.21 ± 24.1, p = 0.045), and in the overall score for all three tasks (27.38 ± 15.06 vs. 39.5 ± 18.66, p = 0.021). CCUs took longer to complete tasks when performing exercises demanding upper and lower limb coordination compared to controls (1.26 ± 0.38 vs. 1.02 ± 0.44 min, p = 0.006). Individuals who used cocaine during the previous month had an independent lower bimanual score compared to controls (1.42 ± 4.91 vs. 18.46 ± 26.64, p = 0.018). No differences in performance among the CCUs were attributable to sporadic cannabis or alcohol use. Chronic use of cocaine negatively impacted fine dexterity as measured by bimanual tasks or maneuvers that required simultaneous coordination of the upper and lower limbs. This was most notable among individuals who used cocaine during the 1-month period before the simulation.

Common and separable neural alterations in substance use disorders: A coordinate-based meta-analyses of functional neuroimaging studies in humans

Delineating common and separable neural alterations in substance use disorders (SUD) is imperative to understand the neurobiological basis of the addictive process and to inform substance‐specific treatment strategies. Given numerous functional MRI (fMRI) studies in different SUDs, a meta‐analysis could provide an opportunity to determine robust shared and substance‐specific alterations. The present study employed a coordinate‐based meta‐analysis covering fMRI studies in individuals with addictive cocaine, cannabis, alcohol, and nicotine use. The primary meta‐analysis demonstrated common alterations in primary dorsal striatal, and frontal circuits engaged in reward/salience processing, habit formation, and executive control across different substances and task‐paradigms. Subsequent sub‐analyses revealed substance‐specific alterations in frontal and limbic regions, with marked frontal and insula‐thalamic alterations in alcohol and nicotine use disorders respectively. Examining task‐specific alterations across substances revealed pronounced frontal alterations during cognitive processes yet stronger striatal alterations during reward‐related processes. Finally, an exploratory meta‐analysis revealed that neurofunctional alterations in striatal and frontal reward processing regions can already be determined with a high probability in studies with subjects with comparably short durations of use. Together the findings emphasize the role of dysregulations in frontostriatal circuits and dissociable contributions of these systems in the domains of reward‐related and cognitive processes which may contribute to substance‐specific behavioral alterations.

Unpacking common and distinct neuroanatomical alterations in cocaine dependent versus pathological gambling

Pathological gambling and cocaine dependence are highly pervasive disorders. Functional neuroimaging evidence implicates aberrant activity of prefrontal striatal pathways in both disorders. It is unclear if the neuroanatomy of these areas is also affected. Participants with pathological gambling (n = 18), cocaine dependence (n = 19) and controls (n = 21) underwent high-resolution structural MRI scan and cognitive assessments. In line with emerging functional neuroimaging findings, we hypothesised (i) lower volumes of corticostriatal areas ascribed to decision-making/inhibitory control, craving and reward processing (i.e., orbitofrontal cortex, inferior frontal gyrus, amygdala, striatum, insula) in both pathological gamblers and cocaine dependent participants versus controls; (ii) selected dopaminergic/glutamatergic pathways directly taxed by cocaine (i.e., superior, dorsolateral and anterior cingulate cortices) would be altered in cocaine dependent versus control participants only. Analyses were conducted with a bonferroni correction. Our results showed that both pathological gambling and cocaine dependent participants, compared to controls, had larger volumes of the right inferior frontal gyrus (ps <.01, ds = 0.66 and 0.62). Cocaine dependent participants had lower nucleus accumbens and medial orbitofrontal cortex volumes than pathological gamblers (ps <.05, ds = 0.51 and 0.72), with the latter being predicted by higher negative urgency scores. Inferior frontal gyrus volume may reflect common alterations of cocaine and gambling addictions, whereas cocaine dependence may be uniquely associated with reduced volume in dorsolateral and middle frontal regions. Cocaine's supra-physiological effects on mesolimbic neurons may explain reduced accumbens-orbitofrontal structure compared to gambling.

White matter integrity alternations associated with cocaine dependence and long-term abstinence: Preliminary findings

Cocaine dependence has been associated with deficits in white matter (WM) integrity. Nevertheless, what happens to WM integrity after long-term abstinence is not fully understood. To bridge this gap, changes in WM integrity were examined with diffusion tensor imaging (DTI) applied to 39 participants: 12 participants who used cocaine in the last year (CURRENT USERS), 20 who were at different stages of cocaine abstinence (ABSTINENCE) [five with 1-5 years of abstinence (ABS1), five with 6-10 years of abstinence (ABS2), and 10 with over 10 years of abstinence (ABS3)], and 7 healthy controls (CONTROLS). The CONTROL group had higher fractional anisotropy (FA) compared to CURRENT USERS in frontal cortex tracts, including the bilateral corpus callosum, bilateral superior longitudinal fasciculus, bilateral inferior fronto-occipital fasciculus, left internal capsule, left middle cingulum, and left ventral and dorsal medial frontal regions. The ABSTINENCE group also had higher FA compared to CURRENT USERS in frontal cortex tracts, such as the bilateral corpus callosum, bilateral superior longitudinal fasciculus, left inferior longitudinal fasciculus, left uncinate fasciculus, left inferior fronto-occipital fasciculus, and the left ventral and dorsal medial frontal regions. Tractography analysis showed (1) deficits in terms of number of fibers and fiber length in these regions, and that (2) while there was some recovery of white matter in dorsolateral regions during abstinence, duration of abstinence was not associated with such recovery. The results identified WM differences among cocaine users, cocaine abstinent participants, and controls. These preliminary findings point to WM tracts that recover, and some that do not, after long-term abstinence from cocaine.

Bouncing back: Brain rehabilitation amid opioid and stimulant epidemics

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Frontoparietal event related potentials predict/track recovery.

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Frontostriatal functional magnetic resonance imaging signals predict/track recovery.

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Transcranial magnetic left prefrontal stimulation reduces craving and drug use.

Recent methamphetamine and opioid use epidemics are a major public health concern. Chronic stimulant and opioid use are characterized by significant psychosocial, physical and mental health costs, repeated relapse, and heightened risk of early death. Neuroimaging research highlights deficits in brain processes and circuitry that are linked to responsivity to drug cues over natural rewards as well as suboptimal goal-directed decision-making. Despite the need for interventions, little is known about (1) how the brain changes with prolonged abstinence or as a function of various treatments; and (2) how symptoms change as a result of neuromodulation. This review focuses on the question: What do we know about changes in brain function during recovery from opioids and stimulants such as methamphetamine and cocaine? We provide a detailed overview and critique of published research employing a wide array of neuroimaging methods – functional and structural magnetic resonance imaging, electroencephalography, event-related potentials, diffusion tensor imaging, and multiple brain stimulation technologies along with neurofeedback – to track or induce changes in drug craving, abstinence, and treatment success in stimulant and opioid users. Despite the surge of methamphetamine and opioid use in recent years, most of the research on neuroimaging techniques for recovery focuses on cocaine use. This review highlights two main findings: (1) interventions can lead to improvements in brain function, particularly in frontal regions implicated in goal-directed behavior and cognitive control, paired with reduced drug urges/craving; and (2) the targeting of striatal mechanisms implicated in drug reward may not be as cost-effective as prefrontal mechanisms, given that deep brain stimulation methods require surgery and months of intervention to produce effects. Overall, more studies are needed to replicate and confirm findings, particularly for individuals with opioid and methamphetamine use disorders.

A Neurobehavioral Approach to Addiction: Implications for the Opioid Epidemic and the Psychology of Addiction

Two major questions about addictive behaviors need to be explained by any worthwhile neurobiological theory. First, why do people seek drugs in the first place? Second, why do some people who use drugs seem to eventually become unable to resist drug temptation and so become "addicted"? We will review the theories of addiction that address negative-reinforcement views of drug use (i.e., taking opioids to alleviate distress or withdrawal), positive-reinforcement views (i.e., taking drugs for euphoria), habit views (i.e., growth of automatic drug-use routines), incentive-sensitization views (i.e., growth of excessive "wanting" to take drugs as a result of dopamine-related sensitization), and cognitive-dysfunction views (i.e., impaired prefrontal top-down control), including those involving competing neurobehavioral decision systems (CNDS), and the role of the insula in modulating addictive drug craving. In the special case of opioids, particular attention is paid to whether their analgesic effects overlap with their reinforcing effects and whether the perceived low risk of taking legal medicinal opioids, which are often prescribed by a health professional, could play a role in the decision to use. Specifically, we will address the issue of predisposition or vulnerability to becoming addicted to drugs (i.e., the question of why some people who experiment with drugs develop an addiction, while others do not). Finally, we review attempts to develop novel therapeutic strategies and policy ideas that could help prevent opioid and other substance abuse.

Cognitive dysfunction in individuals with cocaine use disorder: Potential moderating factors and pharmacological treatments

It is well-documented in the literature that individuals repeatedly exposed to cocaine exhibit cognitive impairment and that cognitive dysfunction is a risk factor for poor treatment outcomes in those with cocaine use disorder (CUD). Specific deficits related to attention, episodic memory, working memory, and executive functioning are the most common deficits noted in this population. Given that cognitive impairment is a risk factor for poor treatment outcomes in those with CUD, identifying possible moderating factors contributing to and/or exacerbating cocaine-related cognitive deficits is of great importance. Some of these factors may include premorbid intellectual functioning, cocaine use patterns, polysubstance use, comorbid emotional symptoms, and sleep dysfunction. It is plausible that by identifying moderating factors impacting cognition, behavioral interventions can then be modified accordingly and/or treatment regimens can be augmented with pharmacological interventions (e.g., cognitive enhancing agents), leading to a reduction in treatment attrition and improved treatment outcomes. The currently available treatments for CUD are mainly behavioral with variable efficacy, and even though there have been great preclinical and clinical research efforts focused on medication development for CUD, there are currently no Food and Drug Administration-approved medications for CUD. A description of some of the several potential moderating factors, along with some pharmacological treatments which have been shown to ameliorate, at least to some extent, cognitive dysfunction in those with CUD are discussed. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Neurobiological substrates of persistent working memory deficits and cocaine-seeking in the prelimbic cortex of rats with a history of extended access to cocaine self-administration

Cocaine use disorder (CUD) is associated with prefrontal cortex dysfunction and cognitive deficits that may contribute to persistent relapse susceptibility. As the relationship between cognitive deficits, cortical abnormalities and drug seeking is poorly understood, development of relevant animal models is of high clinical importance. Here, we used an animal model to characterize working memory and reversal learning in rats with a history of extended access cocaine self-administration and prolonged abstinence. We also investigated immediate and long-term functional changes within the prelimbic cortex (PrL) in relation to cognitive performance and drug-seeking. Adult male rats underwent 6 days of short-access (1 h/day) followed by 12 days of long-access (6 h/day) cocaine self-administration, or received passive saline infusions. Next, rats were tested in delayed match-to-sample (DMS) and (non)match-to-sample (NMS) tasks, and finally in a single context + cue relapse test on day 90 of abstinence. We found that a history of chronic cocaine self-administration impaired working memory, though sparing reversal learning, and that the components of these cognitive measures correlated with later drug-seeking. Further, we found that dysregulated metabolic activity and mGlu5 receptor signaling in the PrL of cocaine rats correlated with past working memory performance and/or drug-seeking, as indicated by the analysis of cytochrome oxidase reactivity, mGlu5 and Homer 1b/c protein expression, as well as Arc mRNA expression in mGlu5-positive cells. These findings advocate for a persistent post-cocaine PrL dysfunction, rooted in ineffective compensatory changes and manifested as impaired working memory performance and hyperreactivity to cocaine cues. Considering the possible interplay between the neural correlates underlying post-cocaine cognitive deficits and drug-seeking, cognitive function should be evaluated and considered when developing neurobiologically-based treatments of cocaine relapse.

Working memory predicts methamphetamine hair concentration over the course of treatment: moderating effect of impulsivity and implications for dual-systems model

High impulsivity and poor executive function are characteristic of methamphetamine use disorder. High arousal in the impulsive system has been proposed to compromise the executive system's regulating ability (i.e. the dual-systems model). While interaction between these variables may partly explain poor treatment outcomes associated with methamphetamine use disorder, previous research has tended to examine each factor separately. We investigated whether high impulsivity (measured with an impulsive choice task) and poor executive function (measured with a working memory task) predict methamphetamine use (determined by hair sample) in the 6 weeks following treatment commencement. We also investigated whether impulsive choice moderates the relationship between working memory and methamphetamine use. One hundred and eight individuals with methamphetamine use disorder (75 percent male) were tested within 3 weeks of commencing treatment; 80 (74 percent) were followed up 6 weeks following baseline testing. Cognitive measures significantly predicted drug use after controlling for nuisance variables. Working memory was a significant predictor, while impulsive choice was not. The interaction model included working memory as a predictor and impulsive choice as a moderator. This model was significant, as was the interaction term. Working memory significantly predicted levels of methamphetamine use in early treatment, and impulsive choice moderated this relationship. Those with working memory deficits are particularly vulnerable to using greater amounts of methamphetamine. As working memory increased methamphetamine use decreased among individuals with low/medium delay discounting. Pre-treatment cognitive testing may identify patients at high risk, while remediation of working memory function may be a treatment target for reducing methamphetamine use.

Modulating Neural Circuits with Transcranial Magnetic Stimulation: Implications for Addiction Treatment Development

Although the last 50 years of clinical and preclinical research have demonstrated that addiction is a brain disease, we still have no neural circuit-based treatments for substance dependence or cue reactivity at large. Now, for the first time, it appears that a noninvasive brain stimulation technique known as transcranial magnetic stimulation (TMS), which is Food and Drug Administration approved to treat depression, may be the first tool available to fill this critical void in addiction treatment development. The goals of this review are to 1) introduce TMS as a tool to induce causal change in behavior, cortical excitability, and frontal-striatal activity; 2) describe repetitive TMS (rTMS) as an interventional tool; 3) provide an overview of the studies that have evaluated rTMS as a therapeutic tool for alcohol and drug use disorders; and 4) outline a conceptual framework for target selection when designing future rTMS clinical trials in substance use disorders. The manuscript concludes with some suggestions for methodological innovation, specifically with regard to combining rTMS with pharmacotherapy as well as cognitive behavioral training paradigms. We have attempted to create a comprehensive manuscript that provides the reader with a basic set of knowledge and an introduction to the primary experimental questions that will likely drive the field of TMS treatment development forward for the next several years.

Working Memory Training for Adolescents With Cannabis Use Disorders: A Randomized Controlled Trial

Adolescent cannabis use is associated with working memory impairment. The present randomized controlled trial assigned adolescents ages 14 to 21 enrolled in cannabis use treatment to receive either working memory training (experimental group) or a control training (control group) as an adjunctive treatment. Cognitive function, drug use, and other outcomes were assessed before and after training. We observed few differences in cognitive, functional, or self-reported drug use outcomes as a function of training group, although tetrahydrocannabinol (THC) urinalysis results favored the experimental group. These findings are similar to previous studies in substance users, which have shown limited transfer effects for working memory training.

Altered anterior cingulate cortex to hippocampus effective connectivity in response to drug cues in men with cocaine use disorder

Drug-related attentional bias may have significant implications for the treatment of cocaine use disorder (CocUD). However, the neurobiology of attentional bias is not completely understood. This study employed dynamic causal modeling (DCM) to conduct an analysis of effective (directional) connectivity involved in drug-related attentional bias in treatment-seeking CocUD subjects. The DCM analysis was conducted based on functional magnetic resonance imaging (fMRI) data acquired from fifteen CocUD subjects while performing a cocaine-word Stroop task, during which blocks of Cocaine Words (CW) and Neutral Words (NW) alternated. There was no significant attentional bias at group level. Although no significant brain activation was found, the DCM analysis found that, relative to the NW, the CW caused a significant increase in the strength of the right (R) anterior cingulate cortex (ACC) to R hippocampus effective connectivity. Greater increase of this connectivity was associated with greater CW reaction time (relative to NW reaction time). The increased strength of R ACC to R hippocampus connectivity may reflect ACC activation of hippocampal memories related to drug use, which was triggered by the drug cues. This circuit could be a potential target for therapeutics in CocUD patients. No significant change was found in the other modeled connectivities.

Salience and default mode network dysregulation in chronic cocaine users predict treatment outcome

While chronic cocaine use is associated with abnormalities in both brain structure and function within and interactions between regions, previous studies have been limited to interrogating structure and function independently, and the detected neural differences have not been applied to independent samples to assess the clinical relevance of results. We investigated consequences of structural differences on resting-state functional connectivity in cocaine addiction and tested whether resting-state functional connectivity of the identified circuits predict relapse in an independent cohort. Subjects included 64 non-treatment-seeking cocaine users (NTSCUs) and 67 healthy control subjects and an independent treatment-completed cohort (n = 45) of cocaine-dependent individuals scanned at the end of a 30-day residential treatment programme. Differences in cortical thickness and related resting-state functional connectivity between NTSCUs and healthy control subjects were identified. Survival analysis, applying cortical thickness of the identified regions, resting-state functional connectivity of the identified circuits and clinical characteristics to the treatment cohort, was used to predict relapse. Lower cortical thickness in bilateral insula and higher thickness in bilateral temporal pole were found in NTSCUs versus healthy control subjects. Whole brain resting-state functional connectivity analyses with these four different anatomical regions as seeds revealed eight weaker circuits including within the salience network (insula seeds) and between temporal pole and elements of the default mode network in NTSCUs. Applying these circuits and clinical characteristics to the independent cocaine-dependent treatment cohort, functional connectivity between right temporal pole and medial prefrontal cortex, combined with years of education, predicted relapse status at 150 days with 88% accuracy. Deficits in the salience network suggest an impaired ability to process physiologically salient events, while abnormalities in a temporal pole-medial prefrontal cortex circuit might speak to the social-emotional functional alterations in cocaine addiction. The involvement of the temporal pole-medial prefrontal cortex circuit in a model highly predictive of relapse highlights the importance of social-emotional functions in cocaine dependence, and provides a potential underlying neural target for therapeutic interventions, and for identifying those at high risk of relapse.

Distinct cognitive performance and patterns of drug use among early and late onset cocaine users

INTRODUCTION

Adolescence is a crucial period for neurodevelopment, but few studies have investigated the impact of early cocaine use on cognitive performance and patterns of substance use.

METHODS

We evaluated 103 cocaine dependent inpatients divided in two groups: early-onset users (EOG; n=52), late-onset users (LOG; n=51), and 63 healthy controls. Neuropsychological functioning was evaluated using Digits Forward (DF) and Backward (DB), Trail Making Test (TMT), Stroop Color Word Test (SCWT), Controlled Oral Word Association Test (COWAT), Wisconsin Card Sorting Test (WCST), Rey Osterrieth Complex Figure Test (ROCFT), Frontal Assessment Battery (FAB), and Iowa Gambling Test (IGT). Use of alcohol and other drugs was assessed with the Addiction Severity Index (ASI-6).

RESULTS

Analyses of covariance controlling for age, IQ and years of education showed that EOG presented worse performance in attention span (DF, p=0.020), working memory (DB, p=0.001), sustained attention (WCST, p=0.030), declarative memory (ROCFT, p=0.031) and general executive functioning (FAB, p=0.003) when compared with the control group. LOG presented impairments on divided attention (TMT, p=0.003) and general executive functioning (FAB, p=0.001) in relation to the control group. EOG presented higher use of cannabis and alcohol than LOG (p≤0.001).

CONCLUSION

Early-onset cocaine users display more pronounced neuropsychological alterations than controls, as well as a greater frequency of polydrug consumption than LOG. The prominent cognitive deficits in EOG probably reflect the deleterious interference of cocaine use with early stages of neurodevelopment. This may be related to more severe clinical characteristics of substance disorder in this subgroup, including polysubstance abuse.

The Role of Working Memory for Cognitive Control in Anorexia Nervosa versus Substance Use Disorder

Prefrontal cortex executive functions, such as working memory (WM) interact with limbic processes to foster impulse control. Such an interaction is referred to in a growing body of publications by terms such as cognitive control, cognitive inhibition, affect regulation, self-regulation, top-down control, and cognitive–emotion interaction. The rising trend of research into cognitive control of impulsivity, using various related terms reflects the importance of research into impulse control, as failure to employ cognitions optimally may eventually result in mental disorder. Against this background, we take a novel approach using an impulse control spectrum model – where anorexia nervosa (AN) and substance use disorder (SUD) are at opposite extremes – to examine the role of WM for cognitive control. With this aim, we first summarize WM processes in the healthy brain in order to frame a systematic review of the neuropsychological, neural and genetic findings of AN and SUD. In our systematic review of WM/cognitive control, we found n = 15 studies of AN with a total of n = 582 AN and n = 365 HC participants; and n = 93 studies of SUD with n = 9106 SUD and n = 3028 HC participants. In particular, we consider how WM load/capacity may support the neural process of excessive epistemic foraging (cognitive sampling of the environment to test predictions about the world) in AN that reduces distraction from salient stimuli. We also consider the link between WM and cognitive control in people with SUD who are prone to ‘jumping to conclusions’ and reduced epistemic foraging. Finally, in light of our review, we consider WM training as a novel research tool and an adjunct to enhance treatment that improves cognitive control of impulsivity.

Machine Learning of Functional Magnetic Resonance Imaging Network Connectivity Predicts Substance Abuse Treatment Completion

BACKGROUND

Successfully treating illicit drug use has become paramount, yet elusive. Devising specialized treatment interventions could increase positive outcomes, but it is necessary to identify risk factors of poor long-term outcomes to develop specialized, efficacious treatments. We investigated whether functional network connectivity (FNC) measures were predictive of substance abuse treatment completion using machine learning pattern classification of functional magnetic resonance imaging data.

METHODS

Treatment-seeking stimulant- or heroin-dependent incarcerated participants (n = 139; 89 women) volunteered for a 12-week substance abuse treatment program. Participants performed a response inhibition Go/NoGo functional magnetic resonance imaging task prior to onset of the substance abuse treatment. We tested whether FNC related to the anterior cingulate cortex would be predictive of those who would or would not complete a 12-week substance abuse treatment program.

RESULTS

Machine learning pattern classification models using FNC between networks incorporating the anterior cingulate cortex, striatum, and insula predicted which individuals would (sensitivity: 81.31%) or would not (specificity: 78.13%) complete substance abuse treatment. FNC analyses predicted treatment completion above and beyond other clinical assessment measures, including age, sex, IQ, years of substance use, psychopathy, anxiety and depressive symptomatology, and motivation for change.

CONCLUSIONS

Aberrant neural network connections predicted substance abuse treatment outcomes, which could illuminate new targets for developing interventions designed to reduce or eliminate substance use while facilitating long-term outcomes. This work represents the first application of machine-learning models of FNC analyses of functional magnetic resonance imaging data to predict which substance abusers would or would not complete treatment.

The effect of task difficulty on motor performance and frontal-striatal connectivity in cocaine users

BACKGROUND

There is growing recognition that chronic cocaine users have alterations in sensorimotor control that are positively related to low frontal-striatal connectivity within the motor system. These frontal-striatal motor circuits however, are modulated by circuits governing attention, which are also disrupted in cocaine users. This study's aim was to determine if sensorimotor control deficits are positively related to the difficulty of a motor task or exist independent of the increasing cognitive demand.

METHODS

Functional MRI data was collected from 40 individuals (20 non-treatment seeking chronic cocaine users, 20 age and gender matched non-drug using controls) as they mimicked an unpredictable finger-tapping sequence at various speeds. Dependent measures included task accuracy, percent BOLD signal change in sensorimotor regions of interest (ROIs), and functional connectivity (temporal correlations) between ROIs.

RESULTS

In both groups, as speed increased, the BOLD signal change increased in the primary motor cortex, supplementary motor area (SMA), cerebellum, and anterior cingulate cortex. Compared to controls, cocaine user SMA-Caudate and ACC-Putamen connectivity was lower at all speeds in the contralateral hemisphere. Furthermore, as speed increased there was a decrease in connectivity between additional ROI pairs among users.

CONCLUSIONS

These data support previous observations of sensorimotor performance deficits and dorsal frontal-striatal connectivity impairments among cocaine users. While previous studies demonstrate these deficits when performing a finger-tapping task at a single speed, we show that these same impairments exist at multiple levels of task difficulty. These data suggest that previously observed frontal-striatal connectivity in cocaine users during sensorimotor task performance are stable and not directly related to cognitive demands of the task.

Novel fMRI working memory paradigm accurately detects cognitive impairment in multiple sclerosis

BACKGROUND

Cognitive impairment (CI) cannot be diagnosed by magnetic resonance imaging (MRI). Functional magnetic resonance imaging (fMRI) paradigms, such as the immediate/delayed memory task (I/DMT), detect varying degrees of working memory (WM). Preliminary findings using I/DMT showed differences in blood oxygenation level dependent (BOLD) activation between impaired (MSCI, n = 12) and non-impaired (MSNI, n = 9) multiple sclerosis (MS) patients.

OBJECTIVES

The aim of the study was to confirm CI detection based on I/DMT BOLD activation in a larger cohort of MS patients. The role of T2 lesion volume (LV) and Expanded Disability Status Scale (EDSS) in magnitude of BOLD signal was also sought.

METHODS

A total of 50 patients (EDSS mean ( m) = 3.2, disease duration (DD) m = 12 years, and age m = 40 years) underwent the Minimal Assessment of Cognitive Function in Multiple Sclerosis (MACFIMS) and I/DMT. Working memory activation (WMa) represents BOLD signal during DMT minus signal during IMT. CI was based on MACFIMS.

RESULTS

A total of 10 MSNI, 30 MSCI, and 4 borderline patients were included in the analyses. Analysis of variance (ANOVA) showed MSNI had significantly greater WMa than MSCI, in the left prefrontal cortex and left supplementary motor area ( p = 0.032). Regression analysis showed significant inverse correlations between WMa and T2 LV/EDSS in similar areas ( p = 0.005, 0.004, respectively).

CONCLUSION

I/DMT-based BOLD activation detects CI in MS. Larger studies are needed to confirm these findings.

Biomarkers for Success: Using Neuroimaging to Predict Relapse and Develop Brain Stimulation Treatments for Cocaine-Dependent Individuals

Cocaine dependence is one of the most difficult substance use disorders to treat. While the powerful effects of cocaine use on behavior were documented in the 19th century, it was not until the late 20th century that we realized cocaine use was affecting brain tissue and function. Following a brief introduction (Section 1), this chapter will summarize our current knowledge regarding alterations in neural circuit function typically observed in chronic cocaine users (Section 2) and highlight an emerging body of literature which suggests that pretreatment limbic circuit activity may be a reliable predictor of clinical outcomes among individuals seeking treatment for cocaine (Section 3). Finally, as the field of addiction research strives to translate this neuroimaging data into something clinically meaningful, we will highlight several new brain stimulation approaches which utilize functional brain imaging data to design noninvasive brain stimulation interventions for individuals seeking treatment for substance dependence disorders (Section 4).

Competing neurobehavioral decision systems theory of cocaine addiction: From mechanisms to therapeutic opportunities

Cocaine dependence is a difficult-to-treat, chronically relapsing disorder. Multiple scientific disciplines provide distinct perspectives on this disorder; however, connections between disciplines are rare. The competing neurobehavioral decision systems (CNDS) theory posits that choice results from the interaction between two decision systems (impulsive and executive) and that regulatory imbalance between systems can induce pathology, including addiction. Using this view, we integrate a diverse set of observations on cocaine dependence, including bias for immediacy, neural activity and structure, developmental time course, behavioral comorbidities, and the relationship between cocaine dependence and socioeconomic status. From the CNDS perspective, we discuss established and emerging behavioral, pharmacological, and neurological treatments and identify possible targets for future treatments. The ability of the CNDS theory to integrate diverse findings highlights its utility for understanding cocaine dependence and supports that dysregulation between the decision systems contributes to addiction.

The Imperial College Cambridge Manchester (ICCAM) platform study: An experimental medicine platform for evaluating new drugs for relapse prevention in addiction. Part A: Study description

Drug and alcohol dependence are global problems with substantial societal costs. There are few treatments for relapse prevention and therefore a pressing need for further study of brain mechanisms underpinning relapse circuitry. The Imperial College Cambridge Manchester (ICCAM) platform study is an experimental medicine approach to this problem: using functional magnetic resonance imaging (fMRI) techniques and selective pharmacological tools, it aims to explore the neuropharmacology of putative relapse pathways in cocaine, alcohol, opiate dependent, and healthy individuals to inform future drug development. Addiction studies typically involve small samples because of recruitment difficulties and attrition. We established the platform in three centres to assess the feasibility of a multisite approach to address these issues. Pharmacological modulation of reward, impulsivity and emotional reactivity were investigated in a monetary incentive delay task, an inhibitory control task, and an evocative images task, using selective antagonists for µ-opioid, dopamine D3 receptor (DRD3) and neurokinin 1 (NK1) receptors (naltrexone, GSK598809, vofopitant/aprepitant), in a placebo-controlled, randomised, crossover design. In two years, 609 scans were performed, with 155 individuals scanned at baseline. Attrition was low and the majority of individuals were sufficiently motivated to complete all five sessions (n=87). We describe herein the study design, main aims, recruitment numbers, sample characteristics, and explain the test hypotheses and anticipated study outputs.

Anti-saccade error rates as a measure of attentional bias in cocaine dependent subjects

Cocaine-dependent (CD) subjects show attentional bias toward cocaine-related cues, and this form of cue-reactivity may be predictive of craving and relapse. Attentional bias has previously been assessed by models that present drug-relevant stimuli and measure physiological and behavioral reactivity (often reaction time). Studies of several CNS diseases outside of substance use disorders consistently report anti-saccade deficits, suggesting a compromise in the interplay between higher-order cortical processes in voluntary eye control (i.e., anti-saccades) and reflexive saccades driven more by involuntary midbrain perceptual input (i.e., pro-saccades). Here, we describe a novel attentional-bias task developed by using measurements of saccadic eye movements in the presence of cocaine-specific stimuli, combining previously unique research domains to capitalize on their respective experimental and conceptual strengths. CD subjects (N = 46) and healthy controls (N = 41) were tested on blocks of pro-saccade and anti-saccade trials featuring cocaine and neutral stimuli (pictures). Analyses of eye-movement data indicated (1) greater overall anti-saccade errors in the CD group; (2) greater attentional bias in CD subjects as measured by anti-saccade errors to cocaine-specific (relative to neutral) stimuli; and (3) no differences in pro-saccade error rates. Attentional bias was correlated with scores on the obsessive-compulsive cocaine scale. The results demonstrate increased saliency and differential attentional to cocaine cues by the CD group. The assay provides a sensitive index of saccadic (visual inhibitory) control, a specific index of attentional bias to drug-relevant cues, and preliminary insight into the visual circuitry that may contribute to drug-specific cue reactivity.

Impaired Bayesian learning for cognitive control in cocaine dependence

BACKGROUND

Cocaine dependence is associated with cognitive control deficits. Here, we apply a Bayesian model of stop-signal task (SST) performance to further characterize these deficits in a theory-driven framework.

METHODS

A "sequential effect" is commonly observed in SST: encounters with a stop trial tend to prolong reaction time (RT) on subsequent go trials. The Bayesian model accounts for this by assuming that each stop/go trial increases/decreases the subject's belief about the likelihood of encountering a subsequent stop trial, P(stop), and that P(stop) strategically modulates RT accordingly. Parameters of the model were individually fit, and compared between cocaine-dependent (CD, n = 51) and healthy control (HC, n = 57) groups, matched in age and gender and both demonstrating a significant sequential effect (p < 0.05). Model-free measures of sequential effect, post-error slowing (PES) and post-stop slowing (PSS), were also compared across groups.

RESULTS

By comparing individually fit Bayesian model parameters, CD were found to utilize a smaller time window of past experiences to anticipate P(stop) (p < 0.003), as well as showing less behavioral adjustment in response to P(stop) (p < 0.015). PES (p = 0.19) and PSS (p = 0.14) did not show group differences and were less correlated with the Bayesian account of sequential effect in CD than in HC.

CONCLUSIONS

Cocaine dependence is associated with the utilization of less contextual information to anticipate future events and decreased behavioral adaptation in response to changes in such anticipation. These findings constitute a novel contribution by providing a computationally more refined and statistically more sensitive account of altered cognitive control in cocaine addiction.

Altered white matter in cocaine-dependent subjects with traumatic brain injury: A diffusion tensor imaging study

BACKGROUND

Diffusion tensor imaging (DTI) is a useful technique for non-invasively investigating the microstructural organization of white matter (WM), and the most consistent DTI finding regarding cocaine-related WM alterations is in the corpus callosum (CC). WM injury has also been observed in subjects with traumatic brain injury (TBI), including in the CC.

METHODS

We used DTI to test if the WM microstructure is relatively more impaired in cocaine-dependent subjects who had suffered a mild TBI (mTBI). Fractional anisotropy (FA), which reflects the degree of alignment of cellular structures within fiber tracts and their structural integrity, was compared across cocaine-dependent subjects with mTBI (COCTBI group, n = 9), matched cocaine-dependent subjects without TBI (COC group, n = 12), and matched healthy controls (CTL group, n = 12).

RESULTS

The COCTBI group had significantly lower FA in the genu, body, and splenium of CC, than the CTL group whenever the education was controlled or not. The COC group had significantly lower FA in the left and right anterior corona radiata than the CTL group only when the education was controlled. There was no significant difference in FA between the COC and COCTBI groups.

CONCLUSION

Cocaine dependence (or mTBI) related WM impairments in the CC were not detectable in this small subject sample. The significant finding in the CC suggests that the concurrence of cocaine dependence and mTBI might result in more severe damage to the CC, which could even be detected in small sample size.

Inhibitory behavioral control: a stochastic dynamic causal modeling study using network discovery analysis

This study employed functional magnetic resonance imaging (fMRI)-based dynamic causal modeling (DCM) to study the effective (directional) neuronal connectivity underlying inhibitory behavioral control. fMRI data were acquired from 15 healthy subjects while they performed a Go/NoGo task with two levels of NoGo difficulty (Easy and Hard NoGo conditions) in distinguishing spatial patterns of lines. Based on the previous inhibitory control literature and the present fMRI activation results, 10 brain regions were postulated as nodes in the effective connectivity model. Due to the large number of potential interconnections among these nodes, the number of models for final analysis was reduced to a manageable level for the whole group by conducting DCM Network Discovery, which is a recently developed option within the Statistical Parametric Mapping software package. Given the optimum network model, the DCM Network Discovery analysis found that the locations of the driving input into the model from all the experimental stimuli in the Go/NoGo task were the amygdala and the hippocampus. The strengths of several cortico-subcortical connections were modulated (influenced) by the two NoGo conditions. Specifically, connectivity from the middle frontal gyrus (MFG) to hippocampus was enhanced by the Easy condition and further enhanced by the Hard NoGo condition, possibly suggesting that compared with the Easy NoGo condition, stronger control from MFG was needed for the hippocampus to discriminate/learn the spatial pattern in order to respond correctly (inhibit), during the Hard NoGo condition.

What goes up, can come down: Novel brain stimulation paradigms may attenuate craving and craving-related neural circuitry in substance dependent individuals

Vulnerability to drug related cues is one of the leading causes for continued use and relapse among substance dependent individuals. Using drugs in the face of cues may be associated with dysfunction in at least two frontal-striatal neural circuits: (1) elevated activity in medial and ventral areas that govern limbic arousal (including the medial prefrontal cortex (MPFC) and ventral striatum) or (2) depressed activity in dorsal and lateral areas that govern cognitive control (including the dorsolateral prefrontal cortex (DLPFC) and dorsal striatum). Transcranial magnetic stimulation (TMS) is emerging as a promising new tool for the attenuation of craving among multiple substance dependent populations. To date however, nearly all repetitive TMS studies in addiction have focused on amplifying activity in frontal-striatal circuits that govern cognitive control. This manuscript reviews recent work using TMS as a tool to decrease craving for multiple substances and provides a theoretical model for how clinical researchers might approach target and frequency selection for TMS of addiction. To buttress this model, preliminary data from a single-blind, sham-controlled, crossover study of 11 cocaine-dependent individuals is also presented. These results suggest that attenuating MPFC activity through theta burst stimulation decreases activity in the striatum and anterior insula. It is also more likely to attenuate craving than sham TMS. Hence, while many TMS studies are focused on applying LTP-like stimulation to the DLPFC, the MPFC might be a new, efficacious, and treatable target for craving in cocaine dependent individuals.

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.

Altered cerebellar and prefrontal cortex function in rhesus monkeys that previously self-administered cocaine

RATIONALE

Differences in brain function in cocaine users can occur even when frank deficits are not apparent, indicating neuroadaptive consequences of use. Using monkeys to investigate altered metabolic activity following chronic cocaine self-administration allows an assessment of altered function due to cocaine use, without confounding pre-existing differences or polysubstance use often present in clinical studies.

OBJECTIVES

To evaluate alterations in metabolic function during a working memory task in the prefrontal cortex and the cerebellum following 1 year of chronic cocaine self-administration followed by a 20 month drug-free period.

METHODS

Fluorodeoxyglucose ((18)F) PET imaging was used to evaluate changes in relative regional metabolic activity associated with a delayed match to sample working memory task. Chronic cocaine animals were compared to a control group, and region of interest analyses focused on the dorsolateral prefrontal cortex (DLPFC) and cerebellum.

RESULTS

Despite no differences in task performance, in the cocaine group, the cerebellum showed greater metabolic activity during the working memory task (relative to the control task) compared to the control group. There was also a trend toward a significant difference between the groups in DLPFC activity (p = 0.054), with the cocaine group exhibiting lower DLPFC metabolic activity during the delay task (relative to the control task) than the control group.

CONCLUSION

The results support clinical indications of increased cerebellar activity associated with chronic cocaine exposure. Consistent with evidence of functional interactions between cerebellum and prefrontal cortex, these changes may serve to compensate for potential impairments in functionality of DLPFC.

PET studies in nonhuman primate models of cocaine abuse: translational research related to vulnerability and neuroadaptations

The current review highlights the utility of positron emission tomography (PET) imaging to study the neurobiological substrates underlying vulnerability to cocaine addiction and subsequent adaptations following chronic cocaine self-administration in nonhuman primate models of cocaine abuse. Environmental (e.g., social rank) and sex-specific influences on dopaminergic function and sensitivity to the reinforcing effects of cocaine are discussed. Cocaine-related cognitive deficits have been hypothesized to contribute to high rates of relapse and are described in nonhuman primate models. Lastly, the long-term consequences of cocaine on neurobiology are discussed. PET imaging and longitudinal, within-subject behavioral studies in nonhuman primates have provided a strong framework for designing pharmacological and behavioral treatment strategies to aid drug-dependent treatment seekers. Non-invasive PET imaging will allow for individualized treatment strategies. Recent advances in radiochemistry of novel PET ligands and other imaging modalities can further advance our understanding of stimulant use on the brain. This article is part of the Special Issue Section entitled 'Neuroimaging in Neuropharmacology'.

Cocaine dependent individuals with attenuated striatal activation during reinforcement learning are more susceptible to relapse

Cocaine-dependent individuals show altered brain activation during decision making. It is unclear, however, whether these activation differences are related to relapse vulnerability. This study tested the hypothesis that brain-activation patterns during reinforcement learning are linked to relapse 1 year later in individuals entering treatment for cocaine dependence. Subjects performed a Paper-Scissors-Rock task during functional magnetic resonance imaging (fMRI). A year later, we examined whether subjects had remained abstinent (n=15) or relapsed (n=15). Although the groups did not differ on demographic characteristics, behavioral performance, or lifetime substance use, abstinent patients reported greater motivation to win than relapsed patients. The fMRI results indicated that compared with abstinent individuals, relapsed users exhibited lower activation in (1) bilateral inferior frontal gyrus and striatum during decision making more generally; and (2) bilateral middle frontal gyrus and anterior insula during reward contingency learning in particular. Moreover, whereas abstinent patients exhibited greater left middle frontal and striatal activation to wins than losses, relapsed users did not demonstrate modulation in these regions as a function of outcome valence. Thus, individuals at high risk for relapse relative to those who are able to abstain allocate fewer neural resources to action-outcome contingency formation and decision making, as well as having less motivation to win on a laboratory-based task.

Overlapping patterns of brain activation to food and cocaine cues in cocaine abusers: association to striatal D2/D3 receptors

Cocaine, through its activation of dopamine (DA) signaling, usurps pathways that process natural rewards. However, the extent to which there is overlap between the networks that process natural and drug rewards and whether DA signaling associated with cocaine abuse influences these networks have not been investigated in humans. We measured brain activation responses to food and cocaine cues with fMRI, and D2/D3 receptors in the striatum with [11C]raclopride and Positron emission tomography in 20 active cocaine abusers. Compared to neutral cues, food and cocaine cues increasingly engaged cerebellum, orbitofrontal, inferior frontal, and premotor cortices and insula and disengaged cuneus and default mode network (DMN). These fMRI signals were proportional to striatal D2/D3 receptors. Surprisingly cocaine and food cues also deactivated ventral striatum and hypothalamus. Compared to food cues, cocaine cues produced lower activation in insula and postcentral gyrus, and less deactivation in hypothalamus and DMN regions. Activation in cortical regions and cerebellum increased in proportion to the valence of the cues, and activation to food cues in somatosensory and orbitofrontal cortices also increased in proportion to body mass. Longer exposure to cocaine was associated with lower activation to both cues in occipital cortex and cerebellum, which could reflect the decreases in D2/D3 receptors associated with chronicity. These findings show that cocaine cues activate similar, though not identical, pathways to those activated by food cues and that striatal D2/D3 receptors modulate these responses, suggesting that chronic cocaine exposure might influence brain sensitivity not just to drugs but also to food cues.

Drugs currently in Phase II clinical trials for cocaine addiction

INTRODUCTION

There are no FDA-approved pharmacotherapies for treating cocaine addiction; thus, developing drugs to treat cocaine dependence is an unmet critical need. Fortunately, there are a number of drugs that are currently in Phase II clinical trial/s. This is due in part to the advances from in vivo imaging in humans which provided a roadmap of the neurochemistry of the cocaine-dependent brain. Most drugs currently in Phase II clinical trials attempt to modulate the disturbed neurochemistry in cocaine dependents to resemble those of healthy individuals. These predominantly modulate dopamine, serotonin, glutamate, GABA or noradrenaline signalling.

AREAS COVERED

This review summarizes the therapeutic potential of each drug as evidenced by clinical and preclinical studies. It also discusses their utility in terms of bioavailability and half-life.

EXPERT OPINION

Amphetamine salts and topiramate clearly stand out in terms of their potential efficacy in treating cocaine addiction. The efficacy of topiramate was closely associated with regular cognitive-behavioural therapy (CBT), which highlights the importance of a combined effort to promote abstinence and enhance retention via CBT. Cognitive/psychological screening appears necessary for a more symptom-based approach with more reasonable outcomes other than abstinence (e.g., improved quality of life) in treating cocaine addiction.

Crack cocaine use impairs anterior cingulate and prefrontal cortex function in women with HIV infection

Crack cocaine use is associated with impaired verbal memory in HIV-infected women more than uninfected women. To understand the neural basis for this impairment, this study examined the effects of crack cocaine use on activation of the prefrontal cortex (PFC) and strategic encoding during a verbal memory task in HIV-infected women. Three groups of HIV-infected women from the Chicago Consortium of the Women's Interagency HIV Study were compared: current users of crack cocaine (n = 10), former users of cocaine (n = 11), and women who had never used cocaine (n = 9). Participants underwent functional magnetic resonance imaging during a verbal memory task and completed a neuropsychological test of verbal memory. On the neuropsychological test, current crack users performed significantly worse than other groups on semantic clustering, a measure of strategic encoding, p < 0.05. During encoding, activation in left anterior cingulate cortex (ACC) was lower in current and former cocaine users compared to never users. During recognition, activation in bilateral PFC, specifically left dorsal medial PFC and bilateral dorsolateral PFC, was lower in current and former users compared to women who had never used cocaine. Lower activation in left dorsolateral PFC was correlated with worse performance on the recognition task, p < 0.05. The verbal learning and memory deficits associated with cocaine use in women with HIV may be partially accounted for by alterations in ACC and PFC function.

Preliminary findings of the effects of rivastigmine, an acetylcholinesterase inhibitor, on working memory in cocaine-dependent volunteers

Long-term cocaine use is a risk factor for the onset of neurocognitive impairment. This study sought to determine whether the cholinesterase inhibitor rivastigmine could improve neurocognitive performance in cocaine-dependent individuals. Cocaine-dependent individuals who were not seeking treatment at the time of enrollment in the study were randomly assigned to receive placebo (n=16), rivastigmine 3mg (n=13), or rivastigmine 6mg (n=12). The baseline neurocognitive assessment, which included measures of attention/information processing (as measured by the Continuous Performance Task-II (CPT-II)), verbal learning/episodic memory (as measured by the Hopkins Verbal Learning Test-Revised (HVLT-R)), and working memory (as measured by the Dual N-Back Task), was conducted prior to the administration of study medication (Day 0). The follow-up assessment was conducted on Day 8 after the participants had received rivastigmine or placebo for 7days (Day 2-8). Rivastigmine administration significantly improved performance on one measure of working memory span (mean n-back span). This study provides additional data showing that cocaine-associated neurocognitive impairment, specifically working memory deficits, can be remediated, at least to some degree.

Cerebral gray matter volumes and low-frequency fluctuation of BOLD signals in cocaine dependence: duration of use and gender difference

BACKGROUND

Magnetic resonance imaging has provided a wealth of information on altered brain activations and structures in individuals addicted to cocaine. However, few studies have considered the influence of age and alcohol use on these changes.

METHODS

We examined gray matter volume with voxel based morphometry (VBM) and low frequency fluctuation (LFF) of BOLD signals as a measure of cerebral activity of 84 cocaine dependent (CD) and 86 healthy control (HC) subjects. We performed a covariance analysis to account for the effects of age and years of alcohol use.

RESULTS

Compared to HC, CD individuals showed decreased gray matter (GM) volumes in frontal and temporal cortices, middle/posterior cingulate cortex, and the cerebellum, at p<0.05, corrected for multiple comparisons. The GM volume of the bilateral superior frontal gyri (SFG) and cingulate cortices were negatively correlated with years of cocaine use, with women showing a steeper loss in the right SFG in association with duration of use. In contrast, the right ventral putamen showed increased GM volume in CD as compared to HC individuals. Compared to HC, CD individuals showed increased fractional amplitude of LFF (fALFF) in the thalamus, with no significant overlap with regions showing GM volume loss.

CONCLUSIONS

These results suggested that chronic cocaine use is associated with distinct changes in cerebral structure and activity that can be captured by GM volume and fALFF of BOLD signals.

Monoamine transporter inhibitors and substrates as treatments for stimulant abuse

The acute and chronic effects of abused psychostimulants on monoamine transporters and associated neurobiology have encouraged development of candidate medications that target these transporters. Monoamine transporters, in general, and dopamine transporters, in particular, are critical molecular targets that mediate abuse-related effects of psychostimulants such as cocaine and amphetamine. Moreover, chronic administration of psychostimulants can cause enduring changes in neurobiology reflected in dysregulation of monoamine neurochemistry and behavior. The current review will evaluate evidence for the efficacy of monoamine transporter inhibitors and substrates to reduce abuse-related effects of stimulants in preclinical assays of stimulant self-administration, drug discrimination, and reinstatement. In considering deployment of monoamine transport inhibitors and substrates as agonist-type medications to treat stimulant abuse, the safety and abuse liability of the medications are an obvious concern, and this will also be addressed. Future directions in drug discovery should identify novel medications that retain efficacy to decrease stimulant use but possess lower abuse liability and evaluate the degree to which efficacious medications can attenuate or reverse neurobiological effects of chronic stimulant use.

Biomarkers for the development of new medications for cocaine dependence

There has been significant progress in personalized drug development. In large part, this has taken place in the oncology field and been due to the ability of researchers/clinicians to discover and develop novel drug development tools (DDTs), such as biomarkers. In cancer treatment research, biomarkers have permitted a more accurate pathophysiological characterization of an individual patient, and have enabled practitioners to target mechanistically the right drug, to the right patient, at the right time. Similar to cancer, patients with substance use disorders (SUDs) present clinically with heterogeneous symptomatology and respond variably to therapeutic interventions. If comparable biomarkers could be identified and developed for SUDs, significant diagnostic and therapeutic advances could be made. In this review, we highlight current opportunities and difficulties pertaining to the identification and development of biomarkers for SUDs. We focus on cocaine dependence as an example. Putative diagnostic, pharmacodynamic (PD), and predictive biomarkers for cocaine dependence are discussed across a range of methodological approaches. A possible cocaine-dependent clinical outcome assessment (COA)--another type of defined DDT--is also discussed. At present, biomarkers for cocaine dependence are in their infancy. Much additional research will be needed to identify, validate, and qualify these putative tools prior to their potential use for medications development and/or application to clinical practice. However, with a large unmet medical need and an estimated market size of several hundred million dollars per year, if developed, biomarkers for cocaine dependence will hold tremendous value to both industry and public health.

Environmental modulation of drug taking: Nonhuman primate models of cocaine abuse and PET neuroimaging

The current review highlights the importance of environmental variables on cocaine self-administration in nonhuman primate models of drug abuse. In addition to describing the behavioral consequences, potential mechanisms of action are discussed, based on imaging results using the non-invasive and translational technique of positron emission tomography (PET). In this review, the role of three environmental variables - both positive and negative - are described: alternative non-drug reinforcers; social rank (as an independent variable) and punishment of cocaine self-administration. These environmental stimuli can profoundly influence brain function and drug self-administration. We focus on environmental manipulations involving non-drug alternatives (e.g., food reinforcement) using choice paradigms. Manipulations such as response cost and social variables (e.g., social rank, social stress) also influence the behavioral effects of drugs. Importantly, these manipulations are amenable to brain imaging studies. Taken together, these studies emphasize the profound impact environmental variables can have on drug taking, which should provide important information related to individual-subject variability in treatment responsiveness, and the imaging work may highlight pharmacological targets for medications related to treating drug abuse. This article is part of a Special Issue entitled 'NIDA 40th Anniversary Issue'.