High-definition Transcranial Direct Current Stimulation Research Articles

Proceedings #41: HD-tDCS Effect on Motor Evoked Potential Amplitude Elicited by Neuronavigated TMS

In a previous validation study, we observed that along with increased amplitude of TMS-Motor Evoked Potential (MEP), anodal stimulation with High-Definition transcranial Direct Current Stimulation (HD-tDCS) produced a MEP variability that was 5 times greater when compared to the sham condition. This outcome was attributed to anatomical gyri and sulci variability across participants, and/or imprecise coil and central anode positioning. In this study, we controlled for coil and electrode placement by employing a neuronavigated TMS system, aiming to obtain a clearer picture of the HD-tDCS effect. Ninety neuronavigated TMS pulses (baseline) were delivered at the cortical hotspot of the right First Digital Interosseous (FDI). Next, 2mA anodal or sham stimulation was delivered through a Soterix 4X1 HD-tDCS system (Soterix Medical Inc. New York, NY), with electrodes arranged on a 4X1-ring configuration with the central electrode precisely placed over the TMS target. Then, 90 MEPs were recorded again. We observed a non-significant trend of post/pre MEP ratio increase in the anodal group, along with a larger variability in comparison to the sham group. These preliminary results with neuronavigated TMS are similar to our previous results without neuronavigation and support the hypothesis that individual anatomical differences account for the greater variability found in the anodal group. Increasing the sample size and including a cathodal condition in a future study will help clarify the observed trends.

Abstract #119: Polarity-dependent effects on postural control after High-definition Transcranial Direct Current Stimulation over the temporo-parietal junction

Introduction: Postural imbalance is a disorder involving complex integration of sensory, motor and cognitive systems, together with musculoskeletal components. A potential tool for the improving postural imbalance is transcranial direct current stimulation (tDCS). Targeting the temporo-parietal junction (TPJ), a critical hub for multisensory integration and processing, we recently showed that bipolar-balanced conventional tDCS can manipulate postural control and verticality perception. There is also evidence that high-definition tDCS (HD-tDCS) can achieve greater cortical stimulation focality and after-effects on motor cortical excitability than conventional tDCS. However, there is limited literature about the effects of HD-tDCS on postural control. Therefore, we aimed to investigate polarity- and intensity-dependent after-effects of HD-tDCS3x1 over the right TPJ on weight-bearing asymmetry (WBA) and head tilt in healthy adults.

Abstract #145: Empirically Supported Methods for Decreasing Impedance in High-Definition Transcranial Direct Current Stimulation

Abstract #145: Empirically Supported Methods for Decreasing Impedance in High-Definition Transcranial Direct Current Stimulation

Effect of High-definition transcranial direct current stimulation (HD-tDCS) on auditory hallucinations in schizophrenia: Correlates with Gray Matter Volume

Effect of High-definition transcranial direct current stimulation (HD-tDCS) on auditory hallucinations in schizophrenia: Correlates with Gray Matter Volume

HD-tDCS in refractory lateral frontal lobe epilepsy patients

Purpose: To evaluate the anticonvulsant effect of the novel high definition transcranial direct current stimulation (HD-tDCS) method on patients with refractory lateral frontal lobe epilepsy. The effects of HDtDCS on working memory were also examined.

Abstract #138: Effects of conventional and high-definition tDCS on the Optokinetic Nystagmus in healthy subjects

Abstract #138: Effects of conventional and high-definition tDCS on the Optokinetic Nystagmus in healthy subjects

Abstract #142: Effects of High Definition tDCS on Problem Solving Networks

Introduction: Idea generation stands at the heart of problem solving. People generate ideas by either having a sudden insight (implicit processing known as an "Aha! moment") or via a step-by-step analysis (explicit deliberation). Behavioral and neuroimaging studies demonstrated that these two ways of solving problems rely on distinct neural networks. Within the insight network, the right anterior temporal lobe has a critical role in the generation of novel associations and original ideas, whereas the left prefrontal cortex has a dominant role in explicit analytical deliberation. While progress has been made toward identifying the associated neural correlates of the idea generation phase during problem solving, its study thus far remains merely correlational. In the reported study, we adopt a causal approach by applying High Definition Transcranial Direct Current Stimulation (HD tDCS) to the brain sites crucial for problem solving, with the final aim of facilitating problem solving by modulating the two networks (insight and analysis).

Abstract #31: Safety and efficacy of high definition tDCS for proprioception and balance in Parkinson’s disease

Abstract #31: Safety and efficacy of high definition tDCS for proprioception and balance in Parkinson’s disease

Abstract #72: High-Definition tDCS to the Dorsolateral Prefrontal Cortex during Cognitive Control in Young and Older Adults

Abstract #72: High-Definition tDCS to the Dorsolateral Prefrontal Cortex during Cognitive Control in Young and Older Adults

Effects of High-Definition Transcranial Direct Current Stimulation (HD-tDCS) of the Intraparietal Sulcus and Dorsolateral Prefrontal Cortex on Working Memory and Divided Attention.

Objective: There is a need to elucidate the underlying neural mechanisms subserving working memory and divided attention functioning. Recent neuroimaging studies provide evidence for anatomical co-localization of both functions. In the present study we used a functional intervention, whereby we applied a novel type of focalised, non-invasive brain stimulation, High-Definition transcranial Direct Current Stimulation (HD-tDCS), to the regions subserving these processes, the left intraparietal sulcus (IPS) and left dorsolateral prefrontal cortex (LDLPFC). Our aim was therefore to modulate activity in these regions using HD-tDCS and thereby assess their relevance for working memory, divided attention and their shared sub-processes.Method: 78 participants were evenly randomized to one of three conditions in a single blind, parallel group study design. Anodal or sham HD-tDCS was applied to either the left IPS or LDLPFC while participants completed a verbal working memory task, a divided attention task, and two tasks measuring subcomponents of working memory (updating and maintenance).Results: Focalised stimulation of the IPS and LDLPFC did not significantly modulate performance compared to sham stimulation. However, moderate effect sizes were obtained for at least one HD-tDCS condition relative to sham for all tasks, warranting further research into the functional importance of the IPS in subserving these abilities.Conclusions: The current results may be useful for informing future tDCS studies for modulating working memory and divided attention functioning.

Concurrent anodal transcranial direct-current stimulation and motor task to influence sensorimotor cortex activation

Functional targeting with anodal high-definition transcranial direct current stimulation (HD-atDCS) of involved brain areas during performance of a motor task (online) may facilitate sensorimotor cortex neuroplasticity compared to performing the motor task after HD-atDCS (offline). The aim of this study was to employ functional near-infrared spectroscopy to compare the time course of motor task-related changes in sensorimotor cortex activation between online and offline HD-atDCS. We hypothesized that online HD-atDCS would have a greater effect on task-related sensorimotor cortex activation than offline HD-atDCS. In a within-subject sham controlled and randomized study design, 9 healthy participants underwent 3 HD-atDCS sessions (online, offline and sham) targeting the left sensorimotor cortex separated by 1 week. Functional near-infrared spectroscopy hemodynamic changes were measured from the left sensorimotor cortex during a simple finger opposition motor task before (Pre), immediately (T1) and 30 min after (T2) each session. The movement rates were not different between (online, offline, sham) or within (Pre, T1, T2) sessions. At T2, online HD-atDCS was associated with a significant increase (large effect size) in sensorimotor cortex activation (Hedges g = 1.01, p < 0.001) when compared to sham; there was a nonsignificant trend to increase activation between offline and sham (Hedges g = 0.52, p = 0.05) and between online and offline (Hedges g = 0.53, p = 0.06). Concurrent application of HD-atDCS during a motor task may produce larger sensorimotor cortex activation than sequential application.

Successful application of add-on high-definition transcranial direct current stimulation in a schizophrenic patient with comorbid alopecia universalis.

Successful application of add-on high-definition transcranial direct current stimulation in a schizophrenic patient with comorbid alopecia universalis.

Cortico-Muscular Coherence Modulated by High-Definition Transcranial Direct Current Stimulation in People With Chronic Stroke.

High-definition transcranial direct current stimulation (HD-tDCS) is a potential neuromodulation apparatus for stroke rehabilitation. However, its modulatory effects in stroke subjects is still not well understood. In this paper, the offline modulatory effects of HD-tDCS on the ipsilesional primary motor cortex were investigated by performing wrist isometric contraction tasks before and after HD-tDCS in eleven unilateral chronic stroke subjects using a synchronized HD-tDCS and electroencephalogram/electromyography measurement system. This paper is a randomized, single blinded, and sham-controlled crossover study. Each subject randomly received three HD-tDCS (anode, cathode, and sham) with at least one-week washout period. Online feedback-guided medium-level wrist isometric contraction tasks were conducted for the affected upper limbs before stimulation and 10, 30, and 50 min after the end of 10-min 1-mA HD-tDCS. The characteristics of corticomuscular coherence (CMC), cortical oscillation power spectral density, and power spectral entropy were analyzed during tasks and compared across all sessions and stimulation conditions. Anode HD-tDCS induced significant CMC changes in stroke subjects, while cathode and sham stimulation did not induce significant CMC changes. The largest neuromodulation effects were observed at 10 min immediately after anodal HD-tDCS.

Sex-based differences in right dorsolateral prefrontal cortex roles in fairness norm compliance

Social norms are a common motivator or de-motivator of behavior through the need of humans to comply with acceptable behaviors of their social groups. Converging evidence from functional neuroimaging and noninvasive brain stimulation studies suggest that the right dorsolateral prefrontal cortex (rDLPFC) is involved in social norm compliance. Extending this view, we suggest that rDLPFC may not act uniformly when men and women face different types of fairness norm compliance situations, and that there may be a sequential update of norm compliance after experiencing punishment. Using High-Definition Transcranial Direct Current Stimulation (HD-tDCS) on 100 participants playing a sequence of economic game trials, the current study showed that (1) the right dorsolateral prefrontal cortex (rDLPFC) is involved in both voluntary and sanction-induced fairness norm compliance, (2) it has an opposite role in the two types of compliance, (3) there are sex-based differences in rDLPFC roles in fairness norm compliance, and (4) post-punishment fairness compliance is reduced compared to baseline.

Sensorimotor Robotic Measures of tDCS- and HD-tDCS-Enhanced Motor Learning in Children.

Transcranial direct-current stimulation (tDCS) enhances motor learning in adults. We have demonstrated that anodal tDCS and high-definition (HD) tDCS of the motor cortex can enhance motor skill acquisition in children, but behavioral mechanisms remain unknown. Robotics can objectively quantify complex sensorimotor functions to better understand mechanisms of motor learning. We aimed to characterize changes in sensorimotor function induced by tDCS and HD-tDCS paired motor learning in children within an interventional trial. Healthy, right-handed children (12–18 y) were randomized to anodal tDCS, HD-tDCS, or sham targeting the right primary motor cortex during left-hand Purdue pegboard test (PPT) training over five consecutive days. A KINARM robotic protocol quantifying proprioception, kinesthesia, visually guided reaching, and an object hit task was completed at baseline, posttraining, and six weeks later. Effects of the treatment group and training on changes in sensorimotor parameters were explored. Twenty-four children (median 15.5 years, 52% female) completed all measures. Compared to sham, both tDCS and HD-tDCS demonstrated enhanced motor learning with medium effect sizes. At baseline, multiple KINARM measures correlated with PPT performance. Following training, visually guided reaching in all groups was faster and required less corrective movements in the trained arm (H(2) = 9.250, p = 0.010). Aspects of kinesthesia including initial direction error improved across groups with sustained effects at follow-up (H(2) = 9.000, p = 0.011). No changes with training or stimulation were observed for position sense. For the object hit task, the HD-tDCS group moved more quickly with the right hand compared to sham at posttraining (χ 2(2) = 6.255, p = 0.044). Robotics can quantify complex sensorimotor function within neuromodulator motor learning trials in children. Correlations with PPT performance suggest that KINARM metrics can assess motor learning effects. Understanding how tDCS and HD-tDCS enhance motor learning may be improved with robotic outcomes though specific mechanisms remain to be defined. Exploring mechanisms of neuromodulation may advance therapeutic approaches in children with cerebral palsy and other disabilities.

Impact of concurrent task performance on transcranial direct current stimulation (tDCS)-Induced changes in cortical physiology and working memory

Transcranial direct current stimulation (tDCS) provides a means of non-invasively inducing plasticity-related changes in neural circuits in vivo and is experiencing increasing use as a potential tool for modulating brain function. There is growing evidence that tDCS-related outcomes are likely to be influenced by an individual's brain state at the time of stimulation, i.e., effects show a degree of ‘state-dependency’. However, few studies have examined the behavioural and physiological impact of state-dependency within cognitively salient brain regions. Here, we applied High-Definition tDCS (HD-tDCS) over the left dorsolateral prefrontal cortex (DLPFC) in 20 healthy participants, whilst they either remained at rest, or performed a cognitive task engaging working memory (WM). In a third condition sham stimulation was administered during task performance. Neurophysiological changes were probed using TMS-evoked potentials (TEPs), event-related potentials (ERPs) recorded during n-back WM tasks, and via resting-state EEG (RS-EEG). From a physiological perspective, our results indicate a degree of neuromodulation following HD-tDCS, regardless of task engagement, as evidenced by changes in TEP amplitudes following both active stimulation conditions. Changes in ERP (P3) amplitudes were also observed for the 2-Back task following stimulation delivered during task performance only. However, no changes were seen on RS-EEG for any condition, nor were any group-level effects of either stimulation condition observed on n-back performance. As such, these findings paint a complex picture of neural and behavioural responses to prefrontal stimulation in healthy subjects and provide only limited support for state-dependent effects of HD-tDCS over the DLPFC overall.

The Effect of High-Definition Transcranial Direct Current Stimulation of the Right Inferior Frontal Gyrus on Empathy in Healthy Individuals.

Empathy, including cognitive and emotional empathy, refers to the ability to infer the mental states of others and to the capacity to share emotions. The neural mechanisms involved in empathy are complex and not yet fully understood, and previous studies have shown that both cognitive and emotional empathy are closely associated with the inferior frontal gyrus (IFG). In this study, we examined whether empathy can be modulated by high-definition transcranial direct current stimulation (HD-tDCS) of the right IFG. Twenty-three healthy participants took part in all three experimental conditions (i.e., anodal, cathodal and sham stimulation) in a randomized order. Participants then completed the Chinese version of the Multifaceted Empathy Test (MET), which assesses both cognitive and emotional empathy. The results show that scores obtained for cognitive empathy following cathodal stimulation are significantly lower than those obtained following sham stimulation. In addition, scores obtained for cognitive empathy following anodal stimulation are higher than those obtained following sham stimulation, though the difference is only marginally significant. However, the results fail to show whether the stimulation of the right IFG via HD-tDCS plays a role in emotional empathy. Our results suggest that the right IFG plays a key role in cognitive empathy and indicate that HD-tDCS can regulate cognitive empathy by inducing excitability changes in the right IFG.

Effects of HD-tDCS on Resting-State Functional Connectivity in the Prefrontal Cortex: An fNIRS Study

Functional connectivity is linked to several degenerative brain diseases prevalent in our aging society. Electrical stimulation is used for the clinical treatment and rehabilitation of patients with many cognitive disorders. In this study, the effects of high-definition transcranial direct current stimulation (HD-tDCS) on resting-state brain networks in the human prefrontal cortex were investigated by using functional near-infrared spectroscopy (fNIRS). The intrahemispheric as well as interhemispheric connectivity changes induced by 1 mA HD-tDCS were examined in 15 healthy subjects. Pearson correlation coefficient-based correlation matrices were generated from filtered time series oxyhemoglobin (ΔHbO) signals and converted into binary matrices. Common graph theory metrics were computed to evaluate the network changes. Systematic interhemispheric, intrahemispheric, and intraregional connectivity analyses demonstrated that the stimulation positively affected the resting-state connectivity in the prefrontal cortex. The poststimulation connectivity was increased throughout the prefrontal region, while focal HD-tDCS effects induced an increased rate of connectivity in the stimulated hemisphere. The graph theory metrics clearly distinguished the prestimulation and poststimulation networks for a range of thresholds. The results of this study suggest that HD-tDCS can be used to increase functional connectivity in the prefrontal cortex. The increase in functional connectivity can be explored clinically for neurorehabilitation of patients with degenerative brain diseases.

Design of NIRS Probe Based on Computational Model to Find Out the Optimal Location for Non-Invasive Brain Stimulation.

The paper presents a computational model to analyse the electric field distribution on the cerebral cortex during high definition transcranial direct current stimulation (HD-tDCS) technique. The current research aims to improve the focality in term of magnitude of electric field (norm [E]) and magnitude of current density (norm [J]) in the gyri and sulci of white matter. The proposed computational model is used to predict the magnitude of current density and magnitude of electric field distribution generated across the target region of cerebral cortex for specific small size 1 × 1cm2 multi-electrode HD-tDCS configurations. The current works aims at optimizing the number of electrodes and current density for multielectrode HD-tDCS configuration and weak current intensity is obtained by calculating surface area and penetration depth of target region of cerebral cortex. In terms of surface area and penetration depth 4 × 1 HD-tDCS and 2mA weak dc current configuration has been selected. The optimized 4 × 1 HD-tDCS configuration is placed on target location of the brain surface and the changes in the magnitude of current density and magnitude of electric field distribution is calculated at the different locations on brain surface including scalp surface, skull surface gray matter and white matter surface. The variation in magnitude electric field distribution is seen in the cerebrospinal fluid (CSF), gray and white matter surface of target cerebral cortex. Based on the insights received from the variation in the magnitude of current density and magnitude of electric field distribution, the design of an appropriate NIRS probe has been proposed to aid in non-invasive brain stimulation. Designed NIRS probe is based on distance of separation between source and photodetector to cover the affected area with 4 × 1 HD-tDCS technique and measurement sensitivity distribution at gray matter surface of cerebral cortex. The estimated percentage of pixel area of measurement sensitivity distribution is 17.094%, which confirm to cover the 7.9384% distributed pixel area in term of calculated magnitude of current density affected with 4 × 1 HD-tDCS configuration.

Manipulation of Human Verticality Using High-Definition Transcranial Direct Current Stimulation.

Background: Using conventional tDCS over the temporo-parietal junction (TPJ) we previously reported that it is possible to manipulate subjective visual vertical (SVV) and postural control. We also demonstrated that high-definition tDCS (HD-tDCS) can achieve substantially greater cortical stimulation focality than conventional tDCS. However, it is critical to establish dose-response effects using well-defined protocols with relevance to clinically meaningful applications.Objective: To conduct three pilot studies investigating polarity and intensity-dependent effects of HD-tDCS over the right TPJ on behavioral and physiological outcome measures in healthy subjects. We additionally aimed to establish the feasibility, safety, and tolerability of this stimulation protocol.Methods: We designed three separate randomized, double-blind, crossover phase I clinical trials in different cohorts of healthy adults using the same stimulation protocol. The primary outcome measure for trial 1 was SVV; trial 2, weight-bearing asymmetry (WBA); and trial 3, electroencephalography power spectral density (EEG-PSD). The HD-tDCS montage comprised a single central, and 3 surround electrodes (HD-tDCS3x1) over the right TPJ. For each study, we tested 3x2 min HD-tDCS3x1 at 1, 2 and 3 mA; with anode center, cathode center, or sham stimulation, in random order across days.Results: We found significant SVV deviation relative to baseline, specific to the cathode center condition, with consistent direction and increasing with stimulation intensity. We further showed significant WBA with direction governed by stimulation polarity (cathode center, left asymmetry; anode center, right asymmetry). EEG-PSD in the gamma band was significantly increased at 3 mA under the cathode.Conclusions: The present series of studies provide converging evidence for focal neuromodulation that can modify physiology and have behavioral consequences with clinical potential.