Low intensity transcranial electric stimulation: Safety, ethical, legal regulatory and application guidelines

Performance in myoelectric pattern recognition improves with transcranial direct current stimulation

Sensorimotor impairments, resulting from conditions like stroke and amputations, can profoundly impact an individual's functional abilities and overall quality of life. Assistive and rehabilitation devices such as prostheses, exo-skeletons, and serious gaming in virtual environments can help to restore some degree of function and alleviate pain after sensorimotor impairments. Myoelectric pattern recognition (MPR) has gained popularity in the past decades as it provides superior control over said devices, and therefore efforts to facilitate and improve performance in MPR can result in better rehabilitation outcomes. One possibility to enhance MPR is to employ transcranial direct current stimulation (tDCS) to facilitate motor learning. Twelve healthy able-bodied individuals participated in this crossover study to determine the effect of tDCS on MPR performance. Baseline training was followed by two sessions of either sham or anodal tDCS using the dominant and non-dominant arms. Assignments were randomized, and the MPR task consisted of 11 different hand/wrist movements, including rest or no movement. Surface electrodes were used to record EMG and the MPR open-source platform, BioPatRec, was used for decoding motor volition in real-time. The motion test was used to evaluate performance. We hypothesized that using anodal tDCS to increase the excitability of the primary motor cortex associated with non-dominant side in able-bodied individuals, will improve motor learning and thus MPR performance. Overall, we found that tDCS enhanced MPR performance, particularly in the non-dominant side. We were able to reject the null hypothesis and improvements in the motion test's completion rate during tDCS (28% change, p-value: 0.023) indicate its potential as an adjunctive tool to enhance MPR and motor learning. tDCS appears promising as a tool to enhance the learning phase of using assistive devices using MPR, such as myoelectric prostheses.

Closed-Loop Transcranial Electrical Neurostimulation for Sustained Attention Enhancement: A Pilot Study towards Personalized Intervention Strategies

Sustained attention is pivotal for tasks like studying and working for which focus and low distractions are necessary for peak productivity. This study explores the effectiveness of adaptive transcranial direct current stimulation (tDCS) in either the frontal or parietal region to enhance sustained attention. The research involved ten healthy university students performing the Continuous Performance Task-AX (AX-CPT) while receiving either frontal or parietal tDCS. The study comprised three phases. First, we acquired the electroencephalography (EEG) signal to identify the most suitable metrics related to attention states. Among different spectral and complexity metrics computed on 3 s epochs of EEG, the Fuzzy Entropy and Multiscale Sample Entropy Index of frontal channels were selected. Secondly, we assessed how tDCS at a fixed 1.0 mA current affects attentional performance. Finally, a real-time experiment involving continuous metric monitoring allowed personalized dynamic optimization of the current amplitude and stimulation site (frontal or parietal). The findings reveal statistically significant improvements in mean accuracy (94.04 vs. 90.82%) and reaction times (262.93 vs. 302.03 ms) with the adaptive tDCS compared to a non-stimulation condition. Average reaction times were statistically shorter during adaptive stimulation compared to a fixed current amplitude condition (262.93 vs. 283.56 ms), while mean accuracy stayed similar (94.04 vs. 93.36%, improvement not statistically significant). Despite the limited number of subjects, this work points out the promising potential of adaptive tDCS as a tailored treatment for enhancing sustained attention.

Multichannel tDCS with Advanced Targeting for Major Depressive Disorder: A Tele-Supervised At-Home Pilot Study

Introduction

Proof-of-principle human studies suggest that transcranial direct current stimulation (tDCS) over the dorsolateral prefrontal cortex (DLPFC) may improve depression severity. This open-label multicenter study tested remotely supervised multichannel tDCS delivered at home in patients (N=35) with major depressive disorder (MDD). The primary aim was to assess the feasibility and safety of our protocol. As an exploratory aim, we evaluated therapeutic efficacy: the primary efficacy measure was the median percent change from baseline to the end of the 4-week post-treatment follow-up period in the observer-rated Montgomery-Asberg Depression Mood Rating Scale (MADRS).

Methods

Participants received 37 at-home stimulation sessions (30 minutes each) of specifically designed multichannel tDCS targeting the left DLPFC administered over eight weeks (4 weeks of daily treatments plus 4 weeks of taper), with a follow-up period of 4 weeks following the final stimulation session. The stimulation montage (electrode positions and currents) was optimized by employing computational models of the electric field generated by multichannel tDCS using available structural data from a similar population (group optimization). Conducted entirely remotely, the study employed the MADRS for assessment at baseline, at weeks 4 and 8 during treatment, and at 4-week follow-up visits.

Results

34 patients (85.3% women) with a mean age of 59 years, a diagnosis of MDD according to DSM-5 criteria, and a MADRS score ≥20 at the time of study enrolment completed all study visits. At baseline, the mean time since MDD diagnosis was 24.0 (SD 19.1) months. Concerning compliance, 85% of the participants (n=29) completed the complete course of 37 stimulation sessions at home, while 97% completed at least 36 sessions. No detrimental effects were observed, including suicidal ideation and/or behavior. The study observed a median MADRS score reduction of 64.5% (48.6, 72.4) 4 weeks post-treatment (Hedge's g = -3.1). We observed a response rate (≥ 50% improvement in MADRS scores) of 72.7% (n=24) from baseline to the last visit 4 weeks post-treatment. Secondary measures reflected similar improvements.

Conclusions

These results suggest that remotely supervised and supported multichannel home-based tDCS is safe and feasible, and antidepressant efficacy motivates further appropriately controlled clinical studies.

Anodal tDCS over the motor cortex improves pain but not physical function in chronic chikungunya arthritis: Randomized controlled trial

BACKGROUND

Chikungunya virus (CHIKV) is a globally prevalent pathogen, with outbreaks occurring in tropical regions. Chronic pain is the main symptom reported and is associated with decreased mobility and disability. Transcranial direct current stimulation (tDCS) is emerging as a new therapeutic tool for chronic arthralgia.

OBJECTIVE

To evaluate the effectiveness of 10 consecutive sessions of anodal tDCS on pain (primary outcome) in participants with chronic CHIKV arthralgia. Secondary outcomes included functional status, quality of life, and mood.

METHODS

In this randomized, double-blind, placebo-controlled trial, 30 participants with chronic CHIKV arthralgia were randomly assigned to receive either active (n = 15) or sham (n = 15) tDCS. The active group received 10 consecutive sessions of tDCS over M1 using the C3/Fp2 montage (2 mA for 20 min). Visual analog scale of pain (VAS), health assessment questionnaire (HAQ), short-form 36 health survey (SF-36), pain catastrophizing scale, Hamilton anxiety scale (HAS), timed up and go (TUG) test, lumbar dynamometry, 30-s arm curl and 2-min step test were assessed at baseline, day 10 and at 2 follow-up visits.

RESULTS

There was a significant interaction between group and time on pain (p = 0.03; effect size 95 % CI 0.9 (-1.67 to -0.16), with a significant time interaction (p = 0.0001). There was no interaction between time and group for the 2-minute step test (p = 0.18), but the groups differed significantly at day 10 (p = 0.01), first follow-up (p = 0.01) and second follow-up (p = 0.03). HAQ and SF-36 improved but not significantly. There was no significant improvement in mental health, and physical tests.

CONCLUSION

tDCS appears to be a promising intervention for reducing pain in participants with chronic CHIKV arthralgia, although further research is needed to confirm these findings and explore potential long-term benefits.

TRIAL REGISTRATION

Brazilian Registry of Clinical Trials (ReBEC): RBR-245rh7.

Temporal Dynamics of Adverse Effects across Five Sessions of Transcranial Direct Current Stimulation

(1) Background: Transcranial direct current stimulation (tDCS) is a safe intervention, only producing mild and transient adverse effects (AEs). However, there is no detailed analysis of the pattern of adverse effects in an application transferable to the clinic. Therefore, our objective is to describe the AEs produced by tDCS and its temporal evolution. (2) Methods: A total of 33 young volunteers were randomized into a tDCS or sham group. Participants performed a hand dexterity task while receiving the tDCS or sham intervention (20 min and 1 mA), for five consecutive days. AEs were assessed daily after each intervention and classified as somatosensory, pain, or other effects. (3) Results: The number of AEs was generally increased by tDCS intervention. Specifically, tDCS led to more frequent somatosensory discomfort, characterized by sensations like itching and tingling, alongside painful sensations such as burning, compared to the sham intervention. Additionally, certain adverse events, including neck and arm pain, as well as dizziness and blurry vision, were exclusive to the tDCS group. Interestingly, tDCS produced similar AEs across the days; meanwhile, the somatosensory AEs in the sham group showed a trend to decrease. (4) Conclusions: tDCS produces mild and temporary somatosensory and pain AEs during and across sessions. The different evolution of the AEs between the tDCS and sham protocol could unmask the blinding protocol most used in tDCS studies. Potential solutions for improving blinding protocols for future studies are discussed.

The efficacy of real versus sham external Trigeminal Nerve Stimulation (eTNS) in youth with Attention-Deficit/Hyperactivity Disorder (ADHD) over 4 weeks: a protocol for a multi-centre, double-blind, randomized, parallel-group, phase IIb study (ATTENS)

BACKGROUND

Attention Deficit/Hyperactivity Disorder (ADHD), if severe, is usually treated with stimulant or non-stimulant medication. However, users prefer non-drug treatments due to side effects. Alternative non-medication treatments have so far only shown modest effects. External trigeminal nerve stimulation (eTNS) is a minimal risk, non-invasive neuromodulation device, targeting the trigeminal system. It was approved for ADHD in 2019 by the USA Food and Drug administration (FDA) based on a small proof of concept randomised controlled trial (RCT) in 62 children with ADHD showing improvement of ADHD symptoms after 4 weeks of nightly real versus sham eTNS with minimal side effects. We present here the protocol of a larger confirmatory phase IIb study testing efficacy, longer-term persistency of effects and underlying mechanisms of action.

METHODS

A confirmatory, sham-controlled, double-blind, parallel-arm, multi-centre phase IIb RCT of 4 weeks of eTNS in 150 youth with ADHD, recruited in London, Portsmouth, and Southampton, UK. Youth with ADHD will be randomized to either real or sham eTNS, applied nightly for 4 weeks. Primary outcome is the change in the investigator-administered parent rated ADHD rating scale. Secondary outcomes are other clinical and cognitive measures, objective hyperactivity and pupillometry measures, side effects, and maintenance of effects over 6 months. The mechanisms of action will be tested in a subgroup of 56 participants using magnetic resonance imaging (MRI) before and after the 4-week treatment.

DISCUSSION

This multi-centre phase IIb RCT will confirm whether eTNS is effective in a larger age range of children and adolescents with ADHD, whether it improves cognition and other clinical measures, whether efficacy persists at 6 months and it will test underlying brain mechanisms. The results will establish whether eTNS is effective and safe as a novel non-pharmacological treatment for ADHD.

TRIAL REGISTRATION

ISRCTN82129325 on 02/08/2021, https://doi.org/10.1186/ISRCTN82129325 .

Aerobic exercise on the treadmill combined with transcranial direct current stimulation on the gait of people with Parkinson's disease: A protocol for a randomized clinical trial

Gait impairments negatively affect the quality of life of people with Parkinson's disease (PwPD). Aerobic exercise (AE) is an alternative to alleviate these impairments and its combination with transcranial direct current stimulation (tDCS) has demonstrated synergistic effects. However, the effect of multitarget tDCS application (i.e., motor, and prefrontal cortices simultaneously) combined with physical exercise on gait impairments is still little known. Thus, the proposed randomized clinical trial will verify the acute effects of AE combined with tDCS applied on motor and prefrontal cortices separately and simultaneously on gait (spatial-temporal and cortical activity parameters) in PwPD. Twenty-four PwPD in Hoehn & Yahr stages I-III will be recruited for this crossover study. PwPD will practice AE on treadmill simultaneously with the application of anodal tDCS during four intervention sessions on different days (∼ one week of interval). Active tDCS will be applied to the primary motor cortex, prefrontal cortex, and both areas simultaneously (multitarget), with an intensity of 2 mA for 20 min. For sham, the stimulation will remain at 2 mA for 10 s. The AE will last a total of 30 min, consisting of warm-up, main part (20 min with application of tDCS), and recovery. Exercise intensity will be controlled by heart rate. Spatial-temporal and cortical activity parameters will be acquired before and after each session during overground walking, walking with obstacle avoidance, and walking with a cognitive dual task at self-preferred velocity. An accelerometer will be positioned on the fifth lumbar vertebra to obtain the spatial-temporal parameters (i.e., step length, duration, velocity, and swing phase duration). Prefrontal cortex activity will be recorded from a portable functional near-infrared spectroscopy system and oxygenated and deoxygenated hemoglobin concentrations will be analyzed. Two-way ANOVAs with repeated measures for stimulation and moment will be performed. The findings of the study may contribute to improving gait in PwPD. Trial registration: Brazilian Clinical Trials Registry (RBR-738zkp7).

No Object-Location Memory Improvement through Focal Transcranial Direct Current Stimulation over the Right Temporoparietal Cortex

Remembering objects and their associated location (object-location memory; OLM), is a fundamental cognitive function, mediated by cortical and subcortical brain regions. Previously, the combination of OLM training and transcranial direct current stimulation (tDCS) suggested beneficial effects, but the evidence remains heterogeneous. Here, we applied focal tDCS over the right temporoparietal cortex in 52 participants during a two-day OLM training, with anodal tDCS (2 mA, 20 min) or sham (40 s) on the first day. The focal stimulation did not enhance OLM performance on either training day (stimulation effect: -0.09, 95%CI: [-0.19; 0.02], p = 0.08). Higher electric field magnitudes in the target region were not associated with individual performance benefits. Participants with content-related learning strategies showed slightly superior performance compared to participants with position-related strategies. Additionally, training gains were associated with individual verbal learning skills. Consequently, the lack of behavioral benefits through focal tDCS might be due to the involvement of different cognitive processes and brain regions, reflected by participant's learning strategies. Future studies should evaluate whether other brain regions or memory-relevant networks may be involved in the modulation of object-location associations, investigating other target regions, and further exploring individualized stimulation parameters.

HD-tDCS mitigates the executive vigilance decrement only under high cognitive demands

Maintaining vigilance is essential for many everyday tasks, but over time, our ability to sustain it inevitably decreases, potentially entailing severe consequences. High-definition transcranial direct current stimulation (HD-tDCS) has proven to be useful for studying and improving vigilance. This study explores if/how cognitive load affects the mitigatory effects of HD-tDCS on the vigilance decrement. Participants (N = 120) completed a modified ANTI-Vea task (single or dual load) while receiving either sham or anodal HD-tDCS over the right posterior parietal cortex (rPPC). This data was compared with data from prior studies (N = 120), where participants completed the standard ANTI-Vea task (triple load task), combined with the same HD-tDCS protocol. Against our hypotheses, both the single and dual load conditions showed a significant executive vigilance (EV) decrement, which was not affected by the application of rPPC HD-tDCS. On the contrary, the most cognitively demanding task (triple task) showed the greatest EV decrement; importantly, it was also with the triple task that a significant mitigatory effect of the HD-tDCS intervention was observed. The present study contributes to a more nuanced understanding of the specific effects of HD-tDCS on the vigilance decrement considering cognitive demands. This can ultimately contribute to reconciling heterogeneous effects observed in past research and fine-tuning its future clinical application.

[Transcranial direct current stimulation to enhance training effectiveness in chronic poststroke aphasia-A challenge for recruiting participants]

INTRODUCTION/BACKGROUND

DC_TRAIN_APHASIA is an ongoing multicenter, randomized controlled trial, conducted since November 2019 under the lead of the University Medicine Greifswald (ClinicalTrials.gov Identifier: NCT03930121). The study seeks to determine whether adjuvant transcranial direct current stimulation (tDCS) can increase the effectiveness of a 3‑week treatment with intensive speech-language therapy in chronic post-stroke aphasia.

MATERIAL AND METHOD

Until the end of 2024, a total of 130 patients are to be included in Germany. Recruitment has been a challenge throughout the study and substantial efforts went into devising innovative recruiting approaches. Standard recruitment strategies were used, such as directly approaching people with aphasia in clinical settings, inpatient and outpatient language rehabilitation facilities, and patient support and advocacy groups, alongside more innovative techniques including radio commercials, dissemination of study information via national television and social media platforms.

PROVISIONAL RESULTS

Up until now, 110 patients have been included into the study. The largest short-term response was achieved via television and radio. The largest long-term response was obtained through recruitment via logopaedic and neurological facilities, patient support groups, and social media. Participants served as "testimonials", expressing that they were satisfied with the therapy and the tDCS application.

DISCUSSION

The multicenter study DC_TRAIN_APHASIA aims to provide evidence on tDCS as an adjuvant application to increase the effect size of intensive speech-language therapy in chronic post-stroke aphasia. The present review may guide future studies in recruiting samples that involve people with impaired communicative abilities.

Inhibitory control in WM gate-opening: Insights from alpha desynchronization and norepinephrine activity under atDCS stimulation

Our everyday activities require the maintenance and continuous updating of information in working memory (WM). To control this dynamic, WM gating mechanisms have been suggested to be in place, but the neurophysiological mechanisms behind these processes are far from being understood. This is especially the case when it comes to the role of oscillatory neural activity. In the current study we combined EEG recordings, and anodal transcranial direct current stimulation (atDCS) and pupil diameter recordings to triangulate neurophysiology, functional neuroanatomy and neurobiology. The results revealed that atDCS, compared to sham stimulation, affected the WM gate opening mechanism, but not the WM gate closing mechanism. The altered behavioral performance was associated with specific changes in alpha band activities (reflected by alpha desynchronization), indicating a role for inhibitory control during WM gate opening. Functionally, the left superior and inferior parietal cortices, were associated with these processes. The findings are the first to show a causal relevance of alpha desynchronization processes in WM gating processes. Notably, pupil diameter recordings as an indirect index of the norepinephrine (NE) system activity revealed that individuals with stronger inhibitory control (as indexed through alpha desynchronization) showed less pupil dilation, suggesting they needed less NE activity to support WM gate opening. However, when atDCS was applied, this connection disappeared. The study suggests a close link between inhibitory controlled WM gating in parietal cortices, alpha band dynamics and the NE system.

Comparing Cerebellar tDCS and Cerebellar tACS in Neurodegenerative Ataxias Using Wearable Sensors: A Randomized, Double-Blind, Sham-Controlled, Triple-Crossover Trial

Cerebellar transcranial direct current stimulation (tDCS) represents a promising therapeutic approach for both motor and cognitive symptoms in neurodegenerative ataxias. Recently, transcranial alternating current stimulation (tACS) was also demonstrated to modulate cerebellar excitability by neuronal entrainment. To compare the effectiveness of cerebellar tDCS vs. cerebellar tACS in patients with neurodegenerative ataxia, we performed a double-blind, randomized, sham controlled, triple cross-over trial with cerebellar tDCS, cerebellar tACS or sham stimulation in twenty-six participants with neurodegenerative ataxia. Before entering the study, each participant underwent motor assessment with wearable sensors considering gait cadence (steps/minute), turn velocity (degrees/second) and turn duration (seconds), and a clinical evaluation with the scale for the Assessment and Rating of Ataxia (SARA) and the International Cooperative Ataxia Rating Scale (ICARS). After each intervention, participants underwent the same clinical assessment along with cerebellar inhibition (CBI) measurement, a marker of cerebellar activity. The gait cadence, turn velocity, SARA, and ICARS significantly improved after both tDCS and tACS, compared to sham stimulation (all p<0.010). Comparable effects were observed for CBI (p<0.001). Overall, tDCS significantly outperformed tACS on clinical scales and CBI (p<0.01). A significant correlation between changes of wearable sensors parameters from baseline and changes of clinical scales and CBI scores was detected. Cerebellar tDCS and cerebellar tACS are effective in ameliorating symptoms of neurodegenerative ataxias, with the former being more beneficial than the latter. Wearable sensors may serve as rater-unbiased outcome measures in future clinical trials. ClinicalTrial.gov Identifier: NCT05621200.

Use of noninvasive brain stimulation and neurorehabilitation devices to enhance poststroke recovery: review of the current evidence and pitfalls

Neurorehabilitation devices and technologies are crucial for enhancing stroke recovery. These include noninvasive brain stimulation devices that provide repetitive transcranial magnetic stimulation or transcranial direct current stimulation, which can remodulate an injured brain. Technologies such as robotics, virtual reality, and telerehabilitation are suitable add-ons or complements to physical therapy. However, the appropriate application of these devices and technologies, which target specific deficits and stages, for stroke therapy must be clarified. Accordingly, a literature review was conducted to evaluate the theoretical and practical evidence on the use of neurorehabilitation devices and technologies for stroke therapy. This narrative review provides a practical guide for the use of neurorehabilitation devices and describes the implications of use and potential integration of these devices into healthcare.

The role of parietal beta-band activity in the resolution of visual crowding

Visual crowding is the difficulty in identifying an object when surrounded by neighbouring flankers, representing a bottleneck for object perception. Crowding arises not only from the activity of visual areas but also from parietal areas and fronto-parietal network activity. Parietal areas would provide the dorsal-to-ventral guidance for object identification and the fronto-parietal network would modulate the attentional resolution. Several studies highlighted the relevance of beta oscillations (15-25 Hz) in these areas for visual crowding and other connatural visual phenomena. In the present study, we investigated the differential contribution of beta oscillations in the parietal cortex and fronto-parietal network in the resolution of visual crowding. During a crowding task with letter stimuli, high-definition transcranial Alternating Current Stimulation (tACS) in the beta band (18 Hz) was delivered bilaterally on parietal sites, on the right fronto-parietal network, and in a sham regime. Resting-state EEG was recorded before and after stimulation to measure tACS-induced aftereffects. The influence of crowding was reduced only when tACS was delivered bilaterally on parietal sites. In this condition, beta power was reduced after the stimulation. Furthermore, the magnitude of tACS-induced aftereffects varied as a function of individual differences in beta oscillations. Results corroborate the link between parietal beta oscillations and visual crowding, providing fundamental insights on brain rhythms underlying the dorsal-to-ventral guidance in visual perception and suggesting that beta tACS can induce plastic changes in these areas. Remarkably, these findings open new possibilities for neuromodulatory interventions for disorders characterised by abnormal crowding, such as dyslexia.

No Benefit in Memory Performance after Nocturnal Memory Reactivation Coupled with Theta-tACS

Targeted memory reactivation (TMR) is an effective technique to enhance sleep-associated memory consolidation. The successful reactivation of memories by external reminder cues is typically accompanied by an event-related increase in theta oscillations, preceding better memory recall after sleep. However, it remains unclear whether the increase in theta oscillations is a causal factor or an epiphenomenon of successful TMR. Here, we used transcranial alternating current stimulation (tACS) to examine the causal role of theta oscillations for TMR during non-rapid eye movement (non-REM) sleep. Thirty-seven healthy participants learned Dutch-German word pairs before sleep. During non-REM sleep, we applied either theta-tACS or control-tACS (23 Hz) in blocks (9 min) in a randomised order, according to a within-subject design. One group of participants received tACS coupled with TMR time-locked two seconds after the reminder cue (time-locked group). Another group received tACS in a continuous manner while TMR cues were presented (continuous group). Contrary to our predictions, we observed no frequency-specific benefit of theta-tACS coupled with TMR during sleep on memory performance, neither for continuous nor time-locked stimulation. In fact, both stimulation protocols blocked the TMR-induced memory benefits during sleep, resulting in no memory enhancement by TMR in both the theta and control conditions. No frequency-specific effect was found on the power analyses of the electroencephalogram. We conclude that tACS might have an unspecific blocking effect on memory benefits typically observed after TMR during non-REM sleep.

Transcranial alternating current stimulation improves quality of life in Parkinson's disease: study protocol for a randomized, double-blind, controlled trial

BACKGROUND

The neural cells in the brains of patients with Parkinson's disease (PWP) display aberrant synchronized oscillatory activity within the beta frequency range. Additionally, enhanced gamma oscillations may serve as a compensatory mechanism for motor inhibition mediated by beta activity and also reinstate plasticity in the primary motor cortex affected by Parkinson's disease. Transcranial alternating current stimulation (tACS) can synchronize endogenous oscillations with exogenous rhythms, thereby modulating cortical activity. The objective of this study is to investigate whether the addition of tACS to multidisciplinary intensive rehabilitation treatment (MIRT) can improve symptoms of PWP so as to enhance the quality of life in individuals with Parkinson's disease based on the central-peripheral-central theory.

METHODS

The present study was a randomized, double-blind trial that enrolled 60 individuals with Parkinson's disease aged between 45 and 70 years, who had Hoehn-Yahr scale scores ranging from 1 to 3. Participants were randomly assigned in a 1:1 ratio to either the tACS + MIRT group or the sham-tACS + MIRT group. The trial consisted of a two-week double-blind treatment period followed by a 24-week follow-up period, resulting in a total duration of twenty-six weeks. The primary outcome measured the change in PDQ-39 scores from baseline (T0) to 4 weeks (T2), 12 weeks (T3), and 24 weeks (T4) after completion of the intervention. The secondary outcome assessed changes in MDS-UPDRS III scores at T0, the end of intervention (T1), T2, T3, and T4. Additional clinical assessments and mechanistic studies were conducted as tertiary outcomes.

DISCUSSION

The objective of this study is to demonstrate that tACS can enhance overall functionality and improve quality of life in PWP, based on the framework of MIRT. Additionally, it seeks to establish a potential correlation between these therapeutic effects and neuroplasticity alterations in relevant brain regions. The efficacy of tACS will be assessed during the follow-up period in order to optimize neuroplasticity and enhance its potential impact on rehabilitation efficiency for PWP.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ChiCTR2300071969. Registered on 30 May 2023.

Effects of online tDCS and hf-tRNS on reading performance in children and adolescents with developmental dyslexia: a study protocol for a cross sectional, within-subject, randomized, double-blind, and sham-controlled trial

Background

Developmental Dyslexia (DD) is a brain-based developmental disorder causing severe reading difficulties. The extensive data on the neurobiology of DD have increased interest in brain-directed approaches, such as transcranial direct current stimulation (tDCS), which have been proposed for DD. While positive outcomes have been observed, results remain heterogeneous. Various methodological approaches have been employed to address this issue. However, no studies have compared the effects of different transcranial electrical stimulation techniques (e.g., tDCS and transcranial random noise stimulation, tRNS), on reading in children and adolescents with DD.

Methods

The present within-subject, double-blind, and sham-controlled trial aims to investigate the effects of tDCS and hf-tRNS on reading in children and adolescents with DD. Participants will undergo three conditions with a one-week interval session: (A) single active tDCS session; (B) single active hf-tRNS session; and (C) single sham session (tDCS/hf-tRNS). Left anodal/right cathodal tDCS and bilateral tRNS will be applied over the temporo-parietal regions for 20 min each. Reading measures will be collected before and during each session. Safety and blinding parameters will be recordered.

Discussion

We hypothesize that tRNS will demonstrate comparable effectiveness to tDCS in improving reading compared to sham conditions. Additionally, we anticipate that hf-tRNS will exhibit a similar safety profile to tDCS. This study will contribute novel insights into the effectiveness of hf-tRNS, expediting the validation of brain-based treatments for DD.

Safety, tolerability and blinding efficiency of non-invasive deep transcranial temporal interference stimulation: first experience from more than 250 sessions

Objective. Selective neuromodulation of deep brain regions has for a long time only been possible through invasive approaches, because of the steep depth-focality trade-off of conventional non-invasive brain stimulation (NIBS) techniques.Approach. An approach that has recently emerged for deep NIBS in humans is transcranial Temporal Interference Stimulation (tTIS). However, a crucial aspect for its potential wide use is to ensure that it is tolerable, compatible with efficient blinding and safe.Main results. Here, we show the favorable tolerability and safety profiles and the robust blinding efficiency of deep tTIS targeting the striatum or hippocampus by leveraging a large dataset (119 participants, 257 sessions), including young and older adults and patients with traumatic brain injury. tTIS-evoked sensations were generally rated as 'mild', were equivalent in active and placebo tTIS conditions and did not enable participants to discern stimulation type.Significance. Overall, tTIS emerges as a promising tool for deep NIBS for robust double-blind, placebo-controlled designs.

Prefrontal theta-gamma transcranial alternating current stimulation improves non-declarative visuomotor learning in older adults

The rise in the global population of older adults underscores the significance to investigate age-related cognitive disorders and develop early treatment modalities. Previous research suggests that non-invasive transcranial Alternating Current Stimulation (tACS) can moderately improve cognitive decline in older adults. However, non-declarative cognition has received relatively less attention. This study investigates whether repeated (16-day) bilateral theta-gamma cross-frequency tACS targeting the Dorsolateral Prefrontal Cortex (DLPFC) enhances non-declarative memory. Computerized cognitive training was applied alongside stimulation to control for the state-of-the-brain. The Alternating Serial Reaction Time (ASRT) task was employed to assess non-declarative functions such as visuomotor skill and probabilistic sequence learning. Results from 35 participants aged 55-82 indicated that active tACS led to more substantial improvements in visuomotor skills immediately after treatment, which persisted 3 months later, compared to sham tACS. Treatment benefit was more pronounced in older adults of younger age and those with pre-existing cognitive decline. However, neither intervention group exhibited modulation of probabilistic sequence learning. These results suggest that repeated theta-gamma tACS can selectively improve distinct non-declarative cognitive aspects when targeting the DLPFC. Our findings highlight the therapeutic potential of tACS in addressing deficits in learning and retaining general skills, which could have a positive impact on the quality of life for cognitively impaired older individuals by preserving independence in daily activities.

Transcranial alternating current stimulation does not affect microscale learning

A theory has been posited that microscale learning, which involves short intervals of a few seconds during explicit motor skill learning, considerably enhances performance. This phenomenon correlates with diminished beta-band activity in the frontal and parietal regions. However, there is a lack of neurophysiological studies regarding the relationship between microscale learning and implicit motor skill learning. In the present study, we aimed to determine the effects of transcranial alternating current stimulation (tACS) during short rest periods on microscale learning in an implicit motor task. We investigated the effects of 20-Hz β-tACS delivered during short rest periods while participants performed an implicit motor task. In Experiments 1 and 2, β-tACS targeted the right dorsolateral prefrontal cortex and the right frontoparietal network, respectively. The participants performed a finger-tapping task using their nondominant left hand, and microscale learning was separately analyzed for micro-online gains (MOnGs) and micro-offline gains (MOffGs). Contrary to our expectations, β-tACS exhibited no statistically significant effects on MOnGs or MOffGs in either Experiment 1 or Experiment 2. In addition, microscale learning during the performance of the implicit motor task was improved by MOffGs in the early learning phase and by MOnGs in the late learning phase. These results revealed that the stimulation protocol employed in this study did not affect microscale learning, indicating a novel aspect of microscale learning in implicit motor tasks. This is the first study to examine microscale learning in implicit motor tasks and may provide baseline information that will be useful in future studies.

Cognitive reserve predicts episodic memory enhancement induced by transcranial direct current stimulation in healthy older adults

Episodic memory shows the largest degree of age-related decline. Anodal transcranial Direct Current Stimulation (tDCS) can enhance episodic memory in aging but there is also evidence of response variability even when using identical stimulation parameters. To explore which inter-individual factors (i.e. age, education, encoding performance, cognitive reserve, tDCS group and timing of tDCS application) may directly and/or indirectly modulate verbal memory recall, we used data from our previous tDCS studies that showed enhanced episodic memory recall in 80 healthy older adults. In these studies we used the same paradigm and stimulation parameters but tDCS was applied during different memory stages. Memory recall was tested 48 hours and 30 days after encoding. Univariate regression models showed that tDCS group (Anodal vs. Sham) predicted memory recall, indicating higher scores in the Anodal group than in the Sham group. Encoding performance predicted memory recall in both tDCS groups. Multiple regression models revealed that cognitive reserve, measured with a life experience questionnaire, predicted memory recall only for the Anodal group. Higher cognitive reserve was linked to better memory recall. Accounting for individual differences in cognitive reserve at baseline helps to explain tDCS responsiveness. This knowledge may contribute to optimize its use in older adults.

Neurorestorative effects of cerebellar transcranial direct current stimulation on social prediction of adolescents and young adults with congenital cerebellar malformations

BACKGROUND

Converging evidence points to impairments of the predictive function exerted by the cerebellum as one of the causes of the social cognition deficits observed in patients with cerebellar disorders.

OBJECTIVE

We tested the neurorestorative effects of cerebellar transcranial direct current stimulation (ctDCS) on the use of contextual expectations to interpret actions occurring in ambiguous sensory sceneries in a sample of adolescents and young adults with congenital, non-progressive cerebellar malformation (CM).

METHODS

We administered an action prediction task in which, in an implicit-learning phase, the probability of co-occurrence between actions and contextual elements was manipulated to form either strongly or moderately informative expectations. Subsequently, in a testing phase, we probed the use of these contextual expectations for predicting ambiguous (i.e., temporally occluded) actions. In a sham-controlled, within-subject design, participants received anodic or sham ctDCS during the task.

RESULTS

Anodic ctDCS, compared to sham, improved patients' ability to use contextual expectations to predict the unfolding of actions embedded in moderately, but not strongly, informative contexts.

CONCLUSIONS

These findings corroborate the role of the cerebellum in using previously learned contextual associations to predict social events and document the efficacy of ctDCS to boost social prediction in patients with congenital cerebellar malformation. The study encourages the further exploration of ctDCS as a neurorestorative tool for the neurorehabilitation of social cognition abilities in neurological, neuropsychiatric, and neurodevelopmental disorders featured by macro- or micro-structural alterations of the cerebellum.

Transcranial direct current stimulation for chronic headaches, a randomized, controlled trial

Background and objectives

Chronic headaches are a frequent cause of pain and disability. The purpose of this randomized trial was to examine whether transcranial direct current stimulation (tDCS) applied to the primary motor cortex, reduces pain and increases daily function in individuals suffering from primary chronic headache.

Materials and methods

A prospective, randomized, controlled trial, where participants and assessors were blinded, investigated the effect of active tDCS vs. sham tDCS in chronic headache sufferers. Forty subjects between 18 and 70 years of age, with a diagnosis of primary chronic headache were randomized to either active tDCS or sham tDCS treatment groups. All patients received eight treatments over four consecutive weeks. Anodal stimulation (2 mA) directed at the primary motor cortex (M1), was applied for 30 min in the active tDCS group. Participants in the sham tDCS group received 30 s of M1 stimulation at the start and end of the 30-minute procedure; for the remaining 29 min, they did not receive any stimulation. Outcome measures based on data collected at baseline, after eight treatments and three months later included changes in daily function, pain levels, and medication.

Results

Significant improvements in both daily function and pain levels were observed in participants treated with active tDCS, compared to sham tDCS. Effects lasted up to 12 weeks post-treatment. Medication use remained unchanged in both groups throughout the trial with no serious adverse effects reported.

Conclusion

These results suggest that tDCS has the potential to improve daily function and reduce pain in patients suffering from chronic headaches. Larger randomized, controlled trials are needed to confirm these findings.

Trial registration

The study was approved by the local ethics committee (2018/2514) and by the Norwegian Centre for Research Data (54483).

The effects of combined transcranial brain stimulation and a 4-week visuomotor stepping training on voluntary step initiation in persons with chronic stroke-a pilot study

Purpose

Evidence suggests that transcranial direct current stimulation (tDCS) can enhance motor performance and learning of hand tasks in persons with chronic stroke (PCS). However, the effects of tDCS on the locomotor tasks in PCS are unclear. This pilot study aimed to: (1) determine aggregate effects of anodal tDCS combined with step training on improvements of the neural and biomechanical attributes of stepping initiation in a small cohort of persons with chronic stroke (PCS) over a 4-week training program; and (2) assess the feasibility and efficacy of this novel approach for improving voluntary stepping initiation in PCS.

Methods

A total of 10 PCS were randomly assigned to one of two training groups, consisting of either 12 sessions of VST paired with a-tDCS (n = 6) or sham tDCS (s-tDCS, n = 4) over 4 weeks, with step initiation (SI) tests at pre-training, post-training, 1-week and 1-month follow-ups. Primary outcomes were: baseline vertical ground reaction force (B-vGRF), response time (RT) to initiate anticipatory postural adjustment (APA), and the retention of B-VGRF and RT.

Results

a-tDCS paired with a 4-week VST program results in a significant increase in paretic weight loading at 1-week follow up. Furthermore, a-tDCS in combination with VST led to significantly greater retention of paretic BWB compared with the sham group at 1 week post-training.

Clinical implications

The preliminary findings suggest a 4-week VST results in improved paretic limb weight bearing (WB) during SI in PCS. Furthermore, VST combined with a-tDCS may lead to better retention of gait improvements (NCT04437251) (https://classic.clinicaltrials.gov/ct2/show/NCT04437251).

Frontal midline theta transcranial alternating current stimulation enhances early consolidation of episodic memory

Evidence implicating theta rhythms in declarative memory encoding and retrieval, together with the notion that both retrieval and consolidation involve memory reinstatement or replay, suggests that post-learning theta rhythm modulation can promote early consolidation of newly formed memories. Building on earlier work employing theta neurofeedback, we examined whether theta-frequency transcranial alternating stimulation (tACS) can engender effective consolidation of newly formed episodic memories, compared with beta frequency stimulation or sham control conditions. We compared midline frontal and posterior parietal theta stimulation montages and examined whether benefits to memory of theta upregulation are attributable to consolidation rather than to retrieval processes by using a washout period to eliminate tACS after-effects between stimulation and memory assessment. Four groups of participants viewed object pictures followed by a free recall test during three study-test cycles. They then engaged in tACS (frontal theta montage/parietal theta montage/frontal beta montage/sham) for a period of 20 min, followed by a 2-h break. Free recall assessments were conducted after the break, 24 h later, and 7 days later. Frontal midline theta-tACS induced significant off-line retrieval gains at all assessment time points relative to all other conditions. This indicates that theta upregulation provides optimal conditions for the consolidation of episodic memory, independent of mental-state strategies.

The effect of transcranial direct current stimulation (tDCS) on cognitive function recovery in patients with depression following electroconvulsive therapy (ECT): protocol for a randomized controlled trial

BACKGROUND

Electroconvulsive therapy (ECT) is a highly effective treatment for depressive disorder. However, the use of ECT is limited by its cognitive side effects (CSEs), and no specific intervention has been developed to address this problem. As transcranial direct current stimulation (tDCS) is a safe and useful tool for improving cognitive function, the main objective of this study was to explore the ability to use tDCS after ECT to ameliorate the cognitive side effects.

METHODS

60 eligible participants will be recruited within two days after completing ECT course and randomly assigned to receive either active or sham stimulation in a blinded, parallel-design trial and continue their usual pharmacotherapy. The tDCS protocol consists of 30-min sessions at 2 mA, 5 times per week for 2 consecutive weeks, applied through 15-cm2 electrodes. An anode will be placed over the left dorsolateral prefrontal cortex (DLPFC), and a cathode will be placed over the right supraorbital cortex. Cognitive function and depressive symptoms will be assessed before the first stimulation (T0), after the final stimulation (T1), 2 weeks after the final stimulation (T2), and 4 weeks after the final stimulation (T3) using the Cambridge Neuropsychological Test Automated Battery (CANTAB).

DISCUSSION

We describe a novel clinical trial to explore whether the administration of tDCS after completing ECT course can accelerates recovery from the CSEs. We hypothesized that the active group would recover faster from the CSEs and be superior to the sham group. If our hypothesis is supported, the use of tDCS could benefit eligible patients who are reluctant to receive ECT and reduce the risk of self-inflicted or suicide due to delays in treatment.

TRIAL REGISTRATION DETAILS

The trial protocol is registered with https://www.chictr.org.cn/ under protocol registration number ChiCTR2300071147 (date of registration: 05.06.2023). Recruitment will start in November 2023.

Anodal transcranial direct current stimulation (atDCS) and functional transcranial Doppler sonography (fTCD) in healthy elderly and patients with MCI: modulation of age-related changes in word fluency and language lateralization

Introduction: In addition to age-related changes in language, hemispheric lateralization of language functions steadily declines with age. Also, performance on word fluency tasks declines and is sensitive to the expression of dementia-related changes. The aim of this study is to evaluate the effect of anodal tDCS combined with a word fluency training on language lateralization and word fluency performance in healthy elderly subjects and in persons with mild cognitive impairment (MCI). Methods: The effect of anodal tDCS over the left inferio frontal gyrus (IFG) was measured in a group of healthy elderly up to the age of 67 years (YG, Ø = 63.9 ± 3.02), a group of healthy elderly aged 68 years and older (OG, Ø = 78.1, ± 4.85), and a group of patients with MCI (Ø = 81.18, ± 7.35) by comparing performance in phonological and semantic word fluency tasks before and after 3 days of tDCS. Half of the experimental participants received sham stimulation. In addition, language lateralization was determined using a lateralization index (LI) measured with functional transcranial Doppler sonography (fTCD) before and after the stimulation period. Results: Anodal tDCS was associated with significantly higher scores in phonological but not semantic word fluency in both YG and OG. In MCI patients, no difference was measured between the tDCS and sham groups in either word fluency task. fTCD showed significantly increased left lateralization in all three groups after the training phase. However, this effect was independent of tDCS and the degree of lateralization could not be predicted by word fluency performance in any of the groups. Discussion: Phonological word fluency can be increased with atDCS in healthy elderly people by stimulating the IFG in a 3-day training. When cognitive decline has reached a certain stage, as is the case with MCI, this paradigm does not seem to be effective enough.

Contrasting MEG effects of anodal and cathodal high-definition TDCS on sensorimotor activity during voluntary finger movements

Introduction

Protocols for noninvasive brain stimulation (NIBS) are generally categorized as "excitatory" or "inhibitory" based on their ability to produce short-term modulation of motor-evoked potentials (MEPs) in peripheral muscles, when applied to motor cortex. Anodal and cathodal stimulation are widely considered excitatory and inhibitory, respectively, on this basis. However, it is poorly understood whether such polarity-dependent changes apply for neural signals generated during task performance, at rest, or in response to sensory stimulation.

Methods

To characterize such changes, we measured spontaneous and movement-related neural activity with magnetoencephalography (MEG) before and after high-definition transcranial direct-current stimulation (HD-TDCS) of the left motor cortex (M1), while participants performed simple finger movements with the left and right hands.

Results

Anodal HD-TDCS (excitatory) decreased the movement-related cortical fields (MRCF) localized to left M1 during contralateral right finger movements while cathodal HD-TDCS (inhibitory), increased them. In contrast, oscillatory signatures of voluntary motor output were not differentially affected by the two stimulation protocols, and tended to decrease in magnitude over the course of the experiment regardless. Spontaneous resting state oscillations were not affected either.

Discussion

MRCFs are thought to reflect reafferent proprioceptive input to motor cortex following movements. Thus, these results suggest that processing of incoming sensory information may be affected by TDCS in a polarity-dependent manner that is opposite that seen for MEPs-increases in cortical excitability as defined by MEPs may correspond to reduced responses to afferent input, and vice-versa.

Motor cortex transcranial direct current stimulation improves non-motor symptoms in early-onset Parkinson's disease: a pilot study

Early-onset Parkinson's Disease (EOPD) demands tailored treatments. The younger age of patients might account for a higher sensitivity to transcranial direct current stimulation (tDCS) based non-invasive neuromodulation, which may raise as an integrative therapy in the field. Accordingly, here we assessed the safety and efficacy of the primary left motor cortex (M1) anodal tDCS in EOPD. Ten idiopathic EOPD patients received tDCS at 2.0 mA per 20 min for 10 days within a crossover, double-blind, sham-controlled pilot study. The outcome was evaluated by measuring changes in MDS-UPDRS part III, Non-Motor Symptoms Scale (NMSS), PD-cognitive rating scale, and PD Quality of Life Questionnaire-39 scores. We showed that anodal but not sham tDCS significantly reduced the NMSS total and "item 2" (sleep/fatigue) scores. Other parameters were not modified. No adverse events occurred. M1 anodal tDCS might thus evoke plasticity changes in cortical-subcortical circuits involved in non-motor functions, supporting the value as a therapeutic option in EOPD.

No Impact of Tdcs on Stress-Induced State Rumination and no Influence of Executive Control and Trait Rumination: A Double-Blind Sham-Controlled Within-Subjects Study

Objective

Rumination is conceptualized as a critical transdiagnostic vulnerability and maintenance factor for affective dysregulation and related emotional disorders. Recent research has pointed to transcranial direct current stimulation (tDCS) as a novel therapeutic tool for alleviating rumination, especially stress-induced rumination. However, the mechanisms of action underlying this effect remain unclear, particularly regarding the potential moderating role of executive control and trait-like rumination. Therefore, in this study, we investigated the impact of anodal tDCS on stress-induced rumination and the potential moderating influence of executive control and trait-like rumination on this efect.

Method

Forty participants from the general community (i.e., unselected sample) took part in a double-blind within-subjects design study wherein we compared anodal stimulation over the left dorsolateral prefrontal cortex(dlPFC) with a sham-stimulation procedure. Participants completed an N-back task, reflecting executive control, during tDCS stimulation, followed by a stress-induction protocol wherein we assessed stress-induced state rumination.

Results

We found no significant effect of tDCS on stress-induced state rumination and no modulation by executive control or trait rumination. Post-hoc Bayesian analyses corroborated these results and even supported the hypothesis that anodal tDCS does not impact stress-induced rumination.

Conclusions

From a clinical perspective, our results are at odds with the current outlook that tDCS is a viable tool for reducing rumination, particularly stress-induced rumination. However, we firmly believe that the results of null-finding studies, such as those from this study, are particularly valuable for future iterations and meta-researchon tDCS as a potential tool for targeting transdiagnostic processes, such as rumination. We also addressed methodological limitations and directions for future research in this area.

Efficacy of transcranial alternating current stimulation in treating chronic insomnia and the impact of age on its effectiveness: A multisite randomized, double-blind, parallel-group, placebo-controlled study

OBJECTIVE

Insomnia is a significant health issue associated with various systemic diseases. Transcranial alternating current stimulation (tACS) has been proposed as a potential intervention for insomnia. However, the efficacy and mechanisms of tACS in chronic insomnia remain unclear. Accordingly, this study aimed to investigate the efficacy of tACS in treating chronic insomnia in adults and assess the impact of age on its effectiveness using a large sample from two centers.

METHODS

A total of 120 participants with chronic insomnia underwent 20 daily sessions of tACS (duration: 40 min, frequency: 77.5 Hz, and intensity: 15 mA) or sham tACS targeting the forehead and both mastoid areas over 4 weeks. Assessments were conducted at baseline, post-treatment, and 4-week follow-up. Primary outcomes included sleep quality and efficiency, onset latency, total sleep time, and daily disturbances. Secondary outcomes included depression, anxiety, and clinical impression.

RESULTS

Compared with the control group, the tACS group demonstrated improved sleep quality and efficiency, increased total sleep time, and reduced daily disturbance (all ps < 0.01). Moreover, tACS had a significant effect on clinical impression (p < 0.001), but not depression and anxiety scores. Subgroup analyses revealed that older participants experienced significant benefits from tACS in sleep quality, efficiency, and overall insomnia reduction at post-treatment and follow-up (p < 0.001). Notably, improved insomnia correlated with attenuated depressive and anxiety symptoms.

CONCLUSIONS

These findings suggest that tACS may be an effective intervention for chronic insomnia within an eight-week timeframe, and age affects the response to tACS in terms of insomnia improvement.

Theta-tACS modulates cerebellar-related motor functions and cerebellar-cortical connectivity

OBJECTIVE

To evaluate the effects of cerebellar transcranial alternating current stimulation (tACS) delivered at cerebellar-resonant frequencies, i.e., theta (θ) and gamma (γ), on upper limb motor performance and cerebellum-primary motor cortex (M1) connectivity, as assessed by cerebellar-brain inhibition (CBI), in healthy subjects.

METHODS

Participants underwent cerebellar-tACS while performing three cerebellar-dependent motor tasks: (i) rhythmic finger-tapping, (ii) arm reaching-to-grasp ('grasping') and (iii) arm reaching-to-point ('pointing') an object. Also, we evaluated possible changes in CBI during cerebellar-tACS.

RESULTS

θ-tACS decreased movement regularity during the tapping task and increased the duration of the pointing task compared to sham- and γ-tACS. Additionally, θ-tACS increased the CBI effectiveness (greater inhibition). The effect of θ-tACS on movement rhythm correlated with CBI changes and less tapping regularity corresponded to greater CBI.

CONCLUSIONS

Cerebellar-tACS delivered at the θ frequency modulates cerebellar-related motor behavior and this effect is, at least in part, mediated by changes in the cerebellar inhibitory output onto M1. The effects of θ-tACS may be due to the modulation of cerebellar neurons that resonate to the θ rhythm.

SIGNIFICANCE

These findings contribute to a better understanding of the physiological mechanisms of motor control and provide new evidence on cerebellar non-invasive brain stimulation.

Modulating preferences during intertemporal choices through exogenous midfrontal transcranial alternating current stimulation: A registered report

Decision conflicts may arise when the costs and benefits of choices are evaluated as a function of outcomes predicted along a temporal dimension. Electrophysiology studies suggest that during performance monitoring a typical oscillatory activity in the theta rhythm, named midfrontal theta, may index conflict processing and resolution. In the present within-subject, sham controlled, cross-over preregistered study, we delivered online midfrontal transcranial Alternating Current Stimulation (tACS) to modulate electrocortical activity during intertemporal decisions. Participants were invited to select choice preference between economic offers at three different intermixed levels of conflict (i.e., low, medium, high) while receiving either theta -, gamma-, or sham tACS in separate blocks and sessions. At the end of each stimulation block, a Letter-Flanker task was also administered to measure behavioural aftereffects. We hypothesized that theta-tACS would have acted on the performance monitoring system inducing behavioural changes (i.e., faster decisions and more impulsive choices) in high conflicting trials, rather than gamma- and sham-tACS. Results very partially confirmed our predictions. Unexpectedly, both theta- and gamma-driven neuromodulation speeded-up decisions compared to sham. However, exploratory analyses revealed that such an effect was stronger in the high-conflict decisions during theta-tACS. These findings were independent from the influence of the sensations induced by the electrical stimulation. Moreover, further analyses highlighted a significant association during theta-tACS between the selection of immediate offers in high-conflict trials and attentional impulsiveness, suggesting that individual factors may account for the tACS effects during intertemporal decisions. Finally, we did not capture long-lasting behavioural changes following tACS in the Flanker task. Our findings may inform scholars to improve experimental designs and boost the knowledge toward a more effective application of tACS.

A translational roadmap for transcranial magnetic and direct current stimulation in stroke rehabilitation: Consensus-based core recommendations from the third stroke recovery and rehabilitation roundtable

BACKGROUND AND AIMS

The purpose of this Third Stroke Recovery and Rehabilitation Roundtable (SRRR3) was to develop consensus recommendations to address outstanding barriers for the translation of preclinical and clinical research using the non-invasive brain stimulation (NIBS) techniques Transcranial Magnetic Stimulation (TMS) and Transcranial Direct Current Stimulation (tDCS) and provide a roadmap for the integration of these techniques into clinical practice.

METHODS

International NIBS and stroke recovery experts (N = 18) contributed to the consensus process. Using a nominal group technique, recommendations were reached via a five-stage process, involving a thematic survey, two priority ranking surveys, a literature review and an in-person meeting.

RESULTS AND CONCLUSIONS

Results of our consensus process yielded five key evidence-based and feasibility barriers for the translation of preclinical and clinical NIBS research, which were formulated into five core consensus recommendations. Recommendations highlight an urgent need for (1) increased understanding of NIBS mechanisms, (2) improved methodological rigor in both preclinical and clinical NIBS studies, (3) standardization of outcome measures, (4) increased clinical relevance in preclinical animal models, and (5) greater optimization and individualization of NIBS protocols. To facilitate the implementation of these recommendations, the expert panel developed a new SRRR3 Unified NIBS Research Checklist. These recommendations represent a translational pathway for the use of NIBS in stroke rehabilitation research and practice.

High-Frequency Language Therapy with Semantic Feature Analysis (SFA) and Transcranial Direct Current Stimulation (tDCS): A Longitudinal Single-Case Report of Semantic Variant of Primary Progressive Aphasia (svPPA)

BACKGROUND

The goal of this study was to investigate whether the combination of semantic feature analysis (SFA) and transcranial direct current stimulation (tDCS) is effective in treating word retrieval in the semantic variant of primary progressive aphasia (svPPA) and how long the potential effects last.

METHODS

A 56-year-old woman diagnosed with frontotemporal dementia (FTD) and svPPA participated in this longitudinal single-subject design. A total of four 2-week stimulation phases were conducted over a 14-month period, each of which was started depending on the participant's language performance. Follow-up testing was conducted shortly after the stimulation period, approximately 2 weeks, and approximately 4 weeks thereafter.

RESULTS

Significant improvement in word retrieval occurred after SFA and tDCS therapy. Two weeks after the end of each stimulation phase, approx. 80% of the trained words could be named correctly. For the untrained words, also significantly more words were correctly named at follow-ups compared to the baseline. Furthermore, the Boston Naming Test (BNT) demonstrated a significant increase in naming performance and showed that phonological cues facilitated word retrieval compared to semantic cues.

CONCLUSION

The combination of SFA and tDCS was able to counteract the expected language deterioration of a participant with svPPA. This effect increased until approximately 2 weeks after each intervention. In addition, a generalization of the effect to untrained words was shown.

From brain to spinal cord: neuromodulation by direct current stimulation and its promising effects as a treatment option for restless legs syndrome

Neuromodulation is a fast-growing field of mostly non-invasive therapies, which includes spinal cord stimulation (SCS), transcranial direct current stimulation (tDCS), vagal nerve stimulation (VNS), peripheral nerve stimulation, transcranial magnetic stimulation (TMS) and transcutaneous spinal direct current stimulation (tsDCS). This narrative review offers an overview of the therapy options, especially of tDCS and tsDCS for chronic pain and spinal cord injury. Finally, we discuss the potential of tsDCS in Restless Legs Syndrome as a promising non-invasive, alternative therapy to medication therapy.

Transcranial direct current stimulation (tDCS) in the treatment of neuropsychiatric symptoms of long COVID

The study aimed to assess the efficacy of transcranial direct current stimulation (tDCS) in the treatment of neuropsychiatric (NP) symptoms of the post-acute sequelae of SARS-CoV-2 infection (PASC), known as the long COVID. A double-blind, randomized, sham-controlled study compared the efficacy and safety of prefrontal cortex active tDCS to sham-tDCS in treating NP-PASC. Patients diagnosed with NP-PASC, with a Fatigue Impact Scale (FIS) score ≥ 40, were eligible for the study. Twenty tDCS sessions were administered within four weeks, with continuous, end-of-treatment, and follow-up measurements. The primary outcome was a change in the FIS at the end-of-treatment, analyzed in the intention-to-treat population. Data from 33 patients assigned to active (n = 16) or sham-tDCS (n = 17) were analyzed. After the treatment, a decrease in the FIS score was more pronounced in the sham than in the active group, yet the intergroup difference was insignificant (11.7 [95% CI -11.1 to 34.5], p = 0.6). Furthermore, no significant intergroup differences were observed regarding anxiety, depression, quality of life, and cognitive performance. The small cohort sample, differences in baseline FIS scores between groups (non-stratified randomization), or chosen stimulation parameters may have influenced our findings. However, it might also be possible that the expected mechanism of action of tDCS is insufficient to treat these conditions.

Balancing Act: Acute and Contextual Vestibular Sensations of Cranial Electrotherapy Stimulation Using Survey and Sensor Outcomes in a Non-Clinical Sample

Cranial electrotherapy stimulation (CES) delivers low-intensity electrical currents to the brain to treat anxiety, depression, and pain. Though CES is considered safe and cost-effective, little is known about side effects emerging across different contexts. Our objective was to investigate how varying physical and cognitive demands impact the frequency and intensity of CES vestibular sensations in a sample of healthy young adults. We used a 2 (stimulation: sham, active) × 2 (physical demand: static sway, dynamic sit-to-stand) × 2 (cognitive demand: single-task remain silent, dual-task count backward) repeated measures design. Vestibular sensations were measured with surveys and wearable sensors capturing balance changes. Active stimulation did not influence reported vestibular sensations. Instead, high physical demand predicted more sensation reports. High cognitive demand, but not active stimulation, predicted postural sway unsteadiness. Significant effects of active stimulation on balance were observed only during the dynamic sit-to-stand transitions. In summary, CES induces vestibular sensations only for a specific outcome under certain circumstances. Our findings imply that consumers can safely maximize the benefits of CES while ensuring they are taking steps to minimize any potential side effects by considering their context and circumstances.

Exploring the impact of intensified multiple session tDCS over the left DLPFC on brain function in MCI: a randomized control trial

Transcranial direct current stimulation combined with cognitive training (tDCS-cog) represents a promising approach to combat cognitive decline among healthy older adults and patients with mild cognitive impairment (MCI). In this 5-day-long double-blinded randomized trial, we investigated the impact of intensified tDCS-cog protocol involving two trains of stimulation per day on working memory (WM) enhancement in 35 amnestic and multidomain amnestic MCI patients. Specifically, we focused to improve WM tasks relying on top-down attentional control and hypothesized that intensified tDCS would enhance performance of visual object matching task (VOMT) immediately after the stimulation regimen and at a 1-month follow-up. Secondarily, we explored whether the stimulation would augment online visual working memory training. Using fMRI, we aimed to elucidate the neural mechanisms underlying the intervention effects by analyzing BOLD activations during VOMT. Our main finding revealed no superior after-effects of tDCS-cog over the sham on VOMT among individuals with MCI as indicated by insignificant immediate and long-lasting after-effects. Additionally, the tDCS-cog did not enhance online training as predicted. The fMRI analysis revealed brain activity alterations in right insula that may be linked to tDCS-cog intervention. In the study we discuss the insignificant behavioral results in the context of the current evidence in tDCS parameter space and opening the discussion of possible interference between trained cognitive tasks.

Cognitive training and brain stimulation in patients with cognitive impairment: a randomized controlled trial

BACKGROUND

Repeated sessions of training and non-invasive brain stimulation have the potential to enhance cognition in patients with cognitive impairment. We hypothesized that combining cognitive training with anodal transcranial direct current stimulation (tDCS) will lead to performance improvement in the trained task and yield transfer to non-trained tasks.

METHODS

In our randomized, sham-controlled, double-blind study, 46 patients with cognitive impairment (60-80 years) were randomly assigned to one of two interventional groups. We administered a 9-session cognitive training (consisting of a letter updating and a Markov decision-making task) over 3 weeks with concurrent 1-mA anodal tDCS over the left dorsolateral prefrontal cortex (20 min in tDCS, 30 s in sham group). Primary outcome was trained task performance (letter updating task) immediately after training. Secondary outcomes included performance in tasks testing working memory (N-back task), decision-making (Wiener Matrices test) and verbal memory (verbal learning and memory test), and resting-state functional connectivity (FC). Tasks were administered at baseline, at post-assessment, and at 1- and 7-month follow-ups (FU). MRI was conducted at baseline and 7-month FU. Thirty-nine participants (85%) successfully completed the intervention. Data analyses are reported on the intention-to-treat (ITT) and the per-protocol (PP) sample.

RESULTS

For the primary outcome, no difference was observed in the ITT (β = 0.1, 95%-CI [- 1.2, 1.3, p = 0.93] or PP sample (β =  - 0.2, 95%-CI [- 1.6, 1.2], p = 0.77). However, secondary analyses in the N-back working memory task showed that, only in the PP sample, the tDCS outperformed the sham group (PP: % correct, β = 5.0, 95%-CI [- 0.1, 10.2], p = 0.06, d-prime β = 0.2, 95%-CI [0.0, 0.4], p = 0.02; ITT: % correct, β = 3.0, 95%-CI [- 3.9, 9.9], p = 0.39, d-prime β = 0.1, 95%-CI [- 0.1, 0.3], p = 0.5). Frontoparietal network FC was increased from baseline to 7-month FU in the tDCS compared to the sham group (pFDR < 0.05). Exploratory analyses showed a correlation between individual memory improvements and higher electric field magnitudes induced by tDCS (ρtDCS = 0.59, p = 0.02). Adverse events did not differ between groups, questionnaires indicated successful blinding (incidence rate ratio, 1.1, 95%-CI [0.5, 2.2]).

CONCLUSIONS

In sum, cognitive training with concurrent brain stimulation, compared to cognitive training with sham stimulation, did not lead to superior performance enhancements in patients with cognitive impairment. However, we observed transferred working memory benefits in patients who underwent the full 3-week intervention. MRI data pointed toward a potential intervention-induced modulation of neural network dynamics. A link between individual performance gains and electric fields suggested dosage-dependent effects of brain stimulation. Together, our findings do not support the immediate benefit of the combined intervention on the trained function, but provide exploratory evidence for transfer effects on working memory in patients with cognitive impairment. Future research needs to explore whether individualized protocols for both training and stimulation parameters might further enhance treatment gains.

TRIAL REGISTRATION

The study is registered on ClinicalTrials.gov (NCT04265378). Registered on 7 February 2020. Retrospectively registered.

The effect of transcranial alternating current stimulation on functional recovery in patients with stroke: a narrative review

Stroke is a common neurological disorder worldwide that can cause significant disabilities. Transcranial alternating current stimulation (tACS) is an emerging non-invasive neuromodulation technique that regulates brain oscillations and reshapes brain rhythms. This study aimed to investigate the effect of tACS on functional recovery in patients with stroke. The MEDLINE (PubMed), Cochrane Library, Embase, SCOPUS, and Web of Science databases were searched for English-language articles on tACS and stroke, published up to October 20, 2023. The following key search phrases were combined to identify potentially relevant articles: 'tACS,' 'transcranial alternating current stimulation,' 'stroke,' 'cerebral infarct,' and 'intracerebral hemorrhage.' The inclusion criteria for study selection were as follows: (1) studies involving patients with stroke and (2) studies that used tACS for functional recovery. A total of 34 potentially relevant studies were identified. Five articles were included in this review after reading the titles and abstracts and assessing their eligibility based on the full-text articles. Among the included studies, one investigated the improvement in overall functional status in patients with stroke after tACS, and two investigated the effect of tACS on motor function and gait patterns. Moreover, one study reported the efficacy of tACS on aphasia recovery, and one study evaluated the effect of tACS on hemispatial neglect. Our findings suggest that tACS improves functional recovery in patients with stroke. The application of tACS was associated with improved overall functional recovery, sensorimotor impairment, aphasia, and hemispatial neglect. The potential clinical application of tACS should be supported by high-quality, evidence-based studies.

A translational roadmap for transcranial magnetic and direct current stimulation in stroke rehabilitation: Consensus-based core recommendations from the third stroke recovery and rehabilitation roundtable

BACKGROUND AND AIMS

The purpose of this Third Stroke Recovery and Rehabilitation Roundtable (SRRR3) was to develop consensus recommendations to address outstanding barriers for the translation of preclinical and clinical research using the non-invasive brain stimulation (NIBS) techniques Transcranial Magnetic Stimulation (TMS) and Transcranial Direct Current Stimulation (tDCS) and provide a roadmap for the integration of these techniques into clinical practice.

METHODS

International NIBS and stroke recovery experts (N = 18) contributed to the consensus process. Using a nominal group technique, recommendations were reached via a five-stage process, involving a thematic survey, two priority ranking surveys, a literature review and an in-person meeting.

RESULTS AND CONCLUSIONS

Results of our consensus process yielded five key evidence-based and feasibility barriers for the translation of preclinical and clinical NIBS research, which were formulated into five core consensus recommendations. Recommendations highlight an urgent need for (1) increased understanding of NIBS mechanisms, (2) improved methodological rigor in both preclinical and clinical NIBS studies, (3) standardization of outcome measures, (4) increased clinical relevance in preclinical animal models, and (5) greater optimization and individualization of NIBS protocols. To facilitate the implementation of these recommendations, the expert panel developed a new SRRR3 Unified NIBS Research Checklist. These recommendations represent a translational pathway for the use of NIBS in stroke rehabilitation research and practice.

Determination of optimal injection current pattern for multichannel transcranial electrical stimulation without individual MRI using multiple head models

BACKGROUND AND OBJECTIVE

Multichannel transcranial electrical stimulation (tES) is widely used to achieve improved stimulation focality. In the multichannel tES, the injection current pattern is generally determined through an optimization process with a finite element (FE) head model extracted from individual magnetic resonance images (MRIs). Although using an individual head model ensures the best outcome, acquiring MRIs of individual subjects in many practical applications is often difficult. Alternatively, a standard head model can be used to determine the optimal injection current pattern to stimulate a specific target; however, this may result in a relatively inaccurate delivery of stimulation current owing to the difference in individual anatomical structures. To address this issue, we propose a new approach for determining the injection current pattern using multiple head models, which can improve the stimulation focality compared to that achieved with a single standard head model.

METHODS

Twenty FE head models were used to optimize the injection current patterns to stimulate three cortical regions that are widely considered targets for tES. The individual injection current patterns were then averaged to obtain each target's mean injection current pattern. The stimulation focality for each target was then calculated by applying different current patterns (the mean current, individual current, and current from a standard model).

RESULTS

Our results showed that the stimulation focality obtained using the mean injection current pattern was significantly higher than that obtained using the injection current pattern from a standard head model. Additionally, our results demonstrated that a minimum of 13 head models are required to determine mean current pattern, allowing for a higher stimulation focality than when using the current from a standard head model.

CONCLUSIONS

Hence, using multiple head models can provide a viable solution for improving the stimulation efficacy of multichannel tES when individual MRIs are not available.

Modulation of Visually Induced Self-motion Illusions by α Transcranial Electric Stimulation over the Superior Parietal Cortex

The growing popularity of virtual reality systems has led to a renewed interest in understanding the neurophysiological correlates of the illusion of self-motion (vection), a phenomenon that can be both intentionally induced or avoided in such systems, depending on the application. Recent research has highlighted the modulation of α power oscillations over the superior parietal cortex during vection, suggesting the occurrence of inhibitory mechanisms in the sensorimotor and vestibular functional networks to resolve the inherent visuo-vestibular conflict. The present study aims to further explore this relationship and investigate whether neuromodulating these waves could causally affect the quality of vection. In a crossover design, 22 healthy volunteers received high amplitude and focused α-tACS (transcranial alternating current stimulation) over the superior parietal cortex while experiencing visually induced vection triggered by optokinetic stimulation. The tACS was tuned to each participant's individual α peak frequency, with θ-tACS and sham stimulation serving as controls. Overall, participants experienced better quality vection during α-tACS compared with control θ-tACS and sham stimulations, as quantified by the intensity of vection. The observed neuromodulation supports a causal relationship between parietal α oscillations and visually induced self-motion illusions, with their entrainment triggering overinhibition of the conflict within the sensorimotor and vestibular functional networks. These results confirm the potential of noninvasive brain stimulation for modulating visuo-vestibular conflicts, which could help to enhance the sense of presence in virtual reality environments.

Transcranial direct current stimulation facilitates backward walking training

Backward walking training presents a great challenge to the physical and neural systems, which may result in an improvement in gait performance. Transcranial direct current electrical stimulation (tDCS), which can non-invasively enhance cortical activity, has been reported to strengthen corticomotor plasticity. We investigated whether excitatory tDCS over the primary motor cortex (M1) or the dorsolateral prefrontal cortex (DLPFC) enhances the effects of backward walking training in healthy participants. Thirty-six healthy participants (16 men and 20 women, mean age 21.3 ± 1.4 years) participated in this study. The participants were randomly assigned to one of the three tDCS groups (M1, DLPFC, and sham). They performed 5 min of backward walking training during 15 min of tDCS. We evaluated dual-task forward and backward walking performance before and after training. Both tDCS groups increased walking speed in the backward condition, but the DLPFC group increased the dual-task backward walking speed more than the M1 group. The M1 group showed decreased gait variability in dual-task backward walking, whereas the DLPFC group showed increased gait variability. Backward walking training combined with M1 stimulation may increase the backward walking speed by reducing gait variability. Backward walking training combined with DLPFC stimulation may prioritize walking speed over gait stability. Our results indicate that backward walking training combined with tDCS may be extended to other rehabilitation methods to improve gait performance.

Virtual neural network-guided optimization of non-invasive brain stimulation in Alzheimer's disease

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique with potential for counteracting disrupted brain network activity in Alzheimer's disease (AD) to improve cognition. However, the results of tDCS studies in AD have been variable due to different methodological choices such as electrode placement. To address this, a virtual brain network model of AD was used to explore tDCS optimization. We compared a large, representative set of virtual tDCS intervention setups, to identify the theoretically optimized tDCS electrode positions for restoring functional network features disrupted in AD. We simulated 20 tDCS setups using a computational dynamic network model of 78 neural masses coupled according to human structural topology. AD network damage was simulated using an activity-dependent degeneration algorithm. Current flow modeling was used to estimate tDCS-targeted cortical regions for different electrode positions, and excitability of the pyramidal neurons of the corresponding neural masses was modulated to simulate tDCS. Outcome measures were relative power spectral density (alpha bands, 8-10 Hz and 10-13 Hz), total spectral power, posterior alpha peak frequency, and connectivity measures phase lag index (PLI) and amplitude envelope correlation (AEC). Virtual tDCS performance varied, with optimized strategies improving all outcome measures, while others caused further deterioration. The best performing setup involved right parietal anodal stimulation, with a contralateral supraorbital cathode. A clear correlation between the network role of stimulated regions and tDCS success was not observed. This modeling-informed approach can guide and perhaps accelerate tDCS therapy development and enhance our understanding of tDCS effects. Follow-up studies will compare the general predictions to personalized virtual models and validate them with tDCS-magnetoencephalography (MEG) in a clinical AD patient cohort.

Transcranial direct current stimulation of the right temporoparietal junction facilitates hippocampal spatial learning in Alzheimer's disease and mild cognitive impairment

OBJECTIVE

Spatial memory deficits are an early symptom in Alzheimer's disease (AD), reflecting the neurodegenerative processes in the neuronal navigation network such as in hippocampal and parietal cortical areas. As no effective treatment options are available, neuromodulatory interventions are increasingly evaluated. Against this backdrop, we investigated the neuromodulatory effect of anodal transcranial direct current stimulation (tDCS) on hippocampal place learning in patients with AD or mild cognitive impairment (MCI).

METHODS

In this randomized, double-blind, sham-controlled study with a cross-over design anodal tDCS of the right temporoparietal junction (2 mA for 20 min) was applied to 20 patients diagnosed with AD or MCI and in 22 healthy controls while they performed a virtual navigation paradigm testing hippocampal place learning.

RESULTS

We show an improved recall performance of hippocampal place learning after anodal tDCS in the patient group compared to sham stimulation but not in the control group.

CONCLUSIONS

These results suggest that tDCS can facilitate spatial memory consolidation via stimulating the parietal-hippocampal navigation network in AD and MCI patients.

SIGNIFICANCE

Our findings suggest that tDCS of the temporoparietal junction may restore spatial navigation and memory deficits in patients with AD and MCI.

Effects of transcranial direct current stimulation combined with Pilates-based exercises in the treatment of chronic low back pain in outpatient rehabilitation service in Brazil: double-blind randomised controlled trial protocol

INTRODUCTION

Chronic low back pain may be associated with pathoanatomical, neurophysiological, physical, psychological and social factors; thus, treatments to reduce symptoms are important to improve the quality of life of this population. We aimed to evaluate the effects of transcranial direct current stimulation (tDCS) combined with Pilates-based exercises compared with sham stimulation on pain, quality of life and disability in patients with chronic non-specific low back pain.

METHODS AND ANALYSIS

This is a protocol for a double-blind randomised controlled trial with participants, outcome assessor and statistician blinded. We will include 36 individuals with a history of non-specific chronic low back pain for more than 12 weeks and minimum pain intensity of 3 points on the Numerical Pain Rating Scale. Individuals will be randomised into two groups: (1) active tDCS combined with Pilates-based exercises and (2) sham tDCS combined with Pilates-based exercises. Three weekly sessions of the protocol will be provided for 4 weeks, and individuals will be submitted to three assessments: the first (T0) will be performed before the intervention protocol, the second (T1) immediately after the intervention protocol and the third (T2) will be a follow-up 1 month after the end of the intervention. We will assess pain, disability, central sensitisation, quality of life, pressure pain threshold, global impression of change, adverse events and medication use. The Numerical Pain Rating Scale and the Roland-Morris Disability Questionnaire will be used at T1 to assess pain and disability, respectively, as primary outcome measures.

ETHICS AND DISSEMINATION

This trial was prospectively registered in ClinicalTrials.gov website and ethically approved by the Ethics and Research Committee of the Faculty of Health Sciences of Trairi (report number: 5.411.244) before data collection. We will publish the results in a peer-reviewed medical journal and on institution websites.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov (NCT05467566).

Remote neurocognitive interventions for attention-deficit/hyperactivity disorder - Opportunities and challenges

Improving neurocognitive functions through remote interventions has been a promising approach to developing new treatments for attention-deficit/hyperactivity disorder (AD/HD). Remote neurocognitive interventions may address the shortcomings of the current prevailing pharmacological therapies for AD/HD, e.g., side effects and access barriers. Here we review the current options for remote neurocognitive interventions to reduce AD/HD symptoms, including cognitive training, EEG neurofeedback training, transcranial electrical stimulation, and external cranial nerve stimulation. We begin with an overview of the neurocognitive deficits in AD/HD to identify the targets for developing interventions. The role of neuroplasticity in each intervention is then highlighted due to its essential role in facilitating neuropsychological adaptations. Following this, each intervention type is discussed in terms of the critical details of the intervention protocols, the role of neuroplasticity, and the available evidence. Finally, we offer suggestions for future directions in terms of optimizing the existing intervention protocols and developing novel protocols.

Neuromodulation of choice-induced preference changes: the tDCS study of cognitive dissonance

Introduction

Difficult choices between two equally attractive options result in a cognitive discrepancy between dissonant cognitions such as preferences and actions often followed by a sense of psychological discomfort known as cognitive dissonance. It can lead to changes in the desirability of options: the chosen option becomes more desirable, whereas the rejected option is devalued. Despite the ample experimental evidence to show this effect, the neural mechanisms and timing of such choice-induced preference changes are not fully understood.

Methods

In this study, we used transcranial direct current stimulation (tDCS) to modulate the activity of the posterior medial frontal cortex (pMFC), which has been associated with conflict monitoring and choice-induced preference changes in neuroimaging studies. Prior to a revised version of Brehm's free-choice paradigm, participants in two experiments underwent cathodal (inhibitory) or anodal (excitatory) tDCS of the pMFC compared to sham (placebo) stimulation prior to the choice phase.

Results

Our results showed that cathodal tDCS significantly decreased the choice-induced preference change relative to a sham, but only in direct comparisons of rejected options. No significant effect of anodal tDCS in comparison with sham was observed.

Discussion

This study replicates the general behavioral effect of cognitive dissonance and provide partial support for the theory of the pMFC contribution to choice-related cognitive dissonance and subsequent preference changes, with possible limitations of an under-sampling for the obtained effect size and an asymmetry in the inhibitory-excitatory effects of non-invasive tDCS.