Sham tDCS: A hidden source of variability? Reflections for further blinded, controlled trials

Transcranial direct current stimulation combined with an intensive training program for upper limb rehabilitation in children with unilateral cerebral palsy. A randomized controlled pilot study

BACKGROUND

Unilateral cerebral palsy (UCP) presents a greater functional alteration of the upper limb. Among the recommended interventions are certain therapeutic tools, such as transcranial direct current stimulation (tDCS) that could increase the therapeutic window and enhance the effect of interventions.

AIMS

To determine the effectiveness of a 3-weeks intervention of cathodal tDCS applied over the motor cortex of the less affected hemisphere combined with a manual function intensive training program in the upper limbs on quality of movement and the spontaneous use of upper limb in children with UCP. Secondarily, quality of life and user´s experience was also assessed.

METHODS AND PROCEDURES

A pilot randomized triple-blind clinical trial was conducted. 18 children with UCP between 4 and 8 years were recruited and randomly allocated to one of the two experimental groups: 1) Active group: cathodal tDCS + intensive motor training; 2) Control group: Sham tDCS + intensive motor training. Assessments were performed before and after the intervention, and at three months follow-up.

OUTCOMES AND RESULTS

Outcome measures: Shriners Hospital Upper Extremity Evaluation children's manual experience questionnaire, Paediatric Quality of Life Questionnaire and the Children's Manual Experience Questionnaire (miniCHEQ). Both groups improved in all variables but in the inter-group analysis only quality of life obtained significant results (p = 0.043).

CONCLUSIONS AND IMPLICATIONS

Adding cathodal tDCS to a program of intensive manual function therapy training did not produce a greater improvement on the spontaneous use, nor improving the experience of use in children with UCP. However, this technique has a short-term beneficial effect on quality of life.

Safety and Blinding of Transcranial Direct Current Stimulation in Schizophrenia Patients

INTRODUCTION

Transcranial direct current stimulation (tDCS) is a method of noninvasive brain stimulation. tDCS clinical efficacy is debatable, but it was proved to be effective at the neurophysiological level. tDCS has a very good safety profile in human subjects. Because the method has been more frequently studied in patients with schizophrenia, we wanted to analyze the safety and tolerability of tDCS treatment in this population. We also evaluated blinding quality of tDCS stimulations.

MATERIAL AND METHODS

All stimulations were performed using the DC-Stimulator PLUS (neuroCare, Germany) with the sham module installed. For all the stimulations, 2.0-mA current and 5 × 7-cm anode and cathode rubber electrodes in saline-soaked sponges were used.

RESULTS

We collected and evaluated safety data in a large dataset of 1139 tDCS stimulations in patients with schizophrenia. No serious adverse events were recorded. None of the subjects discontinued tDCS treatment due to side effects. All the reported events resolved spontaneously within 30 minutes after the tDCS session. In approximately 17% of all the stimulations, no side effects were reported by the patients. The 2 most frequent types of side effects were itching/tingling (reported by 68.4% of the subjects) and burning/warmth sensations (57.4%, when combined).

DISCUSSION

This study confirms that tDCS is safe and well tolerated by patients with schizophrenia. The most frequent side effects are itching/tingling and burning/warmth sensations, all of low severity. We found that blinding of tDCS stimulations is imperfect. We recommend that blinding assessment become a routine part of sham-controlled tDCS studies.

Immediate and long-term effects of transcranial direct current stimulation on pain relief in older adults with Alzheimer's disease and related dementias: A pilot study

We simultaneously assessed the impact of transcranial direct current stimulation (tDCS) on mitigating both self-reported pain and pain behaviors to more objectively explore its effects in older adults with Alzheimer's disease and related dementias. The analysis investigated 40 participants randomly (1:1) subjected to active and sham tDCS for 20 min on 5 consecutive days. Multi-group latent transition analysis enabled the simultaneous evaluation of both pain domains in a single model and analysis of their changes as a function of intervention exposure by modeling the transition probabilities of latent classes and comparing these changes between groups. Two pain categories ("high pain" and "low pain") were identified based on the numeric rating scale and mobilization-observation-behavior-intensity-dementia scale scores. Overall, tDCS demonstrated better effects in helping participants transition to a "low pain" status during and after the intervention (∼3 months) compared with sham stimulation, demonstrating its immediate and enduring effects.

Learning from missteps: Potential of transcranial electrical stimulation in neuropsychological rehabilitation

Transcranial electrical stimulation (tES) holds promise for neuropsychological rehabilitation by leveraging the brain's inherent plasticity to enhance cognitive and motor functions. However, early results have been variable due to oversimplified approaches. This manuscript explores the potential and complexities of tES, particularly focusing on a protocol defined transcranial direct current stimulation as a reference model for all tES protocols, emphasising the need for precision in tailoring stimulation parameters to individual characteristics. By integrating intrinsic (i.e. the neuro-physiological system state) and extrinsic factors (i.e. experimental set up), highlighting the critical role of state-dependent effects and the synergy with cognitive tasks, we aim to refine tES protocols. This approach not only addresses the complexity of the brain system (as defined by its current state) but also highlights the importance of collaborative research and data sharing to understand the underlying mechanisms of tES-induced changes and optimising therapeutic efficacy. Emphasising the integration of tES with targeted tasks and clearer hypotheses, this work underscores the potential for more effective neurorehabilitation strategies.

Ageing changes the proprioceptive contribution to balance control under different types of mastoid vibration: A cross-sectional study

Ageing-related sensory deteriorations are significantly associated with poor balance control among older individuals, resulting in a higher risk of falling in a dark environment. In particular, the proprioceptive system plays a critical role in maintaining balance. This study aimed to determine how ageing-related sensory deteriorations contributed to balance control during standing under various sensory conflicts. Twenty healthy, active adults (10 young and 10 older) participated in this study. Balance control was quantified through two sensory organization test conditions (SOT-1: unblindfolded standing; SOT-2: blindfolded standing). Mastoid vibration (MV) was applied unilaterally (Uni) or bilaterally (Bi) to mastoid processes, for perturbing vestibular inputs. A total of six trials were assigned to each participant in a random order. Dependent variables included traveling route (TR), performance index (PI) and sample entropy (SaEn) in the anterior-posterior (AP) and medial-lateral (ML) directions. Our results showed that (1) compared to without MV, applying MV significantly increased TR_AP (Uni: P = 0.003; Bi: P < 0.001) and TR_ML (Uni: P = 0.009; Bi: P = 0.011) of all participants during blindfolded standing; (2) the application of Uni and Bi significantly increased PI_AP, PI_ML, SaEn_AP and SaEn_ML of young and older adults when standing in the SOT-1 and SOT-2 conditions (P < 0.05); and (3) older adults demonstrated significantly higher PI_AP, PI_ML and SaEn_ML than young adults in standing. This study indicated the potential risk of imbalance attributed to ageing-related proprioceptive and vestibular deteriorations even in healthy older adults. Furthermore, unilateral MV had a stronger effect on disturbing ML balance control than bilateral MV.

Transcranial direct current stimulation and its effect on cognitive symptoms of schizophrenia: An updated review

Objective

Cognitive impairments in schizophrenia significantly affect functional outcomes and quality of life. This meta-analysis evaluates the effectiveness of transcranial direct current stimulation (tDCS) as an intervention for cognitive deficits in individuals with schizophrenia.

Methods

From May 20 to June 15, 2024, a systematic search of PubMed, Medline, Embase, and the Cochrane central register of controlled trials was conducted. After applying eligibility criteria, 13 randomized sham-controlled trials were included, involving 261 participants in the tDCS group and 247 in the sham group. Standardized mean difference (SMD) was computed to measure the effect size of cognitive outcomes. Statistical analyses were performed using a random-effects model to account for heterogeneity.

Results

The pooled analysis yielded an SMD of 0.09 (95 % CI: -0.17 to 0.35), indicating a non-significant difference between tDCS and sham on cognitive outcomes. Moderate heterogeneity (I2 = 44 %) was observed, attributed to variations in tDCS protocols, participant demographics, and cognitive assessment tools. Although certain studies showed improvements in specific domains like working memory, the overall impact of tDCS on cognitive symptoms was not statistically significant.

Conclusions

This meta-analysis underscores the lack of significant evidence for tDCS in improving cognitive deficits in schizophrenia. The findings highlight the urgent need for standardizing tDCS protocols and employing domain-specific cognitive assessments. This standardization, along with the collection of more domain-specific data, is crucial for future research and the improvement of current methodologies.

Neurophysiological approaches for managing pain in multiple sclerosis: a mini review

Chronic pain is a prevalent yet often under-recognized symptom among individuals with multiple sclerosis (MS), affecting 29-86% of the population. This condition can significantly impact the individuals' functionality, including their capacity to engage in professional activities. The pathophysiology underlying this condition remains intricate and not fully elucidated, and inadequate responses to pharmacological interventions or adverse effects can hinder its management. In light of these observations, there is an urgent need to identify new therapeutic interventions. Non-invasive brain stimulation (NIBS) techniques hold promise for addressing MS-related pain. This mini-review aims to analyze the findings from studies using NIBS techniques, such as transcranial direct current stimulation (tDCS) and repetitive transcranial magnetic stimulation (rTMS), to assess their analgesic potential in people with MS. Seven relevant reports are available. Five of these studies used tDCS, one utilized a transcranial random noise stimulation (tDCS variant), and one compared rTMS with transcranial theta burst stimulation (rTMS variant). The results indicate the potential benefits of NIBS for pain management in MS. However, the study's limitations, including the scarcity of data, small sample size, the limited number of sessions, sham design, and brief follow-up, are also noted and discussed. Finally, directions for future research are suggested.

Home-based transcranial direct current stimulation paired with cognitive training to reduce fatigue in multiple sclerosis

Fatigue is a common and often debilitating feature of multiple sclerosis (MS) that lacks reliably effective treatment options for most patients. Transcranial direct current stimulation (tDCS), a safe and well-tolerated type of noninvasive brain stimulation, is a low-cost and home-based approach with the potential to reduce fatigue in MS. We conducted a double-blind, sham-controlled, randomized clinical trial to compare active vs. low-dose (sham) tDCS paired with computer-based cognitive training, delivered as a home-based intervention, to reduce MS-related fatigue. Participants with MS-related fatigue, but without depression, were stratified by neurologic disability using the Extended Disability Status Scale (EDSS) and randomized to complete 30 daily sessions over six weeks of either active or sham tDCS paired with online cognitive training (BrainHQ). The primary outcome was the change in PROMIS Fatigue score from baseline to the end of the intervention. A total of 117 participants were randomized, with 92% completing all treatment sessions. Both groups showed significant reductions in fatigue, with no significant difference between them. This suggests that tDCS does not provide any additional benefit over cognitive training alone in reducing fatigue, but confirms the feasibility and tolerance of this home-based intervention.

Fatigue relief in multiple sclerosis by personalized neuromodulation: A multicenter pilot study [FaremusGE]

BACKGROUND

A recent application of the GRADE guidelines indicated Faremus, a 5-day neuromodulation for 15 min per day via transcranial direct current stimulation (tDCS), as medium to highly recommendable for alleviating fatigue in multiple sclerosis (MS).

METHODS

With this pilot study we aimed to evaluate the feasibility, acceptance, safety, and effectiveness of the Faremus treatment carried out in a multicenter context. The Rome unit prepared the intervention, supplied the personalized electrodes to the San Martino Hospital in Genova, where the neurological team enrolled the population of fatigued people with multiple sclerosis (PwMS) and carried out the treatment.

RESULTS

All 17 enrolled patients completed treatment, reporting optimal acceptance and safety when using Faremus in the multicenter setting. The team involved, including neurologists, neurophysiopathology technicians, engineers, physicists, and psychologists expressed high appreciation (average score 8 out of 10). The treatment improved fatigue symptoms by an average of 27%, to levels comparable with previous studies. Similarly, mild depressive symptoms improved by an average of 38%.

CONCLUSIONS

The Faremus personalized electroceutical intervention, a 5-day anodal tDCS over bilateral whole-body somatosensory cortex with occipital cathode, is well accepted and can be applied feasibly, safely and effectively in a multicenter setting, offering a reliable tool to relieve fatigue-related symptoms, thus supporting the quality of life of fatigued people with MS. The present study lays a starting point for the involvement of multiple MS units nationwide in offering therapeutic enrichment for their fatigued patients.

Stochastic galvanic vestibular stimulation improves kinetic performance in adolescent idiopathic scoliosis during obstacle negotiation

Vestibular dysfunction has been reported as a potential cause in adolescent idiopathic scoliosis (AIS). However, it remained unclear how stochastic galvanic vestibular stimulation (GVS) affected kinetic performance of patients with AIS. This study aimed to investigate the effect of stochastic GVS on ground reaction forces (GRF) measures during obstacle negotiation among patients with AIS. Fifteen patients with AIS and 15 age/sex-matched healthy controls (HC) participated in this study. Stochastic GVS was applied via electrodes placed over bilateral mastoid process with the intensity of 80% of individual sensory thresholds. Six walking trials including 2 types of GVS (stochastic GVS/sham stimulation) and 3 obstacle conditions (Level/Low/High) were randomly allocated to each participant, and each trial was repeated 3 times. Four AMTI force plates were used to measure GRF peaks and impulses in anterior-posterior (AP1/AP2), medial-lateral (ML1/ML2), and vertical (V1/V2) directions. Significant interactions were observed in AP1 (F2,56=3.537, p = 0.036), V1 (F2,56=4.118, p = 0.021), ML1 (F2,56=3.313, p = 0.044) and medial-lateral impulses (F2,56=4.386, p = 0.017) for the step negotiating obstacles. Post-hoc comparisons showed that in comparison to sham stimulation, the application of stochastic GVS significantly (1) increased AP1 (Low: p = 0.038) and V1 (Low: p < 0.001; High: p = 0.035) in two groups; (2) decreased ML1 of two groups (AIS: ps < 0.01; HC: ps < 0.05) and medial-lateral impulses in patients with AIS (Low: p = 0.013; High: p = 0.015) during obstacle negotiation. Additionally, the rates of change in ML1 and medial-lateral impulses among patients with AIS were significantly higher than that of HC, indicating that stochastic GVS demonstrated a greater effect of decreasing ML1 and medial-lateral impulses in AIS. Stochastic GVS ameliorated kinetic performance of patients with AIS during obstacle negotiation, and its potential mechanism may involve the induction of stochastic resonance phenomenon to enhance vestibular perception. Our study offered stochastic GVS as a novel approach to target vestibular-related postural instability in AIS.

Effects of Different Transcranial Direct Current Stimulation Intensities over Dorsolateral Prefrontal Cortex on Brain Electrical Activity and Heart Rate Variability in Healthy and Fibromyalgia Women: A Randomized Crossover Trial

People with fibromyalgia (FM) exhibit alterations in brain electrical activity and autonomic modulation compared to healthy individuals. Objectives: This study aimed to investigate transcranial direct current stimulation (tDCS) effects on brain electrocortical activity and heart rate variability (HRV), specifically targeting the dorsolateral prefrontal cortex in both healthy controls (HC) and FM groups, to identify potential differences in the responses between these groups, and to compare the effectiveness of two distinct tDCS intensities (1 mA and 2 mA) against a sham condition. Methods: Electroencephalography and electrocardiogram signals were recorded pre- and post-tDCS intervention. All participants underwent the three conditions (sham, 1 mA, and 2 mA) over three separate weeks, randomized in order. Results: No statistically significant baseline differences were found in the investigated HRV variables. In the FM group, 1 mA tDCS induced significant increases in LF, LF/HF, mean HR, SDNN, RMSSD, total power, SD1, SD2, and SampEn, and a decrease in HF, suggesting a shift toward sympathetic dominance. Additionally, 2 mA significantly increased SampEn compared to sham and 1 mA. In the HC group, sham increased DFA1 compared to 1 mA, and 2 mA induced smaller changes in SampEn relative to sham and 1 mA. No significant differences were found between FM and HC groups for any tDCS intensity. Conclusions: The effects of dlPFC-tDCS on HRV are intensity- and group-dependent, with the FM group exhibiting more pronounced changes at 1 mA and 2 mA. These findings emphasize the need for individualized stimulation protocols, given the variability in responses across groups and intensities.

Blinding of transcranial direct current stimulation is compromised in typically developing children compared to young adults

Achieving successful blinding is a persistent challenge for clinical trials involving transcranial direct current stimulation. Studies involving populations with increased sensory sensitivity, such as children, could be at risk for increased bias from inadequate blinding due to unique sensation of stimulation relative to adults. The objectives of this study were 1) To examine differences in transcranial stimulation blinding between children and young adults and its relationship to sensory sensitivity. 2) To test the efficacy of an ActiSham protocol for participant blinding, compared to a traditional sham protocol. Typically developing right-handed children (N = 12, 5-14 yr) and young adults (N = 15, 15-25 yr) completed a single-session study to test transcranial stimulation blinding after three conditions counterbalanced across participants: Active, Sham and ActiSham. Stimulation was paired with a motor learning task to simulate a combinatory neurorehabilitation intervention. After each condition, participants reported if they received real or fake stimulation and their response confidence. To quantify sensory sensitivity, participants completed the Sensory Profile (second edition). Compared to a chance level, 1) children and young adults correctly identified Active stimulation, 2) children incorrectly identified Sham and ActiSham stimulation and 3) young adults identified Sham and ActiSham stimulation at chance-level. Blinding accuracy was not related to sensory sensitivity. Children report stimulation as real stimulation with higher confidence for almost all conditions, indicating unsuccessful blinding compared to young adults. Future studies should consider alternative sham protocols or methods to improve blinding in child participants.

Effects of cerebellar transcranial direct current stimulation on the excitability of spinal motor neurons and vestibulospinal tract in healthy individuals

Cerebellar transcranial direct current stimulation (ctDCS) modulates cerebellar cortical excitability in a polarity-dependent manner and affects inhibitory pathways from the cerebellum. The cerebellum modulates spinal reflex excitability via the vestibulospinal tract and other pathways projecting to the spinal motor neurons; however, the effects of ctDCS on the excitability of spinal motor neurons and vestibulospinal tract remain unclear. The experiment involved 13 healthy individuals. ctDCS (sham-ctDCS, anodal-ctDCS, and cathodal-ctDCS) was applied to the cerebellar vermis at 2 mA with an interval of at least 3 days between each condition. We measured the maximal M-wave (Mmax) and maximal H-reflex (Hmax) in the right soleus muscle to assess the excitability of spinal motor neurons. We applied galvanic vestibular stimulation (GVS) for 200 ms at 100 ms before tibial nerve stimulation to measure Hmax conditioned by GVS (GVS-Hmax) and calculated the change rate of Hmax by GVS as the excitability of vestibulospinal tract. We measured the Mmax, Hmax, and GVS-Hmax before, during, and after ctDCS in the sitting posture. No main effects of tDCS condition, main effects of time, or interaction effects were observed in Hmax/Mmax or the change rate of Hmax by GVS. It has been suggested that ctDCS does not affect the excitability of spinal motor neurons and vestibulospinal tract, as measured by neurophysiological methods, such as the H-reflex, in healthy individuals in a sitting posture. Effect of ctDCS on other descending pathways to spinal motor neurons, the neurological mechanism of tDCS and the cerebellar activity during the experiment may have contributed to these results. Therefore, we need to investigate the involvement of the cerebellum in Hmax/Mmax and the change rate of Hmax by GVS under different neuromodulation techniques and postural conditions.

Cognitive potency and safety of tDCS treatment for major depressive disorder: a systematic review and meta-analysis

Background

The benefits of transcranial direct current stimulation (tDCS) for patients with major depression disorders are well-established, however, there is a notable research gap concerning its comprehensive effects on both depressive symptoms and cognitive functions. Existing research is inconclusive regarding the cognitive enhancement effects of tDCS specifically in MDD patients. The present study aims to fill this knowledge gap by scrutinizing the most updated evidence on the effectiveness of tDCS in anti-depressive treatment and its influence on cognitive function.

Methods

A systematic review was performed from the first date available in PubMed, EMBASE, Cochrane Library, and additional sources published in English from 1 January 2001 to 31 May 2023. We examined cognitive outcomes from randomized, sham-controlled trials of tDCS treatment for major depression. The evaluation process strictly followed the Cochrane bias risk assessment tool into the literature, and meta-analysis was performed according to the Cochrane System Reviewer's Manual.

Results

In this quantitative synthesis, we incorporated data from a total of 371 patients across 12 studies. Results showed significant benefits following active tDCS compared to sham for the antidepressant effect [SMD: -0.77 (-1.44, -0.11)]. Furthermore, active relative to sham tDCS treatment was associated with increased performance gains on a measure of verbal memory [SMD: 0.30 (-0.02, 0.62)]. These results did not indicate any cognitive enhancement after active tDCS relative to sham for global cognitive function, whereas there was a noticeable trend toward statistical significance specifically in the effect of verbal memory.

Conclusions

Our study offers crucial evidence-based medical support for tDCS in antidepressant and dimension-specific cognitive benefits. Further well-designed, large-scale randomized sham-controlled trials are warranted to further validate these findings.

Systematic Review Registration

https://inplasy.com/, identifier: INPLASY202360008.

Simultaneous and cumulative effects of tDCS on cerebral metabolic rate of oxygen in multiple sclerosis

Introduction

Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulation technique with simultaneous (during stimulation) and cumulative effects (after repeated sessions) on blood flow and neuronal metabolism. These effects remain mostly unclear especially in multiple sclerosis (MS). This work aims to elucidate brain metabolic and hemodynamic underpinnings of tDCS and its potential therapeutic impact in MS patients using quantitative tDCS-MRI.

Methods

MS participants (n = 20; age = 45.4 ± 12.3 years, 7 males) underwent 3 T MRI scans before and after 20 daily sessions of dorsolateral prefrontal cortex (DLFPC) tDCS (2.0 mA, left anodal) paired with adaptive cognitive training (aCT). During both visits, imaging measurements of cerebral blood flow (CBF), cerebral venous blood oxygenation (Yv) and calculated cerebral metabolic rate of oxygen (CMRO2) were obtained at pre-tDCS, during-tDCS and post-tDCS.

Results

At baseline, significant increase from pre- to during-tDCS was observed in CMRO2 (7.6%; p = 0.002), CBF (11.0%; p < 0.0001) and Yv (1.9%; p = 0.006). At follow up, we observed an increase in pre-tDCS CMRO2 (140.59 ± 13.83 μmol/100 g/min) compared to baseline pre-tDCS levels (128.30 ± 14.00 μmol/100 g/min; p = 0.006). Sustained elevations in CMRO2 and CBF into post-tDCS were also observed (tDCS lingering effects). Cumulative tDCS effects were observed in the form of sustained elevations in CMRO2 and CBF in pre-tDCS follow up, reaching the magnitudes measured at baseline during-tDCS.

Discussion

TDCS induces an acute surge in metabolic activity persisting immediately after the stimulation is removed. Moreover, treatment composed of repeated tDCS-aCT paired sessions contributes to establishing long-lasting increases in neuronal activity.

Treatment expectations and clinical outcomes following repetitive transcranial magnetic stimulation for treatment-resistant depression

BACKGROUND

Patient expectations, including both positive (placebo) and negative (nocebo) effects, influence treatment outcomes, yet their impact on acute repetitive transcranial magnetic stimulation (rTMS) for treatment-resistant depression (TRD) is unclear.

METHODS

In this single-center retrospective chart review, 208 TRD patients completed the Stanford Expectation of Treatment Scale (SETS) before starting open-label rTMS treatment. Patients were offered two excitatory rTMS protocols (deep TMS or intermittent theta-burst stimulation), which stimulated the left dorsolateral prefrontal cortex. A minimum of 20 once daily treatments were provided, delivered over 4-6 weeks. Primary outcomes were 1) remission, measured by a post-treatment score of <8 on the Hamilton Depression Rating Scale (HAMD-17), and 2) premature discontinuation. The change in HAMD-17 scores over time was used as a secondary outcome. Physicians were blinded to SETS scores. Logistic and linear regression, adjusting for covariates, assessed SETS and HAMD-17 relationships.

RESULTS

Of 208 patients, 177 had baseline and covariate data available. The mean positivity bias score (positive expectancy minus negative expectancy subscale averages) was 0.48 ± 2.21, indicating the cohort was neutral regarding the expectations of their treatment on average. Higher positive expectancy scores were significantly associated with greater odds of remission (OR = 1.90, p = 0.003) and greater reduction in HAMD-17 scores (β = 1.30, p = 0.005) at the end of acute treatment, after adjusting for covariates. Negative expectancy was not associated with decreased odds of remission (p = 0.2) or treatment discontinuation (p = 0.8).

CONCLUSIONS

Higher pre-treatment positive expectations were associated with greater remission rates with open-label rTMS in a naturalistic cohort of patients with TRD.

The impact of the left inferior frontal gyrus on fear extinction: A transcranial direct current stimulation study

INTRODUCTION

Fear extinction is a fundamental component of exposure-based therapies for anxiety-related disorders. The renewal of fear in a different context after extinction highlights the importance of contextual factors. In this study, we aimed to investigate the causal role of the left inferior frontal gyrus (LiFG) in the context-dependency of fear extinction learning via administration of transcranial direct current stimulation (tDCS) over this area.

METHODS

180 healthy subjects were assigned to 9 groups: 3 tDCS conditions (anodal, cathodal, and sham) × 3 context combinations (AAA, ABA, and ABB). The fear conditioning/extinction task was conducted over three consecutive days: acquisition, extinction learning, and extinction recall. tDCS (2 mA, 10min) was administered during the extinction learning phase over the LiFG via a 4-electrode montage. Skin conductance response (SCR) data and self-report assessments were collected.

RESULTS

During the extinction learning phase, groups with excitability-enhancing anodal tDCS showed a significantly higher fear response to the threat cues compared to cathodal and sham stimulation conditions, irrespective of contextual factors. This effect was stable until the extinction recall phase. Additionally, excitability-reducing cathodal tDCS caused a significant decrease of the response difference between the threat and safety cues during the extinction recall phase. The self-report assessments showed no significant differences between the conditions throughout the experiment.

CONCLUSION

Independent of the context, excitability enhancement of the LiFG did impair fear extinction, and led to preservation of fear memory. In contrast, excitability reduction of this area enhanced fear extinction retention. These findings imply that the LiFG plays a role in the fear extinction network, which seems to be however context-independent.

A Comparison between the Effectiveness of computerized Cognitive Rehabilitation Training and transcranial Direct Current Stimulation on Dialysis Patients' Executive Functions

Purpose

Executive function impairments are among the most common dialysis side effects. The present study aims to compare the efficiency of transcranial Direct Current Stimulation (tDCS) with computerized Cognitive Rehabilitation Training (cCRT) on dialysis patients' executive functions.

Research method

The present study, a quasi-experimental effort, adopted a pre-test/post-test method that included a control (sham) group.

Design

The study sample consisted of 30 participants, selected through the convenience sampling method, and categorized into three groups of cCRT, tDCS, and sham participants. The cCRT participants were asked to complete 8 tasks in Captain's Log MindPower Builder software. The tDCS participants were treated with a 0.06 mA/cm2 current with the anodal electrode on F3 and the cathodal electrode on Fp2. For the sham participants, the electrodes were put on the same regions but there was no current stimulation. The treatment lasted for 10 sessions carried out every other day.

Results

The results of MANCOVA showed no significant difference between the sham group and the cCRT group in any of the executive function items. . However, between the sham group and the tDCS group was detected a significant difference in spatial working memory (p \< 0.05) and a marginally significant in cognitive flexibility (p = 0.091). No significant difference was reported between cCRT and tDCS groups in any item.

Conclusion

According to the findings of the study, given the efficacy of tDCS on spatial working memory and cognitive flexibility for dialysis patients, it can be used to improve these skills.

Transcranial direct current stimulation (tDCS) improves emotion regulation in children with attention-deficit hyperactivity disorder (ADHD)

Children with attention deficit/hyperactivity disorder (ADHD) typically exhibit difficulties in emotion regulation. It has been shown that the dorsolateral prefrontal cortex (dlPFC) and ventromedial prefrontal cortex (vmPFC) are crucially involved in these deficient processes. In this study, we aimed to explore the impact of electrical stimulation over the left dlPFC and right vmPFC on emotion regulation in children with ADHD. Twenty-four children with ADHD completed the Emotional Go/No-Go and Emotional 1-Back tasks while undergoing transcranial direct current stimulation (tDCS) in three separate sessions, each with a different electrode placement: anodal dlPFC (F3)/cathodal vmPFC (Fp2), anodal vmPFC (Fp2)/cathodal dlPFC (F3), and sham stimulation. During both real tDCS conditions, the accuracy of pre-potent inhibitory control and working memory performance improved, but not speed. This study provides evidence that the left dlPFC and the right vmPFC are involved in emotion regulation in ADHD.

The Efficacy of the Addition of tDCS and TENS to an Education and Exercise Program in Subjects with Knee Osteoarthritis: A Randomized Controlled Trial

Knee osteoarthritis (KOA) has a significant impact on patients' quality of life. This study aimed to assess the effectiveness of integrating transcranial direct current stimulation (tDCS) and transcutaneous electrical nerve stimulation (TENS) into an education and exercise program with the aim of decreasing pain and improving physical function in KOA. A randomized controlled trial with 65 KOA patients was conducted. The subjects were assigned to one of the following three groups: education and active exercise plus (1) double active tDCS and TENS, (2) active tDCS and sham TENS, and (3) double sham tDCS and TENS. Sessions were conducted over a 20 min period, whilst data on pain, chronic pain clinical variables, and physical function were collected. Although all groups showed improvement in pain-related symptoms in the short and medium term, the addition of tDCS and/or TENS did not significantly enhance the benefits of the exercise and education program. These findings suggest that an education and active exercise program in the treatment of KOA has a positive effect on pain, with or without the addition of tDCS and/or TENS.

Treating refractory obsessive compulsive disorder with cathodal transcranial direct current stimulation over the supplementary motor area: a large multisite randomized sham-controlled double-blind study

Background

The present study evaluated the therapeutic efficacy and tolerability of 10 transcranial direct current stimulation (tDCS) sessions in treatment-resistance obsessive-compulsive disorder (OCD) patients using a multisite double-blind sham-controlled design.

Methods

Eighty treatment-resistance outpatients suffering from obsessive-compulsive disorder were randomized to receive either active or sham transcranial direct current stimulation. The cathode was positioned over the supplementary motor area and the anode over the right supraorbital area. Patients were evaluated at baseline, end of treatment (day 14), one-month follow-up (day 45), and three-month follow-up (day 105) on the Yale-Brown Obsessive Compulsive Scale.

Results

Although a significant interaction between time and treatment was observed, the primary endpoint-measuring the change in Yale-Brown obsessive compulsive scale scores after two weeks-was not achieved. Conversely, the secondary endpoint, which concerned the change in Yale-Brown obsessive compulsive scale scores after three months, was successfully met. It is important to note, however, that there were no significant differences in the percentage of responders and remitters at any of the post-treatment assessments. This suggests that the treatment may not have had a clinically relevant impact. Patients well received the transcranial direct current stimulation treatment, indicating its good tolerability.

Conclusion

This is the largest controlled trial using transcranial direct current stimulation in treatment-resistance obsessive-compulsive disorder patients. Our results indicate the importance of studying the placebo effect in transcranial direct current stimulation and the necessity to consider a long follow-up time to best evaluate the effects of the intervention.

Clinical trial registration

ClinicalTrials.gov, identifier NCT03304600.

Unraveling the brain mechanisms of source monitoring with non-invasive brain stimulation: A systematic review

Background/Objective

Source monitoring refers to the ability to determine the source of memories and encompasses three subprocesses: internal source monitoring, reality monitoring, and external source monitoring. Neuroimaging studies provide valuable insights about neural correlates of source monitoring, but the causal relationship between brain and behavior is lacking. This study aimed to identify brain circuits involved in source monitoring by synthesizing the effects of brain stimulation on source monitoring as a function of the targeted brain regions or circuits.

Method

We conducted a systematic review of interventional studies that have examined the effects of brain stimulation on source monitoring across six databases. The principal outcome was the difference of source monitoring performance between active and control stimulation conditions.

Results

23 studies (920 healthy participants and 54 patients with schizophrenia) were included. Our findings revealed the involvement of i) the lateral prefrontal and temporoparietal cortices in internal source monitoring, ii) the medial prefrontal and temporoparietal cortices in reality monitoring, and iii) the precuneus and the left angular gyrus in external source monitoring.

Conclusions

These findings deepen our understanding of the brain mechanisms of source monitoring and highlight specific stimulation targets to alleviate source monitoring deficits.

The importance of individual beliefs in assessing treatment efficacy

In recent years, there has been debate about the effectiveness of treatments from different fields, such as neurostimulation, neurofeedback, brain training, and pharmacotherapy. This debate has been fuelled by contradictory and nuanced experimental findings. Notably, the effectiveness of a given treatment is commonly evaluated by comparing the effect of the active treatment versus the placebo on human health and/or behaviour. However, this approach neglects the individual's subjective experience of the type of treatment she or he received in establishing treatment efficacy. Here, we show that individual differences in subjective treatment - the thought of receiving the active or placebo condition during an experiment - can explain variability in outcomes better than the actual treatment. We analysed four independent datasets (N = 387 participants), including clinical patients and healthy adults from different age groups who were exposed to different neurostimulation treatments (transcranial magnetic stimulation: Studies 1 and 2; transcranial direct current stimulation: Studies 3 and 4). Our findings show that the inclusion of subjective treatment can provide a better model fit either alone or in interaction with objective treatment (defined as the condition to which participants are assigned in the experiment). These results demonstrate the significant contribution of subjective experience in explaining the variability of clinical, cognitive, and behavioural outcomes. We advocate for existing and future studies in clinical and non-clinical research to start accounting for participants' subjective beliefs and their interplay with objective treatment when assessing the efficacy of treatments. This approach will be crucial in providing a more accurate estimation of the treatment effect and its source, allowing the development of effective and reproducible interventions.

Repetitive temporal interference stimulation improves jump performance but not the postural stability in young healthy males: a randomized controlled trial

BACKGROUND

Temporal interference (TI) stimulation, an innovative non-invasive brain stimulation technique, has the potential to activate neurons in deep brain regions. The objective of this study was to evaluate the effects of repetitive TI stimulation targeting the lower limb motor control area (i.e., the M1 leg area) on lower limb motor function in healthy individuals, which could provide evidence for further translational application of non-invasive deep brain stimulation.

METHODS

In this randomized, double-blinded, parallel-controlled trial, 46 healthy male adults were randomly divided into the TI or sham group. The TI group received 2 mA (peak-to-peak) TI stimulation targeting the M1 leg area with a 20 Hz frequency difference (2 kHz and 2.02 kHz). Stimulation parameters of the sham group were consistent with those of the TI group but the current input lasted only 1 min (30 s ramp-up and ramp-down). Both groups received stimulation twice daily for five consecutive days. The vertical jump test (countermovement jump [CMJ], squat jump [SJ], and continuous jump [CJ]) and Y-balance test were performed before and after the total intervention session. Two-way repeated measures ANOVA (group × time) was performed to evaluate the effects of TI stimulation on lower limb motor function.

RESULTS

Forty participants completed all scheduled study visits. Two-way repeated measures ANOVA showed significant group × time interaction effects for CMJ height (F = 8.858, p = 0.005) and SJ height (F = 6.523, p = 0.015). The interaction effect of the average CJ height of the first 15 s was marginally significant (F = 3.550, p = 0.067). However, there was no significant interaction effect on the Y balance (p > 0.05). Further within-group comparisons showed a significant post-intervention increase in the height of the CMJ (p = 0.004), SJ (p = 0.010) and the average CJ height of the first 15 s (p = 0.004) in the TI group.

CONCLUSION

Repetitive TI stimulation targeting the lower limb motor control area effectively increased vertical jump height in healthy adult males but had no significant effect on dynamic postural stability.

TDCS over PPC or DLPFC does not improve visual working memory capacity

Non-invasive brain stimulation has been highlighted as a possible intervention to induce cognitive benefits, including on visual working memory (VWM). However, findings are inconsistent, possibly due to methodological issues. A recent high-profile study by Wang et al.1 reported that anodal transcranial direct current stimulation (tDCS) over posterior parietal cortex (PPC), but not over dorsolateral prefrontal cortex (DLPFC), selectively improved VWM capacity but not precision, especially at a high VWM load. Thus, in the current pre-registered conceptual replication study, we accounted for the key potential methodological issues in the original study and tested an adequate number of participants required to demonstrate the previously reported effects (n = 48 compared to n = 20). Participants underwent counterbalanced PPC, DLPFC and sham stimulation before completing 360 trials of a continuous orientation-reproduction task with a slight variation of task stimuli and setup. We found no evidence for the selective effect of PPC stimulation. Instead, our results showed that tDCS effects were absent regardless of stimulation region and VWM load, which was largely supported by substantial to strong Bayesian evidence. Therefore, our results challenge previously reported benefits of single-session anodal PPC-tDCS on VWM.

Behavioral Validation of Individualized Low-Intensity Transcranial Electrical Stimulation (tES) Protocols

Large interindividual variability in the effects of low-intensity transcranial electrical stimulation (tES) considerably limits its potential for clinical applications. It has been recently proposed that individualizing stimulation dose by accounting for interindividual anatomic differences would reduce the variability in electric fields (E-fields) over the targeted cortical site and therefore produce more consistent behavioral outcomes. However, improvement in behavioral outcomes following individualized dose tES has never been compared with that of conventional fixed dose tES. In this study, we aimed to empirically evaluate the effect of individualized dose tES on behavior and further compare it with the effects of sham and fixed dose stimulations. We conducted a single-blinded, sham-controlled, repeated-measures study to examine the impact of transcranial direct current stimulation on motor learning and that of transcranial alternating current stimulation on the working memory of 42 healthy adult individuals. Each participant underwent three sessions of tES, receiving fixed dose, individualized dose, or sham stimulation over the targeted brain region for the entire behavioral task. Our results showed that the individualized dose reduced the variability in E-fields at the targeted cortical surfaces. However, there was no significant effect of tES on behavioral outcomes. We argue that although the stimulation dose and E-field intensity at the targeted cortical site are linearly correlated, the effect of E-fields on behavior seems to be more complex. Effective optimization of tES protocols warrants further research considering both neuroanatomical and functional aspects of behavior.

HD-tDCS over the left DLPFC increases cued recall and subjective question familiarity rather than other aspects of memory and metamemory

When retrieving information from memory there is an interplay between memory and metamemory processes, and the prefrontal cortex has been implicated in both memory and metamemory. Previous work shown that High Definition transcranial Direct Current Stimulation (HD-tDCS) over the dorsolateral prefrontal cortex (DLPFC) can lead to improvements in memory and metamemory monitoring, but findings are mixed. Our original design targeted metamemory, but because the prefrontal cortex plays a role in both memory and metamemory, we tested for effects of HD-tDCS on multiple memory tasks (e.g., recall, cued recall, and recognition) and multiple aspects of metamemory (e.g., once-knew-it ratings, feeling-of-knowing ratings, metamemory accuracy, and metamemory control). There were HD-tDCS-related improvements in cued recall performance, but not other memory tasks. For metamemory, there were HD-tDCS-related increases in subjective once-knew-it ratings, but not other aspects of metamemory. These results highlight the need to consider the effects of HD-tDCS on memory and metamemory at different timepoints during retrieval, as well as specific conditions that show benefits from HD-tDCS.

Effects of multisession cathodal transcranial direct current stimulation with cognitive training on sociocognitive functioning and brain dynamics in autism: A double-blind, sham-controlled, randomized EEG study

BACKGROUND

Few treatment options are available for targeting core symptoms of autism spectrum disorder (ASD). The development of treatments that target common neural circuit dysfunctions caused by known genetic defects, namely, disruption of the excitation/inhibition (E/I) balance, is promising. Transcranial direct current stimulation (tDCS) is capable of modulating the E/I balance in healthy individuals, yet its clinical and neurobiological effects in ASD remain elusive.

OBJECTIVE

This double-blind, randomized, sham-controlled trial investigated the effects of multisession cathodal prefrontal tDCS coupled with online cognitive remediation on social functioning, information processing efficiency and the E/I balance in ASD patients aged 14-21 years.

METHODS

Sixty individuals were randomly assigned to receive either active or sham tDCS (10 sessions in total, 20 min/session, stimulation intensity: 1.5 mA, cathode: F3, anode: Fp2, size of electrodes: 25 cm2) combined with 20 min of online cognitive remediation. Social functioning, information processing efficiency during cognitive tasks, and theta- and gamma-band E/I balance were measured one day before and after the treatment.

RESULTS

Compared to sham tDCS, active cathodal tDCS was effective in enhancing overall social functioning [F(1, 58) = 6.79, p = .012, ηp2 = 0.105, 90% CI: (0.013, 0.234)] and information processing efficiency during cognitive tasks [F(1, 58) = 10.07, p = .002, ηp2 = 0.148, 90% CI: (0.034, 0.284)] in these individuals. Electroencephalography data showed that this cathodal tDCS protocol was effective in reducing the theta-band E/I ratio of the cortical midline structures [F(1, 58) = 4.65, p = .035, ηp2 = 0.074, 90% CI: (0.010, 0.150)] and that this reduction significantly predicted information processing efficiency enhancement (b = -2.546, 95% BCa CI: [-4.979, -0.113], p = .041).

CONCLUSION

Our results support the use of multisession cathodal tDCS over the left dorsolateral prefrontal cortex combined with online cognitive remediation for reducing the elevated theta-band E/I ratio in sociocognitive information processing circuits in ASD patients, resulting in more adaptive regulation of global brain dynamics that is associated with enhanced information processing efficiency after the intervention.

Effects of prefrontal transcranial direct current stimulation on social functioning in autism spectrum disorder: A randomized clinical trial

LAY ABSTRACT

Currently available pharmacological and behavioral interventions for adolescents and young adults with autism spectrum disorder (ASD) yield only modest effect in alleviating their core behavioral and cognitive symptoms, and some of these treatment options are associated with undesirable side effects. Hence, developing effective treatment protocols is urgently needed. Given emerging evidence shows that the abnormal connections of the frontal brain regions contribute to the manifestations of ASD behavioral and cognitive impairments, noninvasive treatment modalities that are capable in modulating brain connections, such as transcranial direct current stimulation (tDCS), have been postulated to be potentially promising for alleviating core symptoms in ASD. However, whether tDCS can reduce behavioral symptoms and enhance cognitive performance in ASD remains unclear. This randomized controlled trial involving 105 adolescents and young adults with ASD showed that multiple sessions of a tDCS protocol, which was paired up with computerized cognitive training, was effective in improving social functioning in adolescents and young adults with ASD. No prolonged and serious side effects were observed. With more future studies conducted in different clinical settings that recruit participants from a wider age range, this tDCS protocol may be potentially beneficial to a broad spectrum of individuals with autism.

Targeting right orbitofrontal cortex (OFC) with transcranial direct current stimulation (tDCS) can improve cognitive executive function in a major depressive episode, but not depressive mood: A Double-blind Randomized Controlled Pilot Trial

Transcranial direct current stimulation (tDCS) has emerged as a potential treatment for major depressive episodes (MDE). This study aimed to evaluate the efficacy of targeting the right orbitofrontal cortex (rOFC) with tDCS in improving depressed mood and cognitive function in patients with depression. A double-blind, randomized sham-controlled trial was conducted in which 70 patients with depression were randomly assigned to receive rOFC-tDCS (n = 24), left dorsolateral prefrontal cortex (lDLPFC) tDCS (n = 23), or SHAM (n = 23). The treatment course consisted of ten treatments (2 mA, 20 min) delivered over two weeks. Participants were then given once-a-week interventions for the next two weeks. The Hamilton Depression Scale 17 evaluated the severity of depressive symptoms, while the cognitive function was assessed using the Stroop Color-Word Test (SCWT) and the Wisconsin Card Sorting Test (WCST). The primary outcomes were evaluated following ten interventions, with the assessment additionally conducted after maintenance treatment and 4-week follow-up visits. Analyses were performed using linear mixed models. The trial was registered with ChiCTR2000034671. The study did not reveal antidepressant efficacy for rOFC-tDCS or lDLPFC-tDCS over SHAM. Cognitive performance improved for rOFC -tDCS and lDLPFC-tDCS compared to sham for response time on the SWCT and non-perseverative errors in the WCST. However, no statistically significant difference was observed between the two active stimulation groups concerning cognitive performance-enhancing effects. No serious adverse events were noted. In conclusion, while rOFC-tDCS did not present advantages for mood outcomes over lDLPFC-tDCS and SHAM, it may have promising effectiveness in cognitive executive function compared to SHAM.

Right frontal HD-tDCS reveals causal involvement of time perception networks in temporal processing of concepts

Evidence suggests that perceptual and action related features of concepts are grounded in the corresponding sensory-motor networks in the human brain. However, less is known about temporal features of event concepts (e.g., a lecture) and whether they are grounded in time perception networks. We examined this question by stimulating the right dorsolateral prefrontal cortex (rDLPFC)-a part of time perception network-using HD-tDCS and subsequently recording EEG while participants performed semantic and time perception tasks. Semantic tasks were composed of event noun duration judgment (EDur), object noun size judgement (OSize), event (EVal) and object noun valence judgement. In the time perception task, participants judged the durations of pure tones. Results showed that cathodal stimulation accelerated responses for time perception task and decreased the magnitude of global field power (GFP) compared to sham stimulation. Semantic tasks results revealed that cathodal, but not sham, stimulation significantly decreased GFP for EDur relative to OSize, and to EVal. These findings provide first causal evidence that temporal features of event words are grounded in the rDLPFC as part of the temporal cognition network and shed light on the conceptual processing of time.

Transcranial Direct-Current Stimulation Improves Verbal Fluency in Children with Attention Deficit Hyperactivity Disorder (ADHD)

Individuals with attention deficit hyperactivity disorder (ADHD) struggle with impaired verbal fluency as an executive function. The left and right dorsolateral prefrontal cortex (dlPFC) and the right inferior frontal gurus (IFG), which show reduced functionality in individuals with ADHD, are involved in verbal fluency. In this study, a total of thirty-seven children with ADHD participated in two separate experiments. Each experiment included three different stimulation conditions: anodal left dlPFC/cathodal right vmPFC stimulation, the reversed montage, and a sham stimulation in Experiment 1, and anodal right dlPFC, anodal right IFG with extracranial return electrode, and a sham stimulation in Experiment 2. During each session, participants performed semantic and phonemic verbal fluency tasks while receiving tDCS. The results revealed a significant main effect of stimulation condition on phonemic verbal fluency during anodal left dlPFC stimulation in Experiment 1, and on semantic verbal fluency during both real stimulation conditions in Experiment 2. In conclusion, this study suggests that anodal left dlPFC stimulation improves phonemic verbal fluency, while anodal right dlPFC and right IFG stimulation enhance semantic verbal fluency. This domain-specific improvement can be attributed to the distinct cognitive demands of phonemic and semantic verbal fluency tasks. Phonemic verbal fluency heavily relies on working memory processes, whereas semantic verbal fluency requires effective inhibitory control and cognitive flexibility.

Dual-hemisphere anodal transcranial direct current stimulation improves bilateral motor synergies

Transcranial direct current stimulation (tDCS) is one of the non-invasive brain stimulation techniques that can improve motor functions. As bimanual motor actions require high motor cortical activations between hemispheres, applying bilateral anodal stimulation on left and right sides of primary motor cortex (M1) can improve for improvements in bimanual motor tasks. This study investigated which bilateral tDCS protocol effectively improves bimanual hand-grip force control capabilities in healthy young adults. We used three different bilateral tDCS protocols: (a) dual-anodal stimulation on the M1 of bilateral hemispheres (Bi-AA), (b) anodal-cathodal stimulation on the M1 of dominant and nondominant hemispheres (Bi-AC), and (c) sham stimulation (Sham). The results indicated that applying the Bi-AA significantly improved bilateral motor synergies estimated by uncontrolled manifold analysis relative to Sham. However, these differences were not observed in the comparison between Bi-AA and Bi-AC as well as between Bi-AC and Sham. These findings suggest that facilitating motor cortical activations between both hemispheres may be an additional option for advancing interlimb motor coordination patterns.

Reinterpreting published tDCS results in terms of a cranial and cervical nerve co-stimulation mechanism

Transcranial direct current stimulation (tDCS) is a non-invasive neuromodulation method that has been used to alter cognition in hundreds of experiments. During tDCS, a low-amplitude current is delivered via scalp electrodes to create a weak electric field in the brain. The weak electric field causes membrane polarization in cortical neurons directly under the scalp electrodes. It is generally assumed that this mechanism causes the observed effects of tDCS on cognition. However, it was recently shown that some tDCS effects are not caused by the electric field in the brain but rather via co-stimulation of cranial and cervical nerves in the scalp that also have neuromodulatory effects that can influence cognition. This peripheral nerve co-stimulation mechanism is not controlled for in tDCS experiments that use the standard sham condition. In light of this new evidence, results from previous tDCS experiments could be reinterpreted in terms of a peripheral nerve co-stimulation mechanism. Here, we selected six publications that reported tDCS effects on cognition and attributed the effects to the electric field in the brain directly under the electrode. We then posed the question: given the known neuromodulatory effects of cranial and cervical nerve stimulation, could the reported results also be understood in terms of tDCS peripheral nerve co-stimulation? We present our re-interpretation of these results as a way to stimulate debate within the neuromodulation field and as a food-for-thought for researchers designing new tDCS experiments.

A blended neurostimulation protocol to delineate cortico-muscular and spino-muscular dynamics following neuroplastic adaptation

In this paper we propose a novel neurostimulation protocol that provides an intervention-based assessment to distinguish the contributions of different motor control networks in the cortico-spinal system. Specifically, we use a combination of non-invasive brain stimulation and neuromuscular stimulation to probe neuromuscular system behavior with targeted impulse-response system identification. In this protocol, we use an in-house developed human-machine interface (HMI) for an isotonic wrist movement task, where the user controls a cursor on-screen. During the task, we generate unique motor evoked potentials based on triggered cortical or spinal level perturbations. Externally applied brain-level perturbations are triggered through TMS to cause wrist flexion/extension during the volitional task. The resultant contraction output and related reflex responses are measured by the HMI. These movements also include neuromodulation in the excitability of the brain-muscle pathway via transcranial direct current stimulation. Colloquially, spinal-level perturbations are triggered through skin-surface neuromuscular stimulation of the wrist muscles. The resultant brain-muscle and spinal-muscle pathways perturbed by the TMS and NMES, respectively, demonstrate temporal and spatial differences as manifested through the human-machine interface. This then provides a template to measure the specific neural outcomes of the movement tasks, and in decoding differences in the contribution of cortical- (long-latency) and spinal-level (short-latency) motor control. This protocol is part of the development of a diagnostic tool that can be used to better understand how interaction between cortical and spinal motor centers changes with learning, or injury such as that experienced following stroke.

Effects of Prefrontal Transcranial Direct Current Stimulation on Retention of Performance Gains on an Obstacle Negotiation Task in Older Adults

OBJECTIVES

Complex walking in older adults can be improved with task practice and might be further enhanced by pairing transcranial direct current stimulation (tDCS) to the dorsolateral prefrontal cortex. We tested the hypothesis that a single session of practice of a complex obstacle negotiation task paired with active tDCS in older adults would produce greater within-session improvements in walking performance and retention of gains, compared to sham tDCS and no tDCS conditions.

MATERIALS AND METHODS

A total of 50 older adults (mean age = 74.46 years ± 6.49) with self-reported walking difficulty were randomized to receive either active tDCS (active-tDCS group) or sham tDCS (sham-tDCS group) bilaterally to the dorsolateral prefrontal cortex or no tDCS (no-tDCS group). Each group performed ten practice trials of an obstacle negotiation task at their fastest safe speed. Retention of gains in walking performance was assessed with three trials conducted one week later. Within-session effects of practice and between-session retention effects on obstacle negotiation speed were examined.

RESULTS

At the practice session, all three groups exhibited significant within-session gains in walking speed (p ≤ 0.005). However, the gains were significantly greater in the sham-tDCS group than in the active-tDCS and no-tDCS groups (p ≤ 0.03) and were comparable between the active-tDCS and no-tDCS groups (p = 0.89). At one-week follow-up, the active-tDCS group exhibited significant between-session retention of gains and continued "offline" improvement in walking speed (p = 0.005). The active-tDCS group showed significantly greater retention of gains than the no-tDCS (p = 0.02) but not the sham-tDCS group (p = 0.24).

CONCLUSIONS

Pairing prefrontal active tDCS with a single session of obstacle negotiation practice may enhance one-week retention of gains in walking performance compared to no tDCS. However, the evidence is insufficient to suggest a benefit of active tDCS over sham tDCS for enhancing the gains in walking performance. Additional studies with a multisession intervention design and larger sample size are needed to further investigate these findings.

CLINICAL TRIAL REGISTRATION

The Clinicaltrials.gov registration number for the study is NCT03122236.

Transcranial direct current stimulation during a prolonged cognitive task: the effect on cognitive and shooting performances in professional female basketball players

The negative effect of prolonged cognitive demands on psychomotor skills in athletes has been demonstrated. Transcranial direct current stimulation (tDCS) could be used to mitigate this effect. This study examined the effects of tDCS over the left dorsolateral prefrontal cortex (DLPFC) during a 30-min inhibitory Stroop task on cognitive and shooting performances of professional female basketball players. Following a randomised, double-blinded, sham-controlled, cross-over design, players were assigned to receive anodal tDCS (a-tDCS, 2 mA for 20 min) or sham-tDCS in two different sessions. Data from 8 players were retained for analysis. Response Time decreased significantly over time (p < 0.001; partial η² = 0.44; no effect of condition, or condition vs. time interaction). No difference in mean accuracy and shooting performance was observed between tDCS conditions. The results suggest that a-tDCS exert no additional benefits in reducing the negative effects of prolonged cognitive demands on technical performance compared to sham (placebo).Practitioner summary: Prolonged cognitive demands can negatively affect the athletes' performance. We tested whether transcranial direct current stimulation (tDCS) over the left dorsolateral prefrontal cortex (DLPFC) could attenuate these effects on cognitive and shooting performance in professional female basketball players. However, tDCS did not exert any additional benefits compared to sham.Abbreviations: tDCS: transcranial direct current stimulation; a-tDCS: anodal transcranial direct current stimulation; PFC: prefrontal cortex; DLPFC: dorsolateral prefrontal cortex; PCT: prolonged cognitive task; TT: time trial; RT: response time; NASA-TLX: National Aeronautics and Space Administration Task Load Index; RPE: ratings of perceived exertion; CR-10 scale: category rating scale; EEG: electroencephalogram; AU: arbitrary units.

Transcranial direct current stimulation for bipolar depression: systematic reviews of clinical evidence and biological underpinnings

Despite multiple available treatments for bipolar depression (BD), many patients face sub-optimal responses. Transcranial direct current stimulation (tDCS) has been advocated in the management of different conditions, including BD, especially in treatment-resistant cases. The optimal dose and timing of tDCS, the mutual influence with other concurrently administered interventions, long-term efficacy, overall safety, and biological underpinnings nonetheless deserve additional assessment. The present study appraised the existing clinical evidence about tDCS for bipolar depression, delving into the putative biological underpinnings with a special emphasis on cellular and molecular levels, with the ultimate goal of providing a translational perspective on the matter. Two separate systematic reviews across the PubMed database since inception up to August 8^th 2022 were performed, with fourteen clinical and nineteen neurobiological eligible studies. The included clinical studies encompass 207 bipolar depression patients overall and consistently document the efficacy of tDCS, with a reduction in depression scores after treatment ranging from 18% to 92%. The RCT with the largest sample clearly showed a significant superiority of active stimulation over sham. Mild-to-moderate and transient adverse effects are attributed to tDCS across these studies. The review of neurobiological literature indicates that several molecular mechanisms may account for the antidepressant effect of tDCS in BD patients, including the action on calcium homeostasis in glial cells, the enhancement of LTP, the regulation of neurotrophic factors and inflammatory mediators, and the modulation of the expression of plasticity-related genes. To the best of our knowledge, this is the first study on the matter to concurrently provide a synthesis of the clinical evidence and an in-depth appraisal of the putative biological underpinnings, providing consistent support for the efficacy, safety, and tolerability of tDCS.

Modulation of central pain mechanisms using high-definition transcranial direct current stimulation: A double-blind, sham-controlled study

BACKGROUND

The use of high-definition transcranial direct current stimulation (HD-tDCS) has shown analgesic effects in some chronic pain patients, but limited anti-nociceptive effects in healthy asymptomatic subjects.

METHODS

This double-blinded sham-controlled study assessed the effects of HD-tDCS applied on three consecutive days on central pain mechanisms in healthy participants with (N = 40) and without (N = 40) prolonged experimental pain induced by intramuscular injection of nerve growth factor into the right hand on Day 1. Participants were randomly assigned to Sham-tDCS (N = 20 with pain, N = 20 without) or Active-tDCS (N = 20 with pain, N = 20 without) targeting simultaneously the primary motor cortex and dorsolateral prefrontal cortex for 20 min with 2 mA stimulation intensity. Central pain mechanisms were assessed by cuff algometry on the legs measuring pressure pain sensitivity, temporal summation of pain (TSP) and conditioned pain modulation (CPM), at baseline and after HD-tDCS on Day 2 and Day 3. Based on subject's assessment of received HD-tDCS (sham or active), they were effectively blinded.

RESULTS

Compared with Sham-tDCS, Active-tDCS did not significantly reduce the average NGF-induced pain intensity. Tonic pain-induced temporal summation at Day 2 and Day 3 was significantly lower in the NGF-pain group under Active-tDCS compared to the pain group with Sham-tDCS (p ≤ 0.05). No significant differences were found in the cuff pressure pain detection/tolerance thresholds or CPM effect across the 3 days of HD-tDCS in any of the four groups.

CONCLUSION

HD-tDCS reduced the facilitation of TSP caused by tonic pain suggesting that efficacy of HD-tDCS might depend on the presence of sensitized central pain mechanisms.

Inconsistencies in mapping current distribution in transcranial direct current stimulation

INTRODUCTION

tDCS is a non-invasive neuromodulation technique that has been widely studied both as a therapy for neuropsychiatric diseases and for cognitive enhancement. However, recent meta-analyses have reported significant inconsistencies amongst tDCS studies. Enhancing empirical understanding of current flow in the brain may help elucidate some of these inconsistencies.

METHODS

We investigated tDCS-induced current distribution by injecting a low frequency current waveform in a phantom and in vivo. MR phase images were collected during the stimulation and a time-series analysis was used to reconstruct the magnetic field. A current distribution map was derived from the field map using Ampere's law.

RESULTS

The current distribution map in the phantom showed a clear path of current flow between the two electrodes, with more than 75% of the injected current accounted for. However, in brain, the results did evidence a current path between the two target electrodes but only some portion ( 25%) of injected current reached the cortex demonstrating that a significant fraction of the current is bypassing the brain and traveling from one electrode to the other external to the brain, probably due to conductivity differences in brain tissue types. Substantial inter-subject and intra-subject (across consecutive scans) variability in current distribution maps were also observed in human but not in phantom scans.

DISCUSSIONS

An in-vivo current mapping technique proposed in this study demonstrated that much of the injected current in tDCS was not accounted for in human brain and deviated to the edge of the brain. These findings would have ramifications in the use of tDCS as a neuromodulator and may help explain some of the inconsistencies reported in other studies.

Modulating the Activity of the Right Dorsolateral Prefrontal Cortex Alters Altruism in Situations of Advantageous Inequity

Altruism is highly valued and cherished by human society. However, human preferences and behavior are sensitive to inequality considerations. Currently, remarkably little is known about the neurobiological mechanisms underlying the process of altruistic acts in inequity situations. Therefore, to clarify the causal role of the right dorsolateral prefrontal cortex (rDLPFC) in altruism during situations of advantageous and disadvantageous inequity, we applied transcranial direct current stimulation (tDCS) to demonstrate the involvement of the rDLPFC in altruism in situations of inequity. A total of 71 participants (38 female and 33 male) received anodal tDCS at 1.5 mA over the rDLPFC (n = 38) or the primary visual cortex (n = 33) and subsequently participated in a modified dictator game that measures altruism. We found that anodal tDCS over the rDLPFC decreased subjects' sensitivity to altruistic efficiency and cost in situations of advantageous inequity. Our results suggested that the rDLPFC plays an important role in overriding self-interest to enforce altruism in situations of advantageous inequity.

Perspective: Disentangling the effects of tES on neurovascular unit

Transcranial electrical stimulation (tES) can modulate the neurovascular unit, including the perivascular space morphology, but the mechanisms are unclear. In this perspective article, we used an open-source "rsHRF toolbox" and an open-source functional magnetic resonance imaging (fMRI) transcranial direct current stimulation (tDCS) data set to show the effects of tDCS on the temporal profile of the haemodynamic response function (HRF). We investigated the effects of tDCS in the gray matter and at three regions of interest in the gray matter, namely, the anodal electrode (FC5), cathodal electrode (FP2), and an independent site remote from the electrodes (PZ). A "canonical HRF" with time and dispersion derivatives and a finite impulse response (FIR) model with three parameters captured the effects of anodal tDCS on the temporal profile of the HRF. The FIR model showed tDCS onset effects on the temporal profile of HRF for verum and sham tDCS conditions that were different from the no tDCS condition, which questions the validity of the sham tDCS (placebo). Here, we postulated that the effects of tDCS onset on the temporal profile of HRF are subserved by the effects on neurovascular coupling. We provide our perspective based on previous work on tES effects on the neurovascular unit, including mechanistic grey-box modeling of the effects of tES on the vasculature that can facilitate model predictive control (MPC). Future studies need to investigate grey-box modeling of online effects of tES on the neurovascular unit, including perivascular space, neurometabolic coupling, and neurovascular coupling, that can facilitate MPC of the tES dose-response to address the momentary ("state") and phenotypic ("trait") factors.

Neuroimaging-Guided Transcranial Magnetic and Direct Current Stimulation in MCI: Toward an Individual, Effective and Disease-Modifying Treatment

The therapeutic approaches currently applied in Alzheimer's disease (AD) and similar neurodegenerative diseases are essentially based on pharmacological strategies. However, despite intensive research, the effectiveness of these treatments is limited to transient symptomatic effects, and they are still far from exhibiting a true therapeutic effect capable of altering prognosis. The lack of success of such pharmacotherapy-based protocols may be derived from the cases in the majority of trials being too advanced to benefit significantly in therapeutic terms at the clinical level. For neurodegenerative diseases, mild cognitive impairment (MCI) may be an early stage of the disease continuum, including Alzheimer's. Noninvasive brain stimulation (NIBS) techniques have been developed to modulate plasticity in the human cortex in the last few decades. NIBS techniques have made it possible to obtain unique findings concerning brain functions, and design novel approaches to treat various neurological and psychiatric conditions. In addition, its synaptic and cellular neurobiological effects, NIBS is an attractive treatment option in the early phases of neurodegenerative diseases, such as MCI, with its beneficial modifying effects on cellular neuroplasticity. However, there is still insufficient evidence about the potential positive clinical effects of NIBS on MCI. Furthermore, the huge variability of the clinical effects of NIBS limits its use. In this article, we reviewed the combined approach of NIBS with various neuroimaging and electrophysiological methods. Such methodologies may provide a new horizon to the path for personalized treatment, including a more individualized pathophysiology approach which might even define new specific targets for specific symptoms of neurodegenerations.

Digitalized transcranial electrical stimulation: A consensus statement

OBJECTIVE

Although relatively costly and non-scalable, non-invasive neuromodulation interventions are treatment alternatives for neuropsychiatric disorders. The recent developments of highly-deployable transcranial electric stimulation (tES) systems, combined with mobile-Health technologies, could be incorporated in digital trials to overcome methodological barriers and increase equity of access. The study aims are to discuss the implementation of tES digital trials by performing a systematic scoping review and strategic process mapping, evaluate methodological aspects of tES digital trial designs, and provide Delphi-based recommendations for implementing digital trials using tES.

METHODS

We convened 61 highly-productive specialists and contacted 8 tES companies to assess 71 issues related to tES digitalization readiness, and processes, barriers, advantages, and opportunities for implementing tES digital trials. Delphi-based recommendations (>60% agreement) were provided.

RESULTS

The main strengths/opportunities of tES were: (i) non-pharmacological nature (92% of agreement), safety of these techniques (80%), affordability (88%), and potential scalability (78%). As for weaknesses/threats, we listed insufficient supervision (76%) and unclear regulatory status (69%). Many issues related to methodological biases did not reach consensus. Device appraisal showed moderate digitalization readiness, with high safety and potential for trial implementation, but low connectivity.

CONCLUSIONS

Panelists recognized the potential of tES for scalability, generalizability, and leverage of digital trials processes; with no consensus about aspects regarding methodological biases.

SIGNIFICANCE

We further propose and discuss a conceptual framework for exploiting shared aspects between mobile-Health tES technologies with digital trials methodology to drive future efforts for digitizing tES trials.

A systematic review of transcranial direct current stimulation on eye movements and associated psychological function

The last decades have seen a rise in the use of transcranial direct current stimulation (tDCS) approaches to modulate brain activity and associated behavior. Concurrently, eye tracking (ET) technology has improved to allow more precise quantitative measurement of gaze behavior, offering a window into the mechanisms of vision and cognition. When combined, tDCS and ET provide a powerful system to probe brain function and measure the impact on visual function, leading to an increasing number of studies that utilize these techniques together. The current pre-registered, systematic review seeks to describe the literature that integrates these approaches with the goal of changing brain activity with tDCS and measuring associated changes in eye movements with ET. The literature search identified 26 articles that combined ET and tDCS in a probe-and-measure model and are systematically reviewed here. All studies implemented controlled interventional designs to address topics related to oculomotor control, cognitive processing, emotion regulation, or cravings in healthy volunteers and patient populations. Across these studies, active stimulation typically led to changes in the number, duration, and timing of fixations compared to control stimulation. Notably, half the studies addressed emotion regulation, each showing hypothesized effects of tDCS on ET metrics, while tDCS targeting the frontal cortex was widely used and also generally produced expected modulation of ET. This review reveals promising evidence of the impact of tDCS on eye movements and associated psychological function, offering a framework for effective designs with recommendations for future studies.

Ten sessions of transcranial direct current stimulation for chronic chikungunya arthralgia: study protocol for a randomised clinical trial

INTRODUCTION

The chikungunya virus infection is still an epidemic in Brazil with an incidence of 59.4 cases per 100 000 in the Northeast region. More than 60% of the patients present relapsing and remitting chronic arthralgia with debilitating pain lasting for years. Transcranial direct current stimulation (tDCS) appears promising as a novel neuromodulation approach for pain-related networks to alleviate pain in several pain syndromes. Our objective is to evaluate the effectiveness of tDCS (C3/Fp2 montage) on pain, muscle strength, functionality and quality of life in chronic arthralgia.

METHODS AND ANALYSIS

This protocol is a single-centre, parallel-design, double-blind, randomised, sham-controlled trial. Forty participants will be randomised to either an active or sham tDCS. A total of 10 sessions will be administered over 2 weeks (one per weekday) using a monophasic continuous current with an intensity of 2 mA for 20 min. Participants will be evaluated at baseline, after the 10th session, 2 weeks and 4 weeks after intervention.

PRIMARY OUTCOME

pain assessed using numeric rating scale and algometry.

SECONDARY OUTCOMES

muscle strength, functionality and quality of life. The effects of stimulation will be calculated using a mixed analysis of variance model.

ETHICS AND DISSEMINATION

The study was approved by the ethics committee of the Faculty of Health Sciences of Trairí, Federal University of Rio Grande do Norte (No. 2.413.851) and registered on the Brazilian Registry of Clinical Trials. Study results will be disseminated through presentations at conferences and publications in peer-reviewed journals.

TRIAL REGISTRATION NUMBER

RBR-469yd6.

Enhancing Immediate Memory, Potential Learning, and Working Memory with Transcranial Direct Current Stimulation in Healthy Older Adults

BACKGROUND

Transcranial direct current stimulation (tDCS) has emerged as a prevention method or minimizer of the normal cognitive deterioration that occurs during the aging process. tDCS can be used to enhance cognitive functions such as immediate memory, learning, or working memory in healthy subjects. The objective of this study was to analyze the effect of two 20-min sessions of anodal transcranial direct stimulation on immediate memory, learning potential, and working memory in healthy older adults.

METHODS

A randomized, single-blind, repeated-measures, sham-controlled design was used. The sample is made up of 31 healthy older adults, of whom 16 were in the stimulation group and 15 were in the sham group. The anode was placed on position F7, coinciding with the left dorsolateral prefrontal cortex region, and the cathode was placed on Fp2, the right supraorbital area (rSO).

RESULTS

When comparing the results of the treatment group and the sham group, differences were observed in working memory and learning potential; however, no differences in immediate memory were found.

CONCLUSION

The results showed that tDCS is a non-invasive and safe tool to enhance cognitive processes in healthy older adults interested in maintaining some cognitive function.

A Single Session of Bifrontal tDCS Can Improve Facial Emotion Recognition in Major Depressive Disorder: An Exploratory Pilot Study

Emotional processing deficits are key features in major depressive disorder (MDD). Neuroimaging studies indicate that the dorsolateral prefrontal cortex (DLPFC) plays a pivotal role in both depressive symptoms and emotional processing. Recently, transcranial Direct Current Stimulations (tDCS) applied over the DLPFCs have held the promise to alleviate the symptoms in patients with MDD, but the effect on emotional processing in the patients is unclear. Here, we investigated the effect of a single session of tDCS over the DLPFCs on the emotional processing in patients with treatment-resistant MDD. In a randomized sham-controlled study, 35 patients received a single 30 min session of either active (2 mA, n = 18) or sham tDCS (n = 17). The anode was placed over the left and the cathode over the right DLPFC. Emotional processing accuracy was measured by a facial emotion recognition (FER) task. We observed an overall improvement in FER performance after the active tDCS, but not the sham tDCS. These exploratory results suggest that a single session of tDCS over the DLPFCs may improve FER in MDD, a crucial function of social cognition. Further studies are needed to investigate whether this acute improvement of FER in response to a single tDCS session could translate into clinical benefits or predict remission following repeated sessions of stimulation.