Regionally specific gray matter volume is lower in alcohol use disorder: Implications for noninvasive brain stimulation treatment

Abstract

Background There is growing interest in neuromodulation‐based therapeutics as tools for individuals with alcohol use disorder (AUD). Through electromagnetic induction, techniques such as transcranial magnetic stimulation (TMS) can noninvasively depolarize cortical cells in the induced electrical field and monosynaptic afferents. The ability of TMS to modulate the brain is dependent upon two factors, which may be compromised in individuals with AUD: (1) gray matter volume (GMV) at the site of stimulation and (2) scalp‐to‐cortex (STC) distance. This study tested the hypotheses that these aspects of neural architecture are compromised in AUD patients, and thus AUD patients may need a higher TMS dose to depolarize the cortex. Methods High‐resolution magnetic resonance images were acquired from 44 individuals with AUD and 44 age‐matched healthy controls (n = 88). Whole‐brain voxel‐based morphometry was conducted. Subsequent region‐of‐interest analysis was performed at three EEG 10‐20 sites commonly used in TMS for AUD: FP1 (left frontal pole), F3 (left DLPFC), and C3 (left motor cortex). STC distance and TMS electric fields were assessed at these EEG sites. Results Individuals with AUD had significantly lower GMV in the bilateral orbitofrontal cortices, supramarginal gyri, and the left DLPFC (voxel‐threshold p < 0.05, cluster‐threshold p < 0.05) and within all 3 TMS target locations, F (1, 264) = 14.12, p = 0.0002. There was no significant difference in STC distance between the AUD and the healthy control group at any tested cortical location, F (3, 252) = 1.906, p = 0.129. Conclusions Individuals with AUD had significantly lower GMV in multiple areas of interest for TMS treatment; however, these volumetric reductions did not impact STC distance. Given previous studies that have shown TMS‐evoked changes in cortical and subcortical activity to be dependent on GMV, these data suggest that individuals with AUD may require higher doses of TMS to sufficiently modulate the neural circuits of interest.

DLPFC stimulation alters large-scale brain networks connectivity during a drug cue reactivity task: A tDCS-fMRI study

“…Electrode montage (including electrode position, size, and orientation) can affect electric field distribution patterns, and our results [in line with previous dose-response findings ( Kim et al, 2014 ; Kasten et al, 2019 )] suggest that the electric field distribution patterns are a relevant factor for modulating brain activity and corresponding physiological and behavioral effects like craving. Other methodological aspects (e.g., number of participants, number of active sessions, and duration of each session), drug dependency profiles (e.g., type of substance, duration of abstinence, and state of dependency), and brain structural alterations in regions associated with SUDs [e.g., different cortical morphology ( McCalley and Hanlon, 2021 ; Soleimani et al, 2021b )] may also affect stimulation outcomes in the field of addiction.…”

Are we really targeting and stimulating DLPFC by placing transcranial electrical stimulation (tES) electrodes over F3/F4?

“…For instance, previous studies showed that symmetric montages over DLPFC could diminish risk-taking behavior during a Balloon Analogue Risk Task (BART) [62,63], while asymmetric DLPFC stimulation shows no such effect [64]. Between montage difference in terms of peaks' strength only in the healthy group (not MUDs) suggest that generalization of the results obtained from EF distribution patterns fundamentally depends on the population of interest and highlights the importance of head modeling in tES protocol optimization in both individual and group levels [65,66].…”

“…Furthermore, since we did not consider age/sex-matched clinical population and because the imaging protocols were different between the two groups, we did not directly compare our results between MUDs and healthy subjects as conducted by [47]. Because it has been reported that EF distribution patterns in brain stimulation studies may be different in the field of addiction compared to healthy subjects with respect to the brain anatomical alterations [65,66] and because sex differences in skull thickness, for example, would lead to differences in peak EF location/value, comparing EF peaks between SUDs and healthy subjects in age and sex-matched case-control cohorts could be further investigated in future studies. For instance, our results showed that the center of averaged EF peak location is deeper in the brain of our clinical population compared to healthy subjects.…”

Targeting the Salience Network: A Mini-Review on a Novel Neuromodulation Approach for Treating Alcohol Use Disorder

“…This is of particular relevance in AUD, wherein alcohol is known to induce widespread cortical atrophy ( 112 ). That said, a recent study investigating the distance from the scalp to the cortex at the dlPFC and mPFC among a sample of individuals with AUD and healthy controls did not find a significant difference between the groups ( 113 ).…”

“… Proposed theoretical electrical field models ( 113 ). (A) Targeting dACC stimulation and (B) targeting AIns stimulation.…”