The neurobiology of drug addiction: cross-species insights into the dysfunction and recovery of the prefrontal cortex

Repetitive transcranial magnetic stimulation of the left dorsolateral prefrontal cortex in binge eating disorder: a double-blind randomized controlled trial

BACKGROUND

Binge-eating disorder (BED) is characterized by highly distressing episodes of loss-of-control over-eating. We have examined the use of repetitive transcranial magnetic stimulation (rTMS) for the treatment of people with BED and associated obesity. Such non-invasive brain stimulation (NIBS) techniques are used therapeutically in several psychiatric conditions and there is an associated scientific rationale.

METHODS

Sixty participants were randomly allocated to receive 20 sessions of neuronavigated 10 Hz rTMS administered to the left dorsolateral prefrontal cortex (dlPFC) or sham treatment. Primary outcomes were the frequency of binge eating episodes (BEE) and the 'urge to eat' (craving) evaluated at baseline and end-of-treatment (8 weeks post-randomization). Secondary outcomes included body mass index (BMI), hunger, general and specific eating disorder psychopathology. Follow-up analyses were conducted for most outcomes at 16 weeks post-randomization. Multilevel models were used to evaluate group, time, and group-by-time interactions for the association between rTMS exposure and outcomes.

RESULTS

The real rTMS group (compared with sham treatment), showed a significantly greater decrease in the number of BEE at the end of treatment (Estimated Mean [EM]: 2.41 95% CI: 1.84-3.15 versus EM: 1.45 95% CI: 1.05-1.99, p = 0.02), and at follow-up (EM: 3.79 95% CI: 3-4.78 versus EM: 2.45 95% CI: 1.88-3.17, p = 0.02; group × time interaction analysis p = 0.02). No group differences were found for other comparisons.

CONCLUSION

rTMS was associated with reduced BEE during and after treatment: it suggests rTMS is a promising intervention for BED.

The neural signature of methylphenidate-enhanced memory disruption in human drug addiction: a randomized clinical trial

Background

Drug-related memories can hinder abstinence goals in drug addiction. Promoting non-drug memories via ventromedial prefrontal cortex- (vmPFC) and amygdala-guided extinction yields mixed success. Post-retrieval extinction (RE) destabilizes and updates memories during reconsolidation, improving extinction. Supplementing RE, we tested methylphenidate (MPH), a dopamine-agonist that promotes PFC-dependent learning and memory in cocaine use disorder (CUD). In an Early Phase 1 double-blind randomized clinical trial using a within-subjects design, participants received oral MPH (20 mg) or placebo before the retrieval of some of the conditioned stimuli (i.e., reminded CS+ vs. non-reminded CS+) followed by extinction; lab-simulated drug-seeking was measured the following day.

Results

Lower vmPFC activity following non-reminded CS+ (standard extinction) under placebo replicated the putative impairments in CUD; separately, RE (trend) and MPH conditions recruited the vmPFC, and RE's vmPFC-reliance correlated with drug-seeking only under placebo. Crucially, MPH-combined RE normalized cortico-limbic processing, bypassing the vmPFC and its amygdala connectivity.

Conclusions

Pharmacologically-enhanced drug memory modulation may inform intervention development for addiction recovery.

Harnessing neuroimaging-guided transcranial magnetic stimulation for precision therapy in substance use disorders

Substance use disorders (SUDs) are a critical public health challenge characterized by high relapse rates, with existing treatments often proving inadequate. The focus of this review is to provide an update on the current state of transcranial magnetic stimulation (TMS) as a therapeutic intervention for SUDs and discuss neuroimaging-guided TMS practices. This review explores the neurobiology underlying SUDs, emphasizing the roles of the prefrontal cortex, striatal circuits, and dopaminergic pathways, and examines the theory that TMS modulates neurocircuitry to impact addiction-related behaviors. We discuss TMS procedural aspects and provide a comparative analysis of TMS protocols, focusing on repetitive, deep, single-pulse, paired-pulse, and a more recent approach, theta burst stimulation. We review recent randomized clinical trials (RCTs) to demonstrate reductions in cravings and use across SUDs as well as highlight the need for standardized protocols. We emphasize the power of combining neuroimaging techniques to show functional connectivity changes in the brain and identify potential biomarkers predictive of SUD treatment response, an unexplored area of discussion. With these topics, this review highlights the potential of TMS as a versatile and effective therapeutic modality for SUDs, especially when combined with neuroimaging. Key findings emphasize the necessity for future research to address methodological challenges, such as standardizing protocols and optimizing stimulation parameters. The integration of neuroimaging provides insights into functional connectivity changes, enabling enhanced precision and individualized treatment strategies. By validating TMS approaches and incorporating multimodal techniques, this field can advance toward a more robust clinical utility in addressing the complex neurocircuitry of addiction-related behaviors underlying SUDs.

The Impact of Social Media & Technology on Child and Adolescent Mental Health

The prevalence of mental health disorders among youth and adolescents has been rising at an alarming rate over the past few decades, with conditions such as anxiety, depression, attention deficit hyperreactivity disorder, autism spectrum disorder, and body dysmorphic disorder becoming increasingly common. One contributing factor that has received growing attention is the role of social media and technology in shaping adolescent brain development, behavior, and emotional well-being. While digital platforms provide opportunities for social connection, self-expression, and mental health support, they also introduce significant risks, including compulsive social media use, cyberbullying, unrealistic beauty standards, and exposure to substance-related content. This article explores the complex relationship between digital media use and adolescent mental health, focusing on its neurobiological implications, particularly the role of dopaminergic reward pathways in reinforcing compulsive behaviors. The excessive engagement with digital platforms has been associated with heightened impulsivity, attention deficits, and an increased risk of addiction-like behaviors. Furthermore, the impact of social media on self-esteem and body image has been linked to higher rates of body dysmorphic disorder and a rise in cosmetic procedure considerations, often influenced by digitally altered self-perceptions. The increased portrayal of substance-related content online also raises concerns about the normalization of risky behaviors among impressionable youth. Intervention strategies such as digital detox programs, school-based educational initiatives, parental monitoring, and cognitive-behavioral therapy are crucial in mitigating the adverse effects of excessive social media use. A multidisciplinary approach, integrating policy regulation, digital literacy, and targeted mental health interventions, will be essential in fostering a healthier digital environment for adolescents. Future research should prioritize longitudinal studies to better understand the long-term psychological effects of social media use and to distinguish between adaptive and maladaptive digital behaviors. By addressing these challenges proactively, society can work towards promoting responsible social media engagement in youth while protecting adolescent mental health in this digital age.

Emerging medications and pharmacological treatment approaches for substance use disorders

Medications to treat substance use disorders (SUDs) remain suboptimal or, in the case of stimulants and cannabis, non-existent. Many factors have contributed to this paucity, including the biological complexity of addiction, regulatory challenges, and a historical lack of enthusiasm among pharmaceutical companies to commit resources to this disease space. Despite these headwinds, the recent opioid crisis has highlighted the devastating consequences of SUDs for both individuals and society, stimulating urgent efforts to identify novel treatment approaches. In addition, several neurobiological systems have been recently implicated in unique aspects of drug reward, opening the door to candidate medications with novel mechanisms of action. Here, we provide an overview of efforts to target several of these new systems, with a focus on those that are the subject of ongoing clinical trials as well as being areas of interest among the authors' research groups (MHJ, MTB, NAE). Specifically, we discuss new classes of medications targeting the serotonin 2A receptor (i.e., psychedelics), glucagon-like peptide 1 receptor, cannabidiol, dynorphin/kappa opioid receptor, orexin/hypocretin, and oxytocin receptor systems, as well as emergent approaches for modulating the more canonical dopaminergic system via agonist therapies for stimulant use disorders. Collectively, innovations in this space give reason for optimism for an improved therapeutic landscape for substance use disorders in the near future.

Cathodal Transcranial Direct Current Stimulation Does Not Change Implicit Associations Against Alcohol in Alcohol Use Disorder: A Preregistered Clinical Trial

Addictive behaviour is shaped by the dynamic interaction of implicit, bottom-up and explicit, top-down cognitive processes. In alcohol use disorder (AUD), implicit alcohol-related associations have been shown to predict increased subsequent alcohol consumption and are linked to the risk of relapse. Explicit cognitive processes, exerting prefrontal top-down control, are particularly significant during the critical period following the decision to abstain. This study aims to map implicit and explicit cognitive processes in recently abstinent individuals with AUD and to explore the effect of cathodal transcranial direct current stimulation (tDCS) on implicit associations by modulating top-down control. In this preregistered, double-blind, sham-controlled clinical trial, 30 abstinent individuals with AUD participated in two experimental sessions. They received either 2 mA cathodal tDCS to the left dorsolateral prefrontal cortex (dlPFC) or sham tDCS in a crossover design. During tDCS, participants completed the alcohol approach implicit association test (IAT) and the drinking identity IAT, along with two control tasks. Additionally, we collected explicit ratings of the IAT stimuli and assessed craving before and after each experimental session. Preregistered ANOVAs revealed significant implicit alcohol-avoidance and non-drinking identity biases. Cathodal tDCS did not modulate IAT scores. Explicit ratings showed a preference for non-alcoholic drinks and non-drinking identity, correlating moderately with IAT scores. Exploratory analyses indicated that cathodal tDCS mitigated the increase in nicotine craving during the experimental session. This preregistered clinical trial provides robust evidence that single-session cathodal tDCS to the left dorsolateral prefrontal cortex does not modulate implicit associations in AUD, with Bayesian analyses corroborating the absence of tDCS effects. Our results emphasize the impact of contextual factors on the interplay between explicit and implicit cognitive processes and underscore the importance of investigating multisession stimulation paradigms in future research.

A longitudinal study on the effect of aerobic exercise intervention on the inhibitory control in college students with internet addiction

Objectives

This study aimed to investigate the effects of aerobic exercise on reactive inhibitory control in college students with internet addiction, examining both behavioral and electrophysiological changes over time.

Methods

A longitudinal study design was adopted, involving 48 male college students with internet addiction who were randomly assigned to either a control group or an experimental group. Participants in the experimental group engaged in 40 min aerobic cycling sessions three times per week for 12 weeks, while the control group maintained their usual physical activity levels without any intervention. A 3 × 2 × 3 mixed-factorial design was utilized, incorporating three time points (pre-experiment, 6 and 12 weeks), two groups (control and experimental), and three electrode sites (Fz, F3, F4). This design enabled the examination of the effects of aerobic exercise on reactive inhibitory control and its temporal dynamics in college students with internet addiction.

Results

A significant main effect of group was observed. Specifically, the experimental group demonstrated a significantly higher Nogo accuracy rate compared to the control group at both the mid-test (P < 0.01) and post-test (P < 0.001). Within the experimental group, the Nogo accuracy rate at the mid-test and post-test was significantly higher than at the pre-test (P < 0.001), with the post-test accuracy rate also significantly higher than the mid-test (P < 0.05). Time-frequency analysis revealed that, under the Nogo task, the energy values in the beta frequency band during the early (100-500 ms) and late (600-750 ms) time windows were significantly higher at the mid-test and post-test compared to the pre-test (P < 0.05), with the post-test values significantly exceeding those at the mid-test (P < 0.05).

Conclusion

(1) Moderate-intensity aerobic exercise significantly improves reactive inhibitory control in college students with internet addiction, with the magnitude of improvement increasing over the duration of the intervention. (2) Increased beta band energy during the early (100-500 ms) and late (600-750 ms) time windows serve as a key neurophysiological indicator of this enhancement.

Candida albicans Colonization Modulates Murine Ethanol Consumption and Behavioral Responses Through Elevation of Serum Prostaglandin E2 and Impact on the Striatal Dopamine System

Candida albicans is a commensal yeast that is a common component of the gastrointestinal (GI) microbiome of humans. C. albicans has been shown to bloom in the GI tract of individuals with alcohol use disorder (AUD) and can promote and increase the severity of alcoholic liver disease (ALD). However, the effects of C. albicans blooms on the host in the context of AUD or AUD-related phenotypes, such as ethanol preference, have been unstudied. In this work, we report a reduction in ethanol consumption and preference in mice colonized with C. albicans. C. albicans-colonized mice exhibited elevated levels of serum PGE2 and reduced ethanol preference was reversed by injection with antagonists of PGE2 receptors. Further, injection of mice with a PGE2 derivative decreased their ethanol preference. These results show that PGE2 acting on its receptors EP1 and EP2 drives reduced ethanol preference in C. albicans-colonized mice. We also showed altered transcription of dopamine receptors in the dorsal striatum of C. albicans-colonized mice and more rapid acquisition of ethanol conditioned taste aversion, suggesting alterations to reinforcement or aversion learning. Finally, C. albicans-colonized mice were more susceptible to ethanol-induced motor coordination impairment showing significant alterations to the behavioral effects of ethanol. This study identifies a member of the fungal microbiome that alters ethanol preference and demonstrates a role for PGE2 signaling in these phenotypes.

Brain-wide mapping reveals temporal and sexually dimorphic opioid actions

While the molecular and cellular effects of opioids have been extensively studied, the precise mechanisms by which these drugs target specific brain regions over time remain unclear. Similarly, despite well-documented sex differences in opioid responses, the anatomical basis for this sexual dimorphism is not well characterized. To address these questions, we developed an automated, scalable, and unbiased approach for whole-brain anatomical mapping of the neuronal activity marker c-Fos in response to acute morphine exposure. Using ribbon scanning confocal microscopy, we imaged whole cleared brains from male and female wild-type mice at 1 hour and 4 hours post-morphine administration. Our whole-brain analysis of c-Fos expression revealed distinct patterns of morphine-induced regional brain activation across time and sex. Notably, we observed a greater number of structures with significant activity differences at 4 hours compared to 1 hour. In male mice, significant changes were primarily localized to regions within the dopamine system, whereas in female mice, they were concentrated in cortical regions. By combining high-throughput imaging with whole-brain expression analysis, particularly in the context of opioid actions, our approach provides a more comprehensive understanding of how drugs of abuse affect the brain.

Efficacy of Transcranial Direct Current Stimulation (tDCS) on Neuropsychiatric Symptoms in Substance Use Disorder (SUD)-A Review and Insights into Possible Mechanisms of Action

Introduction: Substance use disorder (SUD) is a significant global clinical issue marked by the excessive consumption of alcohol, nicotine, and various psychoactive substances, leading to impaired social, cognitive, and occupational functioning. Individuals with SUD frequently experience depression and anxiety disorders, which exacerbate their prognosis and contribute to substantial health and social burdens. The pathophysiology of SUD and its associated conditions is multifaceted, involving multiple dysfunctions in the brain. This complexity underscores an urgent need for the development of noninvasive treatments that can directly target the brain. One of them is transcranial direct current stimulation (tDCS), an intensively studied technique for safely modulating cortical excitability. The aim of this study is to investigate the effectiveness of tDCS in treating symptoms of depression and anxiety in SUD. Methods: With an emphasis on the underlying mechanisms of action, this mechanistic review investigates the effectiveness of tDCS in treating anxiety and depression in SUD patients. Literature searches were conducted using the PubMed/Medline, ResearchGate, Cochrane, and Google Scholar databases. Results: The review identified 12 relevant studies. The results showed that left dorsolateral prefrontal cortex (DLPFC) stimulation is an effective treatment option for depression in SUD. In anxiety disorders, left and right DLPFC stimulation is effective, with better results observed with right DLPFC stimulation. However, the included studies differed in their methodology, sample characteristics, and measurement methods, which could have influenced the final results of the analysis. The central focus of this mechanistic review is to discuss the potential mechanisms of action of tDCS in treating depression and anxiety in SUD. These mechanisms include the modulation of brain networks, a reduction in neuroinflammation, an enhancement in neuroplasticity, and an increase in P300 amplitude. We also discuss the limitations of the included studies and propose ways to address them in future research. Conclusions: This review provides evidence that tDCS is an effective treatment option for anxiety and depression in SUD. Stimulation of the left DLPFC reduces symptoms of depression, while stimulation of the right DLPFC reduces symptoms of anxiety. However, future research is required to confirm these findings and to deepen our understanding of the mechanisms through which tDCS exerts its effects in this context. Neuroimaging methods (fMRI and EEG) and blood tests could be particularly useful.

Remission from addiction: erasing the wrong circuits or making new ones?

Chronic relapse is a hallmark of substance-use disorders (SUDs), but many people with SUDs do recover and eventually enter remission. Many preclinical studies in this field aim to identify interventions that can precipitate recovery by reversing or erasing the neuronal circuit changes caused by chronic drug use. A better understanding of remission from SUDs can also come from preclinical studies that model factors known to influence recovery in humans, such as the negative consequences of drug use and positive environmental influences. In this Perspective we discuss human neuroimaging studies that have provided information about recovery from SUDs and highlight mechanisms identified in preclinical studies - such as the reconfiguration of neuronal circuits - that could contribute to remission. We also analyse how studies of memory and forgetting can provide insights into the mechanisms of remission. Overall, we propose that remission can be driven by the introduction of new neuronal changes (which outcompete those induced by drugs) as well as by the erasure of drug-induced changes.

Systematic review on resting-state fMRI in people with AUD and people who binge drink

Resting-state functional magnetic resonance imaging (rsfMRI) has become ubiquitous in neuroimaging to study disorders, including alcohol use disorder (AUD), given its potential to serve as a biomarker of psychiatric symptoms. The number of techniques, sample heterogeneity, and findings demand the assessment of results to identify potential biomarkers for the development of treatment. This systematic review aimed to synthesize the alcohol rsfMRI literature by summarizing the results by analysis approach and groups to examine these findings in the context of the neurobiology of addiction model. Three databases were systematically searched, resulting in the inclusion of 17 studies with a total of 784 participants (387 were people with AUD, 38 engaged in binge drinking, and 359 were controls). Seed-based functional connectivity studies were the most prominent. Compared to controls, people who binge drink and people with AUD showed greater connectivity of the Middle Frontal Gyrus-a region associated with the preoccupation/anticipation stage of the theory. Regions of the prefrontal and limbic cortex were most consistently reported in studies. The different types of analyses, sample size, and variability in the sample may have contributed to differences reported across studies. This review synthesizes and examines the results of different studies using the neurobiology of addiction theory, which may inform future studies on potential regions of interest, recruitment approaches, and analysis methods. Standardizing the methods for such a heterogeneous population could lead to more rapid development of neurobiologically-informed treatments for AUD.

Maternal cognitive functioning and psychopathology predict quality of parent-child relationship in the context of substance use disorder: A 15-month longitudinal study

This longitudinal study aimed to investigate the role of maternal cognitive functioning and psychopathology in parent-child relationship quality during residential treatment for mothers with Substance Use Disorder (SUD), in order to identify factors that may enhance or limit intervention effects.We assessed cognitive functioning (Esame Neuropsicologico Breve-2 [ENB-2]) and psychopathology (Symptom Checklist-90 Revised [SCL-90-R]) in 60 mothers diagnosed with SUD (Mage = 30.13 yrs; SD = 6.79) at treatment admission. Parent-child relationship quality was measured during free-play interactions using the Emotional Availability Scales every three months from admission (Child Mage = 17.17m; SD = 23.60) to the 15th month of the residential treatment.A main effect of maternal psychopathology and an interaction effect of time and cognitive functioning were found. More maternal psychopathology predicted lower mother-child relationship quality. Mothers with higher cognitive functioning presented a better treatment trajectory, with an increase in mother-child relationship quality, whereas mothers with lower cognitive functioning showed a decrease in relationship quality after initial improvement.These findings suggest that maternal psychopathology and cognitive functioning may influence the treatment of parent-child relationships in the context of SUD, although causality is not yet established. Implications for assessment and intervention are discussed.

What Chemsex does to the brain - neural correlates (ERP) regarding decision making, impulsivity and hypersexuality

Chemsex describes the use of specific substances (methamphetamine, GHB/GBL, mephedrone, ketamine) which initiate or enhance sexual experiences and is mainly prevalent among men who have sex with men. Many Chemsex users experience somatic complications (for example sexually transmitted diseases) and sometimes adverse sociological, psychological, and neurological symptoms, such as depression, impulse control disorders or hypersexuality. Changes in impulsivity and deficits in executive functions have demonstrated to be associated with addiction and impulse control disorders as well as frontal brain dysfunction and behavioral control deficits. This study aims to explore the effects of neurophysiological correlates of inhibition and decision making in Chemsex users with an EEG paradigm using event-related potentials (N2, P3). 15 Chemsex users and 14 matched control subjects, all of them men who have sex with man, participated in an auditory Go/NoGo/Voluntary Selection EEG paradigm. In addition, clinical data (e.g. regarding depression), demographic information as well as measures of well-being and sexual behavior were collected. The results demonstrated that clinical symptoms, hypersexuality, and sexual risk behavior were more pronounced in Chemsex users compared to non-users. P3 amplitudes did not differ significantly between groups. However, the Chemsex users showed decreased electrophysiological N2 responses in fronto-central brain regions during decision-making, indicating compromised executive function and inhibitory control. The observed impairments may lead to increased risk behavior regarding drug abuse and hypersexuality. Understanding the neurobiological mechanisms can contribute to targeted interventions in order to mitigate the negative consequences of engaging in Chemsex and improve general well-being.

Cognitive control in individuals with heroin use disorder after prolonged methadone maintenance treatment

BACKGROUND

Although impaired cognitive control is common during the acute detoxification phase of substance use disorders (SUD) and is considered a major cause of relapse, it remains unclear after prolonged methadone maintenance treatment (MMT). The aim of the present study was to elucidate cognitive control in individuals with heroin use disorder (HUD) after prolonged MMT and its association with previous relapse.

METHODS

A total of 63 HUD subjects (41 subjects with previous relapse and 22 non-relapse subjects, mean MMT duration: 12.24 ± 2.92 years) and 31 healthy controls were enrolled in this study. Eye tracking tasks, prospective memory tasks, the Behavior Rating Inventory of Executive Function-Adult Version (BRIEF-A) and the Prospective and Retrospective Memory Questionnaire (PRMQ) were used to assess cognitive control.

RESULTS

HUD individuals exhibited worse saccade error rate and executive dysfunction but showed no significant impairment in prospective memory. Additionally, the relapsers performed worse in terms of antisaccade amplitude and velocity at higher difficulty gradients (11° or 16°). Antisaccade performance in terms of amplitude and velocity was negatively correlated with executive function scores. Deficits in inhibition, cognitive flexibility, and self-monitoring were found to mediate the relationship between previous relapse and impaired antisaccade performance.

CONCLUSIONS

Even after prolonged MMT, HUD individuals still show partial impairments in cognitive control and antisaccade performance. Previous relapse exacerbates cognitive control deficits through executive dysfunction in inhibition, cognitive flexibility and self-monitoring, which can be screened by higher difficulty of antisaccade amplitude and velocity. More importantly, saccade error rate can reflect impaired inhibitory control in HUD individuals, whereas antisaccade amplitude and velocity appear to have potential diagnostic value for relapse.

Disruption of relapse to cocaine and morphine seeking by LiCl-induced aversive counterconditioning following memory retrieval

Substance use disorder is conceptualized as a form of maladaptive learning, whereby drug-associated memories, elicited by the presence of stimuli related to drug contexts or cues, contribute to the persistent recurrence of craving and the reinstatement of drug-seeking behavior. Hence, use of pharmacology or non-pharmacology way to disrupt drug-related memory holds promise to prevent relapse. Several studies have shown that memories can be unstable and susceptible to modification during the retrieval reactivation phase, termed the "reconsolidation time window". In this study, we use the classical conditioned place preference (CPP) model to investigate the role of aversive counterconditioning on drug-related memories during reconsolidation. Specifically, we uncovered that reconditioning drug cues through counterconditioning with LiCl-induced aversive outcomes following drug memory retrieval reduces subsequent drug-seeking behavior. Notably, the recall of cocaine- or morphine-CPP was eliminated when LiCl-induced aversive counterconditioning was performed 10 min, but not 6 h (outside the reconsolidation time window) after cocaine or morphine memory retrieval. In addition, the effect of LiCl-induced aversive counterconditioning could last for about 14 days. These results suggest that aversive counterconditioning during the reconsolidation of cocaine or morphine memory can prevent the re-seeking of cocaine or morphine, presumably by updating or replacing cocaine or morphine memories with aversive information.

Frontal White Matter Changes and Craving Recovery in Inpatients With Heroin Use Disorder

Importance

Amidst an unprecedented opioid epidemic, identifying neurobiological correlates of change with medication-assisted treatment of heroin use disorder is imperative. White matter impairments in individuals with heroin use disorder (HUD) have been associated with drug craving, a reliable predictor of treatment outcomes; however, little is known about structural connectivity changes with inpatient treatment and abstinence in individuals with HUD.

Objective

To assess white matter microstructure and associations with drug craving changes with inpatient treatment in individuals with HUD (effects of time and rescan compared with controls).

Design, Setting, and Participants

This cohort study conducted from December 2020 to September 2022 included individuals recruited from urban inpatient treatment facilities treating HUD and surrounding communities in New York City. Participants with HUD were receiving medication-assisted treatment. Data were analyzed from October 2022 to March 2023.

Intervention

Between scans, inpatient individuals with HUD continued treatment and related clinical interventions. Control participants were scanned at similar time intervals.

Main Outcomes and Measures

Changes in white matter diffusion metrics (fractional anisotropy and mean, axial, and radial diffusivities) assessed voxelwise with general linear models in addition to baseline and cue-induced drug craving, and other clinical outcome variables (mood, sleep, affect, perceived stress, and therapy attendance).

Results

Thirty-four individuals with HUD (mean [SD] age, 40.5 [11.0] years; 9 women [36%]; 3 Black [9%], 17 White [50%], 14 other race or ethnicity [41%]) and 25 control (mean [SD] age, 42.1 [9.0]; 7 women [21%]; 8 Black [32%], 10 White [40%], 7 other race or ethnicity [28%]) were included. Main voxelwise findings showed HUD-specific white matter microstructure changes (1 - P > .949), including increased fractional anisotropy and decreased mean and radial diffusivities, encompassing mostly frontal major callosal, projection, and association tracts. The increased fractional anisotropy (r = -0.72, P < .001, slope SE = 9.0 × 10-4) and decreased mean diffusivity (r = 0.69, P < .001, slope SE = 1.25 × 10-6) and/or radial diffusivity (r = 0.67, P < .001, slope SE = 1.16 × 10-6) in the genu and body of the corpus callosum and left anterior corona radiata in individuals with HUD correlated with a reduction in baseline craving (voxelwise 1 - P > .949). No other white matter correlations with outcome variables reached significance.

Conclusions and Relevance

This cohort study of inpatients with HUD on medication-assisted treatment found whole-brain normalization of structural connectivity in frontal white matter pathways implicated in emotional regulation and top-down executive control. Observed associations with decreases in baseline craving further support the possibility of recovery, highlighting the relevance of these white matter markers to a major symptom of addiction, with implications for clinical outcome monitoring.

Social context and drug cues modulate inhibitory control in cocaine addiction: involvement of the STN evidenced through functional MRI

Addictions often develop in a social context, although the influence of social factors did not receive much attention in the neuroscience of addiction. Recent animal studies suggest that peer presence can reduce cocaine intake, an influence potentially mediated, among others, by the subthalamic nucleus (STN). However, there is to date no neurobiological study investigating this mediation in humans. This study investigated the impact of social context and drug cues on brain correlates of inhibitory control in individuals with and without cocaine use disorder (CUD) using functional Magnetic Resonance Imaging (fMRI). Seventeen CUD participants and 17 healthy controls (HC) performed a novel fMRI "Social" Stop-Signal Task (SSST) in the presence or absence of an observer while being exposed to cocaine-related (vs. neutral) cues eliciting craving in drug users. The results showed that CUD participants, while slower at stopping with neutral cues, recovered control level stopping abilities with cocaine cues, while HC did not show any difference. During inhibition (Stop Correct vs Stop Incorrect), activity in the right STN, right inferior frontal gyrus (IFG), and bilateral orbitofrontal cortex (OFC) varied according to the type of cue. Notably, the presence of an observer reversed this effect in most areas for CUD participants. These findings highlight the impact of social context and drug cues on inhibitory control in CUD and the mediation of these effects by the right STN and bilateral OFC, emphasizing the importance of considering the social context in addiction research. They also comfort the STN as a potential addiction treatment target.

Effect of Transcranial Direct Current Stimulation on Craving, Cognitive Functions, and Serum Brain-Derived Neurotrophic Factor Level in Individuals on Maintenance Treatment for Opioid Use Disorder, A Randomized Sham-Controlled Trial

OBJECTIVES

To investigate the effects of transcranial direct current stimulation (tDCS) on brain-derived neurotrophic factor (BDNF) levels, craving, and executive functions in individuals on maintenance treatment for opioid use.

METHODS

We randomized 70 right-handed men aged 18-55 years into 2 groups: the intervention group and the sham group. The intervention was 10 sessions of 2 mA stimulation over 5 days. Each session in the sham group ended after 30 seconds. Craving was measured using the Desire for Drug Questionnaire (DDQ), Obsessive Compulsive Drug Use Scale (OCDUS), and visual analog scale (VAS). The measurements were taken before and after the intervention, as well as 2 months later. BDNF was measured before and after the intervention. Repeated-measures analysis of variance, the generalized estimating equation model, and independent t test were used for data analysis.

RESULTS

The mean differences (95% confidence intervals) in pre and post craving scores in the intervention group were (12.71 [9.10 to 16.32], P = 0.167) for VAS, (1.54 [1.12 to 1.96], P = 0.012) for OCDUS, and (1.71 [1.27 to 2.15], P = 0.125) for DDQ. These measures in the control group were -0.44 (-1.19 to 0.30), 0.01 (-0.21 to 0.23), and 0.126 (-0.11 to 0.36), respectively. BDNF serum levels significantly increased after the intervention (difference, 0.84 [0.69 to 0.99], P < 0.001); however, this change was not significant in the generalized estimating equation model. The effect of tDCS on craving was significant in OCDUS, but not significant in VAS and DDQ.

CONCLUSIONS

The tDCS reduces craving and improves executive functions in the short term. BDNF serum level was not associated with tDCS.

Distinct roles of excitatory and inhibitory neurons in the medial prefrontal cortex in the expression and reconsolidation of methamphetamine-associated memory in male mice

Methamphetamine, a commonly abused drug, is known for its high relapse rate. The persistence of addictive memories associated with methamphetamine poses a significant challenge in preventing relapse. Memory retrieval and subsequent reconsolidation provide an opportunity to disrupt addictive memories. However, the key node in the brain network involved in methamphetamine-associated memory retrieval has not been clearly defined. In this study, using the conditioned place preference in male mice, whole brain c-FOS mapping and functional connectivity analysis, together with chemogenetic manipulations of neural circuits, we identified the medial prefrontal cortex (mPFC) as a critical hub that integrates inputs from the retrosplenial cortex and the ventral tegmental area to support both the expression and reconsolidation of methamphetamine-associated memory during its retrieval. Surprisingly, with further cell-type specific analysis and manipulation, we also observed that methamphetamine-associated memory retrieval activated inhibitory neurons in the mPFC to facilitate memory reconsolidation, while suppressing excitatory neurons to aid memory expression. These findings provide novel insights into the neural circuits and cellular mechanisms involved in the retrieval process of addictive memories. They suggest that targeting the balance between excitation and inhibition in the mPFC during memory retrieval could be a promising treatment strategy to prevent relapse in methamphetamine addiction.

Differential gene expression and chromatin accessibility in the medial prefrontal cortex associated with individual differences in rat behavioral models of opioid use disorder

Opioid use disorder (OUD) is a neuropsychological disease that has a devastating impact on public health. Substantial individual differences in vulnerability exist, the neurobiological substrates of which remain unclear. To address this question, we investigated genome-wide gene transcription (RNA-seq) and chromatin accessibility (ATAC-seq) in the medial prefrontal cortex (mPFC) of male and female rats exhibiting differential vulnerability in behavioral paradigms modeling different phases of OUD: Withdrawal-Induced Anhedonia (WIA), Demand, and Reinstatement. Ingenuity Pathway Analysis (IPA) of RNA-seq revealed greater changes in canonical pathways in Resilient (vs. Saline) rats in comparison to Vulnerable (vs. Saline) rats across 3 paradigms, suggesting brain adaptations that might contribute to resilience to OUD across its trajectory. Analyses of gene networks and upstream regulators implicated processes involved in oligodendrocyte maturation and myelination in WIA, neuroinflammation in Demand, and metabolism in Reinstatement. Motif analysis of ATAC-seq showed changes in chromatin accessibility to a small set of transcription factor (TF) binding sites as a function either of opioid exposure (i.e., morphine versus saline) generally or of individual vulnerability specifically. Some of these were shared across the 3 paradigms and others were unique to each. In conclusion, we have identified changes in biological pathways, TFs, and their binding motifs that vary with paradigm and OUD vulnerability. These findings point to the involvement of distinct transcriptional and epigenetic mechanisms in response to opioid exposure, vulnerability to OUD, and different stages of the disorder.

Cognitive performance as a behavioral phenotype associated with cocaine self-administration in female and male socially housed monkeys

Considerable research has suggested that certain cognitive domains may contribute to cocaine misuse. However, there are gaps in the literature regarding whether cognitive performance before drug exposure predicts susceptibility to cocaine self-administration and how cognitive performance relates to future cocaine intake. Thus, the present study aimed to examine cognitive performance, as measured using automated CANTAB cognitive battery, prior to and following acquisition of cocaine self-administration under a concurrent drug vs. food choice procedure in female and male socially housed cynomolgus macaques. The cognitive battery consisted of measures of associative learning (stimulus and compound discrimination tasks), behavioral flexibility (intradimensional and extradimensional tasks), and behavioral inhibition (stimulus discrimination reversal, SDR, and extra-dimensional reversal tasks). After assessing cognitive performance, monkeys were trained to self-administer cocaine (saline, 0.01-0.1 mg/kg/injection) under a concurrent cocaine vs. food schedule of reinforcement. After a history of cocaine self-administration across 3-4 years, the cognitive battery was re-assessed and compared with sensitivity to cocaine reinforcement. Results showed drug-naïve monkeys that were less accurate on the SDR task, measuring behavioral inhibition, were more sensitive to cocaine reinforcement under the concurrent cocaine vs. food choice procedure. Furthermore, following chronic cocaine self-administration, cocaine intake was a negative predictor of accuracy on the SDR behavioral inhibition task. After cocaine maintenance, monkeys with higher cocaine intakes required more trials to complete the SDR behavioral inhibition task and made more incorrect responses during these trials. No sex or social rank differences were noted. Overall, these findings suggest that cognitive performance may influence vulnerability to cocaine misuse. Also, chronic cocaine may decrease levels of behavioral inhibition as measured via the SDR task in both females and males.

Assessment of rTMS treatment effects for methamphetamine addiction based on EEG functional connectivity

Methamphetamine (MA) addiction leads to impairment of neural communication functions in the brain, and functional connectivity (FC) may be a valid indicator. However, it is unclear how FC in the brain changes in methamphetamine use disorder (MUD) after treatment with repetitive transcranial magnetic stimulation (rTMS). Thirty-four patients with MUD participated in this study. The subjects were randomized to receive the active or sham rTMS for four weeks. Subjects performed electroencephalography (EEG) examinations and visual analogue scale (VAS) assessments before and after the treatment. The FC networks were constructed and visualized, and then the graph theory analysis was carried out. Finally, machine learning was used to classify FC networks before and after rTMS. The results showed that (1) the active group showed a significant enhancement in connectivity in the beta band; (2) the global efficiency, local efficiency, and aggregation coefficient of the active group in the beta band decreased significantly; (3) the LDA algorithm combined with the beta band FC matrix achieved an average accuracy of 82.5% in distinguishing before and after treatment. This study demonstrated that brain FC could effectively assess the therapeutic effect of rTMS, among which the beta band was the most sensitive and effective frequency band.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11571-024-10097-x.

Prefrontal-Limbic Circuitry Is Associated With Reward Sensitivity in Nonhuman Primates

BACKGROUND

Abnormal reward sensitivity is a risk factor for psychiatric disorders, including eating disorders such as overeating and binge-eating disorder, but the brain structural mechanisms that underlie it are not completely understood. Here, we sought to investigate the relationship between multimodal whole-brain structural features and reward sensitivity in nonhuman primates.

METHODS

Reward sensitivity was evaluated through behavioral economic analysis in which monkeys (adult rhesus macaques; 7 female, 5 male) responded for sweetened condensed milk (10%, 30%, 56%), Gatorade, or water using an operant procedure in which the response requirement increased incrementally across sessions (i.e., fixed ratio 1, 3, 10). Animals were divided into high (n = 6) or low (n = 6) reward sensitivity groups based on essential value for 30% milk. Multimodal magnetic resonance imaging was used to measure gray matter volume and white matter microstructure. Brain structural features were compared between groups, and their correlations with reward sensitivity for various stimuli was investigated.

RESULTS

Animals in the high sensitivity group had greater dorsolateral prefrontal cortex, centromedial amygdaloid complex, and middle cingulate cortex volumes than animals in the low sensitivity group. Furthermore, compared with monkeys in the low sensitivity group, high sensitivity monkeys had lower fractional anisotropy in the left dorsal cingulate bundle connecting the centromedial amygdaloid complex and middle cingulate cortex to the dorsolateral prefrontal cortex, and in the left superior longitudinal fasciculus 1 connecting the middle cingulate cortex to the dorsolateral prefrontal cortex.

CONCLUSIONS

These results suggest that neuroanatomical variation in prefrontal-limbic circuitry is associated with reward sensitivity. These brain structural features may serve as predictive biomarkers for vulnerability to food-based and other reward-related disorders.

S-nitrosoglutathione reductase alleviates morphine analgesic tolerance by restricting PKCα S-nitrosation

Morphine, a typical opiate, is widely used for controlling pain but can lead to various side effects with long-term use, including addiction, analgesic tolerance, and hyperalgesia. At present, however, the mechanisms underlying the development of morphine analgesic tolerance are not fully understood. This tolerance is influenced by various opioid receptor and kinase protein modifications, such as phosphorylation and ubiquitination. Here, we established a murine morphine tolerance model to investigate whether and how S-nitrosoglutathione reductase (GSNOR) is involved in morphine tolerance. Repeated administration of morphine resulted in the down-regulation of GSNOR, which increased excessive total protein S-nitrosation in the prefrontal cortex. Knockout or chemical inhibition of GSNOR promoted the development of morphine analgesic tolerance and neuron-specific overexpression of GSNOR alleviated morphine analgesic tolerance. Mechanistically, GSNOR deficiency enhanced S-nitrosation of cellular protein kinase alpha (PKCα) at the Cys78 and Cys132 sites, leading to inhibition of PKCα kinase activity, which ultimately promoted the development of morphine analgesic tolerance. Our study highlighted the significant role of GSNOR as a key regulator of PKCα S-nitrosation and its involvement in morphine analgesic tolerance, thus providing a potential therapeutic target for morphine tolerance.

Degradation of perineuronal nets in the medial prefrontal cortex promotes extinction and reduces reinstatement of methamphetamine-induced conditioned place preference in female mice

The high rate of relapse to compulsive methamphetamine (MA)-taking and seeking behaviors after abstinence constitutes a major obstacle to the treatment of MA addiction. Perineuronal nets (PNNs), essential components of the extracellular matrix, play a critical role in synaptic function, learning, and memory. Abnormalities in PNNs have been closely linked to a series of neurological diseases, such as addiction. However, the exact role of PNNs in MA-induced related behaviors remains elusive. Here, we established a MA-induced conditioned place preference (CPP) paradigm in female mice and found that the number and average optical density of PNNs increased significantly in the medial prefrontal cortex (mPFC) of mice during the acquisition, extinction, and reinstatement stages of CPP. Notably, the removal of PNNs in the mPFC via chondroitinase ABC (ChABC) before extinction training not only facilitated the extinction of MA-induced CPP and attenuated the relapse of extinguished MA preference but also significantly reduced the activation of c-Fos in the mPFC. Similarly, the ablation of PNNs in the mPFC before reinstatement markedly lessened the reinstatement of MA-induced CPP, which was accompanied by the decreased expression of c-Fos in the mPFC. Collectively, our results provide more evidence for the implication of degradation of PNNs in facilitating extinction and preventing relapse of MA-induced CPP, which indicate that targeting PNNs may be an effective therapeutic option for MA-induced CPP memories.

The Effect of Maternal High-Fat or High-Carbohydrate Diet during Pregnancy and Lactation on Cytochrome P450 2D (CYP2D) in the Liver and Brain of Rat Offspring

Cytochrome P450 2D (CYP2D) is important in psychopharmacology as it is engaged in the metabolism of drugs, neurosteroids and neurotransmitters. An unbalanced maternal diet during pregnancy and lactation can cause neurodevelopmental abnormalities and increases the offspring's predisposition to neuropsychiatric diseases. The aim of the present study was to evaluate the effect of maternal modified types of diet: a high-fat diet (HFD) and high-carbohydrate diet (HCD) during pregnancy and lactation on CYP2D in the liver and brain of male offspring at 28 (adolescent) or 63 postnatal days (young adult). The CYP2D activity and protein level were measured in the liver microsomes and the levels of mRNAs of CYP2D1, 2D2 and 2D4 were investigated both in the liver and brain. In the liver, both HFD and HCD increased the mRNA levels of all the three investigated CYP2D genes in adolescents, but an opposite effect was observed in young adults. The CYP2D protein level increased in adolescents but not in young adults. In contrast, young adults showed significantly decreased CYP2D activity. Similar effect of HFD on the CYP2D mRNAs was observed in the prefrontal cortex, while the effect of HCD was largely different than in the liver (the CYP2D2 expression was not affected, the CYP2D4 expression was decreased in young adults). In conclusion, modified maternal diets influence the expression of individual CYP2D1, CYP2D2 and CYP2D4 genes in the liver and brain of male offspring, which may affect the metabolism of CYP2D endogenous substrates and drugs and alter susceptibility to brain diseases and pharmacotherapy outcome.

Incubation of methamphetamine craving in punishment-resistant individuals is associated with activation of specific gene networks in the rat dorsal striatum

Methamphetamine use disorder (MUD) is characterized by loss of control over compulsive drug use. Here, we used a self-administration (SA) model to investigate transcriptional changes associated with the development of early and late compulsivity during contingent footshocks. Punishment initially separated methamphetamine taking rats into always shock-resistant (ASR) rats that continued active lever pressing and shock-sensitive (SS) rats that reduced their lever pressing. At the end of the punishment phase, rats underwent 15 days of forced abstinence at the end of which they were re-introduced to the SA paradigm followed by SA plus contingent shocks. Interestingly, 36 percent of the initial SS rats developed delayed shock-resistance (DSR). Of translational relevance, ASR rats showed more incubation of methamphetamine craving than DSR and always sensitive (AS) rats. RNA sequencing revealed increased striatal Rab37 and Dipk2b mRNA levels that correlated with incubation of methamphetamine craving. Interestingly, Bdnf mRNA levels showed HDAC2-dependent decreased expression in the AS rats. The present SA paradigm should help to elucidate the molecular substrates of early and late addiction-like behaviors.

Subjective and objective assessments of executive functions are independently predictive of aggressive tendencies in patients with substance use disorder

BACKGROUND AND AIMS

Impairments in executive functions have been found to influence violent behavior. Executive functions are crucial in the treatment of patients with substance use disorders because substance use generally impairs cognitive processes and is therefore detrimental for executive functions thereby reducing control of behavior and thus of consumption impulses. We studied correlations between subjective, i.e. self-report, and objective, i.e. behavior-based, assessment of executive functions and the predictive validity of these measures for aggression in patients with substance use disorder.

METHODS

The study included 64 patients with a diagnosed substance use disorder who were convicted according to the German Criminal Code for crimes they committed in the context of their disorder and were therefore in treatment in forensic psychiatric departments in Germany. Multiple self-report and behavior-based instruments were used to assess executive functions, appetitive and facilitative aggression as well as clinical and sociodemographic variables.

RESULTS

Participants showed impaired executive functions, and measures of executive functions predicted aggressive tendencies and violent offenses. Despite ecological validity of the findings, the subjective and objective assessments of executive functions did not correlate with each other, which corroborates studies in other clinical settings.

CONCLUSIONS

We discuss that this finding may be due to the conceptual differences between subjective and objective measures. Therefore, self-report and behavior-based measures should not be used as proxies of each other but as complementary measures that are useful for comprehensive diagnostics of cognitive impairments and assessment of risks for violent behavior.

Predictors of Readmission in Young Adults with First-Episode Psychosis: A Multicentric Retrospective Study with a 12-Month Follow-Up

BACKGROUND

A significant number of young individuals are readmitted one or more times shortly after their first episode of psychosis. Readmission may represent a marker of psychopathological vulnerability. Our primary aim was to evaluate the impact of clinical and socio-demographic variables on readmission at 12-month follow-up. Secondly, our goal was to determine whether the use of Long-Acting Injection (LAI) antipsychotics provides notable benefits compared to oral medications in preventing subsequent readmissions.

SUBJECTS AND METHODS

80 patients hospitalised for the first time with a diagnosis of psychotic disorder (ICD-10 criteria) were retrospectively assessed through clinical records. The mean age was 21.7 years. Patients were predominantly male (n = 62, 77.5%), and 55 subjects had at least 8 years of education. 50% of the sample was "NEET" (not in education, employment, or training).

RESULTS

35 patients (43.8%) were discharged with a LAI antipsychotic, while 45 (56.2%) recieved oral antipsychotic therapy. Substance use (p = 0.04) and oral antipsychotics at discharge (p = 0.003) were significantly associated with readmission at 1 year. We did not find any significant predictors of being discharged with LAI therapy.

CONCLUSION

Our findings underlined the importance of identifying patients at risk of readmission in order to prevent future rehospitalization and promote appropriate prevention strategies. LAIs should be considered as a first-choice treatment for patients hospitalised for FEP since they proved to be effective in preventing relapse.

FRONTAL WHITE MATTER CHANGES INDICATE RECOVERY WITH INPATIENT TREATMENT IN HEROIN ADDICTION

Importance

Amidst an unprecedented opioid epidemic, identifying neurobiological correlates of change with medication-assisted treatment of heroin use disorder is imperative. Distributed white matter (WM) impairments in individuals with heroin use disorder (iHUD) have been associated with increased drug craving, a reliable predictor of treatment outcomes. However, little is known about the extent of whole-brain structural connectivity changes with inpatient treatment and abstinence in iHUD.

Objective

To assess WM microstructure and associations with drug craving changes with inpatient treatment in iHUD (effects of time/re-scan compared to controls; CTL).

Design

Longitudinal cohort study (12/2020-09/2022) where iHUD and CTL underwent baseline magnetic resonance imaging (MRI#1) and follow-up (MRI#2) scans, (mean interval of 13.9 weeks in all participants combined).

Setting

The iHUD and CTL were recruited from urban inpatient treatment facilities and surrounding communities, respectively.

Participants

Thirty-four iHUD (42.1yo; 7 women), 25 age-/sex-matched CTL (40.5yo; 9 women).

Intervention

Between scans, inpatient iHUD continued their medically-assisted treatment and related clinical interventions. CTL participants were scanned at similar time intervals.

Main Outcomes and Measures

Changes in white matter diffusion metrics [fractional anisotropy (FA), mean (MD), axial (AD), and radial diffusivities (RD)] in addition to baseline and cue-induced drug craving, and other clinical outcome variables (mood, sleep, affect, perceived stress, and therapy attendance).

Results

Main findings showed HUD-specific WM microstructure changes encompassing mostly frontal major callosal, projection, and association tracts, characterized by increased FA (.949<1-p<.986) and decreased MD (.949<1-p<.997) and RD (.949<1-p<.999). The increased FA (r=-0.72, p<.00001) and decreased MD (r=0.69, p<.00001) and RD (r=0.67, p<.0001) in the genu and body of the corpus callosum and the left anterior corona radiata in iHUD were correlated with a reduction in baseline craving (.949<1-p<.999). No other WM correlations with outcome variables reached significance.

Conclusions and Relevance

Our findings suggest whole-brain normalization of structural connectivity with inpatient medically-assisted treatment in iHUD encompassing recovery in frontal WM pathways implicated in emotional regulation and top-down executive control. The association with decreases in baseline craving further supports the relevance of these WM markers to a major symptom in drug addiction, with implications for monitoring clinical outcomes.

Cognitive Alterations Associated with Remission and Alcohol Dependence Severity in Ethnically Diverse Patients of Siberia

Background

Impaired cognition in individuals with alcohol dependence may be associated with increased relapse risk. It has been recorded in more than half of patients during six months after treatment. In certain ethnic groups, for example, Tuvinians, the indigenous people of Siberia, relapses occur in extremely short periods of one to three months after treatment. An approach currently used to alcohol dependence treatment may be less effective for these patients.

Objective

The study aimed to investigate cognitive sequelae in indigenous Tuvinian patients with alcohol dependence.

Methods

The sample included 166 patients, 74 of indigenous ethnicity (Tuvinians) and 92 non-indigenous white patients. Data on inhibitory control, cognitive flexibility, attention, and working memory were collected from all the patients and processed using cluster analysis. The clustering data were then complemented by indicators of disorder dynamics, impulsivity, and emotion regulation.

Results

The clustering procedure revealed groups with severe cognitive sequelae. More than four-fold attention decrease was found in 43.5% of non-indigenous patients, and more impaired cognitive flexibility was revealed among 60.8% of indigenous patients. Groups with severe cognitive sequelae had higher impulsivity, maladaptive emotion regulation, more hospitalizations, faster disease progression, and shorter remissions. The latter was significantly reduced to 90 days on average in the severe group of indigenous patients versus 135 days of remission in the non-indigenous severe group.

Conclusion

Results obtained may advance tailored intervention in alcohol-dependent patients of the indigenous Tuvinian ethnicity. While little is still known about the alcohol dependence course and consequences in the indigenous Tuvinians of Siberia, this study contributes to the global mental health data on alcohol abuse and dependence in indigenous communities.

Examining a punishment-related brain circuit with miniature fluorescence microscopes and deep learning

In humans experiencing substance use disorder (SUD), abstinence from drug use is often motivated by a desire to avoid some undesirable consequence of further use: health effects, legal ramifications, etc. This process can be experimentally modeled in rodents by training and subsequently punishing an operant response in a context-induced reinstatement procedure. Understanding the biobehavioral mechanisms underlying punishment learning is critical to understanding both abstinence and relapse in individuals with SUD. To date, most investigations into the neural mechanisms of context-induced reinstatement following punishment have utilized discrete loss-of-function manipulations that do not capture ongoing changes in neural circuitry related to punishment-induced behavior change. Here, we describe a two-pronged approach to analyzing the biobehavioral mechanisms of punishment learning using miniature fluorescence microscopes and deep learning algorithms. We review recent advancements in both techniques and consider a target neural circuit.

Attention-deficit/hyperactivity disorder combined subtype exacerbates opioid use disorder consequences: Mediation by impulsive phenotypes

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is highly prevalent and associated with opioid use disorder (OUD). Yet, little is known about the mechanisms by which ADHD (which is a heterogeneous construct/diagnosis) might alter the trajectory of OUD outcomes in persons who use heroin.

AIM

We examined whether ADHD subtypes are related to heroin-use consequences and the extent to which the effects of ADHD on lifetime heroin-use consequences are mediated by two impulsivity factors that may be partly independent of ADHD: foreshortened time perspective and drug-use impulsivity.

METHODS

Individuals who reported regular heroin use (N=250) were screened using the Assessment of Hyperactivity and Attention (AHA), Impulsive Relapse Questionnaire (IRQ), Stanford Time Perception Inventory (STPI), and a comprehensive assessment of lifetime and current substance use and substance-related consequences. This secondary analysis examined whether ADHD or intermediate phenotypes predicted heroin-use consequences.

RESULTS

Relative to participants whose AHA scores indicated lifetime absence of ADHD (n=88), those with scores indicating persistent ADHD (childhood and adult, n=62) endorsed significantly more total lifetime heroin-use consequences despite comparable heroin-use severity. Likewise, there was a significant indirect effect of the combined ADHD subtype in childhood on lifetime heroin-use consequences. This effect was mediated by STPI scores indicating less future (and more hedonism in the present) temporal orientation and by IRQ scores indicating less capacity for delaying drug use.

CONCLUSION

The combined ADHD subtype is significantly associated with lifetime heroin-use consequences, and this effect is mediated through higher drug-use impulsivity (less capacity for delay) and lower future temporal orientation.

Structural Features Influencing the Bioactive Conformation of Angiotensin II and Angiotensin A: Relationship between Receptor Desensitization, Addiction, and the Blood-Brain Barrier

The N-terminal portion of the octapeptide angiotensin II (DRVYIHPF; AngII), a vasopressor peptide that favorably binds to, and activates, AngII type 1 receptor (AT1R), has an important role in maintaining bioactive conformation. It involves all three charged groups, namely (i) the N-terminal amino group cation, (ii) the Asp sidechain anion and (iii) the Arg guanidino cation. Neutralization of any one of these three charged groups results in a substantial reduction (<5%) in bioactivity, implicating a specialized function for this cluster. In contrast, angiotensin A (ARVYIHPF; AngA) has reduced bioactivity at AT1R; however, replacement of Asp in AngII with sarcosine (N-methyl-glycine) not only restores bioactivity but increases the activity of agonist, antagonist, and inverse agonist analogues. A bend produced at the N-terminus by the introduction of the secondary amino acid sarcosine is thought to realign the functional groups that chaperone the C-terminal portion of AngII, allowing transfer of the negative charge originating at the C-terminus to be transferred to the Tyr hydroxyl-forming tyrosinate anion, which is required to activate the receptor and desensitizes the receptor (tachyphylaxis). Peptide (sarilesin) and nonpeptide (sartans) moieties, which are long-acting inverse agonists, appear to desensitize the receptor by a mechanism analogous to tachyphylaxis. Sartans/bisartans were found to bind to alpha adrenergic receptors resulting in structure-dependent desensitization or resensitization. These considerations have provided information on the mechanisms of receptor desensitization/tolerance and insights into possible avenues for treating addiction. In this regard sartans, which appear to cross the blood-brain barrier more readily than bisartans, are the preferred drug candidates.

Sex-Dependent Differences in the Neural Correlates of Cocaine and Emotional Cue-Reactivity in Regular Cocaine Users and Non-Drug-Using Controls: Understanding the Role of Duration and Severity of Use

INTRODUCTION

The development of cocaine use disorder in females is suggested to be more strongly related to neural mechanisms underlying stress-reactivity, whereas in males it is suggested to be more strongly related to neural mechanisms underlying drug cue-reactivity. Existing evidence, however, is based on neuroimaging studies that either lack a control group and/or have very small sample sizes that do not allow to investigate sex differences.

METHODS

The main objective of the current study was to investigate sex differences in the neural correlates of cocaine and negative emotional cue-reactivity within high-risk intranasal cocaine users (CUs: 31 males and 26 females) and non-cocaine-using controls (non-CUs: 28 males and 26 females). A region of interest (ROI) analysis was applied to test for the main and interaction effects of group, sex, and stimulus type (cocaine cues vs. neutral cocaine cues and negative emotional cues vs. neutral emotional cues) on activity in the dorsal striatum, ventral striatum (VS), amygdala, and dorsal anterior cingulate cortex (dACC).

RESULTS

There were no significant sex or group differences in cocaine cue-reactivity in any of the ROIs. Results did reveal significant emotional cue-reactivity in the amygdala and VS, but these effects were not moderated by group or sex. Exploratory analyses demonstrated that emotional cue-induced activation of the dACC and VS was negatively associated with years of regular cocaine use in female CUs, while this relationship was absent in male CUs.

CONCLUSIONS

While speculative, the sex-specific associations between years of regular use and emotional cue-reactivity in the dACC and VS suggest that, with longer years of use, female CUs become less sensitive to aversive stimuli, including the negative consequences of cocaine use, which could account for the observed "telescoping effect" in female CUs.

No evidence for a reciprocal relationship between daily self-control failures and addictive behavior in a longitudinal study

Introduction

We all experience occasional self-control failures (SCFs) in our daily lives, where we enact behaviors that stand in conflict with our superordinate or long-term goals. Based on the assumption that SCFs share common underlying mechanisms with addictive disorders, we tested the hypothesis that a generally higher susceptibility to daily SCFs predicts more addictive behavior, or vice versa.

Methods

At baseline, 338 individuals (19-27 years, 59% female) from a community sample participated in multi-component assessments. These included among others (1) a clinical interview on addictive behaviors (quantity of use, frequency of use, DSM-5 criteria; n = 338) and (2) ecological momentary assessment of SCFs (n = 329, 97%). At the 3-year and 6 year follow-up, participation rates for both assessment parts were 71% (n = 240) and 50% (n = 170), respectively.

Results

Controlling for age, gender, IQ, and baseline addiction level, random-intercept cross-lagged panel models revealed that participants who reported more SCFs also showed pronounced addictive behavior at the between-person level, but we found no evidence of a predictive relationship at the within-person level over time.

Discussion

A higher rate of SCFs is associated with more addictive behavior, while there is no evidence of an intraindividual predictive relationship. Novel hypotheses suggested by additional exploratory results are that (1) only addiction-related SCFs in daily life are early markers of an escalation of use and thus for addictive disorders and that (2) an explicit monitoring of SCFs increases self-reflection and thereby promotes the mobilization of cognitive control in response to goal-desire conflicts.

The comparison of hot and cold executive functions in patients with bipolar II disorder, borderline personality disorder, and healthy individuals

Background

Differential diagnosis of bipolar II disorder (BD-II) and borderline personality disorder (BPD) has always been challenging for clinicians due to symptoms' overlap. This study aimed to compare hot and cold executive functions (EFs) in BD-II patients, as well as BPD and healthy controls (HCs), in order to differentiate these two disorders.

Methods

In the present study, 30 BD-II and 30 BPD patients undergoing the drug therapy with mood stabilizers, and 30 HC were examined using EFs evaluated tests. The data were then analyzed using ANOVA and Tukey post hoc test.

Results

The BD-II Patients performed significantly less in all cold EFs than the HC. Also, BPD patients had meaningfully lesser performance compared to HC in all cold EFs except sustained attention. No significant difference was perceived between the two patient groups in the cold EFs. In BD-II patients, the risky decision-making as a hot EFs' component was not significantly different from HC; nevertheless, its amount was significantly higher in BPD than in the HC and BD-II patients.

Conclusion

These findings underline the differences between the two mentioned disorders based on the hot EFs, which may indicate further disorder in the emotional information processing system among the BPD patients.

The perception of Mandarin speech conveying communicative functions in Chinese heroin addicts

Drug addiction can cause severe damage to the human brain, leading to significant problems in cognitive processing, such as irritability, speech distortions, and exaggeration of negative stimuli. Speech plays a fundamental role in social interaction, including both the production and perception. The ability to perceive communicative functions conveyed through speech is crucial for successful interpersonal communication and the maintaining good social relationships. However, due to the limited number of previous studies, it remains unclear whether the cognitive disorder caused by drug addiction affects the perception of communicative function conveyed in Mandarin speech. To address this question, we conducted a perception experiment involving sixty male participants, including 25 heroin addicts and 35 healthy controls. The experiment aimed to examine the perception of three communicative functions (i.e., statement, interrogative, and imperative) under three background noise conditions (i.e., no noise, SNR [Signal to Noise Ratio] = 10, and SNR = 0). Eight target sentences were first recorded by two native Mandarin speakers for each of the three communicative functions. Each half was then combined with Gaussian White Noise under two background noise conditions (i.e., SNR = 10 and SNR = 0). Finally, 48 speech stimuli were included in the experiment with four options provided for perceptual judgment. The results showed that, under the three noise conditions, the average perceptual accuracies of the three communicative functions were 80.66% and 38% for the control group and the heroin addicts, respectively. Significant differences were found in the perception of the three communicative functions between the control group and the heroin addicts under the three noise conditions, except for the recognition of imperative under strong noise condition (i.e., SNR = 0). Moreover, heroin addicts showed good accuracy (around 50%) in recognizing imperative and poor accuracy (i.e., lower than the chance level) in recognizing interrogative. This paper not only fills the research gap in the perception of communicative functions in Mandarin speech among drug addicts but also enhances the understanding of the effects of drugs on speech perception and provides a foundation for the speech rehabilitation of drug addicts.

Neurovascular effects of cocaine: relevance to addiction

Cocaine is a highly addictive drug, and its use is associated with adverse medical consequences such as cerebrovascular accidents that result in debilitating neurological complications. Indeed, brain imaging studies have reported severe reductions in cerebral blood flow (CBF) in cocaine misusers when compared to the brains of healthy non-drug using controls. Such CBF deficits are likely to disrupt neuro-vascular interaction and contribute to changes in brain function. This review aims to provide an overview of cocaine-induced CBF changes and its implication to brain function and to cocaine addiction, including its effects on tissue metabolism and neuronal activity. Finally, we discuss implications for future research, including targeted pharmacological interventions and neuromodulation to limit cocaine use and mitigate the negative impacts.

Conflict monitoring and emotional processing in 3,4-methylenedioxymethamphetamine (MDMA) and methamphetamine users - A comparative neurophysiological study

In stimulant use and addiction, conflict control processes are crucial for regulating substance use and sustaining abstinence, which can be particularly challenging in social-affective situations. Users of methamphetamine (METH, "Ice") and 3,4-methylenedioxymethamphetamine (MDMA, "Ecstasy") both experience impulse control deficits, but display different social-affective and addictive profiles. We thus aimed to compare the effects of chronic use of the substituted amphetamines METH and MDMA on conflict control processes in different social-affective contexts (i.e., anger and happiness) and investigate their underlying neurophysiological mechanisms. For this purpose, chronic but recently abstinent users of METH (n = 38) and MDMA (n = 42), as well as amphetamine-naïve healthy controls (n = 83) performed an emotional face-word Stroop paradigm, while event-related potentials (ERPs) were recorded. Instead of substance-specific differences, both MDMA and METH users showed smaller behavioral effects of cognitive-emotional conflict processing (independently of emotional valence) and selective deficits in emotional processing of anger content. Both effects were underpinned by stronger P3 ERP modulations suggesting that users of substituted amphetamines employ altered stimulus-response mapping and decision-making. Given that these processes are modulated by noradrenaline and that both MDMA and METH use may be associated with noradrenergic dysfunctions, the noradrenaline system may underlie the observed substance-related similarities. Better understanding the functional relevance of this currently still under-researched neurotransmitter and its functional changes in chronic users of substituted amphetamines is thus an important avenue for future research.

Neuropsychology of chronic back pain managed with long-term opioid use

Chronic pain is commonly treated with long-term opioids, but the neuropsychological outcomes associated with stable long-duration opioid use remain unclear. Here, we contrasted the psychological profiles, brain activity, and brain structure of 70 chronic back pain patients on opioids (CBP+O, average opioid exposure 6.2 years) with 70 patients managing their pain without opioids. CBP+O exhibited moderately worse psychological profiles and small differences in brain morphology. However, CBP+O had starkly different spontaneous brain activity, dominated by increased mesocorticolimbic and decreased dorsolateral-prefrontal activity, even after controlling for pain intensity and duration. These differences strongly reflected cortical opioid and serotonin receptor densities and mapped to two antagonistic resting-state circuits. The circuits' dynamics were explained by mesocorticolimbic activity and reflected negative affect. We reassessed a sub-group of CBP+O after they briefly abstained from taking opioids. Network dynamics, but not spontaneous activity, reflected exacerbated signs of withdrawal. Our results have implications for the management and tapering of opioids in chronic pain.

Chronic Voluntary Morphine Intake Is Associated with Changes in Brain Structures Involved in Drug Dependence in a Rat Model of Polydrug Use

Chronic opioid intake leads to several brain changes involved in the development of dependence, whereby an early hedonistic effect (liking) extends to the need to self-administer the drug (wanting), the latter being mostly a prefrontal-striatal function. The development of animal models for voluntary oral opioid intake represents an important tool for identifying the cellular and molecular alterations induced by chronic opioid use. Studies mainly in humans have shown that polydrug use and drug dependence are shared across various substances. We hypothesize that an animal bred for its alcohol preference would develop opioid dependence and further that this would be associated with the overt cortical abnormalities clinically described for opioid addicts. We show that Wistar-derived outbred UChB rats selected for their high alcohol preference additionally develop: (i) a preference for oral ingestion of morphine over water, resulting in morphine intake of 15 mg/kg/day; (ii) marked opioid dependence, as evidenced by the generation of strong withdrawal signs upon naloxone administration; (iii) prefrontal cortex alterations known to be associated with the loss of control over drug intake, namely, demyelination, axonal degeneration, and a reduction in glutamate transporter GLT-1 levels; and (iv) glial striatal neuroinflammation and brain oxidative stress, as previously reported for chronic alcohol and chronic nicotine use. These findings underline the relevance of polydrug animal models and their potential in the study of the wide spectrum of brain alterations induced by chronic morphine intake. This study should be valuable for future evaluations of therapeutic approaches for this devastating condition.

Linking drug and food addiction: an overview of the shared neural circuits and behavioral phenotype

Despite a lack of agreement on its definition and inclusion as a specific diagnosable disturbance, the food addiction construct is supported by several neurobiological and behavioral clinical and preclinical findings. Recognizing food addiction is critical to understanding how and why it manifests. In this overview, we focused on those as follows: 1. the hyperpalatable food effects in food addiction development; 2. specific brain regions involved in both food and drug addiction; and 3. animal models highlighting commonalities between substance use disorders and food addiction. Although results collected through animal studies emerged from protocols differing in several ways, they clearly highlight commonalities in behavioral manifestations and neurobiological alterations between substance use disorders and food addiction characteristics. To develop improved food addiction models, this heterogeneity should be acknowledged and embraced so that research can systematically investigate the role of specific variables in the development of the different behavioral features of addiction-like behavior in preclinical models.

Updated Perspectives on the Neurobiology of Substance Use Disorders Using Neuroimaging

Substance use problems impair social functioning, academic achievement, and employability. Psychological, biological, social, and environmental factors can contribute to substance use disorders. In recent years, neuroimaging breakthroughs have helped elucidate the mechanisms of substance misuse and its effects on the brain. Functional magnetic resonance imaging (MRI), positron emission tomography (PET), single-photon emission computed tomography (SPECT), and magnetic resonance spectroscopy (MRS) are all examples. Neuroimaging studies suggest substance misuse affects executive function, reward, memory, and stress systems. Recent neuroimaging research attempts have provided clinicians with improved tools to diagnose patients who misuse substances, comprehend the complicated neuroanatomy and neurobiology involved, and devise individually tailored and monitorable treatment regimens for individuals with substance use disorders. This review describes the most recent developments in drug misuse neuroimaging, including the neurobiology of substance use disorders, neuroimaging, and substance use disorders, established neuroimaging techniques, recent developments with established neuroimaging techniques and substance use disorders, and emerging clinical neuroimaging technology.

Combining noninvasive brain stimulation with behavioral pharmacology methods to study mechanisms of substance use disorder

Psychotropic drugs and transcranial magnetic stimulation (TMS) are effective for treating certain psychiatric conditions. Drugs and TMS have also been used as tools to explore the relationship between brain function and behavior in humans. Combining centrally acting drugs and TMS has proven useful for characterizing the neural basis of movement. This combined intervention approach also holds promise for improving our understanding of the mechanisms underlying disordered behavior associated with psychiatric conditions, including addiction, though challenges exist. For example, altered neocortical function has been implicated in substance use disorder, but the relationship between acute neuromodulation of neocortex with TMS and direct effects on addiction-related behaviors is not well established. We propose that the combination of human behavioral pharmacology methods with TMS can be leveraged to help establish these links. This perspective article describes an ongoing study that combines the administration of delta-9-tetrahydrocannabinol (THC), the main psychoactive compound in cannabis, with neuroimaging-guided TMS in individuals with problematic cannabis use. The study examines the impact of the left dorsolateral prefrontal cortex (DLPFC) stimulation on cognitive outcomes impacted by THC intoxication, including the subjective response to THC and the impairing effects of THC on behavioral performance. A framework for integrating TMS with human behavioral pharmacology methods, along with key details of the study design, are presented. We also discuss challenges, alternatives, and future directions.

Relationship between GABA-Ergic System and the Expression of Mephedrone-Induced Reward in Rats-Behavioral, Chromatographic and In Vivo Imaging Study

Mephedrone is a psychoactive drug that increases dopamine, serotonin and noradrenaline levels in the central nervous system via interaction with transporters or monoamines. The aim of the presented study was to assess the role of the GABA-ergic system in the expression of mephedrone-induced reward. For this purpose, we conducted (a) a behavioral evaluation of the impact of baclofen (a GABA_B receptors agonist) and GS39783 (a positive allosteric modulator of GABA_B receptors) on the expression of mephedrone-induced conditioned place preference (CPP) in rats, (b) an ex vivo chromatographic determination of the GABA level in the hippocampi of rats subchronically treated with mephedrone and (c) an in vivo evaluation of GABA hippocampal concentration in rats subchronically administered with mephedrone using magnetic resonance spectroscopy (MRS). The results show that GS39783 (but not baclofen) blocked the expression of CPP induced by (20 mg/kg of) mephedrone. The behavioral effect was consistent with chromatographic analysis, which showed that mephedrone (5 and 20 mg/kg) led to a decrease in GABA hippocampal concentration. Altogether, the presented study provides a new insight into the involvement of the GABA-ergic system in the rewarding effects of mephedrone, implying that those effects are at least partially mediated through GABA_B receptors, which suggests their potential role as new targets for the pharmacological management of mephedrone use disorder.

The Craving-Manager smartphone app designed to diagnose substance use/addictive disorders, and manage craving and individual predictors of relapse: a study protocol for a multicenter randomized controlled trial

Background

The rate of individuals with addiction who are currently treated are low, and this can be explained by barriers such as stigma, desire to cope alone, and difficulty to access treatment. These barriers could be overcome by mobile technologies. EMI (Ecological Momentary Intervention) is a treatment procedure characterized by the delivery of interventions (messages on smartphones) to people in their daily lives. EMI presents opportunities for treatments to be available to people during times and in situations when they are most needed. Craving is a strong predictor of relapse and a key target for addiction treatment. Studies using Ecological Momentary Assessment (EMA) method have revealed that, in daily life, person-specific cues could precipitate craving, that in turn, is associated with a higher probability to report substance use and relapse in the following hours. Assessment and management of these specific situations in daily life could help to decrease addictive use and avoid relapse. The Craving-Manager smartphone app has been designed to diagnose addictive disorders, and assess and manage craving as well as individual predictors of use/relapse. It delivers specific and individualized interventions (counseling messages) composed of evidence-based addiction treatments approaches (cognitive behavioral therapy and mindfulness). The Craving-Manager app can be used for any addiction (substance or behavior). The objective of this protocol is to evaluate the efficacy of the Craving-Manager app in decreasing use (of primary substance(s)/addictive behavior(s)) over 4 weeks, among individuals on a waiting list for outpatient addiction treatment.

Methods/design

This multicenter double-blind randomized controlled trial (RCT) will compare two parallel groups: experimental group (full interventional version of the app, 4 weeks, EMA + EMI), versus control group (restricted version of the app, 4 weeks, only EMA). Two hundred and seventy-four participants will be recruited in 6 addiction treatment centers in France.

Discussion

This RCT will provide indication on how the Craving-Manager app will reduce addictive use (e.g., better craving management, better stimulus control) in both substance and behavioral addictions. If its efficacy is confirmed, the app could offer the possibility of an easy to use and personalized intervention accessible to the greatest number of individuals with addiction.

Clinical Trial Registration

ClinicalTrials.gov: NCT04732676.

Computational models of behavioral addictions: State of the art and future directions

Non-pharmacological behavioral addictions, such as pathological gambling, videogaming, social networking, or internet use, are becoming major public health concerns. It is not yet clear how behavioral addictions could share many major neurobiological and behavioral characteristics with substance use disorders, despite the absence of direct pharmacological influences. A deeper understanding of the neurocognitive mechanisms of addictive behavior is needed, and computational modeling could be one promising approach to explain intricately entwined cognitive and neural dynamics. This review describes computational models of addiction based on reinforcement learning algorithms, Bayesian inference, and biophysical neural simulations. We discuss whether computational frameworks originally conceived to explain maladaptive behavior in substance use disorders can be effectively extended to non-substance-related behavioral addictions. Moreover, we introduce recent studies on behavioral addictions that exemplify the possibility of such extension and propose future directions.

Common and distinct fronto-striatal volumetric changes in heroin and cocaine use disorders

Different drugs of abuse impact the morphology of fronto-striatal dopaminergic targets in both common and unique ways. While dorsal striatal volume tracks with addiction severity across drug classes, opiates impact ventromedial prefrontal cortex (vmPFC) and nucleus accumbens (NAcc) neuroplasticity in preclinical models, and psychostimulants alter inhibitory control, rooted in cortical regions such as the inferior frontal gyrus (IFG). We hypothesized parallel grey matter volume changes associated with human heroin or cocaine use disorder: lower grey matter volume of vmPFC/NAcc in heroin use disorder and IFG in cocaine use disorder, and putamen grey matter volume to be associated with addiction severity measures (including craving) across both. In this cross-sectional study, we quantified grey matter volume (P < 0.05-corrected) in age/sex/IQ-matched individuals with heroin use disorder (n = 32, seven females), cocaine use disorder (n = 32, six females) and healthy controls (n = 32, six females) and compared fronto-striatal volume between groups using voxel-wise general linear models and non-parametric permutation-based tests. Overall, individuals with heroin use disorder had smaller vmPFC and NAcc/putamen volumes than healthy controls. Bilateral lower IFG grey matter volume patterns were specifically evident in cocaine versus heroin use disorders. Correlations between addiction severity measures and putamen grey matter volume did not reach nominal significance level in this sample. These results indicate alterations in dopamine-innervated regions (in the vmPFC and NAcc) in heroin addiction. For the first time we demonstrate lower IFG grey matter volume specifically in cocaine compared with heroin use disorder, suggesting a signature of reduced inhibitory control, which remains to be tested directly using select behavioural measures. Overall, results suggest substance-specific volumetric changes in human psychostimulant or opiate addiction, with implications for fine-tuning biomarker and treatment identification by primary drug of abuse.