Converging Evidence for Frontopolar Cortex as a Target for Neuromodulation in Addiction Treatment

Neuroimmune regulation of the prefrontal cortex tetrapartite synapse

The prefrontal cortex (PFC) is an essential driver of cognitive, affective, and motivational behavior. There is clear evidence that the neuroimmune system directly influences PFC synapses, in addition to its role as the first line of defense against toxins and pathogens. In this review, we first describe the core structures that form the tetrapartite PFC synapse, focusing on the signaling microdomain created by astrocytic cradling of the synapse as well as the emerging role of the extracellular matrix in synaptic organization and plasticity. Neuroimmune signals (e.g. pro-inflammatory interleukin 1β) can impact the function of each core structure within the tetrapartite synapse, as well as promote intra-synaptic crosstalk, and we will provide an overview of recent advances in this field. Finally, evidence from post mortem human brain tissue and preclinical studies indicate that inflammation may be a key contributor to PFC dysfunction. Therefore, we conclude with a mechanistic discussion of neuroimmune-mediated maladaptive plasticity in neuropsychiatric disorders, with a focus on alcohol use disorder (AUD). Growing recognition of the neuroimmune system's role as a critical regulator of the PFC tetrapartite synapse provides strong support for targeting the neuroimmune system to develop new pharmacotherapeutics.

Memories or decisions? Bridging accounts of frontopolar function

Frontopolar cortex (FPC), for a long time elusive to functional description, is now associated with a wide range of cognitive processes. Prominent accounts of FPC function emerged from studies of memory (e.g., episodic and prospective memory; EM and PM, respectively) and of executive function (e.g., planning, multi-tasking, relational reasoning, cognitive branching, etc). In recent years, FPC function has begun to be described within the context of value-based decision making in terms of monitoring the value of alternatives and optimizing cognitive resources to balance the explore/exploit dilemma in the face of volatile environments. In this perspective, we propose that the broad counterfactual inference and behavioural flexibility account can help re-interpret findings from EM and PM studies and offer an explanatory bridge between the memory and executive function accounts. More specifically, we propose that counterfactual value monitoring in FPC modulates the reallocation of cognitive resources between present and past information and contributes to efficient episodic and prospective retrieval by concurrently assessing the value of competing memories in relation to the decision at hand and proactively evaluating future potential scenarios to anticipate optimal engagement of intentions.

Four dimensions of individualization in brain stimulation for psychiatric disorders: context, target, dose, and timing

Non-invasive Brain Stimulation (NIBS) technologies, including transcranial electrical (tES) and magnetic (TMS) stimulation, have emerged as promising interventions for various psychiatric disorders. FDA-approved TMS protocols in depression, OCD and nicotine use disorder provide a meaningful improvement. Treatment efficacy however remains inconsistent across individuals, and one relevant reason is intervention effect variability based on individual factors. There is a growing effort to develop individualized interventions, reinforced recently by FDA approval of a new TMS protocol that includes individualized fMRI-based targeting along with other modifications with higher reported effect size than previous "one size fits all" protocols. This paper discusses the dimensions for individualizing tES/TMS protocols to enhance therapeutic efficacy. We propose a multifaceted approach to personalizing NIBS, considering four levels: (1) context, (2) target, (3) dose, and (4) timing. By addressing inter- and intra-individual variability, we highlight a path toward precision medicine using individualized Brain Stimulation to treat psychiatric diseases. Despite challenges and limitations, this approach encourages broader and more systematic adoption of personalized Brain Stimulation techniques to improve clinical outcomes.

Theta Burst Stimulation in Patients With Methamphetamine Use Disorder: A Meta-Analysis and Systematic Review

Novel interventions are urgently needed to treat methamphetamine use disorder (MUD), for which there are no FDA-approved treatments. Previous studies in patients with MUD suggest transcranial magnetic stimulation (TMS) over the left dorsolateral prefrontal cortex (L. dlPFC) decreases craving for methamphetamine. Theta burst stimulation (TBS), which includes intermittent TBS and continuous TBS (cTBS), is increasingly being used for substance use disorders, including MUD. Previous reviews of TMS in MUD performed sub-group meta-analyses of studies that delivered TBS in MUD. However, these meta-analyses included studies with overlapping participant cohorts. Given the absence of prior meta-analyses or reviews examining TBS in MUD using unique participant cohorts, we reviewed randomized controlled trials (RCTs) from three databases (PubMed/Medline, EMBASE, Google Scholar) until September 1, 2024, comparing the impact of TBS versus sham TBS on cue-induced methamphetamine cravings in patients with MUD. We performed a meta-analysis with four eligible RCTs that delivered iTBS. Results suggest iTBS was more effective in reducing cue-induced methamphetamine cravings than sham iTBS (standardized mean difference [SMD] in change = 1.04; 95% CI [0.16, 1.92]). Our systematic review included two additional RCTs that did not have sham comparator arms; one of these demonstrated a significant reduction in methamphetamine craving with accelerated iTBS. Future studies should examine if iTBS can impact clinical outcome measures other than craving, such as methamphetamine use, by measuring return to drug use. It is also pertinent to explore accelerated iTBS and cTBS for MUD and study their effects on relevant biomarkers for MUD.

Targeting VMPFC-amygdala circuit with TMS in substance use disorder: A mechanistic framework

The ventromedial prefrontal cortex (VMPFC), located along the medial aspect of the frontal area, plays a critical role in regulating arousal/emotions. Its intricate connections with subcortical structures, including the striatum and amygdala, highlight the VMPFC's importance in the neurocircuitry of addiction. Due to these features, the VMPFC is considered a promising target for transcranial magnetic stimulation (TMS) in substance use disorders (SUD). By the end of 2023, all 21 studies targeting VMPFC for SUD used anatomical landmarks (e.g., Fp1/Fp2 in the EEG system) to define coil location with a fixed orientation. Nevertheless, one-size-fits-all TMS over VMPFC has yielded variable outcomes. Here, we suggested a pipeline based on a tailored TMS targeting framework aimed at optimally modulating the VMPFC-amygdala circuit on an individual basis. We collected MRI data from 60 participants with methamphetamine use disorders (MUDs). We examined the variability in TMS target location based on task-based functional connectivity between VMPFC and amygdala using psychophysiological interaction (PPI) analysis. Electric fields (EF) were calculated for fixed vs. optimized location (Fp1/Fp2 vs. individualized maximal PPI), orientation (AF7/AF8 vs. optimized algorithm) and intensity (constant vs. adjusted) to maximize target engagement. In our pipeline, the left medial amygdala, identified as the brain region with the highest (0.31 ± 0.29) fMRI drug cue reactivity, was selected as the subcortical seed region. The voxel with the most positive amygdala-VMPFC PPI connectivity in each participant was considered the individualized TMS target (MNI-coordinates: [12.6, 64.23, -0.8] ± [13.64, 3.50, 11.01]). This individualized VMPFC-amygdala connectivity significantly correlated with VAS craving after cue exposure (R = 0.27, p = 0.03). Coil orientation was optimized to increase EF strength over the targeted circuit (0.99 ± 0.21 V/m vs. the fixed approach: Fp1: 0.56 ± 0.22 and Fp2: 0.78 ± 0.25 V/m) and TMS intensity was harmonized across the population. This study highlights the potential of an individualized VMPFC targeting framework to enhance treatment outcomes for addiction, specifically modulating the personalized VMPFC-amygdala circuit.

A Randomized Controlled Trial of Medial Prefrontal Cortex Theta Burst Stimulation for Cocaine Use Disorder: A Three-Month Feasibility and Brain Target-Engagement Study

BACKGROUND

Cue-induced craving precipitates relapse in drug and alcohol use disorders. Theta burst stimulation (TBS) to the left frontal pole of the medial prefrontal cortex (MPFC) has previously been shown to reduce drinking and brain reactivity to alcohol cues. This randomized, double-blind, sham-controlled target-engagement study aimed to assess whether TBS has similar effects in individuals with cocaine use disorder (CUD).

METHODS

Thirty-three participants in intensive outpatient treatment received either real or sham TBS over 10 sessions across 3 weeks (36,000 pulses total; continuous TBS, 110% resting motor threshold, 3600 pulses/session). TBS was administered on days of behavioral counseling. Twenty-five individuals completed all 10 TBS sessions. Brain reactivity to cocaine cues was measured using fMRI at baseline, 1-month, 2-months, and 3-months.

RESULTS

Cocaine abstinence during the 3-month follow-up period was greater in the real TBS group (1-month: 92.0%, 2-month: 100.0%, 3-month: 85.0%) compared to sham (1-month: 66.6%, 2-month: 66.6%, 3-month: 66.6%), though not statistically significant [1-month: 6.00, p=0.14; 2-month OR=:14.30, p=0.09, and 3-month OR=2.75, p=0.30]. However, there was a significant effect on cocaine cue reactivity (treatment effect: F1,365= 8.92, p=0.003; time*treatment interaction: F3,365=12.88, p<0.001). Real TBS reduced cocaine cue reactivity in the MPFC (F3,72=5.46, p=0.02) overall, and in the anterior cingulate (F3,72=3.03, p=0.04), and insula (F3,72=3.60, p=0.02).

CONCLUSIONS

This early-stage trial demonstrates TBS to the MPFC reduces brain reactivity to cocaine cues in key nodes of the Salience Network in treatment-seeking cocaine users. Future, well-powered trials are warranted to evaluate clinical efficacy outcomes.

Transcranial magnetic stimulation for the rehabilitation of patients with addiction: current status and future prospects

INTRODUCTION

Substance use disorders (SUDs) are severe conditions that remain extremely challenging to treat in clinical practice. With high rates of non-response to current treatment options and several SUDs with no approved interventions, novel therapies are needed. Repetitive transcranial magnetic stimulation (rTMS) can non-invasively modulate the neurocircuitry of brain-based disorders, and investigation into its therapeutic potential for SUDs is growing rapidly.

AREAS COVERED

In this review, we summarize the clinical research to date evaluating its safety and efficacy for various SUDs. We highlight the investigations comparing different stimulation parameters to present our current understanding on optimal stimulation parameters. Additionally, we cover key research avenues in the use of neuroimaging to guide treatment, cue-induction paradigms, and adjunctive or combination treatments that may optimize outcomes.

EXPERT OPINION

Evidence of rTMS as an effective treatment for certain SUDs has emerged and is preliminary for others. There are a growing number of studies showing benefit and meta-analyses suggesting that rTMS can significantly reduce substance craving and consumption. However, the optimal approach has not been determined, and there is a great deal of heterogeneity in rTMS protocols and mixed outcomes. Further research into strategies for enhancing precision will be crucial in moving the field forward.

Modulation of Alcohol Use Disorder by Brain Stimulation

Currently available therapeutic modalities for alcohol use disorder (AUD) produce limited effect sizes or long-term compliance. Recent methods that were developed to modulate brain activity represent potential novel treatment options. Various methods of brain stimulation, when applied repeatedly, can induce long-term neurobiological, behavioral, and cognitive modifications. Recent studies in alcoholic subjects indicate the potential of brain stimulation methods to reduce alcohol craving, consumption, and relapse. Specifically, deep brain stimulation (DBS) of the nucleus accumbens or non-surgical stimulation of the dorsolateral prefrontal cortex (PFC) or medial PFC and anterior cingulate cortex using transcranial magnetic stimulation (TMS) has shown clinical benefit. However, further preclinical and clinical research is needed to establish understanding of mechanisms and the treatment protocols of brain stimulation for AUD. While efforts to design comparable apparatus in rodents continue, preclinical studies can be used to examine targets for DBS protocols, or to administer temporal patterns of pulsus similar to those used for TMS, to more superficial targets through implanted electrodes. The clinical field will benefit from studies with larger sample sizes, higher numbers of stimulation sessions, maintenance sessions, and long follow-up periods. The effect of symptoms provocation before and during stimulation should be further studied. Larger studies may have the power to explore predictive factors for the clinical outcome and thereby to optimize patient selection and eventually even develop personalization of the stimulation parameters.

From compulsivity to compulsion: the neural basis of compulsive disorders

Compulsive behaviour, an apparently irrational perseveration in often maladaptive acts, is a potential transdiagnostic symptom of several neuropsychiatric disorders, including obsessive-compulsive disorder and addiction, and may reflect the severe manifestation of a dimensional trait termed compulsivity. In this Review, we examine the psychological basis of compulsions and compulsivity and their underlying neural circuitry using evidence from human neuroimaging and animal models. Several main elements of this circuitry are identified, focused on fronto-striatal systems implicated in goal-directed behaviour and habits. These systems include the orbitofrontal, prefrontal, anterior cingulate and insular cortices and their connections with the basal ganglia as well as sensoriomotor and parietal cortices and cerebellum. We also consider the implications for future classification of impulsive-compulsive disorders and their treatment.