Transcranial direct current stimulation as a therapeutic tool for the treatment of major depression: insights from past and recent clinical studies

Machine learning-optimized non-invasive brain stimulation and treatment response classification for major depression

BACKGROUND/OBJECTIVES

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation intervention that shows promise as a potential treatment for depression. However, the clinical efficacy of tDCS varies, possibly due to individual differences in head anatomy affecting tDCS dosage. While functional changes in brain activity are more commonly reported in major depressive disorder (MDD), some studies suggest that subtle macroscopic structural differences, such as cortical thickness or brain volume reductions, may occur in MDD and could influence tDCS electric field (E-field) distributions. Therefore, accounting for individual anatomical differences may provide a pathway to optimize functional gains in MDD by formulating personalized tDCS dosage.

METHODS

To address the dosing variability of tDCS, we examined a subsample of sixteen active-tDCS participants' data from the larger ELECT clinical trial (NCT01894815). With this dataset, individualized neuroimaging-derived computational models of tDCS current were generated for (1) classifying treatment response, (2) elucidating essential stimulation features associated with treatment response, and (3) computing a personalized dose of tDCS to maximize the likelihood of treatment response in MDD.

RESULTS

In the ELECT trial, tDCS was superior to placebo (3.2 points [95% CI, 0.7 to 5.5; P = 0.01]). Our algorithm achieved over 90% overall accuracy in classifying treatment responders from the active-tDCS group (AUC = 0.90, F1 = 0.92, MCC = 0.79). Computed precision doses also achieved an average response likelihood of 99.981% and decreased dosing variability by 91.9%.

CONCLUSION

These findings support our previously developed precision-dosing method for a new application in psychiatry by optimizing the statistical likelihood of tDCS treatment response in MDD.

Cerebellar Neurostimulation for Boosting Social and Affective Functions: Implications for the Rehabilitation of Hereditary Ataxia Patients

Beyond motor deficits, spinocerebellar ataxia (SCA) patients also suffer cognitive decline and show socio-affective difficulties, negatively impacting on their social functioning. The possibility to modulate cerebello-cerebral networks involved in social cognition through cerebellar neurostimulation has opened up potential therapeutic applications for ameliorating social and affective difficulties. The present review offers an overview of the research on cerebellar neurostimulation for the modulation of socio-affective functions in both healthy individuals and different clinical populations, published in the time period 2000-2022. A total of 25 records reporting either transcranial magnetic stimulation (TMS) or transcranial direct current stimulation (tDCS) studies were found. The investigated clinical populations comprised different pathological conditions, including but not limited to SCA syndromes. The reviewed evidence supports that cerebellar neurostimulation is effective in improving social abilities in healthy individuals and reducing social and affective symptoms in different neurological and psychiatric populations associated with cerebellar damage or with impairments in functions that involve the cerebellum. These findings encourage to further explore the rehabilitative effects of cerebellar neurostimulation on socio-affective deficits experienced by patients with cerebellar abnormalities, as SCA patients. Nevertheless, conclusions remain tentative at this stage due to the heterogeneity characterizing stimulation protocols, study methodologies and patients' samples.

The Adjunct of Electric Neurostimulation to Rehabilitation Approaches in Upper Limb Stroke Rehabilitation: A Systematic Review With Network Meta-Analysis of Randomized Controlled Trials

OBJECTIVE

This review analyzed the current evidence and the potential for the application of electric neurostimulation such as transcranial direct current stimulation (tDCS) and vagus nerve stimulation (VNS) in upper limb stroke rehabilitation.

MATERIALS AND METHODS

We performed a systematic review of randomized controlled trials (RCTs) using network meta-analysis (NMA), searching the following data bases: PubMed, Web of Science, Cochrane, and Google Scholar, using specific keywords, from January 2010 to April 2021, and assessing the effects of "tDCS" or "VNS" combined with other therapies on upper limb motor function and activities of daily living (ADL) after stroke.

RESULTS

We included 38 RCTs with 1261 participants. Pairwise NMA showed transcutaneous VNS (tVNS) and anodal tDCS were effective in improving upper limb motor function (tVNS: mean difference [MD]: 5.50; 95% CI [0.67-11.67]; p < 0.05; anodal tDCS: MD: 5.23; 95% CI [2.45-8.01]; p < 0.05). tVNS and tDCS (anodal and cathodal) were also effective in improving ADL performance after stroke (tVNS: standard MD [SMD]: 0.96; 95% CI [0.15-2.06]; p < 0.05; anodal tDCS: SMD: 3.78; 95% CI [0.0-7.56]; p < 0.05; cathodal tDCS: SMD: 5.38; 95% CI [0.22-10.54]; p < 0.05). Surface under the cumulative ranking curve analysis revealed that tVNS is the best ranked treatment in improving upper limb motor function and performance in ADL after stroke. There was no difference in safety between VNS and its control interventions, measured by reported adverse events (VNS: risk ratio = 1.02 [95% CI = 0.48-2.17; I² = 0; p = 0.96]).

CONCLUSION

Moderate- to high-quality evidence suggests that tVNS and anodal tDCS were effective in improving upper limb motor function in both acute/subacute and chronic stroke. In addition to tVNS and anodal tDCS, cathodal tDCS is also effective in improving ADL performance after stroke.

New Horizons on Non-invasive Brain Stimulation of the Social and Affective Cerebellum

The cerebellum is increasingly attracting scientists interested in basic and clinical research of neuromodulation. Here, we review available studies that used either transcranial magnetic stimulation (TMS) or transcranial direct current stimulation (tDCS) to examine the role of the posterior cerebellum in different aspects of social and affective cognition, from mood regulation to emotion discrimination, and from the ability to identify biological motion to higher-level social inferences (mentalizing). We discuss how at the functional level the role of the posterior cerebellum in these different processes may be explained by a generic prediction mechanism and how the posterior cerebellum may exert this function within different cortico-cerebellar and cerebellar limbic networks involved in social cognition. Furthermore, we suggest to deepen our understanding of the cerebro-cerebellar circuits involved in different aspects of social cognition by employing promising stimulation approaches that have so far been primarily used to study cortical functions and networks, such as paired-pulse TMS, frequency-tuned stimulation, state-dependent protocols, and chronometric TMS. The ability to modulate cerebro-cerebellar connectivity opens up possible clinical applications for improving impairments in social and affective skills associated with cerebellar abnormalities.

Acute offline transcranial direct current stimulation does not change pain or anxiety produced by the cold pressor test

Transcranial direct current stimulation (tDCS) over the primary motor cortex (M1) has an antalgic effect on acute experimental pain in healthy volunteers. Many published studies have used online stimulation (i.e., tDCS performed during painful stimulation). On the other hand, daily tDCS sessions have been proposed as a therapy for chronic pain (offline tDCS). In such cases, the therapeutic potential depends on the possible aftereffects of each tDCS session. We set out to investigate whether a single tDCS session before application of a classical experimental pain paradigm (the Cold Pressor Test, CPT) would be capable of modulating physiological measures of anxiety as well as pain perception. tDCS was applied to 30 healthy volunteers, 18-28 years old (mean 18.5), with the anode positioned over either the left M1 or the left dorsolateral prefrontal cortex (l-DLPFC), which has been linked to the affective aspects of experienced pain, including anxiety. All volunteers underwent the CPT procedure before and after a tDCS session. Real 2 mA tDCS sessions for 20 min were compared to sham stimulations. No significant difference was found for any variable after real tDCS sessions when compared to the sham stimulations. This result suggests that effective offline tDCS for chronic pain might have different mechanisms of action. Cumulative effects, functional targeting and the unintended simultaneous stimulation of both M1 and the l-DLPFC are likely responsible for the therapeutic effects of tDCS sessions in the clinical setting.

Different Therapeutic Effects of Transcranial Direct Current Stimulation on Upper and Lower Limb Recovery of Stroke Patients with Motor Dysfunction: A Meta-Analysis

Objective

To explore the effects of transcranial direct current stimulation (tDCS) on the motor recovery of stroke patients and the effect differences between the upper limb and lower limb.

Methods

Randomized control trials published until January 2019 were searched from PubMed, Embase, ScienceDirect, and Cochrane Library databases. The standardized mean difference (SMD) with 95% confidence interval (CI) was estimated separately for upper and lower limb motor outcomes to understand the mean effect size.

Results

Twenty-nine studies with 664 subjects were included in this meta-analysis. The overall analyses of tDCS demonstrated significant effect size both for the upper limb (SMD = 0.26, P = 0.002) and the lower limb (SMD = 0.47, P = 0.002). Compared with acute and subacute stroke patients, chronic stroke patients obtained significant effects after tDCS (SMD = 0.25, P = 0.03) in upper limb function. Furthermore, both anode and cathode stimulations produced significant effect size for stroke patients after ≤10 sessions of tDCS (anode: SMD = 0.40, P = 0.001; cathode: SMD = 0.79, P < 0.0001) with >0.029 mA/cm² of density (anode: SMD = 0.46, P = 0.002; cathode: SMD = 0.79, P < 0.0001). But for lower limb function, more prominent effects were found in subacute stroke patients (SMD = 0.56, P = 0.001) with bilateral tDCS (SMD = 0.59, p = 0.009).

Conclusion

tDCS is effective for the recovery of stroke patients with motor dysfunction. In addition, upper limb and lower limb functions obtain distinct effects from different therapeutic parameters of tDCS at different stages, respectively.

Approach motivation in human cerebral cortex

Different regions of the human cerebral cortex are specialized for different emotions, but the principles underlying this specialization have remained unknown. According to the sword and shield hypothesis, hemispheric specialization for affective motivation, a basic dimension of human emotion, varies across individuals according to the way they use their hands to perform approach- and avoidance-related actions. In a test of this hypothesis, here we measured approach motivation before and after five sessions of transcranial direct current stimulation to increase excitation in the left or right dorsolateral prefrontal cortex, in healthy adults whose handedness ranged from strongly left-handed to strongly right-handed. The strength and direction of participants' handedness predicted whether electrical stimulation to frontal cortex caused an increase or decrease in their experience of approach-related emotions. The organization of approach motivation in the human cerebral cortex varies across individuals as predicted by the organization of the individuals' motor systems. These results show that the large-scale cortical organization of abstract concepts corresponds with the way people use their hands to interact with the world. Affective motivation may re-use neural circuits that evolved for performing approach- and avoidance-related motor actions.This article is part of the theme issue 'Varieties of abstract concepts: development, use and representation in the brain'.

A novel approach for assessing neuromodulation using phase-locked information measured with TMS-EEG

Neuromodulation therapies such as electroconvulsive therapy (ECT) are used to treat several neuropsychiatric disorders, including major depressive disorder (MDD). Recent work has highlighted the use of combined transcranial magnetic stimulation and electroencephalography (TMS-EEG) to evaluate the therapeutic effects of neuromodulation; particularly, the phase locking factor (PLF) and phase locking value (PLV) can reportedly assess neuromodulation-induced functional changes in cortical networks. To examine changes in TMS-induced PLV and PLF before and after ECT, and their relationship with depression severity in patients with MDD, TMS-EEG and the Montgomery–Åsberg Depression Rating Scale (MADRS; depression severity) were implemented before and after ECT in 10 patients with MDD. Single-pulse TMS was applied to the visual and motor areas to induce phase propagation in the visuo-motor network at rest. Functional changes were assessed using PLF and PLV data. Pre-ECT TMS-induced alpha band (9–12 Hz) PLV was negatively correlated with depression severity, and increments of post-ECT from pre-ECT TMS-induced alpha band PLV were positively correlated with the reduction in depression severity. Moreover, we found a negative correlation between pre-ECT TMS-induced PLF at TMS-destination and depression severity. Finally, differences in post-ECT TMS-induced PLF peak latencies between visual and motor areas were positively correlated with depression severity. TMS-EEG-based PLV and PLF may be used to assess the therapeutic effects of neuromodulation and depressive states, respectively. Furthermore, our results provide new insights about the neural mechanisms of ECT and depression.

Effects of Transcranial Direct Current Stimulation on Psychophysiological Responses to Maximal Incremental Exercise Test in Recreational Endurance Runners

Previous studies have suggested that transcranial direct current stimulation (tDCS) might improve exercise performance and alter psychophysiological responses to exercise. However, it is presently unknown whether this simple technique has similar (or greater) effects on running performance. The purpose of this study was, therefore, to test the hypothesis that, compared with sham and cathodal tDCS, anodal tDCS applied over the M1 region would attenuate perception of effort, improve affective valence, and enhance exercise tolerance, regardless of changes in physiological responses, during maximal incremental exercise. In a double-blind, randomized, counterbalanced design, 13 healthy recreational endurance runners, aged 20-42 years, volunteered to participate in this study. On three separate occasions, the subjects performed an incremental ramp exercise test from rest to volitional exhaustion on a motor-driven treadmill following 20-min of brain stimulation with either placebo tDCS (sham) or real tDCS (cathodal and anodal). Breath-by-breath pulmonary gas exchange and ventilation and indices of muscle hemodynamics and oxygenation were collected continuously during the ramp exercise test. Ratings of perceived exertion (RPE) and affective valence in response to the ramp exercise test were also measured. Compared with sham, neither anodal tDCS nor cathodal tDCS altered the physiological responses to exercise (P > 0.05). Similarly, RPE and affective responses during the incremental ramp exercise test did not differ between the three experimental conditions at any time (P > 0.05). The exercise tolerance was also not significantly different following brain stimulation with either sham (533 ± 46 s) or real tDCS (anodal tDCS: 530 ± 44 s, and cathodal tDCS: 537 ± 40 s; P > 0.05). These results demonstrate that acute tDCS applied over the M1 region did not alter physiological responses, perceived exertion, affective valence, or exercise performance in recreational endurance runners.

Chronic Electrical Stimulation Promotes the Excitability and Plasticity of ESC-derived Neurons following Glutamate-induced Inhibition In vitro

Functional electrical stimulation (FES) is rapidly gaining traction as a therapeutic tool for mediating the repair and recovery of the injured central nervous system (CNS). However, the underlying mechanisms and impact of these stimulation paradigms at a molecular, cellular and network level remain largely unknown. In this study, we used embryonic stem cell (ESC)-derived neuron and glial co-cultures to investigate network maturation following acute administration of L-glutamate, which is a known mediator of excitotoxicity following CNS injury. We then modulated network maturation using chronic low frequency stimulation (LFS) and direct current stimulation (DCS) protocols. We demonstrated that L-glutamate impaired the rate of maturation of ESC-derived neurons and glia immediately and over a week following acute treatment. The administration of chronic LFS and DCS protocols individually following L-glutamate infusion significantly promoted the excitability of neurons as well as network synchrony, while the combination of LFS/DCS did not. qRT-PCR analysis revealed that LFS and DCS alone significantly up-regulated the expression of excitability and plasticity-related transcripts encoding N-methyl-D-aspartate (NMDA) receptor subunit (NR2A), brain-derived neurotrophic factor (BDNF) and Ras-related protein (RAB3A). In contrast, the simultaneous administration of LFS/DCS down-regulated BDNF and RAB3A expression. Our results demonstrate that LFS and DCS stimulation can modulate network maturation excitability and synchrony following the acute administration of an inhibitory dose of L-glutamate, and upregulate NR2A, BDNF and RAB3A gene expression. Our study also provides a novel framework for investigating the effects of electrical stimulation on neuronal responses and network formation and repair after traumatic brain injury.

Anodal Transcranial Direct-Current Stimulation Over the Right Dorsolateral Prefrontal Cortex Influences Emotional Face Perception

The dorsolateral prefrontal cortex (DLPFC) is considered to play a crucial role in many high-level functions, such as cognitive control and emotional regulation. Many studies have reported that the DLPFC can be activated during the processing of emotional information in tasks requiring working memory. However, it is still not clear whether modulating the activity of the DLPFC influences emotional perception in a detection task. In the present study, using transcranial direct-current stimulation (tDCS), we investigated (1) whether modulating the right DLPFC influences emotional face processing in a detection task, and (2) whether the DLPFC plays equal roles in processing positive and negative emotional faces. The results showed that anodal tDCS over the right DLPFC specifically facilitated the perception of positive faces, but did not influence the processing of negative faces. In addition, anodal tDCS over the right primary visual cortex enhanced performance in the detection task regardless of emotional valence. Our findings suggest, for the first time, that modulating the right DLPFC influences emotional face perception, especially faces showing positive emotion.

MRI-Guided Regional Personalized Electrical Stimulation in Multisession and Home Treatments

The shape and position of the electrodes is a key factor for the efficacy of transcranial electrical stimulations (tES). We have recently introduced the Regional Personalized Electrode (RePE), a tES electrode fitting the personal cortical folding, that has been able to differentiate the stimulation of close by regions, in particular the primary sensory (S1) and motor (M1) cortices, and to personalize tES onto such an extended cortical district. However, neuronavigation on individual brain was compulsory for the correct montage. Here, we aimed at developing and testing a neuronavigation-free procedure for easy and quick positioning RePE, enabling multisession RePE-tES at home. We used off-line individual MRI to shape RePE via an ad-hoc computerized procedure, while an ad-hoc developed Adjustable Helmet Frame (AHF) was used to properly position it in multisession treatments, even at home. We used neuronavigation to test the RePE shape and position obtained by the new computerized procedure and the re-positioning obtained via the AHF. Using Finite Element Method (FEM) model, we also estimated the intra-cerebral current distribution induced by transcranial direct current stimulation (tDCS) comparing RePE vs. non-RePE with fixed reference. Additionally, we tested, using FEM, various shapes, and positions of the reference electrode taking into account possible small displacements of RePE, to test feasibility of RePE-tES sessions at home. The new RePE neuronavigation-free positioning relies on brain MRI space distances, and produced a mean displacement of 3.5 ± 0.8 mm, and the re-positioning of 4.8 ± 1.1 mm. Higher electric field in S1 than in M1 was best obtained with the occipital reference electrode, a montage that proved to feature low sensitivity to typical RePE millimetric displacements. Additionally, a new tES accessory was developed to enable repositioning the electrodes over the scalp also at home, with a precision which is acceptable according to the modeling-estimated intracerebral currents. Altogether, we provide here a procedure to simplify and make easily applicable RePE-tDCS, which enables efficacious personalized treatments.

Transcranial direct current stimulation combined with visuo-motor training as treatment for chronic stroke patients

BACKGROUND

Recent studies exploring the combined effect of motor learning and transcranial direct current stimulation (tDCS) for stroke rehabilitation have shown partially conflicting results.

OBJECTIVE

To test the efficacy of an optimized hand training approach combined with tDCS in stroke patients.

METHODS

In the present pilot study we investigated motor effects of four-week training with a visuomotor grip force tracking task combined with tDCS in 11 chronic stroke patients. Anodal (0.5 mA) or sham tDCS was applied over the primary motor cortex of the lesioned side for 20 minutes, twice a day, during training.

RESULTS

No difference between the Active and Sham groups in the total upper extremity (UE) Fugl-Meyer Assessment (FMA) score was found. The most prominent recovery occurred in the shoulder-elbow FMA sub-score; in this segment a significantly greater improvement in the Active compared to the Sham group was observed up to two months after the intervention. Mean hold force during the first treatment session predicted the change in the total UE FMA score after treatment.

CONCLUSION

Four-week visuo-motor training combined with tDCS showed no difference between the Active and Sham groups in the total UE FMA score, which may be explained by heterogeneity of the degree of recovery in the Active group. However, the shoulder-elbow FMA sub-score improved significantly more in the Active compared to the Sham group, which deserves further study.

Can 8 months of daily tDCS application slow the cognitive decline in Alzheimer's disease? A case study

This case study presents a patient with early-onset Alzheimer`s disease, who applied transcranial direct current stimulation (tDCS) daily for 8 consecutive months. This was a much higher frequency than previous tDCS studies. Neuropsychological assessments were conducted before the first tDCS session, after 5 months and after 8 months. After 8 months, the patient's immediate recall improved with 39%, whereas delayed recall improved 23%. Overall, the results revealed that patient's cognitive functions were stabilized. There may be slight possibility that tDCS could slow the cognitive decline in Alzheimer`s disease. This should be investigated in clinical trials.

Direct Current-Induced Calcium Trafficking in Different Neuronal Preparations

The influence of direct current (DC) stimulation on radioactive calcium trafficking in sciatic nerve in vivo and in vitro, spinal cord, and synaptosomes was investigated. The exposure to DC enhanced calcium redistribution in all of these preparations. The effect was dependent on the strength of the stimulation and extended beyond the phase of exposure to DC. The DC-induced increase in calcium sequestration by synaptosomes was significantly reduced by cobalt and rupture of synaptosomes by osmotic shock. Although both anodal and cathodal currents were effective, the experiments with two electrodes of different areas revealed that cathodal stimulation exerted stronger effect. The exposure to DC induced not only relocation but also redistribution of calcium within segments of the sciatic nerve. Enzymatic removal of sialic acid by preincubation of synaptosomes with neuroaminidase, or carrying out the experiments in sodium-free environment, amplified DC-induced calcium accumulation.

Impact of Transcranial Direct Current Stimulation (tDCS) on Neuronal Functions

Transcranial direct current stimulation (tDCS), a non-invasive brain stimulation technique, modulates neuronal excitability by the application of a small electrical current. The low cost and ease of the technique has driven interest in potential clinical applications. However, outcomes are highly sensitive to stimulation parameters, leading to difficulty maximizing the technique's effectiveness. Although reversing the polarity of stimulation often causes opposite effects, this is not always the case. Effective clinical application will require an understanding of how tDCS works; how it modulates a neuron; how it affects the local network; and how it alters inter-network signaling. We have summarized what is known regarding the mechanisms of tDCS from sub-cellular processing to circuit level communication with a particular focus on what can be learned from the polarity specificity of the effects.

Brain stimulation treatments in bipolar disorder: A review of the current literature

OBJECTIVES

Brain stimulation techniques are non-pharmacologic strategies which offer additional therapeutic options for treatment-resistant depression (TRD). The purpose of this paper is to review the current literature regarding the use of brain stimulation in resistant bipolar disorder (BD), with particular reference to hypomanic/manic symptoms.

METHODS

Keywords pertaining to the brain simulation techniques used in the treatment of depression (either unipolar or bipolar) along with their role in regard to hypomanic/manic symptoms were used to conduct an electronic search of the literature. Pertinent findings were identified by the authors and reviewed.

RESULTS

Brain stimulation techniques represent a valid therapeutic option in TRD. They have been extensively studied in unipolar depression and, to a minor extent, in the depressive phase of BD, showing encouraging but often limited results. With exception of electroconvulsive therapy, the efficacy of brain stimulation in the treatment of manic symptoms of bipolar patients is still uncertain and needs to be fully evaluated.

CONCLUSIONS

Brain stimulation in BD is derived from its use in unipolar depression. However, there are many important differences between these two disorders and more studies with a systematic approach need to be conducted on larger samples of bipolar patients with treatment-resistant characteristics.

Multimodal approaches to define network oscillations in depression

The renaissance in the use of encephalography-based research methods to probe the pathophysiology of neuropsychiatric disorders is well afoot and continues to advance. Building on the platform of neuroimaging evidence on brain circuit models, magnetoencephalography, scalp electroencephalography, and even invasive electroencephalography are now being used to characterize brain network dysfunctions that underlie major depressive disorder using brain oscillation measurements and associated treatment responses. Such multiple encephalography modalities provide avenues to study pathologic network dynamics with high temporal resolution and over long time courses, opportunities to complement neuroimaging methods and findings, and new approaches to identify quantitative biomarkers that indicate critical targets for brain therapy. Such goals have been facilitated by the ongoing testing of novel invasive neuromodulation therapies, notably, deep brain stimulation, where clinically relevant treatment effects can be monitored at multiple brain sites in a time-locked causal manner. We review key brain rhythms identified in major depressive disorder as foundation for development of putative biomarkers for objectively evaluating neuromodulation success and for guiding deep brain stimulation or other target-based neuromodulation strategies for treatment-resistant depression patients.

The Effect of Transcranial Direct Current Stimulation (tDCS) on Resilience, Compassion Fatigue, Stress and Empathy in Professional Nurses

The purpose of the study is to determine the effect of Transcranial Direct Current Stimulation (tDCS) on measured levels of resilience and empathy in professional nurses with evidence of compassion fatigue and other stress related problems.

Lowered levels of resilience, compassion fatigue and decreased empathy are significant predictors of burnout in nurses. Enhanced levels of resilience are associated with improved empathic responses and overall emotional well-being. Nurses who work in high stress environments often exhibit compassion fatigue and post-traumatic stress disorders that may reduce their ability to function effectively. Because tDCS has been used successfully in a number of chronic disease conditions, it would seem that there is potential for it to be useful in a broader context. The treatment with tDCS may be a potential strategy for improving resilience and eliminating chronic stress responses.

A timed series counterbalanced research design was used for the study. Participants completed 18 sessions of tDCS over a six week period. They also completed a resilience, compassion fatigue, stress and empathy scale before and after each tDCS administration.

A repeated measure analysis was used to determine if tDCS had an impact on scale scores. The analysis showed that tDCS amperage had significant positive effects on empathy. On the outcomes of resilience, compassion fatigue and stress, tDCS did not produce any significant changes. This research provides a new approach to compassion fatigue, an old problem with caregivers. Notably, when implemented with individuals experiencing problems that involve apathy or indifference, tDCS is a non-effortful intervention that offers a pathway that may improve symptoms and does not require extensive outlays of physical or mental energy.

Spreading Effect of tDCS in Individuals with Attention-Deficit/Hyperactivity Disorder as Shown by Functional Cortical Networks: A Randomized, Double-Blind, Sham-Controlled Trial

BACKGROUND

Transcranial direct current stimulation (tDCS) is known to modulate spontaneous neural network excitability. The cognitive improvement observed in previous trials raises the potential of this technique as a possible therapeutic tool for use in attention-deficit/hyperactivity disorder (ADHD) population. However, to explore the potential of this technique as a treatment approach, the functional parameters of brain connectivity and the extent of its effects need to be more fully investigated.

OBJECTIVE

The aim of this study was to investigate a functional cortical network (FCN) model based on electroencephalographic activity for studying the dynamic patterns of brain connectivity modulated by tDCS and the distribution of its effects in individuals with ADHD.

METHODS

Sixty ADHD patients participated in a parallel, randomized, double-blind, sham-controlled trial. Individuals underwent a single session of sham or anodal tDCS at 1 mA of current intensity over the left dorsolateral prefrontal cortex for 20 min. The acute effects of stimulation on brain connectivity were assessed using the FCN model based on electroencephalography activity.

RESULTS

Comparing the weighted node degree within groups prior to and following the intervention, a statistically significant difference was found in the electrodes located on the target and correlated areas in the active group (p < 0.05), while no statistically significant results were found in the sham group (p ≥ 0.05; paired-sample Wilcoxon signed-rank test).

CONCLUSION

Anodal tDCS increased functional brain connectivity in individuals with ADHD compared to data recorded in the baseline resting state. In addition, although some studies have suggested that the effects of tDCS are selective, the present findings show that its modulatory activity spreads. Further studies need to be performed to investigate the dynamic patterns and physiological mechanisms underlying the modulatory effects of tDCS.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01968512.

A pilot study on effects of 4×1 high-definition tDCS on motor cortex excitability

High-Definition transcranial Direct Current Stimulation (HD-tDCS) using specialized small electrodes has been proposed as a focal, non-invasive neuromodulatory technique. Here we provide the first evidence of a change in cortical excitability after HD-tDCS of the motor cortex, using TMS motor evoked potential (MEP) as the measure of excitability. Stimulation for 20 minutes at 1 mA with an anode centered over the hand area of the motor cortex and four surrounding return electrodes (anodal 4×1 montage) produced a significant increase in MEP amplitude and variability after stimulation, compared to sham stimulation. Stimulation was well tolerated by all subjects with adverse effects limited to transient sensation under the electrodes. A high-resolution computational model confirmed predictions of increased focality using the 4×1 HD tDCS montage compared to conventional tDCS. Simulations also indicated that variability in placement of the center electrode relative to the location of the target (central sulcus) could account for increasing variability. These results provide support for the careful use of this technique where focal tDCS is desired.

Transcranial direct-current stimulation increases extracellular dopamine levels in the rat striatum

BACKGROUND

Transcranial direct-current stimulation (tDCS) is a non-invasive procedure that achieves polarity-dependent modulation of neuronal membrane potentials. It has recently been used as a functional intervention technique for the treatment of psychiatric and neurological diseases; however, its neuronal mechanisms have not been fully investigated in vivo.

OBJECTIVE/HYPOTHESIS

To investigate whether the application of cathodal or anodal tDCS affects extracellular dopamine and serotonin levels in the rat striatum.

METHODS

Stimulation and in vivo microdialysis were carried out under urethane anesthesia, and microdialysis probes were slowly inserted into the striatum. After the collection of baseline fractions in the rat striatum, cathodal or anodal tDCS was applied continuously for 10 min with a current intensity of 800 μA from an electrode placed on the skin of the scalp. Dialysis samples were collected every 10 min until at least 400 min after the onset of stimulation.

RESULTS

Following the application of cathodal, but not anodal, tDCS for 10 min, extracellular dopamine levels increased for more than 400 min in the striatum. There were no significant changes in extracellular serotonin levels.

CONCLUSION

These findings suggest that tDCS has a direct and/or indirect effect on the dopaminergic system in the rat basal ganglia.

Treatments in context: transcranial direct current brain stimulation as a potential treatment in pediatric psychosis

Childhood-onset schizophrenia is a chronic, severe form of schizophrenia, and is typically treatment resistant. Even after optimized pharmacotherapy, a majority (over 70%) of these pediatric patients present lasting psychotic symptoms and impaired cognition, necessitating the need for novel treatment modalities. Recent work in transcranial magnetic stimulation suggests moderate efficacy in symptom reduction in adult patients with schizophrenia; however, the transcranial magnetic stimulation treatment is cumbersome for this severely ill population. Transcranial direct current stimulation may provide a safe and effective adjuvant treatment for continued residual symptoms of schizophrenia.

Clinical utility of transcranial direct current stimulation (tDCS) for treating major depression: a systematic review and meta-analysis of randomized, double-blind and sham-controlled trials

OBJECTIVE

tDCS is a promising novel therapeutic intervention for major depression (MD). However, clinical trials to date have reported conflicting results concerning its efficacy, which likely resulted from low statistical power. Thus, we carried out a systematic review and meta-analysis on randomized, double-blind and controlled trials of tDCS in MD with a focus on clinically relevant outcomes, namely response and remission rates.

METHOD

We searched the literature for English language randomized, double-blind and sham-controlled trials (RCTs) on tDCS for treating MD from 1998 through July 2012 using MEDLINE, EMBASE, PsycINFO, Cochrane Central Register of Controlled Trials and SCOPUS. We also consulted the Web of Science's Citations Index Expanded for the selected RCTs up to July 2012. The main outcome measures were response and remission rates. We used a random-effects model and Odds Ratios (OR).

RESULTS

Data were obtained from 6 RCTs that included a total of 200 subjects with MD. After an average of 10.8 ± 3.76 tDCS sessions, no significant difference was found between active and sham tDCS in terms of both response (23.3% [24/103] vs. 12.4% [12/97], respectively; OR = 1.97; 95% CI = 0.85-4.57; p = 0.11) and remission (12.2% [12/98] vs. 5.4% [5/92], respectively; OR = 2.13; 95% CI = 0.64-7.06; p = 0.22). Also, no differences between mean baseline depression scores and dropout rates in the active and sham tDCS groups were found. Furthermore, sensitivity analyses excluding RCTs that involved less than 10 treatment sessions or stimulus intensity of less than 2 mA did not alter the findings. However, tDCS used as monotherapy was associated with higher response rates when compared to sham tDCS (p = 0.043). Finally, the risk of publication bias in this meta-analysis was found to be low.

CONCLUSIONS

The clinical utility of tDCS as a treatment for MD remains unclear when clinically relevant outcomes such as response and remission rates are considered. Future studies should include larger and more representative samples, investigate how tDCS compares to other therapeutic neuromodulation techniques, as well as identify optimal stimulation parameters.

Transcutaneous spinal direct current stimulation

In the past 10 years renewed interest has centered on non-invasive transcutaneous weak direct currents applied over the scalp to modulate cortical excitability ("brain polarization" or transcranial direct current stimulation, tDCS). Extensive literature shows that tDCS induces marked changes in cortical excitability that outlast stimulation. Aiming at developing a new, non-invasive, approach to spinal cord neuromodulation we assessed the after-effects of thoracic transcutaneous spinal DC stimulation (tsDCS) on somatosensory potentials (SEPs) evoked in healthy subjects by posterior tibial nerve (PTN) stimulation. Our findings showed that thoracic anodal tsDCS depresses the cervico-medullary PTN-SEP component (P30) without eliciting adverse effects. tsDCS also modulates post-activation H-reflex dynamics. Later works further confirmed that transcutaneous electric fields modulate spinal cord function. Subsequent studies in our laboratory showed that tsDCS modulates the flexion reflex in the human lower limb. Besides influencing the laser evoked potentials (LEPs), tsDCS increases pain tolerance in healthy subjects. Hence, though the underlying mechanisms remain speculative, tsDCS modulates activity in lemniscal, spinothalamic, and segmental motor systems. Here we review currently available experimental evidence that non-invasive spinal cord stimulation (SCS) influences spinal function in humans and argue that, by focally modulating spinal excitability, tsDCS could provide a novel therapeutic tool complementary to drugs and invasive SCS in managing various pathologic conditions, including pain.

Using Transcranial Direct Current Stimulation to Treat Depression in HIV-Infected Persons: The Outcomes of a Feasibility Study

Transcranial direct current stimulation (tDCS) is a novel non-invasive neuromodulatory method that influences neuronal firing rates and excitability of neuronal circuits in the brain. tDCS has been shown to relieve Major Depressive Disorder (MDD) in the general population, suggesting its potential for other vulnerable populations with high MDD prevalence.

AIMS

This study evaluated the feasibility, safety, acceptability, and clinical outcomes of a 2-week tDCS antidepressant treatment in HIV-MDD co-diagnosed patients, and the feasibility of collecting serum and saliva for analysis of immunity biomarkers.

METHODS

Ten enrolled patients underwent baseline evaluation and started the tDCS treatment (Monday-Friday for 2 weeks) delivered with Phoresor II 850 PM for 20 min at 2 mA at each visit, using two saline-soaked sponge electrodes placed over the F3 position of EEG 10-20 system and the contralateral supraorbital region. Outcome measures were collected at baseline, after the last tDCS and 2 weeks later. A quantitative microarray (Ray Bio Tech Inc.) for TH1/TH2 cytokines was used for saliva and plasma analysis.

RESULTS

Analyzable outcome-data were obtained from eight subjects. Depression scores significantly decreased (p < 0.0005) after the treatment. No serious adverse events occurred. Several transient minor AEs and occasional changes of blood pressure and heart rate were noted. Mini-mental state examination scores remained unchanged or increased after the treatment. All subjects were highly satisfied with the protocol and treatment results and described the desire to find new treatments for HIV-MDD as motivating participation.

CONCLUSION

Findings support feasibility and clinical potential of tDCS for HIV-MDD patients, and justify larger-sample, sham-controlled trials.

Mood and cognitive effects of transcranial direct current stimulation in post-stroke depression

Depression following stroke (PSD) affects up to 33% of patients and is associated with increased mortality. Antidepressant drugs have several side effects; therefore novel treatments are needed. Transcranial direct current stimulation (tDCS) has induced mood and cognitive gain in several neuropsychiatric conditions but has not been tested for PSD to date. Here, we report a patient with significant mood and cognitive impairment who showed marked amelioration of these symptoms following anodal stimulation (2 mA per 30 minutes per 10 days) over the left dorsolateral prefrontal cortex. We discuss the possible mechanisms of tDCS in improving PSD. This initial preliminary data is useful to encourage further controlled trials on the field.

Modulation of human trigeminal and extracranial nociceptive processing by transcranial direct current stimulation of the motor cortex

Objective: The study was conducted to investigate the after-effect of transcranial direct current stimulation (tDCS) applied over the human primary motor cortex (M1) on trigeminal and extracranial nociceptive processing.

Basic procedures: Nineteen healthy volunteers were stimulated using cathodal, anodal (both 1 mA) or sham tDCS for 20 minutes. Pain processing was assessed by recording trigeminal and extracranial pain-related evoked potentials (PREPs) following electrical stimulation of the contralateral forehead and hand at baseline, 0, 20 and 50 minutes post-tDCS.

Main findings: Cathodal tDCS resulted in decreased peak-to-peak amplitudes (PPAs) by 18% while anodal tDCS lead to increased PPAs of PREPs by 35% ( p < .05).

Principal conclusions: The decreased PPAs suggest an inhibition and the increased PPAs of PREPs suggest an excitation of trigeminal and extracranial pain processing induced by tDCS of the M1. These results may provide evidence for the effectiveness of tDCS as a therapeutic instrument in treating headache disorders.

Neuromodulation approaches for the treatment of major depression: challenges and recommendations from a working group meeting

The use of neuromodulation as a treatment for major depressive disorder (MDD) has recently attracted renewed interest due to development of other non-pharmacological therapies besides electroconvulsive therapy (ECT) such as transcranial magnetic stimulation (TMS), transcranial direct current stimulation (tDCS), deep brain stimulation (DBS), and vagus nerve stimulation (VNS). METHOD: We convened a working group of researchers to discuss the updates and key challenges of neuromodulation use for the treatment of MDD. RESULTS: The state-of-art of neuromodulation techniques was reviewed and discussed in four sections: [1] epidemiology and pathophysiology of MDD; [2] a comprehensive overview of the neuromodulation techniques; [3] using neuromodulation techniques in MDD associated with non-psychiatric conditions; [4] the main challenges of neuromodulation research and alternatives to overcome them. DISCUSSION: ECT is the first-line treatment for severe depression. TMS and tDCS are strategies with a relative benign profile of side effects; however, while TMS effects are comparable to antidepressant drugs for treating MDD; further research is needed to establish the role of tDCS. DBS and VNS are invasive strategies with a possible role in treatment-resistant depression. In summary, MDD is a chronic and incapacitating condition with a high prevalence; therefore clinicians should consider all the treatment options including invasive and non-invasive neuromodulation approaches.

Transcranial direct current stimulation - what is the evidence for its efficacy and safety?

Transcranial direct current stimulation (tDCS), a non-invasive brain stimulation technique, has emerged in the past decade as a useful investigative and therapeutic technique. A number of recent studies suggest that tDCS is safe and may be efficacious in the treatment of a variety of psychiatric and neurological disorders, including major depressive disorder, chronic neuropathic pain, and stroke. More evidence is necessary, however, before it can be recommended for general clinical application.