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

Effects of transcranial magnetic stimulation on cocaine addiction: A systematic review of randomized controlled trials

OBJECTIVE

While pharmacological strategies appear to be ineffective in treating long-term addiction, repetitive transcranial magnetic stimulation (rTMS) is emerging as a promising new tool for the attenuation of craving among multiple substance dependent populations.

METHOD

A systematic review of randomized controlled trials (RCTs) was conducted on the efficacy and tolerability of rTMS in treating cocaine use disorder (CUD). Relevant papers published in English through November 30th 2022 were identified, searching the electronic databases MEDLINE, Embase, PsycINFO and the Cochrane Library.

RESULTS

Eight studies matched inclusion criteria. The best findings were reported by the RCTs conducted at high-frequency (≥5 Hz) multiple sessions of rTMS delivered over the left dorsolateral prefrontal cortex (DLPFC): a significant decrease in self-reported cue-induced cocaine craving and lower cocaine craving scores and a considerable amelioration in the tendency to act rashly under extreme negative emotions (impulsivity) were found in the active group compared to controls.

CONCLUSION

Although still scant and heterogeneous, the strongest evidence so far on the use of rTMS on individuals with CUD support the high frequency stimulation over the left DLPFC as a well tolerated treatment of cocaine craving and impulsivity.

Local Brain Network Alterations and Olfactory Impairment in Alzheimer's Disease: An fMRI and Graph-Based Study

Alzheimer's disease (AD) is associated with the abnormal connection of functional networks. Olfactory impairment occurs in early AD; therefore, exploring alterations in olfactory-related regions is useful for early AD diagnosis. We combined the graph theory of local brain network topology with olfactory performance to analyze the differences in AD brain network characteristics. A total of 23 patients with AD and 18 normal controls were recruited for resting-state functional magnetic resonance imaging (fMRI), clinical neuropsychological examinations and the University of Pennsylvania Smell Identification Test (UPSIT). Between-group differences in the topological properties of the local network were compared. Pearson correlations were explored based on differential brain regions and olfactory performance. Statistical analysis revealed a correlation of the degree of cognitive impairment with olfactory recognition function. Local node topological properties were significantly altered in many local brain regions in the AD group. The nodal clustering coefficients of the bilateral temporal pole: middle temporal gyrus (TPOmid), degree centrality of the left insula (INS.L), degree centrality of the right middle temporal gyrus (MTG.R), and betweenness centrality of the left middle temporal gyrus (MTG.L) were related to olfactory performance. Alterations in local topological properties combined with the olfactory impairment can allow early identification of abnormal olfactory-related regions, facilitating early AD screening.

Identifying cerebral microstructural changes in patients with COVID-19 using MRI: A systematic review

Coronavirus disease 2019 (COVID-19) is an epidemic viral disease caused by a novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Despite the excessive number of neurological articles that have investigated the effect of COVID-19 on the brain from the neurological point of view, very few studies have investigated the impact of COVID-19 on the cerebral microstructure and function of the brain. The aim of this study was to summarize the results of the existing studies on cerebral microstructural changes in COVID-19 patients, specifically the use of quantitative volumetric analysis, blood oxygen level dependent (BOLD), and diffusion tensor imaging (DTI). We searched PubMed/MEDLINE, ScienceDirect, Semantic Scholar, and Google Scholar from December 2020 to April 2022. A well-constructed search strategy was used to identify the articles for review. Seven research articles have met this study's inclusion and exclusion criteria, which have applied neuroimaging tools such as quantitative volumetric analysis, BOLD, and DTI to investigate cerebral microstructure changes in COVID-19 patients. A significant effect of COVID-19 was found in the brain such as hypoperfusion of cerebral blood flow, increased gray matter (GM) volume, and reduced cortical thickness. The insula and thalamic radiation were the most frequent GM region and white matter tract, respectively, that are involved in SARS-CoV-2. COVID-19 was found to be associated with changes in cerebral microstructures. These abnormalities in brain areas might lead to be associated with behaviors, mental and neurological alterations that need to be considered carefully in future studies.

A review of functional brain differences predicting relapse in substance use disorder: Actionable targets for new methods of noninvasive brain stimulation

Neuroimaging studies have identified a variety of brain regions whose activity predicts substance use (i.e., relapse) in patients with substance use disorder (SUD), suggesting that malfunctioning brain networks may exacerbate relapse. However, this knowledge has not yet led to a marked improvement in treatment outcomes. Noninvasive brain stimulation (NIBS) has shown some potential for treating SUDs, and a new generation of NIBS technologies offers the possibility of selectively altering activity in both superficial and deep brain structures implicated in SUDs. The goal of the current review was to identify deeper brain structures involved in relapse to SUD and give an account of innovative methods of NIBS that might be used to target them. Included studies measured fMRI in currently abstinent SUD patients and tracked treatment outcomes, and fMRI results were organized with the framework of the Addictions Neuroclinical Assessment (ANA). Four brain structures were consistently implicated: the anterior and posterior cingulate cortices, ventral striatum and insula. These four deeper brain structures may be appropriate future targets for the treatment of SUD using these innovative NIBS technologies.

Data-driven study on resting-state functional magnetic resonance imaging during early abstinence of alcohol dependence in male patients and its predictive value for relapse

BACKGROUND

Alcohol dependence is a mental disorder with a high relapse rate. However, specific neuroimaging biomarkers have not been determined for alcohol dependence and its relapse. We conducted data-driven research to investigate resting-state functional magnetic resonance imaging (rs-fMRI) during early abstinence from alcohol dependence and its potential ability to predict relapse.

METHODS

Participants included 68 alcohol-dependent patients and 68 healthy controls (HCs). The regional homogeneity (ReHo) and fractional amplitude of low-frequency fluctuations (fALFF) were compared between the alcohol dependence group and the HCs and between the relapse group and the nonrelapse group. The brain regions that presented significantly different ReHo and/or fALFF between the alcohol-dependent patients and HCs and/or between the relapsed and nonrelapsed patients were selected as the seeds to calculate the functional connectivities (FCs).

RESULTS

During a 6-month follow-up period, 52.24% of alcohol-dependent patients relapsed. A regression model for differentiating alcohol-dependent patients and HCs showed that reductions in ReHo in the left postcentral region, fALFF in the right fusiform region, and FC in the right fusiform region to the right middle cingulum were independently associated with alcohol dependence, with an area under the receiver operating characteristic curve (AUC) of 0.841. The baseline FC of the left precentral to the left cerebellum of the relapse group was significantly lower than that of the nonrelapse group. The AUC of this FC to predict relapse was 0.774.

CONCLUSIONS

Our findings contribute to advancing research on the neurobiological etiology and predictive biomarkers for relapse associated with alcohol dependence.

Examining the Neurobiology of Non-Suicidal Self-Injury in Children and Adolescents: The Role of Reward Responsivity

Although prior work has shown heightened response to negative outcomes and reduced response to positive outcomes in youth with a history of non-suicidal self-injury (NSSI), little is known about the neural processes underlying these responses. Thus, this study examined associations between NSSI engagement and functional activation in specific regions of interest (ROIs) and whole-brain connectivity between striatal, frontal, and limbic region seeds during monetary and social reward tasks. To test for specificity of the influence of NSSI, analyses were conducted with and without depressive symptoms as a covariate. We found that NSSI was associated with decreased activation following monetary gains in all ROIs, even after controlling for depressive symptoms. Exploratory connectivity analyses found that NSSI was associated with differential connectivity between regions including the DS, vmPFC, insula, and parietal operculum cortex when controlling for depressive symptoms. Disrupted connectivity between these regions could suggest altered inhibitory control of emotions and pain processing in individuals with NSSI. Findings suggest dysfunctional reward processes in youth with NSSI, even very early in the course of the behavior.

Repetitive transcranial magnetic stimulation as a potential treatment approach for cannabis use disorder

The expanding legalization of cannabis across the United States is associated with increases in cannabis use, and accordingly, an increase in the number and severity of individuals with cannabis use disorder (CUD). The lack of FDA-approved pharmacotherapies and modest efficacy of psychotherapeutic interventions means that many of those who seek treatment for CUD relapse within the first few months. Consequently, there is a pressing need for innovative, evidence-based treatment development for CUD. Preliminary evidence suggests that repetitive transcranial magnetic stimulation (rTMS) may be a novel, non-invasive therapeutic neuromodulation tool for the treatment of a variety of substance use disorders (SUDs), including recently receiving FDA clearance (August 2020) for use as a smoking cessation aid in tobacco cigarette smokers. However, the potential of rTMS for CUD has not yet been reviewed. This paper provides a primer on therapeutic neuromodulation techniques for SUDs, with a particular focus on reviewing the current status of rTMS research in people who use cannabis. Lastly, future directions are proposed for rTMS treatment development in CUD, with suggestions for study design parameters and clinical endpoints based on current gold-standard practices for therapeutic neuromodulation research.

Transcranial magnetic stimulation and neuroimaging for cocaine use disorder: Review and future directions

Background: Cocaine use disorder (CUD) is a public health problem with limited treatment options and a significant relapse rate. Neuroimaging studies have identified abnormal functional connectivity in individuals with substance use disorders. Neuromodulation has been proposed to target this altered neurocircuitry. Combining TMS with neuroimaging has the potential to inform identification of biomarkers, diagnosis, and treatment.Objectives: We review the literature of transcranial magnetic stimulation (TMS) with neuroimaging for CUD and outline a research path forward whereby TMS can be used to identify brain network features as diagnostic or prognostic biomarkers for treatment.Methods: We reviewed the literature for primary research studies of TMS with neuroimaging for CUD. We searched PubMed using search terms of "cocaine," "transcranial magnetic stimulation," and "neuroimaging." Identified studies were screened by title and abstract. Full-text studies were reviewed for inclusion.Results: In our initial search, we identified 73 studies. Six studies met our inclusion criteria. These studies used rTMS (n = 3) and single or paired pulse TMS (n = 3) and included a total of 289 participants. All studies used fMRI as the neuroimaging modality. The most common outcome measure was craving and cue-reactivity (n = 3).Conclusion: The literature combining TMS with neuroimaging is small and heterogeneous. We propose that combining TMS with neuroimaging will accelerate our understanding of substance use disorder neurobiology and treatment. Once network biomarkers of substance use have been identified, TMS can be used to manipulate the dysfunctional circuits in order to identify a causal relationship between connectivity and psychopathology.

Caudothalamic dysfunction in drug-free suicidally depressed patients: an MEG study

Major depressive disorder (MDD), characterized by low mood or anhedonia, is commonly associated with a greater suicidal susceptibility. There are numerous suicide-related findings pertaining to the dorsolateral prefrontal cortex (DLPFC), caudate nucleus and thalamus, which form a cortico-striato-thalamo-cortical (CSTC) circuit responsible for executive function and working memory. An aberrant CSTC circuitry is hypothesized to be implicated in depressed patients with a high suicidal risk. 27 MDD patients were assessed with the Nurses Global Assessment of Suicide Risk (NGASR), following which 14 patients were classified into a high suicide risk group (NGASR ≥ 12) and 13 patients were assigned to a low suicide risk group (NGASR < 6). All 27 patients were enrolled with 25 healthy controls for resting-state magnetoencephalography (MEG). Cross-frequency coupling (CFC) measured the phase of alpha-band (8-13 Hz) as it modulated to cortical gamma-band (30-48 Hz). There was a significantly lower alpha-to-gamma phase-amplitude coupling (PAC) between the right caudate and left thalamus in high-risk suicide group compared to both the low-risk suicide group and healthy controls. The presence of a weaker coupling between the right caudate and left thalamus is indicative of a caudothalamic abnormality in suicidally depressed patients. This implies that a disruption of CSTC loop could result in executive dysfunction and working memory impairment, leading to an increased suicidal risk in MDD patients. In the future, this preliminary study has the possibility of being replicated on a larger scale, and hence validates caudothalamic dysfunction as a reliable neuroimaging biomarker for suicide in depression.

Oxytocin modulates alcohol-cue induced functional connectivity in the nucleus accumbens of social drinkers

The brain oxytocin system is involved in a wide range of addictive behaviors, inhibiting prime- and cue-induced relapse in preclinical models of substance use disorders. Especially the ability of oxytocin to modulate connectivity between the nucleus accumbens (NAc) and cortical regions has been identified as a factor likely to be critical to its effects on relapse. We thus investigated the effect of oxytocin on NAc functional connectivity during an alcohol cue-reactivity task. Thirteen male social drinkers participated in a randomized double-blind placebo-controlled cross-over functional magnetic resonance imaging (fMRI) alcohol cue-reactivity task with and without prior intranasal application of 24 IU oxytocin. Effects of oxytocin and functional connectivity during presentation of alcohol cues were assessed using ROI-to-ROI generalized psychophysiological interaction analyses. Oxytocin application significantly reduced NAc connectivity with the cuneus and thalamo-occipital connectivity, while enhancing connectivity between the paracingulate gyrus and precentral gyrus. This effect was specific to the alcohol presentation and was not found during processing of neutral pictures. In addition, the NAc-cuneus connectivity significantly correlated with alcohol cue-induced craving during the scanning session. For the first time, we could show that oxytocin selectively attenuates NAc connectivity during an alcohol cue-reactivity task which was related to changes in subjective craving for alcohol. This might reflect an attenuation of alcohol-cue saliency by oxytocin, which improves inhibitory control over craving and cue reactivity.

Effects of Non-invasive Brain Stimulation on Stimulant Craving in Users of Cocaine, Amphetamine, or Methamphetamine: A Systematic Review and Meta-Analysis

Dopamine system plays a pivotal role in specific kinds of substance use disorders (SUD, i. e., cocaine and methamphetamine use disorders). Many studies addressed whether dopamine-involved craving could be alleviated by non-invasive brain stimulation (NIBS) techniques. Nevertheless, the outcomes were highly inconsistent and the stimulating parameters were highly variable. In the current study, we ran a meta-analysis to identify an overall effect size of NIBS and try to find stimulating parameters of special note. We primarily find 2,530 unduplicated studies in PubMed, Psychology and Behavioral Sciences Collection, PsycARTICLES, PsycINFO, and Google Scholar database involving “Cocaine”/“Amphetamine”/“Methamphetamine” binded with “TMS”/“tDCS”/“non-invasive stimulation” in either field. After visual screening, 26 studies remained. While 16 studies were further excluded due to the lack of data, invalid craving scoring or the absence of sham condition. At last, 16 units of analysis in 12 eligible studies were coded and forwarded to a random-effect analysis. The results showed a large positive main effect of stimulation (Hedge's g = 1.116, CI = [0.597, 1.634]). Further subgroup analysis found that only high-frequency repetitive transcranial magnetic stimulation (rTMS) could elicit a significant decrease in craving, while the outcome of low-frequency stimulation was relatively controversial. Moreover, univariate meta regression revealed that the number of pulses per session could impose negative moderation toward the intervention. No significant moderation effect was found in types of abuse, overall days of stimulation and other variables of stimulating protocol. In conclusion, this meta-analysis offered a persuasive evidence for the feasibility of using NIBS to remit substance addictive behavior directly based on dopamine system. We also give clear methodological guidance that researchers are expected to use high-frequency, sufficiently segmented rTMS to improve the efficacy in future treatments.

Transcranial electrical and magnetic stimulation (tES and TMS) for addiction medicine: A consensus paper on the present state of the science and the road ahead

There is growing interest in non-invasive brain stimulation (NIBS) as a novel treatment option for substance-use disorders (SUDs). Recent momentum stems from a foundation of preclinical neuroscience demonstrating links between neural circuits and drug consuming behavior, as well as recent FDA-approval of NIBS treatments for mental health disorders that share overlapping pathology with SUDs. As with any emerging field, enthusiasm must be tempered by reason; lessons learned from the past should be prudently applied to future therapies. Here, an international ensemble of experts provides an overview of the state of transcranial-electrical (tES) and transcranial-magnetic (TMS) stimulation applied in SUDs. This consensus paper provides a systematic literature review on published data - emphasizing the heterogeneity of methods and outcome measures while suggesting strategies to help bridge knowledge gaps. The goal of this effort is to provide the community with guidelines for best practices in tES/TMS SUD research. We hope this will accelerate the speed at which the community translates basic neuroscience into advanced neuromodulation tools for clinical practice in addiction medicine.

Functional Neurocircuits and Neuroimaging Biomarkers of Tobacco Use Disorder

Drug abuse and addiction remain major public health issues, exemplified by the opioid epidemic currently devastating the United States. Treatment outcomes across substance use disorders remain unacceptably poor, wherein drug discovery/development for this multifaceted neuropsychiatric disorder focuses on single molecular-level targets. Rather, our opinion is that a systems-level neuroimaging perspective is crucial for identifying novel therapeutic targets, biomarkers to stratify patients, and individualized treatment strategies. Focusing on tobacco use disorder, we advocate a brain systems-level perspective linking two abuse-related facets (i.e., statelike withdrawal and traitlike addiction severity) with specific neurocircuitry (insula- and striatum-centered networks). To the extent that precise neurocircuits mediate distinct facets of abuse, treatment development must adopt not only a systems-level perspective, but also multi-intervention rather than mono-intervention practices.

Brain activity associated with social exclusion overlaps with drug-related frontal-striatal circuitry in cocaine users: A pilot study

Background

Exposure to various types of stress can elevate craving for cocaine and hasten relapse among substance dependent individuals. This investigation evaluated the effects of social exclusion on brain activity in cocaine dependent individuals.

Method

Forty three individuals (18 crack-cocaine users, 25 controls) were recruited from the community to participate in functional neuroimaging study in which they performed a simulated 3 person ball-tossing game (Cyberball). Each participant was told that the other 2 players were in nearby MRI scanners. Task blocks included: Inclusion (likelihood of our participant receiving the ball = 50%), Exclusion (likelihood gradually decreases to 0%), and Rest. Self-worth variables (e.g self-esteem, locus of control) were measured before and after the ball-tossing game. General linear model-based statistics were used to measure the brain response to inclusion and exclusion within and between the groups with respect to rest.

Results

Relative to controls, cocaine users had significantly more activity during Exclusion versus Inclusion in 3 areas: the right medial frontal gyrus (Brodmann Area 9,10), left ventral lateral frontal gyrus (Brodmann Area 10,47) and right caudate. This was driven by a higher response to social exclusion in the cocaine users. There was no difference between groups in the brain reactivity to social inclusion.

Conclusion

Cocaine dependent individuals have an amplified brain response to social exclusion stress in cortical regions associated with emotional regulation, arousal, craving and perception of physical pain. These data suggest that there may be a neurological basis for the well-established relationship between social stress and addiction.

Environmental, genetic and epigenetic contributions to cocaine addiction

Decades of research on cocaine has produced volumes of data that have answered many important questions about the nature of this highly addictive drug. Sadly, none of this information has translated into the development of effective therapies for the treatment of cocaine addiction. This review endeavors to assess the current state of cocaine research in an attempt to identify novel pathways for therapeutic development. For example, risk of cocaine addiction is highly heritable but genome-wide analyses comparing cocaine-dependent individuals to controls have not resulted in promising targets for drug development. Is this because the genetics of addiction is too complex or because the existing research methodologies are inadequate? Likewise, animal studies have revealed dozens of enduring changes in gene expression following prolonged exposure to cocaine, none of which have translated into therapeutics either because the resulting compounds were ineffective or produced intolerable side-effects. Recently, attention has focused on epigenetic modifications resulting from repeated cocaine intake, some of which appear to be heritable through changes in the germline. While epigenetic changes represent new vistas for therapeutic development, selective manipulation of epigenetic marks is currently challenging even in animals such that translational potential is a distant prospect. This review will reveal that despite the enormous progress made in understanding the molecular and physiological bases of cocaine addiction, there is much that remains a mystery. Continued advances in genetics and molecular biology hold potential for revealing multiple pathways toward the development of treatments for the continuing scourge of cocaine addiction.

Regional cerebral blood flow predictors of relapse and resilience in substance use recovery: A coordinate-based meta-analysis of human neuroimaging studies

BACKGROUND

Predicting relapse vulnerability can inform level-of-care and personalized substance use treatment. Few reliable predictors of relapse risk have been identified from traditional clinical, psychosocial, and demographic variables. However, recent neuroimaging findings highlight the potential prognostic import of brain-based signals, indexing the degree to which neural systems have been perturbed by addiction. These proposed "neuromarkers" forecast the likelihood, severity, and timing of relapse but the reliability and generalizability of such effects remains to be established.

METHODS

Activation likelihood estimation was used to conduct a preliminary quantitative, coordinate-based meta-analysis of the addiction neuroprediction literature; specifically, studies wherein baseline measures of regional cerebral blood flow were prospectively associated with substance use treatment outcomes. Consensus patterns of activation associated with relapse vulnerability (greater activation predicts poorer outcomes) versus resilience (greater activation predicts improved outcomes) were specifically investigated.

RESULTS

Twenty-four eligible studies yielded 134 foci, representing 923 subjects. Consensus activation was identified in right putamen and claustrum (p < .05, cluster-corrected) in relation to positive and negative treatment outcomes - likely reflecting variability in measurement context (e.g., task, sample characteristics) across datasets. A single cluster in rostral-ventral anterior cingulate cortex (rACC) was associated with relapse resilience, specifically (p < .05, cluster-corrected); no significant vulnerability-related clusters were identified.

CONCLUSIONS

Right putamen activation has been associated with relapse vulnerability and resilience, while increased baseline rACC activation has been consistently associated with improved treatment outcomes. Methodological heterogeneity within the existing literature, however, limits firm conclusions and future work will be necessary to confirm and clarify these results.

Rehabilitating the addicted brain with transcranial magnetic stimulation

Substance use disorders (SUDs) are one of the leading causes of morbidity and mortality worldwide. In spite of considerable advances in understanding the neural underpinnings of SUDs, therapeutic options remain limited. Recent studies have highlighted the potential of transcranial magnetic stimulation (TMS) as an innovative, safe and cost-effective treatment for some SUDs. Repetitive TMS (rTMS) influences neural activity in the short and long term by mechanisms involving neuroplasticity both locally, under the stimulating coil, and at the network level, throughout the brain. The long-term neurophysiological changes induced by rTMS have the potential to affect behaviours relating to drug craving, intake and relapse. Here, we review TMS mechanisms and evidence that rTMS is opening new avenues in addiction treatments.

Left frontal pole theta burst stimulation decreases orbitofrontal and insula activity in cocaine users and alcohol users

BACKGROUND

Preclinical research has demonstrated a causal relationship between medial prefrontal cortex activity and cocaine self-administration. As a step towards translating those data to a neural circuit-based intervention for patients, this study sought to determine if continuous theta burst stimulation (cTBS) to the left frontal pole (FP), would attenuate frontal-striatal activity in two substance-dependent populations.

METHODS

Forty-nine substance dependent individuals (25 cocaine, 24 alcohol) completed a single-blind, sham-controlled, crossover study wherein they received 6 trains of real or sham cTBS (110% resting motor threshold, FP1) each visit. Baseline evoked BOLD signal was measured immediately before and after real and sham cTBS (interleaved TMS/BOLD imaging: single pulses to left FP; scalp-to-cortex distance covariate, FWE correction p<0.05) RESULTS: Among cocaine users, real cTBS significantly decreased evoked BOLD signal in the caudate, accumbens, anterior cingulate, orbitofrontal (OFC) and parietal cortex relative to sham cTBS. Among alcohol users, real cTBS significantly decreased evoked BOLD signal in left OFC, insula, and lateral sensorimotor cortex. There was no significant difference between the groups.

CONCLUSIONS

These data suggest that 6 trains of left FP cTBS delivered in a single day decreases TMS-evoked BOLD signal in the OFC and several cortical nodes which regulate salience and are typically activated by drug cues. The reliability of this pattern across cocaine- and alcohol-dependent individuals suggests that cTBS may be an effective tool to dampen neural circuits typically engaged by salient drug cues. Multiday studies are required to determine it this has a sustainable effect on the brain or drug use behavior.

Reward Circuitry in Addiction

Understanding the brain circuitry that underlies reward is critical to improve treatment for many common health issues, including obesity, depression, and addiction. Here we focus on insights into the organization and function of reward circuitry and its synaptic and structural adaptations in response to cocaine exposure. While the importance of certain circuits, such as the mesocorticolimbic dopamine pathway, are well established in drug reward, recent studies using genetics-based tools have revealed functional changes throughout the reward circuitry that contribute to different facets of addiction, such as relapse and craving. The ability to observe and manipulate neuronal activity within specific cell types and circuits has led to new insight into not only the basic connections between brain regions, but also the molecular changes within these specific microcircuits, such as neurotrophic factor and GTPase signaling or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor function, that underlie synaptic and structural plasticity evoked by drugs of abuse. Excitingly, these insights from preclinical rodent work are now being translated into the clinic, where transcranial magnetic simulation and deep brain stimulation therapies are being piloted in human cocaine dependence. Thus, this review seeks to summarize current understanding of the major brain regions implicated in drug-related behaviors and the molecular mechanisms that contribute to altered connectivity between these regions, with the postulation that increased knowledge of the plasticity within the drug reward circuit will lead to new and improved treatments for addiction.