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

Transcranial direct current stimulation (tDCS) in psychiatric disorders in early childhood (aged under 10 years): a systematic review

Transcranial direct current stimulation (tDCS) remains experimental for many psychiatric disorders in adults. Particularly in childhood, there is limited research on the evidence for the efficacy and mechanisms of action of tDCS on the developing brain. The objective of this review is to identify published experimental studies to examine the efficacy and mechanisms of tDCS in children with psychiatric or developmental disorders in early (prepubertal) childhood (aged under 10 years). Included Studies should meet the following criteria: (1) experimental studies (no reviews, no case reports), (2) studies published in international peer-reviewed journals, (3) written in English, (4) conducted on children under 10 under years of age, (5) at enrolment with a psychiatric or developmental disorder.Eight studies were identified that fulfilled the specified criteria. All studies investigated effect on children with autism-spectrum-disorder (ASD). Anodal tDCS, mainly targeting the left dorsolateral prefrontal cortex (dlPFC), showed positive effects on the reduction of ASD symptoms. There has also been evidence that these stimulations are feasible, have good tolerability and are safe. tDCS was found to be safe and partially effective, but a long-term effect of tDCS and changes in connectivity during tDCS in autism has not been proven. Other developmental or psychiatric diseases were not investigated. This results in a lack of knowledge regarding the reactivity of the brain during the prepubertal period, which is a critical phase in the pathogenesis of neurodevelopmental disorders such as attention deficit hyperactivity disorder (ADHD), ASD, Tourette's syndrome or dyslexia.

The role of 15 mA and 77.5 Hz transcranial alternating current stimulation in blood pressure regulation: A post hoc analysis of a randomized controlled trial

BACKGROUND

Transcranial alternating current stimulation (tACS) at 77.5 Hz and 15 mA, targeting the forehead and mastoid areas, has proven efficacious in patients with major depressive disorder (MDD) by simultaneously stimulating multiple brain nuclei and regions, many of which are critical for blood pressure regulation. This post hoc analysis aimed to assess the potential blood pressure-lowering effects of 77.5 Hz, 15 mA tACS in first-episode drug-naive MDD patients with normotension.

METHODS

Data from a previous randomized controlled trial (RCT) involving first-episode drug-naive MDD patients were analyzed. Participants underwent 20 sessions of either active tACS or sham stimulation. Vital signs, including systolic blood pressure (SBP) and diastolic blood pressure (DBP), were measured at baseline, after treatment (Week 4), and at follow-up (Week 8). Multivariate linear regression and Generalized Estimating Equations (GEE) models were used to evaluate the effects of the treatment on blood pressure.

RESULTS

Totally 68 participants were analysis (33 in the sham group and 35 in the active group). By Week 4, the active tACS group exhibited a significant reduction in both SBP and DBP compared to the sham group (coefficient - 2.04, 95 % CI -3.01 to -1.07, p < 0.001 on SBP, and coefficient - 1.92, 95 % CI -2.69 to -1.18, p < 0.001 on DBP).

CONCLUSIONS

tACS at 77.5 Hz and 15 mA can effectively reduce SBP and DBP in first-episode drug-naive depressive individuals with normotension, with greater reductions observed in those with higher baseline levels.

Modulating delirium through stimulation (MoDeSt): study protocol for a randomized, double-blind, sham-controlled trial assessing the effect of postoperative transcranial electrical stimulation on delirium incidence

BACKGROUND

Postoperative delirium (POD) is the most common neurological adverse event among elderly patients undergoing surgery. POD is associated with an increased risk for postoperative complications, long-term cognitive decline, an increase in morbidity and mortality as well as extended hospital stays. Delirium prevention and treatment options are currently limited. This study will evaluate the effect of transcranial electrical stimulation (tES) on the incidence of POD.

METHODS

We will perform a randomized, double-blind, sham-controlled trial using single-session postoperative application of tES in the recovery room in 225 patients (> 65 years) undergoing elective major surgery. Patients will be randomly allocated (ratio 1:1:1) to one of three study groups: (1) alpha-tACS over posterior parietal cortex [2 mA, 20 min], (2) anodal tDCS over left dorsolateral prefrontal cortex [2 mA, 20 min], (3) sham [2 mA, 30 s]. Delirium will be screened twice daily with the 3-min diagnostic interview Confusion Assessment Method (3D-CAM) in the 5 days following surgery. The primary outcome is the incidence of POD defined as at least one positive screening during the five first postoperative days compared between tACS and sham groups. Secondary outcomes include delirium severity, duration, phenotype, postoperative pain, postoperative nausea and vomiting, electroencephalographic (EEG) markers, and fluid biomarkers.

DISCUSSION

If effective, tES is a novel, easily applicable, non-invasive method to prevent the occurrence of POD. The comprehensive neurophysiological and biofluid assessments for markers of (neuro-)inflammation and neurodegeneration will shed light on the pathomechanisms behind POD and further elucidate the (after-)effects of tES. The potential implications for the postoperative recovery comprise enhanced patient safety, neurocognitive outcome, perioperative manageability but also reduced healthcare costs.

TRIAL REGISTRATION

German Clinical Trial Registry DRKS00033703. Registered on February 23, 2024.

Dissociable components of visual perceptual learning characterized by non-invasive brain stimulation: Stage 1 Registered Report

Visual perceptual learning (VPL), the training-induced improvement in visual tasks, has long been considered the product of neural plasticity at early and local stages of signal processing. However, recent evidence suggests that multiple networks and mechanisms, including stimulus- and task-specific plasticity, concur in generating VPL. Accordingly, early models of VPL, which characterized learning as being local and mostly involving early sensory areas, such as V1, have been updated to embrace these newfound complexities, acknowledging the involvement on parietal (i.e. intra-parietal sulcus) and frontal (i.e. dorsolateral prefrontal cortex) areas, in aspects concerning decision-making, feedback integration and task structure. However, evidence of multiple brain regions differentially involved in different aspects of learning is thus far mostly correlational, emerging from electrophysiological and neuroimaging techniques. To directly address these multiple components of VPL, we propose to use a causal neuromodulation technique, namely transcranial random noise stimulation, to selectively modulate the activity of different brain regions suggested to be involved in various aspects of learning. Specifically, we will target a region in the occipital cortex, which has been associated with stimulus-specific plasticity, and one in the parietal cortex, which has been associated with task-specific plasticity, in a between-subject design. Measures of transfer of learning to untrained stimuli and tasks will be used to evaluate the role of different regions and test for double dissociations between learning effects and stimulated area, shedding lights on learning mechanisms in the visual system. Evidence of dissociable mechanisms of learning can help refine current models of VPL and may help develop more effective visual training and rehabilitation protocols.

Investigating the Working Mechanism of Transcranial Direct Current Stimulation

BACKGROUND

Transcranial direct current stimulation (tDCS) is used to modulate neuronal activity, but the exact mechanism of action (MOA) is unclear. This study investigates tDCS-induced modulation of the corticospinal excitability and the underlying MOA. By anesthetizing the scalp before applying tDCS and by stimulating the cheeks, we investigated whether stimulation of peripheral and/or cranial nerves contributes to the effects of tDCS on corticospinal excitability.

MATERIALS AND METHODS

In a randomized cross-over study, four experimental conditions with anodal direct current stimulation were compared in 19 healthy volunteers: 1) tDCS over the motor cortex (tDCS-MI), 2) tDCS over the motor cortex with a locally applied topical anesthetic (TA) on the scalp (tDCS-MI + TA), 3) DCS over the cheek region (DCS-C), and 4) sham tDCS over the motor cortex(sham). tDCS was applied for 20 minutes at 1 mA. Motor evoked potentials (MEPs) were measured before tDCS and immediately, 15, 30, 45, and 60 minutes after tDCS. A questionnaire was used to assess the tolerability of tDCS.

RESULTS

A significant MEP amplitude increase compared with baseline was found 30 minutes after tDCS-MI, an effect still observed 60 minutes later; no time∗condition interaction effect was detected. In the other three conditions (tDCS-MI + TA, DCS-C, sham), no significant MEP modulation was found. The questionnaire indicated that side effects are significantly lower when the local anesthetic was applied before stimulation than in the other three conditions.

CONCLUSIONS

The significant MEP amplitude increase observed from 30 minutes on after tDCS-MI supports the modulatory effect of tDCS on corticospinal neurotransmission. This effect lasted one hour after stimulation. The absence of a significant modulation when a local anesthetic was applied suggests that effects of tDCS are not solely established through direct cortical stimulation but that stimulation of peripheral and/or cranial nerves also might contribute to tDCS-induced modulation.

Recommendations for the Safe Application of Temporal Interference Stimulation in the Human Brain Part II: Biophysics, Dosimetry, and Safety Recommendations

Temporal interference stimulation (TIS) is a new form of transcranial electrical stimulation (tES) that has been proposed as a method for targeted, noninvasive stimulation of deep brain structures. While TIS holds promise for a variety of clinical and nonclinical applications, little data is yet available regarding its effects in humans and its mechanisms of action. To inform the design and safe conduct of experiments involving TIS, researchers require quantitative guidance regarding safe exposure limits and other safety considerations. To this end, we undertook a two-part effort to determine frequency-dependent thresholds for applied currents below which TIS is unlikely to pose risk to humans in terms of heating or unwanted stimulation. In Part II of this effort, described here, we draw on a previously compiled list (see Part I) of adverse effects (AEs) reported for transcranial direct/alternating current stimulation (tDCS/ACS), deep brain stimulation (DBS), and TIS to determine biophysics-informed exposure metrics for assessing safety. Using an in silico approach, we conduct multiphysics simulations of various tACS, DBS, and TIS exposure scenarios in an anatomically detailed head and brain model. By matching the stimulation in terms of the identified exposure metrics, we infer frequency-dependent TIS parameters that produce exposure conditions equivalent to those known to be safe for tACS and DBS. Based on the results of our simulations and existing knowledge regarding tES and DBS safety, we propose frequency-dependent thresholds below which TIS voltages and currents are unlikely to pose a risk to humans. Safety-related data from ongoing and future human studies are required to verify and refine the thresholds proposed here.

Independent effects of transcranial direct current stimulation and social influence on pain

ABSTRACT

Transcranial direct current stimulation (tDCS) is a noninvasive neuromodulatory technique with the potential to provide pain relief. However, tDCS effects on pain are variable across existing studies, possibly related to differences in stimulation protocols and expectancy effects. We investigated the independent and joint effects of contralateral motor cortex tDCS (anodal vs cathodal) and socially induced expectations (analgesia vs hyperalgesia) about tDCS on thermal pain. We employed a double-blind, randomized 2 × 2 factorial cross-over design, with 5 sessions per participant on separate days. After calibration in Session 1, Sessions 2 to 5 crossed anodal or cathodal tDCS (20 minutes 2 mA) with socially induced analgesic or hyperalgesic expectations, with 6 to 7 days between the sessions. The social manipulation involved videos of previous "participants" (confederates) describing tDCS as inducing a low-pain state ("analgesic expectancy") or hypersensitivity to sensation ("hyperalgesic expectancy"). Anodal tDCS reduced pain compared with cathodal stimulation (F(1,19.9) = 19.53, P < 0.001, Cohen d = 0.86) and analgesic expectancy reduced pain compared with hyperalgesic expectancy (F(1,19.8) = 5.62, P = 0.027, Cohen d = 0.56). There was no significant interaction between tDCS and social expectations. Effects of social suggestions were related to expectations, whereas tDCS effects were unrelated to expectancies. The observed additive effects provide novel evidence that tDCS and socially induced expectations operate through independent processes. They extend clinical tDCS studies by showing tDCS effects on controlled nociceptive pain independent of expectancy effects. In addition, they show that social suggestions about neurostimulation effects can elicit potent placebo effects.

Bilateral tDCS over the DLPFC enhances baroreceptor reflex sensitivity and inhibits blood pressure-related hypoalgesia

OBJECTIVE

This study investigated the impact of transcranial direct stimulation (tDCS) on pain perception, baroreflex sensitivity (BRS), and blood pressure (BP)-related hypoalgesia.

METHOD

Fifty-eight healthy participants were randomized to receive 1) bi-hemispheric tDCS over the dorsolateral prefrontal cortex (DLPFC) at 2 mA for 20 min, or 2) non-stimulation (Sham). Pain measures (threshold, tolerance, intensity and unpleasantness), emotional state (anxiety and mood), continuous BP, and electrocardiogram (ECG) data were recorded before, during, and after stimulation.

RESULTS

tDCS stimulation was followed by increases in BRS, pain intensity and unpleasantness. Anxiety decreased in the Sham group, but not in the tDCS group. Positive correlations between BP and pain threshold and tolerance before stimulation were observed. These remained during stimulation in the Sham group, but not in the tDCS group. Moreover, negative associations between BRS and BP only persisted in the Sham group.

DISCUSSION

The results suggest that bilateral tDCS over the DLPFC enhances BRS and modulates pain perception and BP-related mechanisms. tDCS increases pain perception by inhibiting BP-related hypoalgesia and preventing habituation of anxiety.

SIGNIFICANCE

Low BRS is a powerful prognostic factor of cardiovascular disease, such that its increase via tDCS may be a new therapeutic strategy for cardiovascular health promotion.

Mapping the electric field of high-definition transcranial electrical stimulation across the lifespan

Transcranial electrical stimulation (tES) is a non-invasive technique widely used in modulating brain activity and behavior, but its effects differ across individuals and are influenced by head anatomy. In this study, we investigated how the electric field (EF) generated by high-definition tES varies across the lifespan among different demographic groups and its relationship with neural responses measured by functional magnetic resonance imaging (fMRI). We employed an MRI-guided finite element method to simulate the EF for the two most common tES montages (i.e., targeting the dorsolateral prefrontal cortex and motor cortex, respectively) in two large cohorts of white and Asian participants aged 12 to 100 years. We found that the EF intensity decreased with age, particularly in individuals under 25 years of age, and was influenced by gender and ethnicity. We identified skull thickness, scalp thickness, and epidural cerebrospinal fluid thickness, as the primary anatomical factors accounting for the inter-individual EF variability. Using a concurrent tES-fMRI approach, we observed a spatial consistency between the simulated EF and the brain activity changes induced by tES in the target region. Finally, we developed an open-source toolbox incorporating age-stratified head models to facilitate efficient EF calculations. These findings characterize and quantify the individual differences in tES-induced EF, offering a reference for implementing personalized neuromodulation strategies.

Boosting Psychotherapy With Noninvasive Brain Stimulation: The Whys and Wherefores of Modulating Neural Plasticity to Promote Therapeutic Change

The phenomenon of neural plasticity pertains to the intrinsic capacity of neurons to undergo structural and functional reconfiguration through learning and experiential interaction with the environment. These changes could manifest themselves not only as a consequence of various life experiences but also following therapeutic interventions, including the application of noninvasive brain stimulation (NIBS) and psychotherapy. As standalone therapies, both NIBS and psychotherapy have demonstrated their efficacy in the amelioration of psychiatric disorders' symptoms, with a certain variability in terms of effect sizes and duration. Consequently, scholars suggested the convenience of integrating the two interventions into a multimodal treatment to boost and prolong the therapeutic outcomes. Such an approach is still in its infancy, and the physiological underpinnings substantiating the effectiveness and utility of combined interventions are still to be clarified. Therefore, this opinion paper aims to provide a theoretical framework consisting of compelling arguments as to why adding NIBS to psychotherapy can promote therapeutic change. Namely, we will discuss the physiological effects of the two interventions, thus providing a rationale to explain the potential advantages of a combined approach.

High-density theta oscillatory-modulated tDCS over the parietal cortex for targeted memory enhancement

OBJECTIVES

Associative memory (AM) declines due to healthy aging as well as in various neurological conditions. Standard transcranial electrical stimulation (tES) protocols show inconclusive facilitatory effects on AM, often lacking function specificity and stimulation focality. We tested the effectiveness of high-density electrode montage delivering anodal theta oscillatory-modulated transcranial direct current stimulation (HD-Theta-otDCS) over the left posterior parietal cortex (PPC), aiming to target AM in a spatially focused and function-specific manner.

METHODS

In a sham-controlled cross-over experiment we explored the differential effects of HD-Theta-otDCS applied during either encoding or the retrieval phases of two AM tasks (Face-Word and Object-Location). The stimulation protocol consisted of an anode over the left PPC (P3) and four surrounding return electrodes (CP1, CP5, PO3, POz) with electrical current oscillating in theta rhythm (5 Hz, 1.5 ± 0.5 mA).

RESULTS

HD-Theta-otDCS stimulation applied during both encoding and retrieval increased AM performance compared to sham control in the Face-Word task. We found no differences between the two active stimulation conditions.

CONCLUSIONS

HD-Theta-otDCS showed to be a promising tool for enhancing AM, regardless of the stimulation timing. The results provide further support for our previous findings with bipolar otDCS and confirm that PPC stimulation can induce behaviorally relevant modulation in the memory-related cortico-subcortical networks.

SIGNIFICANCE

The presented approach is one step forward towards precision brain stimulation for memory neuromodulation. The novelty lies in the combination of increased focality and function-specific current waveform. Positive results set the ground for further research on HD-theta-otDCS effectiveness in clinical populations.

Neuromodulation Strategies in Lifelong Bipolar Disorder: A Narrative Review

Bipolar disorder is a debilitating psychiatric condition characterized by recurrent episodes of mania and depression, affecting millions worldwide. While pharmacotherapy remains the cornerstone of treatment, a significant proportion of patients exhibit inadequate response or intolerable side effects to conventional medications. In recent years, neuromodulation techniques have emerged as promising adjunctive or alternative treatments for bipolar disorder. We performed a narrative review, according to the Scale for the Assessment of Narrative Review Articles (SANRA) guidelines, to provide a comprehensive overview of the current literature on neuromodulation interventions in bipolar disorder across the course of lifespan. Specifically, it examines the efficacy, safety, and mechanisms of action of various neuromodulation strategies, including, among others, transcranial magnetic stimulation (TMS), electroconvulsive therapy (ECT), vagus nerve stimulation (VNS), deep brain stimulation (DBS), and it describes the therapeutic experiences across the different ages of illness. Additionally, this review discusses the clinical implications, challenges, and future directions of the integration, in clinical practice, of neuromodulation into the management of bipolar disorder. By synthesizing evidence from different studies, this review aims to inform clinicians, researchers, and stakeholders about the evolving landscape of neuromodulation treatments and their potential role in improving outcomes for individuals with bipolar disorder.

Immediate Effects of Distinct Intensities of Transcutaneous Spinal Direct Current Stimulation on Chronic Pain: A Randomized Controlled Trial

This study aimed to assess the immediate effects of transcutaneous spinal direct current stimulation (tsDCS) on pain outcomes, measured using the visual analog scale (VAS) and pressure pain thresholds in a cohort of 55 participants experiencing chronic pain using a controlled, randomized trial with 55 participants allocated into 2 groups: 2 mA and 0.5 mA of tsDCS for 20 min. Anodal stimulation was applied on the 12th thoracic vertebra, with the cathode positioned on the 7th cervical vertebra. Pain outcomes were assessed before and post intervention using the VAS and pressure algometry. Between- and within-group differences, along with chi-square tests, were used to determine the differences and responsiveness. Significance was established at p < 0.05. Findings showed significant temporal effects for both VAS (p < 0.001) and pressure algometry (p = 0.04). However, no between-group differences were noted for the time × group factor for VAS (p = 0.46) and pressure algometry (p = 0.78). No significant between-group differences were observed for the responsiveness analysis. The results indicate that a single 20-min session of 2 and 0.5 mA tsDCS improves pain scores for both intensities equally. However, there were no statistically significant between-group differences in pain perception or pressure pain threshold.

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

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

Investigating Cerebello-Frontal Circuits Associated with Emotional Prosody: A Double-Blind tDCS and fNIRS study

The emotional and cognitive cerebellum has been explored by several studies in the past years. Recent evidence suggested the possible contribution of the cerebellum in processing emotional prosody, namely the ability to comprehend the emotional content of a given vocal utterance, likely mediated by anatomical and functional cerebello-prefrontal connections. In the present study, the involvement of a functional cerebello-prefrontal network in recognising emotional prosody was assessed by combining non-invasive anodal transcranial direct current stimulation (tDCS) over the right or the left cerebellum and functional Near Infrared Spectroscopy of the prefrontal cortex, in a double-blind within-subject experimental design on healthy participants. The results showed that right and, to a less extent, left cerebellar tDCS (as compared to sham stimulation) reduced neural activation in the prefrontal cortex while accuracy and reaction times at the vocal recognition task remained unchanged. These findings highlight functional properties of the cerebello-frontal connections and the psychophysiological effects of cerebellar brain stimulation, with possible clinical applications in psychiatric and neurological conditions.

Effects of cervical transcutaneous spinal direct current stimulation on spinal excitability

OBJECTIVE

To investigate the effects of transcutaneous spinal direct current stimulation (tsDCS) on spinal cord excitability using neurophysiological methods.

METHODS

Spinal cord motoneuron excitability was assessed using various neurophysiological techniques in a sham-controlled randomized experiment, which involved delivering 2 mA tsDCS and testing four different montages. Transcranial magnetic stimulation (TMS), F-waves to supramaximal ulnar nerve stimulation and somatosensory evoked potentials to upper limb nerves stimulation were measured in the participants with the electrode configuration that yielded the greatest effect, for a total of about 18 min. 18 young volunteers were recruited.

RESULTS

Among the tested ones, the most promising tsDCS montage was the one with the anode placed on the 7th cervical spinous process and the cathode on the glottis. With this configuration, a significant enhancement of motor responses in the hand muscles to TMS of the contralateral hand motor area was observed during tsDCS (p<0.00001), reaching a plateau after 6 min. This facilitation rapidly declined within a few minutes after the tsDCS was stopped.

CONCLUSION

Results of the different techniques suggest a possible contribution to facilitatory neuromodulation of the motoneurons at the cervical spine level.

SIGNIFICANCE

The occurrence of enhanced excitability after tsDCS suggests potential application in individuals with partial corticospinal fiber impairment affecting hand motor function.

The safety and efficacy of applying a high-current temporal interference electrical stimulation in humans

Background

Temporal interference electrical stimulation (TI) is promise in targeting deep brain regions focally. However, limited electric field intensity challenges its efficacy.

Objective

This study aimed to introduce a high-current TI electrical stimulation protocol to enhance its intensity and evaluate its safety and efficacy when applied to the primary motor cortex (M1) in the human brain.

Methods

Safety assessments included a battery of biochemical and neuropsychological tests (NSE, MoCA, PPT, VAMS-R, and SAS measurements), 5-min resting-state electroencephalography (EEG) recordings before and after 30-min high-current TI electrical stimulation sessions (20 Hz, 70 Hz, sham). Adverse reactions were also documented post-stimulation. Efficacy evaluations involved two motor tasks, the simple reaction time (SRT) task and the one-increment task, to investigate the distinct contributions of beta (20 Hz) and gamma (70 Hz) oscillations to motor functions.

Results

Biochemical and neuropsychological tests revealed no significant differences between the groups. Additionally, no epileptic activities were detected in the EEG recordings. In the one-increment task, 20 Hz stimulation delayed participants' reaction time compared to the 70 Hz and sham groups. Conversely, in the SRT task, 70 Hz stimulation exhibited a tendency to enhance participants' performance relative to the sham group.

Conclusion

The proposed high-current TI electrical stimulation is both safe and effective for stimulating the human brain. Moreover, the distinct effects observed in motor tasks underscore the dissociative roles of beta and gamma oscillations in motor functions, offering valuable insights into the potential applications of high-current TI electrical stimulation in brain stimulation research.

Advances in non-invasive brain stimulation: enhancing sports performance function and insights into exercise science

The cerebral cortex, as the pinnacle of human complexity, poses formidable challenges to contemporary neuroscience. Recent advancements in non-invasive brain stimulation have been pivotal in enhancing human locomotor functions, a burgeoning area of interest in exercise science. Techniques such as transcranial direct current stimulation, transcranial alternating current stimulation, transcranial random noise stimulation, and transcranial magnetic stimulation are widely recognized for their neuromodulator capabilities. Despite their broad applications, these methods are not without limitations, notably in spatial and temporal resolution and their inability to target deep brain structures effectively. The advent of innovative non-invasive brain stimulation modalities, including transcranial focused ultrasound stimulation and temporal interference stimulation technology, heralds a new era in neuromodulation. These approaches offer superior spatial and temporal precision, promising to elevate athletic performance, accelerate sport science research, and enhance recovery from sports-related injuries and neurological conditions. This comprehensive review delves into the principles, applications, and future prospects of non-invasive brain stimulation in the realm of exercise science. By elucidating the mechanisms of action and potential benefits, this study aims to arm researchers with the tools necessary to modulate targeted brain regions, thereby deepening our understanding of the intricate interplay between brain function and human behavior.

Neuromodulation on the ground and in the clouds: a mini review of transcranial direct current stimulation for altering performance in interactive driving and flight simulators

Transcranial direct current stimulation (tDCS) has emerged as a promising tool for cognitive enhancement, especially within simulated virtual environments that provide realistic yet controlled methods for studying human behavior. This mini review synthesizes current research on the application of tDCS to improve performance in interactive driving and flight simulators. The existing literature indicates that tDCS can enhance acute performance for specific tasks, such as maintaining a safe distance from another car or executing a successful plane landing. However, the effects of tDCS may be context-dependent, indicating a need for a broader range of simulated scenarios. Various factors, including participant expertise, task difficulty, and the targeted brain region, can also influence tDCS outcomes. To further strengthen the rigor of this research area, it is essential to address and minimize different forms of research bias to achieve true generalizability. This comprehensive analysis aims to bridge the gap between theoretical understanding and practical application of neurotechnology to study the relationship between the brain and behavior, ultimately providing insights into the effectiveness of tDCS in transportation settings.

Native learning ability and not age determines the effects of brain stimulation

Healthy aging often entails a decline in cognitive and motor functions, affecting independence and quality of life in older adults. Brain stimulation shows potential to enhance these functions, but studies show variable effects. Previous studies have tried to identify responders and non-responders through correlations between behavioral change and baseline parameters, but results lack generalization to independent cohorts. We propose a method to predict an individual's likelihood of benefiting from stimulation, based on baseline performance of a sequential motor task. Our results show that individuals with less efficient learning mechanisms benefit from stimulation, while those with optimal learning strategies experience none or even detrimental effects. This differential effect, first identified in a public dataset and replicated here in an independent cohort, was linked to one's ability to integrate task-relevant information and not age. This study constitutes a further step towards personalized clinical-translational interventions based on brain stimulation.

Shaping tomorrow: how the STEP training course pioneered noninvasive brain stimulation training for psychiatry in France

Over the past three decades, non-invasive brain stimulation (NIBS) techniques have gained worldwide attention and demonstrated therapeutic potential in various medical fields, particularly psychiatry. The emergence of these novel techniques has led to an increased need for robust training programs to provide practitioners, whether clinicians or scientists, with the necessary skills and knowledge. In response, a comprehensive training curriculum for NIBS in psychiatry has been developed in France. This curriculum was developed by a group of researchers and psychiatrists interested in the clinical application of NIBS in psychiatry, called STEP - Stimulation Transcranienne en Psychiatrie, under the auspices of the French Association of Biological Psychiatry. This perspective outlines the development and implementation of this course, tracing its inception, the evolution of the program, and the challenges encountered along the way. The position of the course in the national and international environment and its future prospects are also discussed. Through this perspective, we aim to summarize the collaborative efforts to promote NIBS teaching and research in French psychiatry.

Synchronized application of closed-loop NMES and precision tACS in post-stroke hand rehabilitation: a protocol of neurorehabilitation trial

Background

Severe upper extremity paresis due to stroke is a significant clinical sequela. Neuromuscular electrical stimulation (NMES)-based rehabilitation has demonstrated promising results along with cortical plasticity. Transcranial alternating current stimulation (tACS) has gained attention due to its unique ability to entrain endogenous oscillatory brain rhythms with injected AC frequency, offering the potential for modifying brain conditions to enhance rehabilitative interventions. Because repetitive motor execution in rehabilitation training requires a smooth transition of the brain state despite often being impaired secondary to stroke, combining NMES and tACS may offer better treatment efficacy.

Aim

This study proposes a phase I/II trial of an outpatient comprehensive rehabilitative treatment combining the integrated volitional-control electrical stimulation (IVES), a closed-loop NMES, and the timing-specified focal tACS in individualized beta frequency (dynamic-precision tACS) targeting severe hand paresis in patients with chronic stroke, aiming to demonstrate the feasibility of combination treatment.

Design

Double-blind randomized cross-over trial.

Methods

The repetitive facilitative finger extension training utilizing closed-loop NMES is combined with dynamic-precision tACS on the primary motor cortex to assist post-movement beta-rebound. Together with regular occupational therapy, we propose a comprehensive outpatient neurorehabilitative regimen. Here, a total of 10 sessions will be conducted using a cross-over design using real and sham tACS.

Analysis

The perception and fatigue from stimulation will be investigated as the primary outcomes. The efficacy of improving sensorimotor function and their background physiological mechanisms will be evaluated as the secondary outcomes.

Discussion

This phase I/II trial will be the first to combine tACS and neurorehabilitation using functional electrical stimulation. A weekly outpatient protocol with cheap devices may offer a new treatment paradigm toward functional recovery for chronic stroke patients with severe upper extremity paresis.

Ethics and trial registration

This study was approved by the Ethics Committee of Kyorin University Faculty of Medicine (814-01). The trial was registered in a public database: UMIN000048274.

Stakeholder perspectives on non-invasive brain stimulation

Non-invasive brain stimulation (NIBS) techniques such as transcranial direct current stimulation (tDCS) or transcranial magnetic stimulation (TMS) have made great progress in recent years and offer boundless potential for the neuroscientific research and treatment of disorders. However, the possible use of NIBS devices for neuro-doping and neuroenhancement in healthy individuals and the military are poorly regulated. The great potentials and diverse applications can have an impact on the future development of the technology and society. This participatory study therefore aims to summarize the perspectives of different stakeholder groups with the help of qualitative workshops. Nine qualitative on-site and virtual workshops were conducted in the study with 91 individuals from seven stakeholder groups: patients, students, do-it-yourself home users of tDCS, clinical practitioners, industry representatives, philosophers, and policy experts. The co-creative and design-based workshops were tailored to each group to document the wishes, fears, and general comments of the participants. The outlooks from each group were collected in written form and summarized into different categories. The result is a comprehensive overview of the different aspects that need to be considered in the field of NIBS. For example, several groups expressed the wish for home-based tDCS under medical supervision as a potential therapeutic intervention and discussed the associated technical specifications. Other topics that were addressed were performance enhancement for certain professional groups, training requirements for practitioners, and questions of agency, among others. This qualitative participatory research highlights the potential of tDCS and repetitive TMS as alternative therapies to medication, with fewer adverse effects and home-based use for tDCS. The ethical and societal impact of the abuse of NIBS for non-clinical use must be considered for policy-making and regulation implementations. This study adds to the neuroethical debate on the responsible use and application of NIBS technologies, taking into consideration the different perspectives of important stakeholders in the field.

Exploring whether home-based neuromodulation can boost the analgesic effects of exercise in people with knee osteoarthritis: protocol for a double-blinded, pilot randomised controlled trial

INTRODUCTION

Knee osteoarthritis (OA) represents a leading cause of disability globally. Exercise has been demonstrated to improve pain and function in people with knee OA. However, when in pain, commencement of exercise is difficult, and clinical effects with such interventions are often modest. Recently, transcranial direct current stimulation (tDCS), a form of non-invasive brain stimulation, has been shown to bolster the pain-relieving effect of exercise in experimental settings. While promising, the utility of employing this approach beyond the research environment is yet to be elucidated. Therefore, this pilot study aims to investigate the feasibility, safety, adherence, tolerability and preliminary efficacy of tDCS and exercise in home-based settings to improve pain and function in people with knee OA.

METHODS AND ANALYSIS

This protocol is for a pilot randomised, double-blinded, sham-controlled trial. 24 individuals with idiopathic knee OA will be randomised to receive either active tDCS+exercise (Intervention) or sham tDCS+exercise (Control) at home. Participants will receive 20 min of tDCS 5 days per week for the first 2 weeks of this 8-week trial. Participants in both groups will complete a lower limb strengthening programme 3 days per week for the entire 8 weeks. Outcome measures of feasibility (acceptability, satisfaction, retention), safety, adherence and tolerability will be assessed throughout the trial period, with clinical outcomes of pain and function assessed before and following the intervention. Feasibility, safety, adherence and tolerability outcomes will be explored descriptively using frequencies and percentages. To examine preliminary efficacy, within-group and between-group changes in pain and functional measures will be analysed.

ETHICS AND DISSEMINATION

This protocol obtained ethical approval from the Queensland University of Technology Human Research Ethics Committee (HREA 2024-8302-20200). All participants will provide written informed consent. The findings of the study will be disseminated via journal publications and international conference proceedings.

TRIAL REGISTRATION NUMBER

ACTRN12624000397516p.

Evaluation of tolerability and safety of transcranial electrical stimulation with gel particle electrodes in healthy subjects

Background

With the advancement of transcranial electrical stimulation (tES) technology, an increasing number of stimulation devices and treatment protocols have emerged. However, safety and tolerability remain critical concerns before new strategies can be implemented. Particularly, the use of gel particle electrodes brings new challenges to the safety and tolerability of tES, which hinders its widespread adoption and further research.

Objective

Our study utilized a specially designed and validated transcranial electrical stimulation stimulator along with preconfigured gel particle electrodes placed at F3 and F4 in the prefrontal lobes. We aimed to assess the tolerance and safety of these electrodes in healthy subjects by administering different durations and types of tES.

Methods

Each participant underwent ten sessions of either transcranial direct current stimulation (tDCS) or transcranial alternating current stimulation (tACS), with session durations varying. In the experiment, we collected various measurement data from participants, including self-report questionnaire data and behavioral keystroke data. Tolerability was evaluated through adverse events (AEs), the relationship of adverse events with tES (AEs-rela), the Self-Rating Anxiety Scale (SAS), and the Visual Analog Mood Scale-Revised (VAMS-R). Safety was assessed using the Visual Analog Scale (VAS), the Skin Sensation Rating (SSR), Montreal Cognitive Assessment (MoCA), and Stroop task. These data were analyzed to determine the impact of different parameters on the tolerability and safety of tES.

Results

There were no significant changes in the results of the MoCA and SAS scales before and after the experiment. However, significant differences were observed in VAS, SSR, AEs, and AEs-rela between tDCS and tACS. Additionally, fatigue increased, and energy levels decreased on VAMS-R with longer durations. No significant differences were found in other neuropsychological tests.

Conclusion

Our study revealed significant differences in tolerability and safety between tDCS and tACS, underscoring the importance of considering the stimulation type when evaluating these factors. Although tolerance and safety did not vary significantly across different stimulation durations in this study, future research may benefit from exploring shorter durations to further assess tolerability and safety efficiently.

Effects of different types of high-definition transcranial electrical stimulation on visual working memory and contralateral delayed activity

BACKGROUND AND PURPOSE

Working memory is critical for individuals and has been found to be improved by electrical stimulation of the left dorsolateral prefrontal cortex (DLPFC). However, the effects of different types of transcranial electrical stimulation on working memory are controversial, and the underlying mechanism remains uncertain. In this study, high-definition transcranial direct current stimulation (HD-tDCS) and high-definition transcranial random noise stimulation (HD-tRNS) were applied to the DLPFC to observe the different effects on visual working memory (VWM). The aim was to explore the causal relationship between the electrical activity of the DLPFC and the posterior parietal cortex (PPC) electrical activity and the contralateral delayed activity (CDA).

METHODS

Thirty-three healthy subjects received HD-tDCS, HD-tRNS and sham stimulation in a random order. Stimulation was applied to the left DLPFC for 20 min. The subjects underwent a color change-detection task as our VWM task and an auditory digit span test (DST) immediately after stimulation. Event-related potential (ERP) data were collected during the VWM task.

RESULTS

The results revealed significant differences between the different types of HD-tES. There was a remarkable increase in VWM capacity following HD-tDCS compared with both HD-tRNS (pa = 0.038) and sham stimulation (pa = 0.038). Additionally, the CDA from the PPC differed after stimulation of the DLPFC. Both HD-tDCS and HD-tRNS expanded the maximum CDA amplitude from set size of 4 to 6, whereas after sham stimulation, the maximum CDA was maintained at a set size of 4. Compared with the sham condition, only HD-tDCS induced a noteworthy increase in CDA amplitude (pa = 0.012). Notably, a significant correlation emerged between the mean CDA amplitude and VWM capacity (p < 0.001, r = - 0.402).

CONCLUSION

These findings underscore the ability of HD-tDCS to target the DLPFC to augment working memory capacity while concurrently amplifying CDA amplitudes in the PPC through the frontoparietal network. Trial registration ChiCTR2300074898.

Research progress of tDCS in the treatment of ADHD

TDCS is one of the most widely used non-invasive neuromodulation techniques, which changes the excitability of local cortical tissue by applying weak continuous direct current to the scalp, effectively improves the attention and concentration of ADHD children, and improves the impulse disorder of patients, but related research is still in its infancy. Based on a review of a large number of existing literatures and an analysis of the pathogenesis and principle of ADHD, this paper summarized the research on tDCS in the treatment of ADHD in recent years from the aspects of treatment mechanism, safety and stimulation parameters, and simply compared the application of tDCS with other non-traumatic neuromodulation techniques in the treatment of ADHD. The future development direction of this technology is further discussed.

Noninvasive modulation of the hippocampal-entorhinal complex during spatial navigation in humans

Because of the depth of the hippocampal-entorhinal complex (HC-EC) in the brain, understanding of its role in spatial navigation via neuromodulation was limited in humans. Here, we aimed to better elucidate this relationship in healthy volunteers, using transcranial temporal interference electric stimulation (tTIS), a noninvasive technique allowing to selectively neuromodulate deep brain structures. We applied tTIS to the right HC-EC in either continuous or intermittent theta-burst stimulation patterns (cTBS or iTBS), compared to a control condition, during a virtual reality-based spatial navigation task and concomitant functional magnetic resonance imaging. iTBS improved spatial navigation performance, correlated with hippocampal activity modulation, and decreased grid cell-like activity in EC. Collectively, these data provide the evidence that human HC-EC activity can be directly and noninvasively modulated leading to changes of spatial navigation behavior. These findings suggest promising perspectives for patients suffering from cognitive impairment such as following traumatic brain injury or dementia.

Can Neuromodulation Improve Sleep and Psychiatric Symptoms?

PURPOSE OF REVIEW

In this review, we evaluate recent studies that employ neuromodulation, in the form of non-invasive brain stimulation, to improve sleep in both healthy participants, and patients with psychiatric disorders. We review studies using transcranial electrical stimulation, transcranial magnetic stimulation, and closed-loop auditory stimulation, and consider both subjective and objective measures of sleep improvement.

RECENT FINDINGS

Neuromodulation can alter neuronal activity underlying sleep. However, few studies utilizing neuromodulation report improvements in objective measures of sleep. Enhancements in subjective measures of sleep quality are replicable, however, many studies conducted in this field suffer from methodological limitations, and the placebo effect is robust. Currently, evidence that neuromodulation can effectively enhance sleep is lacking. For the field to advance, methodological issues must be resolved, and the full range of objective measures of sleep architecture, alongside subjective measures of sleep quality, must be reported. Additionally, validation of effective modulation of neuronal activity should be done with neuroimaging.

Effects of Transcranial Direct Current Stimulation Targeting Dorsolateral Prefrontal Cortex and Orbitofrontal Cortex on Somatic Symptoms in Patients With Major Depressive Disorder: A Randomized, Double-Blind, Controlled Clinical Trial

AIM

There is a lack of research on transcranial direct current stimulation (tDCS) for the treatment of somatic symptoms in major depressive disorder (MDD) and the suitable stimulating brain region. We investigated the efficacy of tDCS targeting the dorsolateral prefrontal cortex (DLPFC) versus orbitofrontal cortex (OFC) on depressive somatic symptoms and somatic anxiety in patients with MDD and aimed to identify the appropriate stimulating brain regions.

METHODS

In this randomized, double-blind, sham-controlled study, a total of 70 patients diagnosed with MDD were randomly allocated into DLPFC group, OFC group, and Sham group. Subjects participated in 2 weeks of 10 primary interventions and subsequently 2-week maintenance interventions weekly (20 min, 2 mA).

RESULTS

The DLPFC group showed a more significant improvement in somatic symptoms compared to the Sham group at week 2. At the maintenance and follow-up stages, the DLPFC group outperformed the Sham and OFC groups, but the difference with the Sham group was not significant. Neither active group demonstrated superiority over the Sham group in improving depression and anxiety.

CONCLUSION

In conclusion, the tDCS targeting DLPFC may be a potentially effective therapeutic target for alleviating somatic symptoms in patients with MDD.

Safety and feasibility of home-based transcranial alternating current stimulation in youths with 22q11.2 deletion syndrome

Neurodevelopmental disorders such as attention deficit and/or hyperactivity disorder (ADHD) and schizophrenia are characterized by core impairment in executive functions (EF). Despite the development of various behavioral interventions to enhance EF, the evidence is still scarce. Alternatively, non-invasive brain stimulation tools such as transcranial alternating current stimulation (tACS) has emerged as a potential strategy to alleviate cognitive deficits. Previous studies have demonstrated the safety, feasibility, and efficacy of one single tACS session in different clinical populations. However, the effects of tACS appear limited and need to be sustained to be considered an effective cognitive neurorehabilitation tool. Recent studies have used home-based, repeated tACS sessions in individuals with neurodegenerative diseases. To our knowledge, the safety and feasibility of such an intensive protocol remains to be tested in a younger population with neurodevelopmental disorders. Using a randomized double-blind sham-controlled design, we administered home-based, repeated tACS sessions to seven individuals aged 14-25 with 22q11.2 deletion syndrome (22q11.2DS), which confers an increased risk for neurodevelopmental disorders. We aimed to assess the safety, tolerability, and feasibility of tACS. Findings from this ongoing clinical trial revealed a favorable safety profile, with frequent yet transient and mainly mild adverse effects. The intervention proved to be feasible, shown by very high adherence rates and positive user experiences. Future studies should therefore investigate whether prolonged exposure to tACS can lead to long-lasting cognitive outcomes.

Clinical trial registration

ClinicalTrials.gov, identifier NCT05664412.

The subjective experience of transcranial electrical stimulation: a within-subject comparison of tolerability and side effects between tDCS, tACS, and otDCS

Low-intensity transcranial electrical stimulation (tES), including techniques like transcranial direct current stimulation (tDCS), transcranial alternating current stimulation (tACS), and oscillatory transcranial direct current stimulation (otDCS), has been widely explored for its neuromodulatory effects on motor, cognitive, and behavioral processes. Despite well-established safety, these techniques can induce varying degrees of discomfort and side effects, potentially impacting their application. This study presents a within-subject sham-controlled experiment directly comparing the subjective experience and side effects of tDCS, tACS, and otDCS. Participants reported their discomfort levels at multiple time points during 20-min stimulation sessions and completed a side-effects questionnaire before and after each session. Results indicated that the overall discomfort levels were low across all conditions, with ≥95% reporting the absence of discomfort or mild procedure-induced discomfort. Nevertheless, tDCS and otDCS were slightly less comfortable compared to sham, especially at the beginning of stimulation, with tACS-induced discomfort levels being overall comparable to sham. The most common side / adverse effects were mild skin sensations, including itching and tingling, particularly with tDCS and otDCS, while tACS occasionally caused phosphenes and blurred vision. These findings provide a systematic comparison of tES-induced discomfort and side effects between different tES techniques, highlighting the high safety of tES, but also the importance of considering within- and between-person variability and time-course effects in tES applications.

Is transcranial alternating current stimulation effective for improving working memory? A three-level meta-analysis

Working memory, an essential component of cognitive function, can be improved through specific methods. This meta-analysis evaluates the effectiveness of transcranial alternating current stimulation (tACS), an emerging technique for enhancing working memory, and explores its efficacy, influencing factors, and underlying mechanisms. A PRISMA systematic search was conducted. Hedges's g was used to quantify effect sizes. We constructed a three-level meta-analytic model to account for all effect sizes and performed subgroup analyses to assess moderating factors. Recognizing the distinct neural underpinnings of various working memory processes, we separately assessed the effects on n-back tasks and traditional working memory tasks. A total of 39 studies with 405 effect sizes were included (170 from n-back tasks and 235 from other tasks). The overall analysis indicated a net benefit of g = 0.060 of tACS on working memory. Separate analyses showed that tACS had a small positive effect on n-back tasks (g = 0.102), but almost no effect on traditional working memory tasks (g = 0.045). Further analyses revealed mainly: A moderately positive effect of theta tACS (without anti-phase stimulation) on n-back tasks (g = 0.207); and a small effect of offline stimulation on working memory maintenance (g = 0.127). Overall, tACS has minimal impact on working memory improvement, but it shows potential under certain conditions. Specifically, both online and offline theta tACS can improve n-back task performance, while only offline stimulation enhances working memory maintenance. More research is needed to understand the mechanisms behind these effects to make tACS an effective method.

The role of the somatosensory system in the feeling of emotions: a neurostimulation study

Emotional experiences deeply impact our bodily states, such as when we feel 'anger', our fists close and our face burns. Recent studies have shown that emotions can be mapped onto specific body areas, suggesting a possible role of the primary somatosensory system (S1) in emotion processing. To date, however, the causal role of S1 in emotion generation remains unclear. To address this question, we applied transcranial alternating current stimulation (tACS) on the S1 at different frequencies (beta, theta, and sham) while participants saw emotional stimuli with different degrees of pleasantness and levels of arousal. Results showed that modulation of S1 influenced subjective emotional ratings as a function of the frequency applied. While theta and beta-tACS made participants rate the emotional images as more pleasant (higher valence), only theta-tACS lowered the subjective arousal ratings (more calming). Skin conductance responses recorded throughout the experiment confirmed a different arousal for pleasant versus unpleasant stimuli. Our study revealed that S1 has a causal role in the feeling of emotions, adding new insight into the embodied nature of emotions. Importantly, we provided causal evidence that beta and theta frequencies contribute differently to the modulation of two dimensions of emotions-arousal and valence-corroborating the view of a dissociation between these two dimensions of emotions.

Differing effectiveness of transcranial random noise stimulation and transcranial direct current stimulation for enhancing working memory in healthy individuals: a randomized controlled trial

BACKGROUND

Transcranial direct current stimulation (tDCS) applied to the left dorsolateral prefrontal cortex (DLPFC) is a promising technique for enhancing working memory (WM) performance in healthy and psychiatric populations. However, limited information is available about the effectiveness of transcranial random noise stimulation (tRNS) applied to the left DLPFC on WM. This study investigated the effectiveness of tRNS on WM compared with that of tDCS, which has established functional evidence.

METHODS

This randomized, double-blind, sham-controlled trial enrolled 120 healthy right-handed adults who were randomly allocated to four stimulation groups: tRNS + direct current (DC) offset, tRNS, tDCS, or sham. Each stimulus was placed over the left DLPFC and had a current intensity of 2 mA applied for 20 min during the dual n-back task. The dual n-back task was repeated thrice: pre-stimulation, during stimulation, and post-stimulation. The d-prime scores, and response times were calculated as the main outcome measures. A linear mixed model was created to identify the main effects and interactions between the groups and times, with the group and time as fixed effects, and baseline performance and the subject as a covariate and random effect, respectively. The relationships between the benefit of each stimulus and baseline WM performance were also examined.

RESULTS

For the d-prime score during stimulation, the tRNS group significantly performed better than the sham group at online assessment (β = 0.310, p = 0.001). In the relationships between the benefit of each stimulus and baseline WM performance, the tRNS group had significantly larger negative line slopes than the sham group for the d-prime score (β = -0.233, p = 0.038).

CONCLUSIONS

tRNS applied to the left DLPFC significantly improved WM performance and generated greater benefits for healthy individuals with lower WM performance. These findings highlight the potential utility of tRNS for enhancing WM performance in individuals with lower WM performance and contribute evidence for clinical application to patients with cognitive decline.

TRIAL REGISTRATION

This study was registered in the University Hospital Medical Information Network Clinical Trial Registry in Japan (UMIN000047365) on April 1, 2022; https://center6.umin.ac.jp/cgi-open-bin/ctr/ctr_view.cgi?recptno=R000054021 .

tDCS Cranial Nerve Co-Stimulation: Unveiling Brainstem Pathways Involved in Trigeminal Nerve Direct Current Stimulation in Rats

The effects of transcranial direct current stimulation (tDCS) are typically attributed to the polarization of cortical neurons by the weak electric fields it generates in the cortex. However, emerging evidence indicates that certain tDCS effects may be mediated through the co-stimulation of peripheral or cranial nerves, particularly the trigeminal nerve (TN), which projects to critical brainstem nuclei that regulate the release of various neurotransmitters throughout the central nervous system. Despite this, the specific pathways involved remain inadequately characterized. In this study, we examined the effects of acute transcutaneous TN direct current stimulation (TN-DCS) on tonic (i.e. mean spike rate and spike rate over time) and phasic (number of bursts, spike rate per burst, burst duration, and inter-burst interval) activities while simultaneously recording single-neuron activity across three brainstem nuclei in rats: the locus coeruleus (LC), dorsal raphe nucleus (DRN), and median raphe nucleus (MnRN). We found that TN-DCS significantly modulated tonic activity in the LC, with notable interactions between stimulation amplitude, polarity, and time epoch affecting mean spike rates. Similar effects were observed in the DRN regarding tonic activity. Further, phasic activity in the LC was influenced by TN-DCS, with changes in burst number, duration, and inter-burst intervals linked to stimulation parameters. Conversely, MnRN tonic activity following TN-DCS remained unchanged. Importantly, xylocaine administration to block TN abolished the effects on tonic activities in both the LC and DRN. These results suggest that tDCS effects may partially arise from indirect modulation of the TN, leading to altered neuronal activity in DRN and LC. Besides, the differential changes in tonic and phasic LC activities underscore their complementary roles in mediating TN-DCS effects on higher cortical regions. This research bears significant translational implications, providing mechanistic insights that could enhance the efficacy of tDCS applications and deepen our understanding of its neurophysiological effects.

Enhancing motor skill learning through multiple sessions of online high-definition transcranial direct current stimulation in healthy adults: insights from EEG power spectrum

The purpose of this study was to evaluate the influence of high-definition transcranial direct current stimulation (HD-tDCS) on finger motor skill acquisition. Thirty-one healthy adult males were randomly assigned to one of three groups: online HD-tDCS (administered during motor skill learning), offline HD-tDCS (delivered before motor skill learning), and a sham group. Participants engaged in a visual isometric pinch task for three consecutive days. Overall motor skill learning and speed-accuracy tradeoff function were used to evaluate the efficacy of tDCS. Electroencephalography was recorded and power spectral density was calculated. Both online and offline HD-tDCS total motor skill acquisition was significantly higher than the sham group (P < 0.001 and P < 0.05, respectively). Motor skill acquisition in the online group was higher than offline (P = 0.132, Cohen's d = 1.46). Speed-accuracy tradeoff function in the online group was higher than both offline and sham groups in the post-test. The online group exhibited significantly lower electroencephalography activity in the frontal, fronto-central, and centro-parietal alpha band regions compared to the sham (P < 0.05). The findings suggest that HD-tDCS application can boost finger motor skill acquisition, with online HD-tDCS displaying superior facilitation. Furthermore, online HD-tDCS reduces the power of alpha rhythms during motor skill execution, enhancing information processing and skill learning efficiency.

Reduced plasma interleukin-6 concentration after transcranial direct current stimulation to the prefrontal cortex

OBJECTIVES

Transcranial direct stimulation (tDCS) targeted to the dorsolateral prefrontal cortex (DLPFC) reduces food intake and hunger, but its effects on circulating factors are unclear. We assessed the effect of repeated administration of tDCS to the left DLPFC (L-DLPFC) on concentrations of pro/anti-inflammatory and appetitive hormone concentrations.

MATERIALS AND METHODS

Twenty-nine healthy adults with obesity (12 M; 42±11 y; BMI=39±8 kg/m2) received 3 consecutive inpatient sessions of either anodal or sham tDCS targeted to the L-DLPFC during a period of ad libitum food intake. Fasting plasma concentrations of IL-6, orexin, cortisol, TNF-α, IL-1β, ghrelin, PYY, and GLP-1 were measured before the initial and after the final tDCS sessions.

RESULTS

IL-6 (β=-0.92 pg/ml p=0.03) decreased in the anodal group compared with sham, even after adjusting for kcal intake; there were no changes in other hormones. Mean kcal intake was associated with higher IL-1β and ghrelin concentrations after the ad libitum period (β=0.00018 pg/ml/kcal, p=0.03; β=0.00011 pg/ml/kcal, p=0.02; respectively), but not differ by intervention groups.

CONCLUSIONS

IL-6 concentrations were reduced following anodal tDCS to the L-DLPFC independent of ad libitum intake. IL-6 concentrations reflect the inflammatory state of adiposity and may affect eating behavior and weight gain. These findings provide evidence of therapeutic benefit of tDCS.

Attention improvement to transcranial alternating current stimulation at gamma frequency over the right frontoparietal network: a preliminary report

Applying transcranial alternating current stimulation (tACS) at 40 Hz to the frontal and parietal regions, either unilaterally (left or right) or bilaterally, can improve cognitive dysfunctions. This study aimed to explore the influence of tACS at gamma frequency over right fronto-parietal (FP) region on attention. The analysis is based on retrospective data from a clinical intervention. We administered test of variables of attention (TOVA; visual mode) to 44 participants with various neuropsychiatric diagnoses before and after 12 sessions of tACS treatment. Alternating currents at 2.0 mA were delivered to the electrode positions F4 and P4, following the 10-20 EEG convention, for 20 mins in each session. We observed significant improvement across 3 indices of the TOVA, including reduction of variability in reaction time (p = 0.0002), increase in d-Prime (separability of targets and non-targets; p = 0.0157), and decrease in commission error rate (p = 0.0116). The mean RT and omission error rate largely remained unchanged. Artificial injection of tACS at 40 Hz over right FP network may improve attention function, especially in the domains of consistency in performance, target/non-target discrimination, and inhibitory control.

Non-Invasive Brain Stimulation (NIBS), Hypnosis, and Hypnotizability: Literature Review and Future Directions

Non-Invasive Brain Stimulation (NIBS) stands as an advanced technology embraced by researchers and clinicians to influence thoughts, emotions, and behaviors. The prevalent NIBS methods include transcranial Direct Current Stimulation (tDCS) and Transcranial Magnetic Stimulation (TMS), both proficient in either exciting or depressing neural activities in specific cortical regions. Recently, NIBS has been integrated into hypnosis research with the goal of enhancing hypnotizability. Specifically, the limited existing studies have predominantly focused on the dorsolateral prefrontal cortex (DLPFC) due to its significant role in neutral hypnosis. Overall, these studies suggest the fascinating potential to alter hypnotizability and hypnotic phenomena, although the impact on responsiveness to suggestions remains modest. In contrast to psychological and pharmacological methods, NIBS enables alterations in hypnotic experiences that are independent of operators and noninvasive. This grants researchers the chance to employ a causal approach in investigating the brain-behavior relationship associated with suggestibility. The present paper evaluates existing NIBS studies in this domain, delving into the neurocognitive mechanisms at play and their potential implications for hypnosis research and practice.

Treating Alzheimer's disease with brain stimulation: From preclinical models to non-invasive stimulation in humans

Alzheimer's disease (AD) is a severe and progressive neurodegenerative condition that exerts detrimental effects on brain function. As of now, there is no effective treatment for AD patients. This review explores two distinct avenues of research. The first revolves around the use of animal studies and preclinical models to gain insights into AD's underlying mechanisms and potential treatment strategies. Specifically, it delves into the effectiveness of interventions such as Optogenetics and Chemogenetics, shedding light on their implications for understanding pathophysiological mechanisms and potential therapeutic applications. The second avenue focuses on non-invasive brain stimulation (NiBS) techniques in the context of AD. Evidence suggests that NiBS can successfully modulate cognitive functions associated with various neurological and neuropsychiatric disorders, including AD, as demonstrated by promising findings. Here, we critically assessed recent findings in AD research belonging to these lines of research and discuss their potential impact on the clinical horizon of AD treatment. These multifaceted approaches offer hope for advancing our comprehension of AD pathology and developing novel therapeutic interventions.

Improving mentalizing deficits in older age with region-specific transcranial direct current stimulation

Older adults have difficulties to detect the intentions, thoughts, and feelings of others, indicating an age-associated decline of socio-cognitive abilities that are known as "mentalizing". These deficits in mental state recognition are driven by neurofunctional alterations in brain regions that are implicated in mentalizing, such as the right temporo-parietal junction (rTPJ) and the dorso-medial prefrontal cortex (dmPFC). We tested whether focal transcranial current stimulation (tDCS) of the rTPJ and dmPFC has the potential to eliminate mentalizing deficits in older adults. Mentalizing deficits were assessed with a novel mindreading task that required the recognition of mental states in child faces. Older adults (n = 60) performed worse than younger adults (n = 30) on the mindreading task, indicating age-dependent deficits in mental state recognition. These mentalizing deficits were ameliorated in older adults who received sham-controlled andodal tDCS over the rTPJ (n = 30) but remained unchanged in older adults who received sham-controlled andodal tDCS over the dmPFC (n = 30). We, thus, showed for the first time that anodal tDCS over the rTPJ has the potential to remediate age-dependent mentalizing deficits in a region-specific way. This provides a rationale for exploring stimulation-based interventions targeting mentalizing deficits in older age.

Multisession tDCS combined with intrastimulation training improves emotion recognition in adolescents with autism spectrum disorder

Previous studies indicate that transcranial direct current stimulation (tDCS) is a promising emerging treatment option for autism spectrum disorder (ASD) and its efficacy could be augmented using concurrent training. However, no intrastimulation social cognition training for ASD has been developed so far. The objective of this two-armed, double-blind, randomized, sham-controlled clinical trial is to investigate the effects of tDCS combined with a newly developed intrastimulation social cognition training on adolescents with ASD. Twenty-two male adolescents with ASD were randomly assigned to receive 10 sessions of either anodal or sham tDCS at F3/right supraorbital region together with online intrastimulation training comprising basic and complex emotion recognition tasks. Using baseline magnetic resonance imaging data, individual electric field distributions were simulated, and brain activation patterns of the training tasks were analyzed. Additionally, questionnaires were administered at baseline and following the intervention. Compared to sham tDCS, anodal tDCS significantly improved dynamic emotion recognition over the course of the sessions. This task also showed the highest activations in face processing regions. Moreover, the improvement was associated with electric field density at the medial prefrontal cortex and social awareness in exploratory analyses. Both groups showed high tolerability and acceptability of tDCS, and significant improvement in overall ASD symptoms. Taken together, multisession tDCS improved dynamic emotion recognition in adolescents with ASD using a task that activates brain regions associated with the social brain network. The variability in the electric field might diminish tDCS effects and future studies should investigate individualized approaches.

Analgesia of noninvasive electrical stimulation of the dorsolateral prefrontal cortex: A systematic review and meta-analysis

OBJECTIVE

The dorsolateral prefrontal cortex (DLPFC) is implicated in pain modulation, suggesting its potential as a therapeutic target for pain relief. However, studies on transcranial electrical stimulation (tES) over the DLPFC yielded diverse results, likely due to differences in stimulation protocols or pain assessment methods. This study aims to evaluate the analgesic effects of DLPFC-tES using a meta-analytical approach.

METHODS

A meta-analysis of 29 studies involving 785 participants was conducted. The effects of genuine and sham DLPFC-tES on pain perception were examined in healthy individuals and patients with clinical pain. Subgroup analyses explored the impact of stimulation parameters and pain modalities.

RESULTS

DLPFC-tES did not significantly affect pain outcomes in healthy populations but showed promise in reducing pain-intensity ratings in patients with clinical pain (Hedges' g = -0.78, 95% CI = [-1.33, -0.24], p = 0.005). Electrode placement significantly influenced the analgesic effect, with better results observed when the anode was at F3 and the cathode at F4.

CONCLUSIONS

DLPFC-tES holds potential as a cost-effective pain management option, particularly for clinical populations. Optimizing electrode placement, especially with an symmetrical configuration, may enhance therapeutic efficacy. These findings underscore the promise of DLPFC-tES for alleviating perceived pain intensity in clinical settings, emphasizing the importance of electrode placement optimization.

Transcranial Direct Current Stimulation for Cognitive Impairment Rehabilitation: A Bibliometric Analysis

BACKGROUND AND AIMS

As global demographics shift toward an older population, cognitive impairment is becoming increasingly critical. Transcranial Direct Current Stimulation (tDCS), an innovative brain stimulation technique, has the potential to significantly improve cognitive function. Our main aim is to comprehensively analyze the existing literature, identify key aspects of tDCS research in the rehabilitation of cognitive impairment, and predict future trends in this field.

METHODS

We used the Web of Science (WOS) database to search for English articles and reviews relevant to this topic. For visual analysis of the literature, we employed the WOS analysis tool, CiteSpace, along with VOSviewer software to ensure comprehensive analysis.

RESULTS

We included 2940 articles published between 1998 and 2023. Over 25 years, annual publications and citations in this field increased steadily, peaking at 379 articles in 2021. Michael A. Nitsche was a major contributor. Most articles came from developed countries, primarily North America and Europe, and journals generally had modest impact factors. Research in this field primarily aims to treat cognitive impairment resulting from pathological aging or neuropsychiatric disorders, with a particular focus on specific brain regions. Recently, researchers have integrated various treatment modalities with tDCS techniques to actively investigate effective strategies to mitigate cognitive impairments associated with pathological aging.

CONCLUSION

This study presents the first bibliometric analysis of the literature on tDCS in the rehabilitation of cognitive impairment, highlighting key areas of research and emerging trends. These findings provide critical insights for future tDCS interventions targeting cognitive impairment associated with pathological aging.

Effectiveness of Transcranial Direct Current Stimulation (tDCS) during a Virtual Reality Task in Women with Fibromyalgia-A Randomized Clinical Study

BACKGROUND/OBJECTIVES

Fibromyalgia (FM) is a chronic condition characterized by widespread musculoskeletal pain, fatigue, and impaired motor performance. This study aimed to investigate the effects of transcranial direct current stimulation (tDCS) during virtual reality (VR) tasks on the motor performance of women with FM.

METHODS

Participants were divided into two groups: Group A received active tDCS for 10 days followed by sham tDCS for 10 days, while Group B received the opposite sequence. Both groups performed VR tasks using MoveHero software (v. 2.4) during the tDCS sessions. Motor performance was assessed by the number of hits (movement with correct timing to reach the targets) and absolute (accuracy measure) and variable (precision measure) errors during VR tasks. Participants were 21 women, aged 30-50 years, and diagnosed with FM.

RESULTS

Group A, which received active tDCS first, presented significant improvements in motor performance (number of hits and absolute and variable errors). The benefits of active tDCS persisted into the sham phase, suggesting a lasting neuroplastic effect.

CONCLUSIONS

tDCS during VR tasks significantly improved motor performance in women with FM, particularly in complex, extensive movements. These findings indicate that tDCS enhances neuroplasticity, leading to sustained motor improvements, making it a promising therapeutic tool in FM rehabilitation.

Is non-invasive neuromodulation a viable technique to improve neuroplasticity in individuals with acquired brain injury? A review

Objective

This study aimed to explore and evaluate the efficacy of non-invasive brain stimulation (NIBS) as a standalone or coupled intervention and understand its mechanisms to produce positive alterations in neuroplasticity and behavioral outcomes after acquired brain injury (ABI).

Data sources

Cochrane Library, Web of Science, PubMed, and Google Scholar databases were searched from January 2013 to January 2024.

Study selection

Using the PICO framework, transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) randomized controlled trials (RCTs), retrospective, pilot, open-label, and observational large group and single-participant case studies were included. Two authors reviewed articles according to pre-established inclusion criteria.

Data extraction

Data related to participant and intervention characteristics, mechanisms of change, methods, and outcomes were extracted by two authors. The two authors performed quality assessments using SORT.

Results

Twenty-two studies involving 657 participants diagnosed with ABIs were included. Two studies reported that NIBS was ineffective in producing positive alterations or behavioral outcomes. Twenty studies reported at least one, or a combination of, positively altered neuroplasticity and improved neuropsychological, neuropsychiatric, motor, or somatic symptoms. Twenty-eight current articles between 2020 and 2024 have been studied to elucidate potential mechanisms of change related to NIBS and other mediating or confounding variables.

Discussion

tDCS and TMS may be efficacious as standalone interventions or coupled with neurorehabilitation therapies to positively alter maladaptive brain physiology and improve behavioral symptomology resulting from ABI. Based on postintervention and follow-up results, evidence suggests NIBS may offer a direct or mediatory contribution to improving behavioral outcomes post-ABI.

Conclusion

More research is needed to better understand the extent of rTMS and tDCS application in affecting changes in symptoms after ABI.