High-definition Transcranial Direct Current Stimulation Research Articles

Safety, Tolerability, Blinding Efficacy and Behavioural Effects of a Novel MRI-Compatible, High-Definition tDCS Set-Up.

High-definition transcranial direct current stimulation (HD-tDCS) may allow more specific neural modulation than conventional-tDCS. We compared safety, tolerability, blinding efficacy and cognitive effects of a novel HD-tDCS set-up to that of conventional-tDCS and established compatibility with simultaneous functional magnetic resonance imaging (fMRI). Two groups of healthy participants completed a visual flanker task either with conventional (N = 30) or HD-tDCS (N = 30) administered to the right dorsolateral prefrontal cortex (1 mA) in a double-blind, sham-tDCS-controlled, cross-over design. HD-tDCS was administered with a one-channel DC-stimulator using a small conductive rubber "centre" electrode and a circular return electrode, mimicking the frequently used 4 × 1 HD-tDCS set-up. Tolerability, adverse effects, impact on performance and blinding efficacy were compared within and between the two montages. In a separate experiment, potential heating and impact on image quality of the novel HD-tDCS set-up were assessed during simultaneous fMRI. Both montages elicited only mild adverse effects and those were less pronounced for the novel HD-tDCS set-up. Participant and investigator blinding was achieved with both montages. Only HD-tDCS resulted in significant modulation of the conflict adaptation effect during the flanker task; however, no differences were found for the direct comparison of the two montages. No significant heating occurred during fMRI and only minor effects on image quality were observed during HD-tDCS. This study confirmed safety, tolerability and blinding efficacy of a novel, re-usable and MRI-compatible HD-tDCS set-up. It also highlights its potential to exert beneficial effects on behavioural performance. Use of this novel set-up during simultaneous fMRI in future studies will help clarify the neural mechanisms by which this HD-tDCS impacts on behavioural and neural function.

High-Definition Transcranial Direct Current Stimulation Enhances Conditioned Pain Modulation in Healthy Volunteers: A Randomized Trial

Transcranial direct current stimulation (tDCS) is a form of brain stimulation that allows for the selective increase or decrease in the cortical excitability of a targeted region. When applied over the motor cortex it has been shown to induce changes in cortical and subcortical brain regions involved in descending pain inhibition or conditioned pain modulation (CPM). The aim of the current study was to assess whether activation of pain inhibitory pathways via tDCS of the motor cortex facilitates the CPM response. Elevated CPM after active tDCS of the motor cortex was hypothesized. Thirty healthy male volunteers attended 2 experimental sessions separated by 7days. Both sessions consisted of CPM assessment after 20minutes of either active or sham (placebo) tDCS over the motor cortex. CPM capacity was assessed via the pain-inhibits-pain protocol; CPM responses were shown to be elevated after active compared with sham tDCS. This report concludes that tDCS of the motor cortex enhances the CPM response in healthy men. This finding supports the potential utility of tDCS interventions in clinical pain treatment. The use of noninvasive brain stimulation over the motor cortex was shown to enhance the CPM effect. This finding supports the use of tDCS in the treatment of chronic pain, particularly in sufferers exhibiting maladaptive CPM.

Effects of Anodal High-Definition Transcranial Direct Current Stimulation on Bilateral Sensorimotor Cortex Activation During Sequential Finger Movements: An fNIRS Study.

Transcranial direct current stimulation (tDCS) is a non-invasive electrical brain stimulation technique that can modulate cortical neuronal excitability and activity. This study utilized functional near infrared spectroscopy (fNIRS) neuroimaging to determine the effects of anodal high-definition (HD)-tDCS on bilateral sensorimotor cortex (SMC) activation. Before (Pre), during (Online), and after (Offline) anodal HD-tDCS (2mA, 20min) targeting the left SMC, eight healthy subjects performed a simple finger sequence (SFS) task with their right or left hand in an alternating blocked design (30-s rest and 30-s SFS task, repeated five times). In order to determine the level of bilateral SMC activation during the SFS task, an Oxymon MkIII fNIRS system was used to measure from the left and right SMC, changes in oxygenated (O2Hb) and deoxygenated (HHb) haemoglobin concentration values. The fNIRS data suggests a finding that compared to the Pre condition both the "Online" and "Offline" anodal HD-tDCS conditions induced a significant reduction in bilateral SMC activation (i.e., smaller decrease in HHb) for a similar motor output (i.e., SFS tap rate). These findings could be related to anodal HD-tDCS inducing a greater efficiency of neuronal transmission in the bilateral SMC to perform the same SFS task.

Clinically Effective Treatment of Fibromyalgia Pain With High-Definition Transcranial Direct Current Stimulation: Phase II Open-Label Dose Optimization

Despite promising preliminary results in treating fibromyalgia (FM) pain, no neuromodulation technique has been adopted in clinical practice because of limited efficacy, low response rate, or poor tolerability. This phase II open-label trial aims to define a methodology for a clinically effective treatment of pain in FM by establishing treatment protocols and screening procedures to maximize efficacy and response rate. High-definition transcranial direct current stimulation (HD-tDCS) provides targeted subthreshold brain stimulation, combining tolerability with specificity. We aimed to establish the number of HD-tDCS sessions required to achieve a 50% FM pain reduction, and to characterize the biometrics of the response, including brain network activation pain scores of contact heat-evoked potentials. We report a clinically significant benefit of a 50% pain reduction in half (n = 7) of the patients (N = 14), with responders and nonresponders alike benefiting from a cumulative effect of treatment, reflected in significant pain reduction (P = .035) as well as improved quality of life (P = .001) over time. We also report an aggregate 6-week response rate of 50% of patients and estimate 15 as the median number of HD-tDCS sessions to reach clinically meaningful outcomes. The methodology for a pivotal FM neuromodulation clinical trial with individualized treatment is thus supported. Online RegistrationRegistered in Clinicaltrials.gov under registry number NCT01842009. PerspectiveIn this article, an optimized protocol for the treatment of fibromyalgia pain with targeted subthreshold brain stimulation using high-definition transcranial direct current stimulation is outlined.

High-Definition tDCS of Noun and Verb Retrieval in Naming and Lexical Decision

High-definition transcranial direct current stimulation (HD-tDCS) is a novel brain stimulation method that has high potential for use in language therapy for speakers with aphasia, due to its safety and focality. This study aimed to obtain foundational data on using HD-tDCS to modulate language processing in healthy speakers. Participants received stimulation either of Broca’s area or of the left angular gyrus (20 min of anodal, cathodal, and sham stimulation on separate days), followed by naming and lexical decision tasks with single-word verb and noun stimuli. We found that cathodal stimulation over both Broca’s area and the left angular gyrus increased naming speed for both verbs and nouns, challenging the traditional view of cathodal stimulation as suppressive or leading to decreased performance. The effect did not extend to the lexical decision task. Additionally, effects of specific stimulation types depended on the order of their administration, suggesting possible physiological carry-over and/or task novelty effects. These results are relevant to the application of HD-tDCS to enhance and direct neural plasticity in patients with neurogenic language disorders.

Cathodal HD-tDCS on the right V5 improves motion perception in humans.

Brain lesions in the visual associative cortex are known to impair visual perception, i.e., the capacity to correctly perceive different aspects of the visual world, such as motion, color, or shapes. Visual perception can be influenced by non-invasive brain stimulation such as transcranial direct current stimulation (tDCS). In a recently developed technique called high definition (HD) tDCS, small HD-electrodes are used instead of the sponge electrodes in the conventional approach. This is believed to achieve high focality and precision over the target area. In this paper we tested the effects of cathodal and anodal HD-tDCS over the right V5 on motion and shape perception in a single blind, within-subject, sham controlled, cross-over trial. The purpose of the study was to prove the high focality of the stimulation only over the target area. Twenty one healthy volunteers received 20 min of 2 mA cathodal, anodal and sham stimulation over the right V5 and their performance on a visual test was recorded. The results showed significant improvement in motion perception in the left hemifield after cathodal HD-tDCS, but not in shape perception. Sham and anodal HD-tDCS did not affect performance. The specific effect of influencing performance of visual tasks by modulating the excitability of the neurons in the visual cortex might be explained by the complexity of perceptual information needed for the tasks. This provokes a “noisy” activation state of the encoding neuronal patterns. We speculate that in this case cathodal HD-tDCS may focus the correct perception by decreasing global excitation and thus diminishing the “noise” below threshold.

Probing the involvement of the primary somatosensory cortex in pain perception using high-definition transcranial direct current stimulation (HD-tDCS).

Probing the involvement of the primary somatosensory cortex in pain perception using high-definition transcranial direct current stimulation (HD-tDCS).

Intensity, Duration, and Location of High-Definition Transcranial Direct Current Stimulation for Tinnitus Relief

Background and Objective. Tinnitus is the perception of a phantom sound. The aim of this study was to compare current intensity (center anode 1 mA and 2 mA), duration (10 minutes and 20 minutes), and location (left temporoparietal area [LTA] and dorsolateral prefrontal cortex [DLPFC]) using 4 × 1 high-definition transcranial direct current stimulation (HD-tDCS) for tinnitus reduction. Methods. Twenty-seven participants with chronic tinnitus (>2 years) and mean age of 53.5 years underwent 2 sessions of HD-tDCS of the LTA and DLPFC in a randomized order with a 1 week gap between site of stimulation. During each session, a combination of 4 different settings were used in increasing dose (1 mA, 10 minutes; 1 mA, 20 minutes; 2 mA, 10 minutes; and 2 mA, 20 minutes). The impact of different settings on tinnitus loudness and annoyance was documented. Results. Twenty-one participants (77.78%) reported a minimum of 1 point reduction on tinnitus loudness or annoyance scales. There were significant changes in loudness and annoyance for duration of stimulation, F(1, 26) = 10.08, P < .005, and current intensity, F(1, 26) = 14.24, P = .001. There was no interaction between the location, intensity, and duration of stimulation. Higher intensity (2 mA) and longer duration (20 minutes) of stimulation were more effective. Conclusions. A current intensity of 2 mA for 20-minute duration was the most effective setting used for tinnitus relief. The stimulation of the LTA and DLPFC were equally effective for suppressing tinnitus loudness and annoyance.

State-of-art neuroanatomical target analysis of high-definition and conventional tDCS montages used for migraine and pain control.

Although transcranial direct current stimulation (tDCS) studies promise to modulate cortical regions associated with pain, the electric current produced usually spreads beyond the area of the electrodes’ placement. Using a forward-model analysis, this study compared the neuroanatomic location and strength of the predicted electric current peaks, at cortical and subcortical levels, induced by conventional and High-Definition-tDCS (HD-tDCS) montages developed for migraine and other chronic pain disorders. The electrodes were positioned in accordance with the 10–20 or 10–10 electroencephalogram (EEG) landmarks: motor cortex-supraorbital (M1-SO, anode and cathode over C3 and Fp2, respectively), dorsolateral prefrontal cortex (PFC) bilateral (DLPFC, anode over F3, cathode over F4), vertex-occipital cortex (anode over Cz and cathode over Oz), HD-tDCS 4 × 1 (one anode on C3, and four cathodes over Cz, F3, T7, and P3) and HD-tDCS 2 × 2 (two anodes over C3/C5 and two cathodes over FC3/FC5). M1-SO produced a large current flow in the PFC. Peaks of current flow also occurred in deeper brain structures, such as the cingulate cortex, insula, thalamus and brainstem. The same structures received significant amount of current with Cz-Oz and DLPFC tDCS. However, there were differences in the current flow to outer cortical regions. The visual cortex, cingulate and thalamus received the majority of the current flow with the Cz-Oz, while the anterior parts of the superior and middle frontal gyri displayed an intense amount of current with DLPFC montage. HD-tDCS montages enhanced the focality, producing peaks of current in subcortical areas at negligible levels. This study provides novel information regarding the neuroanatomical distribution and strength of the electric current using several tDCS montages applied for migraine and pain control. Such information may help clinicians and researchers in deciding the most appropriate tDCS montage to treat each pain disorder.

High-Definition and Non-invasive Brain Modulation of Pain andMotor Dysfunction in Chronic TMD.

Temporomandibular disorders (TMD) have a high prevalence and in many patients pain and masticatory dysfunction persist despite a range of treatments. Non-invasive brain neuromodulatory methods, namely transcranial direct current stimulation (tDCS), can provide relatively long-lasting pain relief in chronic pain patients. To define the neuromodulatory effect of five daily 2x2 motor cortex high-definition tDCS (HD-tDCS) sessions on clinical pain and motor measures in chronic TMD patients. It is predicted that M1 HD-tDCS will selectively modulate clinical measures, by showing greater analgesic after-effects compared to placebo, and active treatment will increase pain free jaw movement more than placebo. Twenty-four females with chronic myofascial TMD pain underwent five daily, 20-min sessions of active or sham 2 milliamps (mA) HD-tDCS. Measurable outcomes included pain-free mouth opening, visual analog scale (VAS), sectional sensory-discriminative pain measures tracked by a mobile application, short form of the McGill Pain Questionnaire, and the Positive and Negative Affect Schedule. Follow-up occurred at one-week and four-weeks post-treatment. There were significant improvements for clinical pain and motor measurements in the active HD-tDCS group compared to the placebo group for: responders with pain relief above 50% in the VAS at four-week follow-up (P=0.04); pain-free mouth opening at one-week follow-up (P<0.01); and sectional pain area, intensity and their sum measures contralateral to putative M1 stimulation during the treatment week (P<0.01). No changes in emotional values were shown between groups. Putative M1 stimulation by HD-tDCS selectively improved meaningful clinical sensory-discriminative pain and motor measures during stimulation, and up to four-weeks post-treatment in chronic myofascial TMD pain patients.

On the Use of the Terms Anodal and Cathodal in High-Definition Transcranial Direct Current Stimulation: A Technical Note.

The terms "anodal" and "cathodal" are widely used to describe transcranial direct current stimulation (tDCS) of opposing polarities, often interpreted as excitatory and inhibitory, respectively. However, high-definition tDCS allows for complex electrode configurations that may not be characterized accurately as "anodal" and "cathodal." To illustrate challenges to data interpretation that may result from unclarity about the neuromodulatory effects of different field orientations, we present two high-definition tDCS experiments in the language domain, with different electrode configurations. We also present the modeled electric fields for a traditional tDCS setup, showing how brain stimulation may far exceed target regions. More research is warranted on the hypothesized inhibitory or excitatory effects of different electrode configurations. Moreover, conventional bicephalic 1 × 1 configurations using sponges or HD electrodes may not be accurately described by the terms "anodal" and "cathodal" either, as these terms only pertain to the desired effects over an area of interest, but not any other areas affected. Therefore, design and interpretation of (HD-)tDCS and conventional tDCS research studies should not be constrained by the anodal/cathodal dichotomy.

Effects of Cortical Stimulation on Self-Monitoring Performance in People who Stutter

IntroductionPeople who stutter (PWS) have been shown to be slower and less accurate than controls on a phoneme monitoring task designed to tap into the phonological encoding stage of speech production (Garnett & Den Ouden, 2013; Sasisekaran et al., 2006). The left posterior superior temporal gyrus (pSTG) is involved in phonological processing tasks (Den Ouden et al., 2013; Indefrey, 2011). The purpose of this study is to investigate the effects of cortical stimulation using High Definition Transcranial Direct Current Stimulation (HD-tDCS) on the performance of PWS during phoneme monitoring. Methods20 PWS and 20 controls will participate in this study. Presently, 4 PWS and 5 controls have completed the study. Participants received 20minutes of HD-tDCS targeting the left pSTG in three different conditions (left posterior field orientation [LPFO], right anterior field orientation [RAFO], and sham) over three separate days. Following stimulation, participants monitored for the presence of a target phoneme during silent picture naming. Reaction times (RT) as well as accuracy (ACC) were measured. ResultsData collection is ongoing. Preliminary data suggest that LPFO decreases RT in PWS, approaching the sham (baseline) RT of controls, while RAFO increases RT in controls to nearly that of sham (baseline) for PWS (Figure 1). There is a trend for stimulation to increase ACC in PWS, and decrease ACC in controls, irrespective of field orientation (Figure 2). DiscussionFindings should be considered tentative at this time, but if the present trends hold, this study yields two important contributions to the field of stuttering. First, results suggest that the left pSTG is involved in phonological processing and/or speech monitoring, as focal stimulation of this cortical area affects performance in all subjects. Second, results would support further investigation into clinical application of HD-tDCS to target phonological encoding as a process that may affect stuttering.

Focalised stimulation using high definition transcranial direct current stimulation (HD-tDCS) to investigate declarative verbal learning and memory functioning

BackgroundDeclarative verbal learning and memory are known to be lateralised to the dominant hemisphere and to be subserved by a network of structures, including those located in frontal and temporal regions. These structures support critical components of verbal memory, including working memory, encoding, and retrieval. Their relative functional importance in facilitating declarative verbal learning and memory, however, remains unclear. ObjectiveTo investigate the different functional roles of these structures in subserving declarative verbal learning and memory performance by applying a more focal form of transcranial direct current stimulation, “High Definition tDCS” (HD-tDCS). Additionally, we sought to examine HD-tDCS effects and electrical field intensity distributions using computer modelling. MethodsHD-tDCS was administered to the left dorsolateral prefrontal cortex (LDLPFC), planum temporale (PT), and left medial temporal lobe (LMTL) to stimulate the hippocampus, during learning on a declarative verbal memory task. Sixteen healthy participants completed a single blind, intra-individual cross-over, sham-controlled study which used a Latin Square experimental design. Cognitive effects on working memory and sustained attention were additionally examined. ResultsHD-tDCS to the LDLPFC significantly improved the rate of verbal learning (p=0.03, η2=0.29) and speed of responding during working memory performance (p=0.02, η2=0.35), but not accuracy (p=0.12, η2=0.16). No effect of tDCS on verbal learning, retention, or retrieval was found for stimulation targeted to the LMTL or the PT. Secondary analyses revealed that LMTL stimulation resulted in increased recency (p=0.02, η2=0.31) and reduced mid-list learning effects (p=0.01, η2=0.39), suggesting an inhibitory effect on learning. ConclusionsHD-tDCS to the LDLPFC facilitates the rate of verbal learning and improved efficiency of working memory may underlie performance effects. This focal method of administrating tDCS has potential for probing and enhancing cognitive functioning.

Modulation of pre-attentive spectro-temporal feature processing in the human auditory system by HD-tDCS.

The present study examined the functional lateralization of the human auditory cortex (AC) for pre-attentive spectro-temporal feature processing. By using high-definition transcranial direct current stimulation (HD-tDCS), we systematically modulated neuronal activity of the bilateral AC. We assessed the influence of anodal and cathodal HD-tDCS delivered over the left or right AC on auditory mismatch negativity (MMN) in response to temporal as well as spectral deviants in 12 healthy subjects. The results showed that MMN to temporal deviants was significantly enhanced by anodal HD-tDCS applied over the left AC only. Our data indicate a left hemispheric dominance for the pre-attentive processing of low-level temporal information.

High-definition Transcranial Direct Current Stimulation effect and its time-course on 2-back task: An event-related potential (ERP) study

High-definition Transcranial Direct Current Stimulation effect and its time-course on 2-back task: An event-related potential (ERP) study

A novel EEG-based tool for objective assessment of pain in fibromyalgia patients under high-definition tDCS treatment

A novel EEG-based tool for objective assessment of pain in fibromyalgia patients under high-definition tDCS treatment

High-definition tDCS modulates activation during spatial navigation in healthy older adults

High-definition tDCS modulates activation during spatial navigation in healthy older adults

Feasibility of using high-definition transcranial direct current stimulation (HD-tDCS) to enhance treatment outcomes in persons with aphasia.

Transcranial direct current stimulation (tDCS) enhances treatment outcomes post-stroke. Feasibility and tolerability of high-definition (HD) tDCS (a technique that increases current focality and intensity) for consecutive weekdays as an adjuvant to behavioral treatment in a clinical population has not been demonstrated. To determine HD-tDCS feasibility outcomes: 1) ability to implement study as designed, 2) acceptability of repeated HD-tDCS administration to patients, and 3) preliminary efficacy. Eight patients with chronic post-stroke aphasia participated in a randomized crossover trial with two arms: conventional sponge-based (CS) tDCS and HD-tDCS. Computerized anomia treatment was administered for five consecutive days during each treatment arm. Individualized modeling/targeting procedures and an 8-channel HD-tDCS device were developed. CS-tDCS and HD-tDCS were comparable in terms of implementation, acceptability, and outcomes. Naming accuracy and response time improved for both stimulation conditions. Change in accuracy of trained items was numerically higher (but not statistically significant) for HD-tDCS compared to CS-tDCS for most patients. Regarding feasibility, HD-tDCS treatment studies can be implemented when designed similarly to documented CS-tDCS studies. HD-tDCS is likely to be acceptable to patients and clinicians. Preliminary efficacy data suggest that HD-tDCS effects, using only 4 electrodes, are at least comparable to CS-tDCS.

Validating a Sham Condition for Use in High Definition Transcranial Direct Current Stimulation.

High Definition Transcranial Direct Current Stimulation (HD-tDCS) offers improved focality for targeting specific brain areas to modulate neural excitability, compared to conventional tDCS. HD-tDCS is associated with increased scalp sensation during stimulation, potentially rendering conventional tDCS sham methods ineffective due to lack of blinding. Here we report validation data on a novel method for modeling the sham condition in HD-tDCS studies. Thirty-one participants completed sensation ratings during 20 min of continuous active versus sham stimulation. Over half of the participants reported feeling the stimulation for the duration of the experiment. There were no statistically significant differences in sensation ratings between sham and active stimulation. Further, participants were unable to guess above chance level when they received sham stimulation.

Simultaneous high-definition transcranial direct current stimulation of the motor cortex and motor imagery.

Transcranial direct current stimulation (tDCS) has been used to affect the excitability of neurons within the cerebral cortex. Improvements in motor learning have been found in multiple studies when tDCS was applied to the motor cortex during or before task learning is performed. The application of tDCS to motor imagery, a cognitive task showing activation in similar areas to motor execution, has resulted in differing effects based on the amplitude and duration of stimulation. We utilize high definition tDCS, a more spatially localized version of tDCS, to investigate the effect of anodal stimulation on human motor imagery performance. In parallel, we model this stimulation using a finite element model to calculate stimulation area and electrical field amplitude within the brain in the motor cortex and non-stimulated frontal and parietal regions. Overall, we found a delayed increase in resting baseline power 30 minutes post stimulation in both the right and left sensorimotor cortices which resulted in an increase in event-related desynchronization.