Effects Of Transcranial Direct Current Stimulation Research Articles

Effect of Transcranial Direct current stimulation on Stroke patients

Objective To investigate the effects of traditional rehabilitation training, motor relearning and transcranial direct current stimulation on FMA,ARAT score and ADL of stroke patients. Methods Sixty-five patients with initial stroke who were admitted to Rehabilitation center of Beijing rehabilitation hospital from August 2016 to August 2018 were selected. All the patients were randomly divided into two groups: the control group and the experimental group. On this basis, the experimental group received transcranial direct current stimulation for 6 weeks, while the control group received only false stimulation. The arm motion survey test scale (ARAT) and the simplified fugl-meyer motor function scale (FMA) were used to evaluate the upper limb motor function of patients, and the modified Barthel index scale (MBI) was used to evaluate the daily living activity ability of patients. Results There was no significant difference in FMA score, ARAT score and MBI score before and after treatment between the two groups (P > 0.05). After treatment, FMA and ARAT scores of the upper limbs in the experimental group were (39.44±4.09) and (18.92±3.28), respectively, while those in the control group were (34.22±4.20) and (15.30±3.22), respectively. The differences between the two groups were statistically significant (t=3.239, 2.939, all P < 0.05). Conclusion Traditional rehabilitation training, exercise relearning combined with transcranial direct current stimulation (TDCS) for stroke patients improved the upper limb motor function to some extent, and effectively improved the daily living ability of the patients. It is worth popularizing in clinic. Key words: Stroke; Rehabilitation training; Sports re-learning; Transcranial direct current stimulation; Daily life activity ability

Task load modulates tDCS effects on language performance.

Transcranial direct current stimulation (tDCS) effects in cognition are inconsistent across studies. This study aimed to discuss why typical models might be insufficient to explain these effects, and to investigate a brain state factor, task load, with behavioral experiments on phonological processing. The motor theory of speech perception states that motor codes for articulation take part in speech perception, a view sharpened by neuroimaging findings, which show that the motor role in phonological processing is weighted by the nature of the tasks. Three groups of 20 participants, each under a different tDCS condition (anodal, cathodal, or sham), performed a categorical perception (CP), a lexical decision(LD), and a word naming (WN) task while stimulated on the pars opercularis of the left inferior frontal gyrus, a language area typically involved with the motor role. These tasks were assumed to be subserved by a network of nodes which included the target, believed to be increasingly relevant for performance from speech perception to speech production. A-tDCS facilitation and C-tDCS downregulation should directly increase with the relevance of the target for the task. Downregulation of a low relevance node could result in facilitation by compensation from other nodes. Overall, our brain stimulation findings support the neuroimaging literature in that motor participation in phonological processing depends on task nature and show that tDCS effects are modulated by task load relative to the target. Outcomes such as the improved performance following cathodal tDCS in CP and WN suggest that compensatory mechanisms may take place when the tasks involve more complex neuronal networks.

Comparison of Hypnotic Suggestion and Transcranial Direct-Current Stimulation Effects on Pain Perception and the Descending Pain Modulating System: A Crossover Randomized Clinical Trial.

Objectives: This paper aims to determine if hypnotic analgesia suggestion and transcranial direct-current stimulation (tDCS) have a differential effect on pain perception. We hypothesized that transcranial direct-current stimulation would be more effective than hypnotic analgesia suggestion at changing the descending pain modulating system, whereas the hypnotic suggestion would have a greater effect in quantitative sensory testing.Design: This is a randomized, double blind and crossover trial.Settings: All stages of this clinical trial were performed at the Laboratory of Pain and Neuromodulation of the Hospital de Clínicas de Porto Alegre.Subjects: Were included 24 healthy females aged from 18 to 45 years old, with a high susceptibility to hypnosis, according to the Waterloo-Stanford Group Scale of Hypnotic Susceptibility, Form C (15).Methods: The subjects received a random and crossover transcranial direct-current stimulation over the dorsolateral prefrontal cortex (2 mA for 20 min) and hypnotic analgesia (20 min).Results: Only hypnotic suggestion produced changes that are statistically significant from pre- to post-intervention in the following outcomes measures: heat pain threshold, heat pain tolerance, cold pressure test, and serum brain-derivate-neurotrophic-factor. The analysis showed a significant main effect for treatment (F = 4.32; P = 0.04) when we compared the delta-(Δ) of conditioned pain modulation task between the transcranial direct-current stimulation and hypnotic suggestion groups. Also, the change in the brain-derivate-neurotrophic-factor was positively correlated with the conditioned pain modulation task.Conclusion: The results confirm a differential effect between hypnotic suggestion and transcranial direct-current stimulation on the pain measures. They suggest that the impact of the interventions has differential neural mechanisms, since the hypnotic suggestion improved pain perception, whereas the transcranial direct-current stimulation increased inhibition of the descending pain modulating system.Clinical Trial Registration: www.ClinicalTrials.gov, identifier NCT03744897.Perspective: These findings highlight the effect of hypnotic suggestion on contra-regulating mechanisms involved in pain perception, while the transcranial direct-current stimulation increased inhibition of the descending pain modulating system. They could help clinicians comprehend the mechanisms involved in hypnotic analgesia and transcranial direct-current stimulation and thus may contribute to pain and disability management.

Effectiveness of Transcranial Direct-Current Stimulation (tDCS) and Emotion Regulation Training in Reducing Current Drug Craving and Drug-Use Thoughts and Fantasies in Opioid-Dependent Patients: The Issue of Precedence

Background: Craving is an important factor in predicting relapse in opioid-dependent patients. Objectives: The aim of the present study was to determine which combination therapy, including emotion regulation training followed by tDCS or tDCS followed by emotion regulation training, is more effective in reducing current drug craving and drug-use thoughts and fantasies in opioid-dependent patients in Zahedan, Iran. Patient and Methods: A quasi-experimental study with a pretest-posttest design and two intervention groups was conducted. From eight randomly-selected centers, asample of 28 patients was selected based on the inclusion and exclusion criteria. They were randomly divided into two intervention groups. The first group received eight sessions of tDCS, followed by eight sessions of emotion regulation training. The second group received eight sessions of emotion regulation training followed by eight sessions of tDCS. The statistical population included all opioid-dependent patients at medium-term residential drug rehabilitation centers in Zahedan, Iran, in 2018 - 2019. The data were gathered using the personal drug use questionnaire, the desires for drug questionnaire (DDQ), and the drug use thoughts, fantasies, and temptations questionnaire. All analyses were performed using SPSS-16. Results: The results of repeated measures ANOVA showed that both sequences had a significant, long-term effect on the reduction of current drug craving and drug-use thoughts and fantasies in opioid-dependent patients. In addition, emotion regulation training followed by tDCS was more effective in reducing current drug craving and drug-use thoughts and fantasies than tDCS followed by emotion regulation training. Conclusions: Combination therapy can significantly reduce drug craving in opioid-dependent patients and starting treatment with emotion regulation training followed by tDCS can lead to better results.

Interaction of task-related learning and transcranial direct current stimulation of the prefrontal cortex in modulating executive functions.

The effects of transcranial direct-current stimulation (tDCS) on cognitive functions, such as response inhibition, might be mediated through plastic changes within the prefrontal cortex. Previous studies have also confirmed learning-related plasticity in prefrontal neurocircuitry. The susceptibility of prefrontal neurocircuitry for tDCS-induced plastic changes and consequent behavioural modulations might depend on the level of learning in a particular task. Variabilities in the cognitive outcome of tDCS might be related to the interaction of tDCS and task-relevant learning. 73 participants completed the Stop Task before and after tDCS over the dorsolateral prefrontal cortex. Participants had to deliver a speeded response upon the onset of a visual go-cue and inhibit the response when the go-cue was replaced by a stop signal. We measured response time (RT) in Go trials, and stop signal reaction time (SSRT) as an index of inhibition ability. A shorter SSRT indicates a better inhibition ability. Participants received either anodal or sham stimulation in two separate sessions (one week apart). RT was increased and SSRT became shorter from pre-stimulation to post-stimulation testing, indicating within-session learning. Furthermore, compared to the first week of testing, RT was increased and SSRT became shorter in the second week, indicating across-session learning. Within-session learning was significantly higher if anodal stimulation was given in the first week rather than the second week indicating that the behavioural effects of tDCS were dependent on the level of learning. Our findings indicate that tDCS effects on executive functions are dependent on the level of experience (learning) in the cognitive task.

Somatosensory and transcranial direct current stimulation effects on manual dexterity and motor cortex function: A metaplasticity study

BackgroundNon-invasive neuromodulation may provide treatment strategies for neurological deficits affecting movement, such as stroke. For example, weak electrical stimulation applied to the hand by wearing a “mesh glove” (MGS) can transiently increase primary motor cortex (M1) excitability. Conversely, transcranial direct current stimulation with the cathode over M1 (c-tDCS) can decrease corticomotor excitability.Objective/Hypothesis: We applied M1 c-tDCS as a priming adjuvant to MGS and hypothesised metaplastic effects would be apparent in improved motor performance and modulation of M1 inhibitory and facilitatory circuits. MethodsSixteen right-handed neurologically healthy individuals participated in a repeated measures cross-over study; nine minutes of sham- or c-tDCS followed by 30 min of suprasensory threshold MGS. Dexterity of the non-dominant (left) hand was assessed using the grooved pegboard task, and measures of corticomotor excitability, intracortical facilitation, short-latency afferent inhibition (SAI), short-interval intracortical inhibition (SICI), and SAI in the presence of SICI (SAIxSICI), were obtained at baseline, post-tDCS, and 0, 30 and 60 min post-MGS. ResultsThere was a greater improvement in grooved pegboard completion times with c-tDCS primed MGS than sham + MGS. There was also more pronounced disinhibition of SAI. However, disinhibition of SAI in the presence of SICI was less and rest motor threshold higher compared to sham + MGS. ConclusionsThe results indicate a metaplastic modulation of corticomotor excitability with c-tDCS primed MGS. Further studies are warranted to determine how various stimulation approaches can induce metaplastic effects on M1 neuronal circuits to boost functional gains obtained with motor practice.

Transcranial direct current stimulation (tDCS) and trigeminal pain: A preclinical study.

Our objective was to evaluate the Transcranial direct current stimulation (tDCS) effect on facial allodynia induced by chronic constriction of the infraorbital nerve (CCI-ION) and on the brainstem levels of TNF-α, NGF, IL-10, and serum LDH in rats. Rats were exposed to the CCI-ION model. Facial allodynia was assessed by von Frey filaments test at baseline, 3, 7, 10, and 14days postsurgery and 24hr and 7days after the bimodal tDCS sessions for 20min/day/8days. Chronic constriction of the infraorbital nerve induced a significant decrease in the mechanical threshold 14days after surgery. This effect was reversed by tDCS treatment, with the mechanical threshold returning to basal levels at 24hr after the end of the treatment and it persisted for 7days after the end of the treatment. tDCS also decreased LDH serum levels compared to those in the control group. There was an interaction between pain and treatment with respect to brainstem levels of NGF, TNF-α, and IL-10. Chronic constriction of the infraorbital nerve model was effective in establishing trigeminal neuropathic pain on 14days after surgery, and tDCS reduced allodynia and LDH serum levels and promoted alterations in NGF, TNF-α, and IL-10 brainstem levels. Thus, we suggest that tDCS may be a potential therapy in the trigeminal pain treatment.

Direction of TDCS current flow in human sensorimotor cortex influences behavioural learning

BackgroundRecent studies have shown that neurophysiological outcomes of transcranial direct current stimulation (TDCS) are influenced by current flow in brain regions between the electrodes, and in particular the orientation of current flow relative to the cortical surface. ObjectiveWe asked whether the directional effects of TDCS on physiological measures in the motor system would also be observed on motor behaviours. MethodsWe applied TDCS during the practice of a ballistic movement task to test whether it affected learning or the retention of learning 48 h later. TDCS electrodes were oriented perpendicular to the central sulcus and two current orientations were used (posterior-anterior, TDCSPA; and anterior-posterior, TDCSAP). Transcranial magnetic stimulation (TMS) was used to assess whether changes in corticospinal excitability reflected any behavioural changes. ResultsDirectional TDCSAP impaired the retention of learning on the ballistic movement task compared to TDCSPA and a sham condition. Although TDCSPA had no effect on learning or retention, it blocked the typical increase in corticospinal excitability after a period of motor practice. ConclusionsOur results extend on previous reports of TDCS producing directionally specific changes in neurophysiological outcomes by showing that current direction through a cortical target also impacts upon behavioural outcomes. In addition, changes in corticospinal excitability after a period of motor practice are not causally linked to behavioural learning.

A Review of Acute Aerobic Exercise and Transcranial Direct Current Stimulation Effects on Cognitive Functions and Their Potential Synergies.

Today, several pharmaceutic and non-pharmaceutic approaches exist to treat psychiatric and neurological diseases. Because of the lack of treatment procedures that are medication free and without severe side effects, transcranial direct current stimulation (tDCS) and aerobic exercise (AE) have been tested to explore the potential for initiating and modulating neuroplasticity in the human brain. Both tDCS and AE could support cognition and behavior in the clinical and non-clinical context to improve the recovery process within neurological or psychiatric conditions or to increase performance. As these techniques still lack meaningful effects, although they provide multiple beneficial opportunities within disease and health applications, there is emerging interest to find improved tDCS and AE protocols. Since multimodal approaches could provoke synergetic effects, a few recent studies have begun to combine tDCS and AE within different settings such as in cognitive training in health or for treatment purposes within clinical settings, all of which show superior effects compared to single technique applications. The beneficial outcomes of both techniques depend on several parameters and the understanding of neural mechanisms that are not yet fully understood. Recent studies have begun to directly combine tDCS and AE within one session, although their interactions on the behavioral, neurophysiological and neurochemical levels are entirely unclear. Therefore, this review: (a) provides an overview of acute behavioral, neurophysiological, and neurochemical effects that both techniques provoke within only one single application in isolation; (b) gives an overview regarding the mechanistic pathways; and (c) discusses potential interactions and synergies between tDCS and AE that might be provoked when directly combining both techniques. From this literature review focusing primarily on the cognitive domain in term of specific executive functions (EFs; inhibition, updating, and switching), it is concluded that a direct combination of tDCS and AE provides multiple beneficial opportunities for synergistic effects. A combination could be useful within non-clinical settings in health and for treating several psychiatric and neurologic conditions. However, there is a lack of research and there are several possibly interacting moderating parameters that must be considered and more importantly must be systematically investigated in the future.

Transcranial direct current stimulation (tDCS) effects on traumatic brain injury (TBI) recovery: A systematic review.

ABSTRACT.Traumatic brain injury (TBI) is a major cause of chronic disability. Less than a quarter of moderate and severe TBI patients improved in their cognition within 5 years. Non-invasive brain stimulation, including transcranial direct current stimulation (tDCS), may help neurorehabilitation by boosting adaptive neuroplasticity and reducing pathological sequelae following TBI.Methods:we searched MEDLINE/PubMed and Web of Science databases. We used Jadad scale to assess methodological assumptions.Results:the 14 papers included reported different study designs; 2 studies were open-label, 9 were crossover randomized clinical trials (RCTs), and 3 were parallel group RCTs. Most studies used anodal tDCS of the left dorsolateral prefrontal cortex, but montages and stimulation parameters varied. Multiple studies showed improved coma recovery scales in disorders of consciousness, and improved cognition on neuropsychological assessments. Some studies showed changes in neurophysiologic measures (electroencephalography (EEG) and transcranial magnetic stimulation (TMS), correlating with clinical findings. The main methodological biases were lack of blinding and randomization reports.Conclusion:tDCS is a safe, non-invasive neuromodulatory technique that can be given as monotherapy but may be best combined with other therapeutic strategies (such as cognitive rehabilitation and physical therapy) to further improve clinical cognitive and motor outcomes. EEG and TMS may help guide research due to their roles as biomarkers for neuroplasticity.

Transcranial Direct-Current Stimulation on Motor Function in Pediatric Cerebral Palsy: A Systematic Review.

To determine effects of transcranial direct-current stimulation (tDCS) on motor function for children with cerebral palsy. Six electronic databases were searched using terms related to tDCS, combined with functional deficits/associated clinical measures. Results were filtered, including randomized controlled trials in English and children with cerebral palsy. Data were extracted using standardized procedures, and the PEDro scale was used to assess quality and meta-analyses conducted. From 135 articles, 9 studies with moderate quality met inclusion criteria. Six were included in 7 separate meta-analyses supporting a benefit of tDCS for static balance, only at follow-up. Benefits of tDCS on dynamic balance, step length, and mobility were not established. The findings from meta-analyses suggest that tDCS may provide improvements in static balance at follow-up in children with cerebral palsy and positive effects on gait velocity; however, there was heterogeneity. Further research is needed before this therapy can be endorsed.

Using functional near infrared spectroscopy (FNIRS) to assess the effect of transcranial direct-current stimulation (TDCS) on spinal cord injury patient, during robot-assisted gait

Neuroplasticity is believed to be an important mechanism related to motor improvement of spinal cord injury (SCI) during rehabilitation program, which may be enhanced using transcranial direct-current stimulation (tDCS). The better understanding of this process is important for the improvement of rehabilitation therapy since it can be used as a prognostic biomarker, surrogate outcome and to guide the parameters of tDCS. Functional Near Infrared Spectroscopy (fNIRS) is an instrument to measures hemodynamic responses in the brain, which allows studying functional brain connectivity reorganization. So, this study aims to demonstrate the feasibility of fNIRS to evaluate real-time activation of motor cortex SCI patients during robot-assisted gait. Besides, to compare changes induced by active vs. sham tDCS. It is a preliminary analysis of SCI patients enrolled in a randomized double-blind clinical trial, with two arms (active tDCS vs. sham tDCS). Both groups received 30 sessions of tDCS for 20 minutes immediately before gait training with robotic-assisted device Lokomat-Pro ® (Hocoma). For fNIRS, 32 optodes was positioned parallel to the coronal plane. Software and hardware are from NIRX Medical Technologies. The differential hemoglobin index at rest (standing) and during movement were evaluated using paired T-test. The null hypothesis was that during gait, metabolic consumption would increase in the primary motor cortex (M1). Patients had an enhanced activation of M1, next to Cz, C1 and C2 (10-20 EEG system) during gait, when compared with standing position. This activation seems to be higher in active group comparing to sham group ( Fig. 1 ). This study shows the viability of use fNIRS to measure brain activity of SCI patients during robot-assisted gait. Future analyses, with a larger sample, are necessary to confirm these findings and correlate it with clinical outcomes.

Effects of transcranial direct-current stimulation on laparoscopic surgical skill acquisition.

BackgroundChanges in medical education may limit opportunities for trainees to gain proficiency in surgical skills. Transcranial direct‐current stimulation (tDCS) can augment motor skill learning and may enhance surgical procedural skill acquisition. The aim of this study was to determine the effects of tDCS on simulation‐based laparoscopic surgical skill acquisition.MethodsIn this double‐blind, sham‐controlled randomized trial, participants were randomized to receive 20 min of anodal tDCS or sham stimulation over the dominant primary motor cortex, concurrent with Fundamentals of Laparoscopic Surgery simulation‐based training. Primary outcomes of laparoscopic pattern‐cutting and peg transfer tasks were scored at baseline, during repeated performance over 1 h, and again at 6 weeks. Intent‐to‐treat analysis examined the effects of treatment group on skill acquisition and retention.ResultsOf 40 participants, those receiving tDCS achieved higher mean(s.d.) final pattern‐cutting scores than participants in the sham group (207·6(30·0) versus 186·0(32·7) respectively; P = 0·022). Scores were unchanged at 6 weeks. Effects on peg transfer scores were not significantly different (210·2(23·5) in the tDCS group versus 201·7(18·1) in the sham group; P = 0·111); the proportion achieving predetermined proficiency levels was higher for tDCS than for sham stimulation. Procedures were well tolerated with no serious adverse events and no decreases in motor measures.ConclusionThe addition of tDCS to laparoscopic surgical training may enhance skill acquisition. Trials of additional skills and translation to non‐simulated performance are required to determine the potential value in medical education and impact on patient outcomes. Registration number: NCT02756052 (https://clinicaltrials.gov/).

Bilateral anodal transcranial direct current stimulation effect on balance and fearing of fall in patient with Parkinson's disease.

A number of studies have examined the therapeutic effects of transcranial direct current stimulation (tDCS) stimulation in patients with Parkinson's disease (PD) using unilateral anodal stimulation applied either on the left or right brain hemisphere. However, PD involves the dysfunctions of both brain hemispheres. This study investigates the therapeutic effects of bilateral anodal tDCS stimulation on balance and fear of fall outcomes in patient with PD. Eighteen patients with idiopathic PD completed the study. Ten sessions of bilateral anodal tDCS stimulation were applied over the FC1 and FC2 targeting both pre-frontal and motor areas for each patient, 5 sessions per week for 2 weeks. Berg Balance Scale (BBS), Falls Efficacy Scale-International (FES-I), and 10 meters walk test (10mwt) were applied before and after the stimulation therapy. Paired t-test showed a significant increase in the BBS scores and decrease in the FES-I scores after the bilateral tDCS compared with those scores before tDCS therapy (P < 0.05), as well improvement in the 10mwt scores. Our data showed that bilateral anodal tDCS serves as an effective, safe and feasible approach for rehabilitation of patients with PD with the issues related to balance and fear of fall.

Transcranial direct current stimulation effects on menopausal vasomotor symptoms.

To assess the effects of transcranial direct current stimulation (tDCS) compared with tDCS-sham on vasomotor symptoms of postmenopausal women. Postmenopausal women (N = 30), aged between 45 and 68 years, with at least four episodes of vasomotor symptoms per day, were recruited from a specialized outpatient clinic at a tertiary hospital in the south of Brazil and through a media call after inclusion and exclusion criteria were ensured. Active and tDCS-sham were administered over the motor cortex position (anode electrode) and contralateral supraorbital region (cathode electrode) for 10 consecutive days, except weekends. The number and intensity records of hot flashes were evaluated for 7 days before and along 30 days after the intervention. The Women's Health Questionnaire and the Hamilton Depression Rating Scale were applied to assess the quality of life and the depressive symptoms, respectively. The frequencies of hot flashes per day happened in a similar way in both groups, with a reduction in the first 3 weeks after the intervention. There was a return in hot flash frequencies to baseline in the fourth week (week 0: 79.0 ± 6.2 and 75.8 ± 6.0, week 1: 61.6 ± 9.6 and 57.0 ± 7.8, week 2: 56.8 ± 8.9 and 55.9 ± 7.1, week 3: 56.8 ± 8.9 and 54.2 ± 7.2, week 4: 64.9 ± 10.7, 70.1 ± 8.9; tDCS-sham and tDCS groups, respectively). In the tDCS group, a trend towards a conversion of intensive hot flashes into mild ones was observed. Our results suggest that the tDCS technique showed small trends on postmenopausal vasomotor symptoms, justifying searches for more effective methods by which tDCS could reduce hot flashes.

Effects of Transcranial Direct-Current Stimulation on Neurosurgical Skill Acquisition: A Randomized Controlled Trial.

Recent changes in surgical training environments may have limited opportunities for trainees to gain proficiency in skill. Complex skills such as neurosurgery require extended periods of training. Methods to enhance surgical training are required to overcome duty-hour restrictions, to ensure the acquisition of skill proficiency. Transcranial direct-current stimulation (tDCS) can enhance motor skill learning, but is untested in surgical procedural training. We aimed to determine the effects of tDCS on simulation-based neurosurgical skill acquisition. Medical students were trained to acquire tumor resection skills using a virtual reality neurosurgical simulator. The primary outcome of change in tumor resection was scored at baseline, over 8 repetitions, post-training, and again at 6 weeks. Participants received anodal tDCS or sham over the primary motor cortex. Secondary outcomes included changes in brain resected, resection effectiveness, duration of excessive forces (EF) applied, and resection efficiency. Additional outcomes included tDCS tolerability. Twenty-two students consented to participate, with no dropouts over the course of the trial. Participants receiving tDCS intervention increased the amount of tumor resected, increased the effectiveness of resection, reduced the duration of EF applied, and improved resection efficiency. Little or no decay was observed at 6 weeks in both groups. No adverse events were documented, and sensation severity did not differ between stimulation groups. The addition of tDCS to neurosurgical training may enhance skill acquisition in a simulation-based environment. Trials of additional skills in high-skill residents, and translation to nonsimulated performance are needed to determine the potential utility of tDCS in surgical training.

Polarity-specific transcranial direct current stimulation effects on object-selective neural responses in the inferior parietal lobe

Neuromodulation techniques such as transcranial direct current stimulation (tDCS) are routinely used for treating neurological and neuropsychiatric disorders, and for enhancement of cognitive abilities. Recently, their effectiveness in modulating behavioral and neural responses has been questioned. Here we use excitatory and inhibitory tDCS prior to a functional magnetic resonance imaging (fMRI) experiment to show that neural responses for an area's preferred stimuli depend on the polarity of stimulation. This is an important, yet overlooked, data point in demonstrating the effectiveness of these stimulation techniques. Our results show that response preferences in the target area are dependent on the polarity of the tDCS session preceding the fMRI experiment – these preferences are less distinct in the cathodal than in the anodal session. As such, we show unequivocally that tDCS modulates neural responses. This result is of the utmost importance in demonstrating the effectiveness of tDCS for clinical and experimental purposes.

The effects of transcranial direct-current stimulation on offline visual entrainment: A magnetoencephalography study

While a wealth of literature shows changes in behavior and cognition following transcranial direct-current stimulation (tDCS), the underlying neuronal mechanisms remain largely unknown. Neuroimaging studies in general have shown only limited consensus to date, and the few electrophysiological studies have reported mostly null or counterintuitive findings. The goal of the current investigation was to quantify tDCS-induced alterations in the oscillatory dynamics of visual processing. To this end, we performed 20 minutes of either active or sham tDCS using an occipital-frontal electrode configuration while participants received passive visual stimulation. We then recorded magnetoencephalography (MEG) offline during a visual entrainment task using a 15 Hz flicker stimulus. Significant oscillatory responses were imaged in the time-frequency domain using beamforming, and the effects of tDCS on absolute and relative power were quantified. The results indicated significantly increased basal alpha levels in the occipital cortex following anodal tDCS, as well as reduced occipital synchronization at the second harmonic of the stimulus-flicker frequency (i.e., 30 Hz) relative to sham stimulation. Interestingly, basal alpha power and the induced 30 Hz synchronization were negatively correlated. Additionally, we found reduced power in brain regions near the cathode following active tDCS, which were absent in the sham group. Taken together, these results suggest that anodal tDCS of the occipital cortices differentially modulates basal levels and induced activity, and may interfere with the entrainment of neural populations by a visual-flicker stimulus. These findings also demonstrate the importance of electrode configuration, and highlight the deceptively complicated nature of tDCS in the context of neurophysiology.

Proceedings #7. Transcranial direct current stimulation effects on prefrontal cortex in major depressive disorder (MDD) measured by in vivo proton magnetic resonance spectroscopy (1H MRS)

Proceedings #7. Transcranial direct current stimulation effects on prefrontal cortex in major depressive disorder (MDD) measured by in vivo proton magnetic resonance spectroscopy (1H MRS)

Test-retest reliability of prefrontal transcranial Direct Current Stimulation (tDCS) effects on functional MRI connectivity in healthy subjects

Transcranial Direct Current Stimulation (tDCS) of the prefrontal cortex (PFC) can be used for probing functional brain connectivity and meets general interest as novel therapeutic intervention in psychiatric and neurological disorders. Along with a more extensive use, it is important to understand the interplay between neural systems and stimulation protocols requiring basic methodological work. Here, we examined the test-retest (TRT) characteristics of tDCS-induced modulations in resting-state functional-connectivity MRI (RS fcMRI). Twenty healthy subjects received 20minutes of either active or sham tDCS of the dorsolateral PFC (2mA, anode over F3 and cathode over F4, international 10–20 system), preceded and ensued by a RS fcMRI (10minutes each). All subject underwent three tDCS sessions with one-week intervals in between. Effects of tDCS on RS fcMRI were determined at an individual as well as at a group level using both ROI-based and independent-component analyses (ICA). To evaluate the TRT reliability of individual active-tDCS and sham effects on RS fcMRI, voxel-wise intra-class correlation coefficients (ICC) of post-tDCS maps between testing sessions were calculated. For both approaches, results revealed low reliability of RS fcMRI after active tDCS (ICC(2,1) = −0.09 – 0.16). Reliability of RS fcMRI (baselines only) was low to moderate for ROI-derived (ICC(2,1) = 0.13 – 0.50) and low for ICA-derived connectivity (ICC(2,1) = 0.19 – 0.34). Thus, for ROI-based analyses, the distribution of voxel-wise ICC was shifted to lower TRT reliability after active, but not after sham tDCS, for which the distribution was similar to baseline. The intra-individual variation observed here resembles variability of tDCS effects in motor regions and may be one reason why in this study robust tDCS effects at a group level were missing. The data can be used for appropriately designing large scale studies investigating methodological issues such as sources of variability and localisation of tDCS effects.