The effect of non-invasive brain stimulation on executive functioning in healthy controls: A systematic review and meta-analysis

A structured framework for emotion-cognition dynamics: Implications for assessment and intervention

This paper presents a novel framework for understanding the interaction between cognitive and emotional processes, recognizing the complex and dynamic relationship between these two constructs. The framework categorizes cognitive functions into four distinct categories: Cold Cognition, Hot Cognition, Warm Cognition, and Cool Cognition. By distinguishing between the style of processing (intuitive vs. analytical) and the content of information (emotional vs. non-emotional), the framework provides a model for both assessment and intervention. For assessment, it helps categorize cognitive and emotional processes, enabling targeted evaluations based on specific processing styles and content. For interventions, it supports the development of training programs that address processing styles in relation to the target function, improving the effectiveness of therapeutic and developmental strategies. Overall, this framework has the potential to advance both theoretical understanding and practical applications in cognitive and emotional assessment and training.

Affective state-dependent effects of prefrontal rTMS on the cognitive control of negative stimuli in healthy and depressed individuals

INTRODUCTION

High-frequency repetitive transcranial magnetic stimulation (HF-rTMS) targeting the left dorsolateral prefrontal cortex (lDLPFC) is an established, clinically effective treatment for major depressive disorder (MDD). However, evidence of the cognitive effects of lDLPFC HF-rTMS, especially those cognitive functions affected by MDD, is mixed.

METHODS

We here assessed the cognitive effects of a single, offline, 10Hz rTMS session on task performance in an emotional faces N-back (EFNBACK) task, in both healthy and depressed individuals. We measured response times, accuracy, and sensitivity, in a sham-controlled, pre-post design. Importantly, using the Beck Depression Inventory (BDI-II), we assessed whether the cognitive effects of the stimulation are state-dependent on trait-state depression.

RESULTS

We found lDLPFC HF-rTMS enhanced cognitive control over angry distractors. More importantly, these cognitive control effects were state-dependent on trait-state depression. HF-rTMS produced distinct performance changes dependent on baseline BDI-II scores. As a function of BDI-II scores, we observed either increased or decreased response times on the task. Further, we observed improved accuracy and sensitivity only on angry distractor trials as BDI-II scores increased, as a consequence of lDLPFC stimulation.

CONCLUSION

These results underscore the role of HF-rTMS in enhancing executive control over negative emotional information by modulating lDLPFC, with effects varying according to depression state at the moment of the treatment session. HF-rTMS thus not only enhances inhibitory control over emotional stimuli but also exhibits such cognitive effects contingent on depressive state, contributing to our understanding of the state-dependence of therapeutic rTMS.

The effects of intermittent theta burst stimulation (iTBS) on resting-state brain entropy (BEN)

Intermittent theta burst stimulation (iTBS), a novel protocol within repetitive transcranial magnetic stimulation (rTMS), has shown superior therapeutic effects for depression compared to conventional high-frequency rTMS (HF-rTMS). However, the neural mechanisms underlying iTBS remain poorly understood. Brain entropy (BEN), a measure of the irregularity of brain activity, has recently emerged as a promising marker for regional brain function and has demonstrated sensitivity to depression and HF-rTMS. Given its potential, BEN may help elucidate the mechanisms of iTBS. In this study, we computed BEN using resting-state fMRI data from sixteen healthy participants obtained from OpenNeuro. Participants underwent iTBS over the left dorsolateral prefrontal cortex (L-DLPFC) at two different intensities (90 ​% and 120 ​% of resting motor threshold (rMT)) on separate days. We used a 2 ​× ​2 repeated measures analysis of variance (ANOVA) to analyze the interaction between iTBS stimulation intensity and the pre- vs. post-stimulation effects on BEN and paired sample t-tests to examine the specific BEN effects of iTBS at different intensities. Additionally, spatial correlation analysis was conducted to determine whether iTBS altered the baseline coupling between BEN and neurotransmitter receptors/transporters, to investigate potential neurotransmitter changes induced by iTBS. Our results indicate that subthreshold iTBS (90 ​% rMT) reduced striatal BEN, while suprathreshold iTBS (120 ​% rMT) increased it. Subthreshold iTBS led to changes in the baseline coupling between BEN and several neurotransmitter receptor/transporter maps, primarily involving serotonin (5-HT), cannabinoid (CB), acetylcholine (ACh), and glutamate (Glu). Our findings suggest that BEN is sensitive to the effects of iTBS, with different stimulation intensities having distinct effects on neural activity. Notably, subthreshold iTBS may offer more effective stimulation. This research highlights the crucial role of stimulation intensity in modulating brain activity and lays the groundwork for future clinical studies focused on optimizing therapeutic outcomes through precise stimulation intensity.

Enhancing Equanimity With Noninvasive Brain Stimulation: A Novel Framework for Mindfulness Interventions

Mindfulness has gained widespread recognition for its benefits for mental health, cognitive performance, and well-being. However, the multifaceted nature of mindfulness, which encompasses elements such as attentional focus, emotional regulation, and present-moment awareness, complicates its definition and measurement. A key component that may underlie its broad benefits is equanimity-the ability to maintain an open and nonreactive attitude toward all sensory experiences. Empirical research suggests that mindfulness works through a combination of top-down attentional control and bottom-up sensory and emotional processes and that equanimity's role in regulating those bottom-up processes drives the psychological and physiological benefits, making it a promising target for both theoretical and practical exploration. Given these findings, the development of interventions that specifically augment equanimity could improve the impact of mindfulness practices. Research into noninvasive brain stimulation (NIBS) suggests that it is a potential tool for altering neural circuits involved in mindfulness. However, most NIBS studies reported to date have focused on improving cognitive control systems and have left equanimity relatively unexplored. Preliminary findings from focused ultrasound interventions targeting the posterior cingulate cortex suggest that NIBS can directly facilitate equanimity by inhibiting self-referential processing in the default mode network to promote a more present-centered state of awareness. Future research should prioritize the integration of NIBS with well-defined mindfulness training protocols, focusing on equanimity as a core target. This approach could provide a novel framework for advancing both contemplative neuroscience and clinical applications, offering new insights into the mechanisms of mindfulness and refining NIBS methodologies to support individualized, precision wellness interventions.

Transcranial Direct Current Stimulation of the Dorsolateral Prefrontal Cortex Modulates Voluntary Task-order Coordination in Dual-task Situations

Dual tasks (DTs) require additional control processes that temporally coordinate the processing of the two component tasks. Previous studies employing imaging as well as noninvasive stimulation techniques have demonstrated that the dorsolateral prefrontal cortex (dlPFC) is causally involved in these task-order coordination processes. However, in these studies, participants were instructed to match their processing order to an externally provided and mandatory order criterion during DT processing. Hence, it is still unknown whether the dlPFC is also recruited for rather voluntary order control processes, which are required in situations that allow for intentional and internally generated order choices. To address this issue, in two experiments, we applied anodal (Experiment 1) and cathodal (Experiment 2) transcranial direct current stimulation during a random-order DT in which participants could freely decide about their order of task processing. In our results, we found facilitatory and inhibitory effects on voluntary task-order coordination because of anodal and cathodal transcranial direct current stimulation, respectively. This was indicated by shorter RTs when participants intentionally switched the task order relative to the preceding trial during anodal as well as a reduced tendency to switch the task order relative to the preceding trial during cathodal stimulation compared with the sham stimulation. Overall, these findings indicate that the dlPFC is also causally involved in voluntary task-order coordination processes. In particular, we argue that the dlPFC is recruited for intentionally updating and implementing task-order information that is necessary for scheduling the processing of two temporally overlapping tasks.

Accelerated Theta Burst Transcranial Magnetic Stimulation for Refractory Depression in Autism Spectrum Disorder

PURPOSE

Major depressive disorder (MDD) disproportionately affects those living with autism spectrum disorder (ASD) and is associated with significant impairment and treatment recidivism.

METHODS

We studied the use of accelerated theta burst stimulation (ATBS) for the treatment of refractory MDD in ASD (3 treatments daily x 10 days). This prospective open-label 12-week trial included 10 subjects with a mean age of 21.5 years, randomized to receive unilateral or bilateral stimulation of the dorsolateral prefrontal cortex.

RESULTS

One participant dropped out of the study due to intolerability. In both treatment arms, depressive symptoms, scored on the Hamilton Depression Rating Scale scores, diminished substantially. At 12 weeks post-treatment, full remission was sustained in 5 subjects and partial remission in 3 subjects. Treatment with ATBS, regardless of the site of stimulation, was associated with a significant, substantial, and sustained improvement in depressive symptomatology via the primary outcome measure, the Hamilton Depression Rating Scale. Additional secondary measures, including self-report depression scales, fluid cognition, and sleep quality, also showed significant improvement. No serious adverse events occurred during the study. Mild transient headaches were infrequently reported, which are expected side effects of ATBS.

CONCLUSION

Overall, ATBS treatment was highly effective and well-tolerated in individuals with ASD and co-occurring MDD. The findings support the need for a larger, sham-controlled randomized controlled trial to further evaluate efficacy of ATBS in this population.

The Effects of Transcranial Direct Current Stimulation (tDCS) on the Cognitive Functions: A Systematic Review and Meta-analysis

Previous studies have investigated the effect of transcranial direct current stimulation (tDCS) on cognitive functions. However, these studies reported inconsistent results due to differences in experiment design, measurements, and stimulation parameters. Nonetheless, there is a lack of meta-analyses and review studies on tDCS and its impact on cognitive functions, including working memory, inhibition, flexibility, and theory of mind. We performed a systematic review and meta-analysis of tDCS studies published from the earliest available data up to October 2021, including studies reporting the effects of tDCS on cognitive functions in human populations. Therefore, these systematic review and meta-analysis aim to comprehensively analyze the effects of anodal and cathodal tDCS on cognitive functions by investigating 69 articles with a total of 5545 participants. Our study reveals significant anodal tDCS effects on various cognitive functions. Specifically, we observed improvements in working memory reaction time (RT), inhibition RT, flexibility RT, theory of mind RT, working memory accuracy, theory of mind accuracy and flexibility accuracy. Furthermore, our findings demonstrate noteworthy cathodal tDCS effects, enhancing working memory accuracy, inhibition accuracy, flexibility RT, flexibility accuracy, theory of mind RT, and theory of mind accuracy. Notably, regarding the influence of stimulation parameters of tDCS on cognitive functions, the results indicated significant differences across various aspects, including the timing of stimulation (online vs. offline studies), population type (clinical vs. healthy studies), stimulation duration (< 15 min vs. > 15 min), electrical current intensities (1-1.5 m.A vs. > 1.5 m.A), stimulation sites (right frontal vs. left frontal studies), age groups (young vs. older studies), and different cognitive tasks in each cognitive functioning aspect. In conclusion, our results demonstrate that tDCS can effectively enhance cognitive task performance, offering valuable insights into the potential benefits of this method for cognitive improvement.

Effects of Dual-Site Anodal Transcranial Direct Current Stimulation on Attention, Decision-Making, and Working Memory during Sports Fatigue in Elite Soccer Athletes

BACKGROUND

Sports fatigue in soccer athletes has been shown to decrease neural activity, impairing cognitive function and negatively affecting motor performance. Transcranial direct current stimulation (tDCS) can alter cortical excitability, augment synaptic plasticity, and enhance cognitive function. However, its potential to ameliorate cognitive impairment during sports fatigue remains largely unexplored. This study investigated the effect of dual-site tDCS targeting the dorsolateral prefrontal cortex (DLPFC) or primary motor cortex (M1) on attention, decision-making, and working memory in elite soccer athletes during sports fatigue.

METHODS

Sports fatigue was induced in 23 (non-goalkeeper) elite soccer athletes, who then participated in three counterbalanced intervention sessions: dual-site tDCS over the M1, dual-site tDCS over the DLPFC, and sham tDCS. Following tDCS, participants completed the Stroop, Iowa Gambling, and 2-back tasks.

RESULTS

We found a significant improvement in Stroop task accuracy following dual-site anodal tDCS over the M1 compared with the sham intervention in the incongruent condition (p = 0.036). Net scores in the Iowa Gambling task during blocks 4 (p = 0.019) and 5 (p = 0.014) significantly decreased under dual-site tDCS targeting the DLPFC compared with the sham intervention. No differences in 2-back task performance were observed between sessions (all p > 0.05).

CONCLUSIONS

We conclude that dual-site anodal tDCS applied to the M1 enhanced attention performance while tDCS targeting the DLPFC increased risk propensity in a decision-making task during sports fatigue in elite soccer athletes. However, dual-site anodal tDCS targeting either the M1 or DLPFC did not significantly influence working memory performance during sports fatigue in this population. These preliminary findings suggest that dual-site tDCS targeting the M1 has beneficial effects on attention performance, potentially informing future research on sports fatigue in athletes.

CLINICAL TRIAL REGISTRATION

No: NCT06594978. Registered 09 September, 2024; https://clinicaltrials.gov/search?cond=NCT06594978.

Efficacy and Safety of Transcranial Magnetic Stimulation for Attention-Deficit Hyperactivity Disorder: A Systematic Review and Meta-Analysis

BACKGROUND

Transcranial magnetic stimulation (TMS) is a promising neuromodulation technique that has been widely used in neuropsychiatric disorders, but there was no evidence on its effect on the improvement attention-deficit hyperactivity disorder (ADHD).

OBJECTIVE

This systematic review and meta-analysis aimed to investigate the efficacy and safety of TMS in reducing ADHD symptoms.

METHOD

We systematically searched four databases (PubMed, Embase, Web of Science, and Cochrane Library databases) for randomized controlled/crossover trials on the efficacy and safety of TMS on ADHD symptom improvement compared to sham rTMS or non-TMS interventions, published until September 18, 2024. Extracted data from the included studies involved patient characteristics, intervention protocols, and main outcomes. The effect size of the TMS treatment was evaluated using the standardized mean difference (SMD) with a 95% confidence interval (CI), calculated with either a random effects model or fixed effects model depending on the level of heterogeneity.

RESULT

Eight studies (325 ADHD patients in total) were included in this systematic review and meta-analysis. According to the core symptoms, TMS significantly improved inattention (SMD = -0.94, 95% CI = -1.33 to -0.56, p < 0.001) and hyperactivity/impulsivity (SMD = -0.98, 95% CI = -1.27 to -0.69, p < 0.001) compared to non-TMS interventions after 3-6 weeks of intervention. During the 1-month follow-up, the TMS group still demonstrated a significant improvement in inattention symptoms compared to the non-TMS group (SMD = -0.67, 95% CI = -1.06 to 0.28, p < 0.001). The total symptoms in the TMS group only showed improvement in the 1-month follow-up compared to the non-TMS group. (SMD = -0.48, 95% CI = -0.82 to -0.14, p = 0.005). Only minor adverse events were reported in the included studies, comprising headache and scalp discomfort.

CONCLUSION

TMS significantly improved the inattention, hyperactivity/impulsivity, and total symptom scores in ADHD patients with minor adverse events. Future research should focus on the association between different brain regions and symptoms in ADHD patients, which is crucial for stimulation navigation in TMS interventions. The trial is registered in PROSPERO (PROSPERO registry number: CRD42023473853).

Effects of non-invasive brain stimulation on emotion regulation in patients with attention deficit hyperactivity disorder: a systematic review

Background and objective

A growing body of research evidence suggests that many patients with attention deficit hyperactivity disorder (ADHD) have difficulties with emotion regulation. Non-invasive brain stimulation (NIBS), which mainly includes transcranial electrical stimulation (tES) and repetitive transcranial magnetic stimulation (rTMS), has been considered a potential new direction in the treatment of emotion dysregulation in ADHD patients. The key components of tES are transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS). However, there is no systematic evaluation exploring the effects of non-invasive brain stimulation on emotion regulation in ADHD patients. Therefore, this systematic review aimed to summarize the effects of NIBS on emotion regulation in ADHD patients.

Methods

This systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We searched PubMed, Embase, Web of Science, and the Cochrane Library electronic databases up to 1 July 2024. We also hand-searched the reference lists of retrieved articles and reviews. Assessing risk of bias using the Cochrane Assessment Tool.

Results

Through database search, we obtained a total of 1134 studies, of which 5 met the inclusion criteria. Statistically significant improvements in emotion regulation in children with ADHD were observed in 1 study after treatment with tDCS. In the remaining 4 studies (2 with tDCS and 2 with rTMS), there were no statistically significant changes in emotion regulation in ADHD patients after treatment with either tDCS or rTMS.

Conclusions

The data from our preliminary study do not allow us to draw definitive conclusions that non-invasive brain stimulation improves emotion regulation in ADHD patients. This is because there is a paucity of literature on the effects of tES or rTMS on emotion regulation in ADHD patients and a limited number of randomized controlled trials. More high-quality multicenter randomized controlled trials exploring the efficacy of non-invasive brain stimulation on emotion regulation in ADHD patients are needed in the future to provide strong evidence for definitive conclusions before it can be considered as a potential treatment option.

Systematic review registration

https://www.crd.york.ac.uk/PROSPERO/, identifier CRD42024569041.

Comparing the effectiveness of CBT and low-frequency rTMS in reducing symptom severity and depression and improving working memory in adults with OCD: a clinical trial

OBJECTIVE

This study aims to compare the effectiveness of cognitive-behavioral therapy (CBT) and low-frequency (LF) repetitive transcranial magnetic stimulation (rTMS) in reducing symptom severity and depression and improving working memory in adults with obsessive-compulsive disorder (OCD).

METHODS

This is a randomized clinical trial conducted on 24 adults with OCD, randomly assigned into two groups of CBT (n = 12, received CBT with exposure and response prevention (ERP) individually at 20 sessions) and rTMS (n = 12, received LF (1-Hz) rTMS over the right dorsolateral prefrontal cortex (DLPFC) at 10 sessions). They completed the Yale-Brown Obsessive Compulsive Scale, the Hamilton Depression Rating Scale, and two N-Back tasks before, immediately, and 1 month after interventions.

RESULTS

Results showed a significant difference between the two methods in reducing the severity of OCD symptoms (p < 0.05) and depression (p = 0.002) immediately after interventions where the CBT with ERP was more effective, but no significant difference was found in terms of working memory (p > 0.05). No significant difference was found between groups in any study variables 1 month after interventions.

CONCLUSION

Individual CBT with ERP is superior to LF rTMS for reducing the severity of symptoms and depression in OCD patients. However, there is no difference between them in improving working memory.

Transcranial Magnetic Stimulation Applications in the Study of Executive Functions: A Review

PURPOSE

Executive functions (EFs) are a set of advanced cognitive functions essential for human survival and behavioral regulation. Understanding neurophysiological mechanisms of EFs as well as exploring methods to enhance them are still challenging problems in cognitive neuroscience. In recent years, transcranial magnetic stimulation (TMS) has been widely used in the field of EF research and has made notable progress. This article aimed to discuss the impact of TMS technology on EF research from both basic and applied research perspectives.

METHODS

We searched for literature on TMS and EFs published in the last decade (2013-2023) and reviewed how TMS has been applied in the field of EF.

FINDINGS

We found that the combination of TMS with neuroimaging techniques was helpful in exploring the brain mechanisms of EFs and investigating the executive dysfunctions caused by other neuropsychiatric disorders. Moreover, TMS could be considered as one of the most important techniques to enhance EFs among patient populations, even healthy people, with high safety and credibility. Meanwhile, we discussed the application of TMS in the research of EFs and made suggestions for future research directions. We suggested that a multidisciplinary structure of methods such as epigenetics and endocrinology could be integrated with TMS for investigating deeper in EF domains, and a substantial number of high-quality clinical studies are required to further elucidate the effects of TMS on EFs.

CONCLUSIONS

TMS holds great promise for gaining insight into investigating the neural mechanisms of EFs and improving executive functions among different populations.

tDCS-enhanced cognitive training improves attention and alters connectivity in control and somatomotor networks: A triple blind study

BACKGROUND

Executive dysfunction such as inattention or forgetfulness can lead to disruptions in a person's daily functioning and quality of life.

OBJECTIVE/HYPOTHESIS

This triple-blinded randomized clinical trial assessed the efficacy of bifrontal (over the forehead) transcranial direct current stimulation (tDCS) concurrent with cognitive training to improve cognitive performance in a healthy sample.

METHODS

Fifty-eight participants were randomly assigned to one of three stimulation conditions (2 mA left anode-right cathode, 2 mA right anode-left cathode, or sham), which was administered with cognitive training tasks 3x/week over 12 weeks with assessments at baseline, midpoint (6 weeks), and post-training (12 weeks). We assessed cognitive performance, functional connectivity, and the influence of individual differences in training advancement.

RESULTS

Forty participants completed training. We found that at midpoint and post, all groups improved significantly on overall cognitive performance. The left anode group's attention & vigilance score improved significantly at post, but the other two groups did not. Greater attention training advancement predicted attention improvement by post, most notably in the left anode group. Finally, within-network connectivity decreased in the control network and increased in the somatomotor network across all groups.

CONCLUSIONS

These results suggest that, given cognitive training, the left anode montage is more effective at improving attention than the right anode montage and sham. Future research may focus on the application of the left anode montage during cognitive training to assess its effectiveness in improving cognition in neuropsychiatric disorders.

The Cerebellum and Cognitive Function: Anatomical Evidence from a Transdiagnostic Sample

Multiple lines of evidence across human functional, lesion, and animal data point to a cerebellar role, in particular of crus I, crus II, and lobule VIIB, in cognitive function. However, a mapping of distinct facets of cognitive function to cerebellar structure is missing. We analyzed structural neuroimaging data from the Healthy Brain Network (HBN). Cerebellar parcellation was performed with a validated automated segmentation pipeline (CERES) and stringent visual quality check (n = 662 subjects retained from initial n = 1452). Canonical correlation analyses (CCA) examined regional gray matter volumetric (GMV) differences in association to cognitive function (quantified with NIH Toolbox Cognition domain, NIH-TB), accounting for psychopathology severity, age, sex, scan location, and intracranial volume. Multivariate CCA uncovered a significant correlation between two components entailing a latent cognitive canonical (NIH-TB subscales) and a brain canonical variate (cerebellar GMV and intracranial volume, ICV), surviving bootstrapping and permutation procedures. The components correspond to partly shared cerebellar-cognitive function relationship with a first map encompassing cognitive flexibility (r = 0.89), speed of processing (r = 0.65), and working memory (r = 0.52) associated with regional GMV in crus II (r = 0.57) and lobule X (r = 0.59) and a second map including the crus I (r = 0.49) and lobule VI (r = 0.49) associated with working memory (r = 0.51). We show evidence for a structural subspecialization of the cerebellum topography for cognitive function in a transdiagnostic sample.

Neurobiological Effects of Transcranial Direct Current Stimulation over the Inferior Frontal Gyrus: A Systematic Review on Cognitive Enhancement in Healthy and Neurological Adults

The neurobiological effects of transcranial direct current stimulation (tDCS) have still not been unequivocally clarified. Some studies have suggested that the application of tDCS over the inferior frontal gyrus (IFG) enhances different aspects of cognition in healthy and neurological individuals, exerting neural changes over the target area and its neural surroundings. In this systematic review, randomized sham-controlled trials in healthy and neurological adults were selected through a database search to explore whether tDCS over the IFG combined with cognitive training modulates functional connectivity or neural changes. Twenty studies were finally included, among which twelve measured tDCS effects through functional magnetic resonance (fMRI), two through functional near-infrared spectroscopy (fNIRS), and six through electroencephalography (EEG). Due to the high heterogeneity observed across studies, data were qualitatively described and compared to assess reliability. Overall, studies that combined fMRI and tDCS showed widespread changes in functional connectivity at both local and distant brain regions. The findings also suggested that tDCS may also modulate electrophysiological changes underlying the targeted area. However, these outcomes were not always accompanied by corresponding significant behavioral results. This work raises the question concerning the general efficacy of tDCS, the implications of which extend to the steadily increasing tDCS literature.

Mood moderates the effects of prefrontal tDCS on executive functions: A meta-analysis testing the affective state-dependency hypothesis

BACKGROUND

In recent decades, numerous studies have investigated the effects of transcranial direct current stimulation (tDCS) on cognitive functioning. However, results of these studies frequently display inconsistency and pose challenges regarding replicability. The present work aimed at testing the hypothesis of mood as potential moderator of prefrontal tDCS effects on executive functions (EF). This hypothesis refers to the relationship between mood and EF, as well as to the association of mood with the dorsolateral prefrontal cortex (dlPFC) activity.

METHODS

We conducted a meta-analysis of 11 articles where the dlPFC was stimulated with anodal tDCS, EF were measured, and mood was assessed prior to the stimulation. We then conducted a meta-regression to examine whether mood moderated the tDCS effects on EF.

RESULTS

While no significant effect of tDCS on EF emerged from the meta-analysis, the meta-regression indicated that mood plays a significant role as moderator, with greater tDCS effects on EF in individuals with higher depressive symptoms.

LIMITATIONS

The limited number of studies included, the heterogeneous samples considered, and the limited generalizability to other non-invasive brain stimulation techniques and affective states.

CONCLUSIONS

Findings suggest that evaluating mood prior to stimulation could increase the sensitivity and specificity of tDCS application, and provide the first meta-analytic evidence in favor of the affective state-dependency hypothesis.

Stress priming transcranial direct current stimulation (tDCS) enhances updating of emotional content in working memory

Transcranial direct current stimulation (tDCS) targeting the prefrontal cortex has emerged as a valuable tool in psychiatric research. Understanding the impact of affective states, such as stress at the time of stimulation, on the efficacy of prefrontal tDCS is crucial for advancing tDCS interventions. Stress-primed tDCS, wherein stress is used as a priming agent, has the potential to modulate neural plasticity and enhance cognitive functions, particularly in emotional working memory. However, prior research using stress-primed tDCS focused solely on non-emotional working memory performance, yielding mixed results. In this sham-controlled study, we addressed this gap by investigating the effects of stress-primed bifrontal tDCS (active versus sham) on both non-emotional and emotional working memory performance. The study was conducted in 146 healthy individuals who were randomly assigned to four experimental groups. The Trier Social Stress Test (TSST) or a control variant of the test was used to induce a stress versus control state. The results showed that stress priming significantly enhanced the effects of tDCS on the updating of emotional content in working memory, as evidenced by improved accuracy. Notably, no significant effects of stress priming were found for non-emotional working memory performance. These findings highlight the importance of an individual's prior affective state in shaping their response to tDCS, especially in the context of emotional working memory.

Advancements in non-invasive microwave brain stimulation: A comprehensive survey

This survey provides a comprehensive insight into the world of non-invasive brain stimulation and focuses on the evolving landscape of deep brain stimulation through microwave research. Non-invasive brain stimulation techniques provide new prospects for comprehending and treating neurological disorders. We investigate the methods shaping the future of deep brain stimulation, emphasizing the role of microwave technology in this transformative journey. Specifically, we explore antenna structures and optimization strategies to enhance the efficiency of high-frequency microwave stimulation. These advancements can potentially revolutionize the field by providing a safer and more precise means of modulating neural activity. Furthermore, we address the challenges that researchers currently face in the realm of microwave brain stimulation. From safety concerns to methodological intricacies, this survey outlines the barriers that must be overcome to fully unlock the potential of this technology. This survey serves as a roadmap for advancing research in microwave brain stimulation, pointing out potential directions and innovations that promise to reshape the field.

Cognitive Effects Following Offline High-Frequency Repetitive Transcranial Magnetic Stimulation (HF-rTMS) in Healthy Populations: A Systematic Review and Meta-Analysis

High-frequency repetitive transcranial magnetic stimulation (HF-rTMS) is a commonly used form of rTMS to treat neuropsychiatric disorders. Emerging evidence suggests that 'offline' HF-rTMS may have cognitive enhancing effects, although the magnitude and moderators of these effects remain unclear. We conducted a systematic review and meta-analysis to clarify the cognitive effects of offline HF-rTMS in healthy individuals. A literature search for randomised controlled trials with cognitive outcomes for pre and post offline HF-rTMS was performed across five databases up until March 2022. This study was registered on the PROSPERO international prospective protocol for systematic reviews (PROSPERO 2020 CRD 42,020,191,269). The Risk of Bias 2 tool was used to assess the risk of bias in randomised trials. Separate analyses examined the cognitive effects of excitatory and inhibitory forms of offline HF-rTMS on accuracy and reaction times across six cognitive domains. Fifty-three studies (N = 1507) met inclusion criteria. Excitatory offline HF-rTMS showed significant small sized effects for improving accuracy (k = 46, g = 0.12) and reaction time (k = 44, g = -0.13) across all cognitive domains collapsed. Excitatory offline HF-rTMS demonstrated a relatively greater effect for executive functioning in accuracy (k = 24, g = 0.14). Reaction times were also improved for the executive function (k = 21, g = -0.11) and motor (k = 3, g = -0.22) domains following excitatory offline HF-rTMS. The current review was restricted to healthy individuals and future research is required to examine cognitive enhancement from offline HF-rTMS in clinical cohorts.

Effects of transcranial magnetic stimulation on reactive response inhibition

Reactive response inhibition cancels impending actions to enable adaptive behavior in ever-changing environments and has wide neuropsychiatric implications. A canonical paradigm to measure the covert inhibition latency is the stop-signal task (SST). To probe the cortico-subcortical network underlying motor inhibition, transcranial magnetic stimulation (TMS) has been applied over central nodes to modulate SST performance, especially to the right inferior frontal cortex and the presupplementary motor area. Since the vast parameter spaces of SST and TMS enabled diverse implementations, the insights delivered by emerging TMS-SST studies remain inconclusive. Therefore, a systematic review was conducted to account for variability and synthesize converging evidence. Results indicate certain protocol specificity through the consistent perturbations induced by online TMS, whereas offline protocols show paradoxical effects on different target regions besides numerous null effects. Ancillary neuroimaging findings have verified and dissociated the underpinning network dynamics. Sources of heterogeneity in designs and risk of bias are highlighted. Finally, we outline best-practice recommendations to bridge methodological gaps and subserve the validity as well as replicability of future work.

Lateralization of self-control over the dorsolateral prefrontal cortex in decision-making: a systematic review and meta-analytic evidence from noninvasive brain stimulation

The dorsolateral prefrontal cortex (DLPFC) has been widely recognized as a crucial brain "control area." Recently, its causal role in promoting deliberate decision-making through self-control and the asymmetric performance of the left and right DLPFC in control functions have attracted the interest of many researchers. This study was designed to investigate the role of DLPFC in decision-making behaviors and lateralization of its control function by systematically examining the effects of noninvasive brain stimulation (NIBS) over the DLPFC on intertemporal choice, risk decision-making, and social fairness-related decision-making tasks. Literature searches were implemented at PubMed, Embase, Cochrane, Web of Science, Wanfang Data, China Science and Technology Journal Database, and China National Knowledge Infrastructure until May 10, 2022. Meta-analytic results for included studies were estimated by random-effect models. A total of 33 eligible studies were identified, yielding 130 effect sizes. Our results indicated that compared to sham group, excitatory NIBS over the left DLPFC reduced delay discounting rate (standardized mean differences, SMD = -0.51; 95% confidence interval, 95% CI: [-0.81, -0.21]) and risk-taking performance (SMD = -0.39, 95% CI [-0.68, -0.10]), and inhibitory NIBS over the right DLPFC increased self-interested choice of unfair offers (SMD = 0.50, 95% CI [0.04, 0.97]). Finding of current work indicated that neural excitement of the DLPFC activation improve individuals' self-control during decision-makings, whereas neural inhibition results in impaired control. In addition, our analyses furnish causal evidence for the presence of functional lateralization in the left and right DLPFC in monetary impulsive decision-making and social decision-making, respectively.

Non-invasive brain stimulation for patients and healthy subjects: Current challenges and future perspectives

Non-invasive brain stimulation (NIBS) techniques have a rich historical background, yet their utilization has witnessed significant growth only recently. These techniques encompass transcranial electrical stimulation and transcranial magnetic stimulation, which were initially employed in neuroscience to explore the intricate relationship between the brain and behaviour. However, they are increasingly finding application in research contexts as a means to address various neurological, psychiatric, and neurodegenerative disorders. This article aims to fulfill two primary objectives. Firstly, it seeks to showcase the current state of the art in the clinical application of NIBS, highlighting how it can improve and complement existing treatments. Secondly, it provides a comprehensive overview of the utilization of NIBS in augmenting the brain function of healthy individuals, thereby enhancing their performance. Furthermore, the article delves into the points of convergence and divergence between these two techniques. It also addresses the existing challenges and future prospects associated with NIBS from ethical and research standpoints.

Sex matters for the enhancement of cognitive training with transcranial direct current stimulation (tDCS)

BACKGROUND

Transcranial direct current stimulation (tDCS) can influence brain network activity and associated cognitive and behavioural functions. In addition to the extensive variety in stimulation parameters, numerous biological factors drive these effects, however these are yet poorly understood. Here, we investigate one of the major biological factors by focusing on sex-dependent effects of tDCS on a challenging cognitive control task (adaptive paced auditory serial addition task [PASAT]) in healthy humans.

METHODS

This sex-specific re-analysis was performed on data of 163 subjects who underwent a 2-week cognitive control training (6 sessions in total). Subjects received either verum (anodal/cathodal) or sham tDCS. Electrodes were placed over the left or right dorsolateral prefrontal cortex and the respective contralateral deltoid muscle. Cognitive control was measured as performance in the PASAT and was analysed in respect to stimulation conditions (sham, anodal, cathodal) and sex.

RESULTS

Regardless of stimulation condition, performance gains between the sexes were higher in females compared to males (p = 0.0038). Female's performance during anodal tDCS exceeded male's (p = 0.0070), yet no effects were found for cathodal or sham tDCS. Moreover, in females we found a superior effect for anodal tDCS over sham stimulation (fanodal: p = 0.0354; fcathodal: p = 0.6181), but no such effect in males (manodal: p = 0.6882; mcathodal: p = 0.4822).

CONCLUSIONS

This study highlights the relevance of biological sex for the effects of tDCS on cognitive training. Thus, an increased attention to biological sex is advisable in future brain stimulation research to highlight and in consequence better understand potentially underlying sex-specific mechanisms. Considering biological sex will further advance customisation and individualisation of tDCS interventions. Trial registration ClinicalTrials.gov, NCT04108663.

Cortical thickness is related to working memory performance after non-invasive brain stimulation

Non-invasive brain stimulation (NIBS) probing the dorsolateral prefrontal cortex (DLPFC) has been shown to have little effect on working memory. The variability of NIBS responses might be explained by inter-subject brain anatomical variability. We investigated whether baseline cortical brain thickness of regions of interest was associated with working memory performance after NIBS by performing a secondary analysis of previously published research. Structural magnetic resonance imaging data were analyzed from healthy subjects who received transcranial direct current stimulation (tDCS), intermittent theta-burst stimulation (iTBS), and placebo. Twenty-two participants were randomly assigned to receive all the interventions in a random order. The working memory task was conducted after the end of each NIBS session. Regions of interest were the bilateral DLPFC, medial prefrontal cortex, and posterior cingulate cortex. Overall, 66 NIBS sessions were performed. Findings revealed a negative significant association between cortical thickness of the bilateral dorsolateral prefrontal cortex and reaction time for both tDCS (left: P=0.045, right: P=0.037) and iTBS (left: P=0.007, right: P=0.007) compared to placebo. A significant positive association was found for iTBS and posterior cingulate cortex (P=0.03). No association was found for accuracy. Our findings provide the first evidence that individual cortical thickness of healthy subjects might be associated with working memory performance following different NIBS interventions. Therefore, cortical thickness could explain - to some extent - the heterogeneous effects of NIBS probing the DLPFC.

Boosting affective control with bifrontal transcranial direct current stimulation (tDCS): a proof-of-concept study in healthy individuals

Affective control refers to the ability to regulate emotions and is considered a marker of mental health. Transcranial direct current stimulation (tDCS), a non-invasive brain stimulation technique, holds promise to enhance affective control. In this between-subjects study in healthy individuals, we investigated the effects of bifrontal tDCS on core processes and higher-level markers of affective control. As such, we assessed direct tDCS effects on emotional interference during an affective control task and indirect effects on an instructed reappraisal task afterward. Results showed that the affective control task combined with active tDCS, compared to sham, resulted in enhanced cognitive emotion regulation. Specifically, participants in the active tDCS condition showed an increased propensity to use reappraisal and were more successful in doing so. Moreover, there was reduced vagally mediated heart rate variability indicative of attenuated emotion and self-regulation, in the sham, but not in the active condition. Surprisingly, there were no effects of tDCS on emotional interference during the affective control task, with Bayesian analyses showing extreme evidence against these effects. Nevertheless, there was a positive association between the emotional interference during the affective control task and participants' reappraisal success afterward for the active, but not the sham tDCS condition. The study offers valuable insights to guide future work on combined tDCS with affective control tasks or training on the ability to regulate emotions.

Spatiotemporal evidence uncovers differential neural activity patterns in cognitive and affective conflict control

Studies have shown that there are overlapping neural bases for cognitive and affective conflict control, but whether the neural activity patterns caused by the two types of conflict are similar remains to be explored. The present study utilizes electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI) to temporally and spatially analyze the differences between cognitive and affective conflict control. We employ a semantic conflict task which includes blocks of cognitive and affective judgements primed by conflicting and non-conflicting contexts. The results showed a typical neural conflict effect in the cognitive judgment blocks as reflected by greater amplitudes of P2, N400, and the late positive potential (LPP), as well as greater activation of the left pre-supplementary motor area (pre-SMA) and the right inferior frontal gyrus (IFG) in the conflict condition relative to the non-conflict condition. These patterns did not emerge in the affective judgments, but instead, showed reversed effects of the LPP and in the left SMA. Taken together, these findings suggest that cognitive and affective conflict control result in different neural activity patterns.

The effects of transcranial direct current stimulation on corticospinal excitability: A systematic review of nonsignificant findings

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that can modulate brain activity through the application of low-intensity electrical currents. Based on its reported effects on corticospinal excitability (CSE), tDCS has been used to study cognition in healthy individuals and reduce symptoms in a variety of clinical conditions. Despite its increasing popularity as a research and clinical tool, high interindividual variability has been reported in the response to protocols using transcranial magnetic stimulation (TMS) to assess tDCS-induced changes in CSE leading to several nonsignificant findings. In this systematic review, studies that reported no significant modulation of CSE following tDCS were identified from PubMed and Embase (Ovid) databases. Forty-three articles were identified where demographic, TMS and tDCS parameters were extracted. Overall, stimulation parameters, CSE measurements and participant characteristics were similar to those described in studies reporting positive results and were likewise heterogeneous between studies. Small sample sizes and inadequate blinding were notable features of the reviewed studies. This systematic review suggests that studies reporting nonsignificant findings do not markedly differ from those reporting significant modulation of CSE.

Using a Pulse Protocol to Fix the Individual Dosage of Transcranial and Transspinal Direct Current Electrical Stimulation

The non-invasive current stimulation protocol differs significantly between the brain and spinal cord, such that when comparing the two, there is a clear predominance of protocols using transcranial direct current stimulation (tDCS) for the brain and of protocols using pulsed stimulation for the spinal cord (psSC). These protocols differ in their effects on the central nervous system and in such important parameters as stimulation intensity. In most cases, tDCS has a fixed amplitude for all subjects/patients, while psSC is usually chosen on a case-by-case basis, according to the thresholds of muscle responses. In our opinion, it is possible to use the experience of identifying thresholds during psSC to adjust the dose of the direct current for transcranial and transspinal electrical stimulation, an approach that may provide more homogeneous tDCS data.

Neural correlates of impulsivity in bipolar disorder: A systematic review and clinical implications

Impulsivity is a common feature of bipolar disorder (BD) with ramifications for functional impairment and premature mortality. This PRISMA-guided systematic review aims to integrate findings on the neurocircuitry associated with impulsivity in BD. We searched for functional neuroimaging studies that examined rapid-response impulsivity and choice impulsivity using the Go/No-Go Task, Stop-Signal Task, and Delay Discounting Task. Findings from 33 studies were synthesized with an emphasis on the effect of mood state of the sample and affective salience of the task. Results suggest trait-like brain activation abnormalities in regions implicated in impulsivity that persist across mood states. During rapid-response inhibition, BD exhibit under-activation of key frontal, insular, parietal, cingulate, and thalamic regions, but over-activation of these regions when the task involves emotional stimuli. Delay discounting tasks with functional neuroimaging in BD are lacking, but hyperactivity of orbitofrontal and striatal regions associated with reward hypersensitivity may be related to difficulty delaying gratification. We propose a working model of neurocircuitry dysfunction underlying behavioral impulsivity in BD. Clinical implications and future directions are discussed.

Long-term effects of repeated multitarget high-definition transcranial direct current stimulation combined with cognitive training on response inhibition gains

Background

Few studies have investigated the effects of repeated sessions of transcranial direct current stimulation (tDCS) combined with concurrent cognitive training on improving response inhibition, and the findings have been heterogeneous in the limited research. This study investigated the long-lasting and transfer effects of 10 consecutive sessions of multitarget anodal HD-tDCS combined with concurrent cognitive training on improving response inhibition compared with multitarget stimulation or training alone.

Methods

Ninety-four healthy university students aged 18–25 were randomly assigned to undergo different interventions, including real stimulation combined with stop-signal task (SST) training, real stimulation, sham stimulation combined with SST training, and sham stimulation. Each intervention lasted 20 min daily for 10 consecutive days, and the stimulation protocol targeted right inferior frontal gyrus (rIFG) and pre-supplementary motor area (pre-SMA) simultaneously with a total current intensity of 2.5 mA. Performance on SST and possible transfer effects to Stroop task, attention network test, and N-back task were measured before and 1 day and 1 month after completing the intervention course.

Results

The main findings showed that the combined protocol and the stimulation alone significantly reduced stop-signal reaction time (SSRT) in the post-intervention and follow-up tests compared to the pre-intervention test. However, training alone only decreased SSRT in the post-test. The sham control exhibited no changes. Subgroup analysis revealed that the combined protocol and the stimulation alone induced a decrease in the SSRT of the low-performance subgroup at the post-test and follow-up test compared with the pre-test. However, only the combined protocol, but not the stimulation alone, improved the SSRT of the high-performance subgroup. The transfer effects were absent.

Conclusion

This study provides supportive evidence for the synergistic effect of the combined protocol, indicating its superiority over the single intervention method. In addition, the long-term after-effects can persist for up to at least 1 month. Our findings also provide insights into the clinical application and strategy for treating response inhibition deficits.

Individual response to transcranial direct current stimulation as a function of working memory capacity and electrode montage

Introduction

Attempts to improve cognitive abilities via transcranial direct current stimulation (tDCS) have led to ambiguous results, likely due to the method’s susceptibility to methodological and inter-individual factors. Conventional tDCS, i.e., using an active electrode over brain areas associated with the targeted cognitive function and a supposedly passive reference, neglects stimulation effects on entire neural networks.

Methods

We investigated the advantage of frontoparietal network stimulation (right prefrontal anode, left posterior parietal cathode) against conventional and sham tDCS in modulating working memory (WM) capacity dependent transfer effects of a single-session distractor inhibition (DIIN) training. Since previous results did not clarify whether electrode montage drives this individual transfer, we here compared conventional to frontoparietal and sham tDCS and reanalyzed data of 124 young, healthy participants in a more robust way using linear mixed effect modeling.

Results

The interaction of electrode montage and WM capacity resulted in systematic differences in transfer effects. While higher performance gains were observed with increasing WM capacity in the frontoparietal stimulation group, low WM capacity individuals benefited more in the sham condition. The conventional stimulation group showed subtle performance gains independent of WM capacity.

Discussion

Our results confirm our previous findings of WM capacity dependent transfer effects on WM by a single-session DIIN training combined with tDCS and additionally highlight the pivotal role of the specific electrode montage. WM capacity dependent differences in frontoparietal network recruitment, especially regarding the parietal involvement, are assumed to underlie this observation.

Effects of non-invasive brain stimulation (NIBS) for executive function on subjects with ADHD: a protocol for a systematic review and meta-analysis

INTRODUCTION

Attention-deficit/hyperactivity disorder (ADHD) is a prevalent neurodevelopmental disorder with a high risk of multiple mental health and social difficulties. Executive function domains are associated with distinct ADHD symptom burdens. Non-invasive brain stimulation (NIBS) mainly includes repetitive transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), which is a promising technique, but its impact on the executive function of ADHD is uncertain. Therefore, the aim of this systematic review and meta-analysis is to derive solid and updated estimates on the effect of NIBS on executive function in children/adults with ADHD.

METHODS AND ANALYSIS

A systematic search will be performed through EMBASE, MEDLINE, PsycINFO and Web of Science databases from inception until 22 August 2022. Handsearching of grey literature and the reference lists of selected articles will also be conducted. Empirical studies assessing the effect of NIBS (TMS or tDCS) on executive function in children or adults with ADHD will be included. Two investigators will independently perform literature identification, data extraction and risk of bias assessment. Relevant data will be pooled by a fixed-effects or random-effects model according to I2 statistic. Sensitivity analysis will be performed to test the robustness of the pooled estimates. Subgroup analyses will be conducted to investigate the potential heterogeneity. This protocol will generate a systematic review and meta-analysis that comprehensively synthesises the evidence on the NIBS treatment of executive function deficit of ADHD.Ethics approval is not required as this is a protocol for a systematic review of published literature. The results will be submitted to a peer-reviewed journal or a conference.

PROSPERO REGISTRATION NUMBER

CRD42022356476.

The effects of prefrontal vs. parietal cortex transcranial direct current stimulation on craving, inhibition, and measures of self-esteem

While prefrontal cortex dysfunction has been implicated in high food cravings, other cortical regions, like the parietal cortex, are potentially also involved in regulating craving. This study explored the effects of stimulating the inferior parietal lobule (IPL) and dorsolateral prefrontal cortex (DLPFC) on food craving state and trait. Transcranial direct current stimulation (tDCS) was administered at 1.5 mA for 5 consecutive days. Participants received 20 min of IPL, DLPFC, or sham stimulation (SHAM) each day which consisted of two rounds of 10-min stimulation, divided by a 10-min mindfulness task break. In addition, we studied inhibition and subjective psychological aspects like body image and self-esteem state and trait. To decompose immediate and cumulative effects, we measured the following on days 1 and 5: inhibition through the Go/No-go task; and food craving, self-esteem, and body appreciation through a battery of questionnaires. We found that false alarm errors decreased in the participants receiving active stimulation in the DLPFC (DLPFC-group). In contrast, false alarm errors increased in participants receiving active stimulation in the IPL (IPL-group). At the same time, no change was found in the participants receiving SHAM (SHAM-group). There was a trending reduction in craving trait in all groups. Momentary craving was decreased in the DLPFC-group and increased in IPL-group, yet a statistical difference was not reached. According to time and baseline, self-esteem and body perception improved in the IPL-group. Furthermore, self-esteem trait significantly improved over time in the DLPFC-group and IPL-group. These preliminary results indicate that tDCS modulates inhibition in frontoparietal areas with opposite effects, enhancing it in DLPFC and impairing it in IPL. Moreover, craving is moderately linked to inhibition, self-esteem, and body appreciation which seem not to be affected by neuromodulation but may rely instead on broader regions as more complex constructs. Finally, the fractionated protocol can effectively influence inhibition with milder effects on other constructs.

Alpha-beta decoupling relevant to inhibition deficits leads to suicide attempt in major depressive disorder

BACKGROUND

One devastating outcome of major depressive disorder (MDD) is high suicidality, especially for patients with suicide attempt (SA). Evidence indicated that SA may be strongly associated with inhibitory control deficits. We hypothesized that the inhibition function deficits of patient with SA might be underpinned by abnormal neuronal oscillations.

METHODS

Our study recruited 111 subjects including 74 patients and 37 controls, who performed a GO/NOGO task during magnetoencephalography recording. Time-frequency-representations and phase-amplitude-coupling were measured for the brain circuits involved in the inhibitory function. Phase-slope-indexes were calculated between regions to determine the direction of power flow.

RESULTS

Significant increased reaction time and decreased judgment accuracy were observed in SA group. During the perception stage of GO task (approximately 125 ms), SA group manifested elevated alpha power in ventral prefrontal cortex (VPFC) and attenuated beta power in dorsal anterior cingulate (dACC) compared with other groups (p < 0.01). In the processing stage of NOGO task (approximately 300 ms), they showed decreased beta power in VPFC and increased alpha power in dACC (p < 0.01). Alpha-beta decoupling during both tasks was observed in SA group. Furthermore, the decoupling from VPFC to dACC under NOGO tasks was significantly correlated with suicide risk level.

LIMITATIONS

The number of participants was relatively small, and psychological elements were not involved in current study.

CONCLUSION

Dysregulated oscillatory activities of dACC and VPFC suggested deficits in execution and inhibition functions triggering high suicide risks. The alpha-beta decoupling from VPFC to dACC could be served as a neuro-electrophysiological biomarker for identifying potential suicide risk.

Transcranial Direct Current Stimulation vs Sham for the Treatment of Inattention in Adults With Attention-Deficit/Hyperactivity Disorder: The TUNED Randomized Clinical Trial

IMPORTANCE

Transcranial direct current stimulation (tDCS) may improve symptoms of inattention in adults with attention-deficit/hyperactivity disorder (ADHD). However, previous trials are characterized by small sample sizes, heterogeneous methodologies, and short treatment periods using clinic-based tDCS.

OBJECTIVE

To determine the efficacy and safety of home-based tDCS in treating inattention symptoms in adult patients with ADHD.

DESIGN, SETTING, AND PARTICIPANTS

Randomized, double-blind, parallel, sham-controlled clinical trial (tDCS for the Treatment of Inattention Symptoms in Adult Patients With ADHD [TUNED]), conducted from July 2019 through July 2021 in a single-center outpatient academic setting. Of 277 potential participants screened by phone, 150 were assessed for eligibility on site, and 64 were included. Participants were adults with ADHD, inattentive or combined subtype. Exclusion criteria included current stimulant drug treatment, current moderate to severe symptoms of depression or anxiety, diagnosis of bipolar disorder with a manic or depressive episode in the last year, diagnosis of schizophrenia or another psychotic disorder, and diagnosis of autism spectrum disorder; 55 of participants completed follow-up after 4 weeks.

INTERVENTIONS

Thirty-minute daily sessions of home-based tDCS for 4 weeks, 2 mA anodal-right and cathodal-left prefrontal stimulation with 35-cm2 carbon electrodes.

MAIN OUTCOMES AND MEASURES

Inattentive scores in the clinician-administered version of the Adult ADHD Self-report Scale version 1.1 (CASRS-I).

RESULTS

Included in this trial were 64 participants with ADHD (31 [48%] inattentive presentation and 33 [52%] combined presentation), with a mean (SD) age of 38.3 (9.6) years. Thirty participants (47%) were women and 34 (53%) were men. Fifty-five finished the trial. At week 4, the mean (SD) inattention score, as measured with CASRS-I, was 18.88 (5.79) in the active tDCS group and 23.63 (3.97) in the sham tDCS group. Linear mixed-effects models revealed a statistically significant treatment by time interaction for CASRS-I (βinteraction = -3.18; 95% CI, -4.60 to -1.75; P < .001), showing decreased symptoms of inattention in the active tDCS group over the 3 assessments compared to the sham tDCS group. Mild adverse events were more frequent in the active tDCS group, particularly skin redness, headache, and scalp burn.

CONCLUSIONS AND RELEVANCE

In this randomized clinical trial, daily treatment with a home-based tDCS device over 4 weeks improved attention in adult patients with ADHD who were not taking stimulant medication. Home-based tDCS could be a nonpharmacological alternative for patients with ADHD.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT04003740.

A cognitive neurogenetic approach to uncovering the structure of executive functions

One central mission of cognitive neuroscience is to understand the ontology of complex cognitive functions. We addressed this question with a cognitive neurogenetic approach using a large-scale dataset of executive functions (EFs), whole-brain resting-state functional connectivity, and genetic polymorphisms. We found that the bifactor model with common and shifting-specific components not only was parsimonious but also showed maximal dissociations among the EF components at behavioral, neural, and genetic levels. In particular, the genes with enhanced expression in the middle frontal gyrus (MFG) and the subcallosal cingulate gyrus (SCG) showed enrichment for the common and shifting-specific component, respectively. Finally, High-dimensional mediation models further revealed that the functional connectivity patterns significantly mediated the genetic effect on the common EF component. Our study not only reveals insights into the ontology of EFs and their neurogenetic basis, but also provides useful tools to uncover the structure of complex constructs of human cognition.

Assessing the Effect of Simultaneous Combining of Transcranial Direct Current Stimulation and Transcutaneous Auricular Vagus Nerve Stimulation on the Improvement of Working Memory Performance in Healthy Individuals

A previous study found that combining transcranial direct current stimulation (tDCS) and transcutaneous auricular vagus nerve stimulation (taVNS) could evoke significantly larger activation on a range of cortical and subcortical brain regions than the numerical summation of tDCS and taVNS effects. In this study, two within-subject experiments were employed to investigate its effects on working memory (WM). In experiment 1, the WM modulatory effects of tDCS over the left dorsolateral prefrontal cortex (DLPFC), taVNS, and simultaneous joint simulation of tDCS over the left DLPFC and taVNS (SJS-L) were compared among 60 healthy subjects. They received these three interventions between the baseline test and post-test in a random manner three times. In spatial 3-back task, there was a significant interaction between time and stimulations in the accuracy rate of matching trials (mACC, p=0.018). MACCs were significantly improved by SJS (p = 0.001) and taVNS (p = 0.045), but not by tDCS (p = 0.495). Moreover, 41 subjects in the SJS group showed improvement, which was significantly larger than that in the taVNS group (29 subjects) and tDCS group (26 subjects). To further investigate the generalization effects of SJS, 72 students were recruited in experiment 2. They received tDCS over the right DLPFC, taVNS, simultaneous joint simulation of tDCS over the right DLPFC and taVNS (SJS-R), and sham stimulation in a random manner four times. No significant results were found, but there was a tendency similar to experiment 1 in the spatial 3-back task. In conclusion, combining tDCS and taVNS might be a potential non-invasive neuromodulation technique which is worthy of study in future.

The Effect of Non-Invasive Brain Stimulation on the Downregulation of Negative Emotions: A Meta-Analysis

(1) Background: Emotion regulation (ER) is regarded as a core treatment target for depression and other mental illnesses. In recent years, non-invasive brain stimulation (NIBS) has been extensively used as an intervention for mental illnesses, but there has been no systematic review conducted regarding its effect on emotion regulation. Therefore, we conducted a meta-analysis of the effectiveness of NIBS for emotion regulation; (2) Methods: Systematic searches were conducted in Embase, Web of Science, PubMed, and Cochrane Library. We analyzed the effects of NIBS on tasks assessing emotion regulation using a random-effects model, and further explored the moderating role of the following factors on transcranial direct current stimulation (tDCS) studies by conducting subgroup analyses and meta-regression: target electrode placement, return electrode placement, current intensity, target electrode size, and duration of intervention; (3) Results: A total of 17 studies were included. Our meta-analysis indicated a small but significant effect of NIBS on the downregulation of negative emotions. Separate analyses indicated that repetitive transcranial magnetic stimulation (rTMS) had a medium and significant effect on the downregulation of negative emotions, whereas tDCS had no significant effect. Subgroup analyses showed that the effect of tDCS was moderated by target and return electrode placemen; (4) Conclusions: These results indicate that NIBS had a positive effect on the downregulation of negative emotions. The stimulation protocols should be carefully considered and the underlying mechanisms should be further explored.

Effects of tDCS on the attentional blink revisited: A statistical evaluation of a replication attempt

The attentional blink (AB) phenomenon reveals a bottleneck of human information processing: the second of two targets is often missed when they are presented in rapid succession among distractors. In our previous work, we showed that the size of the AB can be changed by applying transcranial direct current stimulation (tDCS) over the left dorsolateral prefrontal cortex (lDLPFC) (London & Slagter, Journal of Cognitive Neuroscience, 33, 756-68, 2021). Although AB size at the group level remained unchanged, the effects of anodal and cathodal tDCS were negatively correlated: if a given individual's AB size decreased from baseline during anodal tDCS, their AB size would increase during cathodal tDCS, and vice versa. Here, we attempted to replicate this finding. We found no group effects of tDCS, as in the original study, but we no longer found a significant negative correlation. We present a series of statistical measures of replication success, all of which confirm that both studies are not in agreement. First, the correlation here is significantly smaller than a conservative estimate of the original correlation. Second, the difference between the correlations is greater than expected due to sampling error, and our data are more consistent with a zero-effect than with the original estimate. Finally, the overall effect when combining both studies is small and not significant. Our findings thus indicate that the effects of lDPLFC-tDCS on the AB are less substantial than observed in our initial study. Although this should be quite a common scenario, null findings can be difficult to interpret and are still under-represented in the brain stimulation and cognitive neuroscience literatures. An important auxiliary goal of this paper is therefore to provide a tutorial for other researchers, to maximize the evidential value from null findings.

Intermittent theta burst stimulation over the parietal cortex has a significant neural effect on working memory

The crucial role of the parietal cortex in working memory (WM) storage has been identified by fMRI studies. However, it remains unknown whether repeated parietal intermittent theta‐burst stimulation (iTBS) can improve WM. In this within‐subject randomized controlled study, under the guidance of fMRI‐identified parietal activation in the left hemisphere, 22 healthy adults received real and sham iTBS sessions (five consecutive days, 600 pulses per day for each session) with an interval of 9 months between the two sessions. Electroencephalography signals of each subject before and after both iTBS sessions were collected during a change detection task. Changes in contralateral delay activity (CDA) and K‐score were then calculated to reflect neural and behavioral WM improvement. Repeated‐measures ANOVA suggested that real iTBS increased CDA more than the sham one (p = .011 for iTBS effect). Further analysis showed that this effect was more significant in the left hemisphere than in the right hemisphere (p = .029 for the hemisphere‐by‐iTBS interaction effect). Pearson correlation analyses showed significant correlations for two conditions between CDA changes in the left hemisphere and K score changes (ps <.05). In terms of the behavioral results, significant K score changes after real iTBS were observed for two conditions, but a repeated‐measures ANOVA showed a nonsignificant main effect of iTBS (p = .826). These results indicate that the current iTBS protocol is a promising way to improve WM capability based on the neural indicator (CDA) but further optimization is needed to produce a behavioral effect.

Transcranial direct current stimulation combined with alcohol cue inhibitory control training reduces the risk of early alcohol relapse: A randomized placebo-controlled clinical trial

BACKGROUND

Approximately half of all people with alcohol use disorder (AUD) relapse into alcohol reuse in the next few weeks after a withdrawal treatment. Brain stimulation and cognitive training represent recent forms of complementary interventions in the context of AUD.

OBJECTIVE

To evaluate the clinical efficacy of five sessions of 2 mA bilateral transcranial direct current stimulation (tDCS) for 20 min over the dorsolateral prefrontal cortex (DLPFC) (left cathodal/right anodal) combined with alcohol cue inhibitory control training (ICT) as part of rehabilitation. The secondary outcomes were executive functioning (e.g. response inhibition) and craving intensity, two mechanisms strongly related to abstinence.

METHODS

A randomized clinical trial with patients (n = 125) with severe AUD at a withdrawal treatment unit. Each patient was randomly assigned to one of four conditions, in a 2 [verum vs. sham tDCS] x 2 [alcohol cue vs. neutral ICT] factorial design. The main outcome of treatment was the abstinence rate after two weeks or more (up to one year).

RESULTS

Verum tDCS improved the abstinence rate at the 2-week follow-up compared to the sham condition, independently of the training condition (79.7% [95% CI = 69.8-89.6] vs. 60.7% [95% CI = 48.3-73.1]; p = .02). A priori contrasts analyses revealed higher abstinence rates for the verum tDCS associated with alcohol cue ICT (86.1% [31/36; 95% CI = 74.6-97.6]) than for the other three conditions (64% [57/89; 95% CI = 54-74]). These positive clinical effects on abstinence did not persist beyond two weeks after the intervention. Neither the reduction of craving nor the improvement in executive control resulted specifically from prefrontal-tDCS and ICT.

CONCLUSIONS

AUD patients who received tDCS applied to DLPFC showed a significantly higher abstinence rate during the weeks following rehabilitation. When combined with alcohol specific ICT, brain stimulation may provide better clinical outcomes.

TRIAL REGISTRATION

ClinicalTrials.gov number NCT03447054 https://clinicaltrials.gov/ct2/show/NCT03447054.