Prefrontal direct current stimulation modulates resting EEG and event-related potentials in healthy subjects: A standardized low resolution tomography (sLORETA) study

Noisy Galvanic Vestibular Stimulation (Stochastic Resonance) Changes Electroencephalography Activities and Postural Control in Patients with Bilateral Vestibular Hypofunction

Patients with bilateral vestibular hypofunction (BVH) often suffer from imbalance, gait problems, and oscillopsia. Noisy galvanic vestibular stimulation (GVS), a technique that non-invasively stimulates the vestibular afferents, has been shown to enhance postural and walking stability. However, no study has investigated how it affects stability and neural activities while standing and walking with a 2 Hz head yaw turning. Herein, we investigated this issue by comparing differences in neural activities during standing and walking with a 2 Hz head turning, before and after noisy GVS. We applied zero-mean gaussian white noise signal stimulations in the mastoid processes of 10 healthy individuals and seven patients with BVH, and simultaneously recorded electroencephalography (EEG) signals with 32 channels. We analyzed the root mean square (RMS) of the center of pressure (COP) sway during 30 s of standing, utilizing AMTI force plates (Advanced Mechanical Technology Inc., Watertown, MA, USA). Head rotation quality when walking with a 2 Hz head yaw, with and without GVS, was analyzed using a VICON system (Vicon Motion Systems Ltd., Oxford, UK) to evaluate GVS effects on static and dynamic postural control. The RMS of COP sway was significantly reduced during GVS while standing, for both patients and healthy subjects. During walking, 2 Hz head yaw movements was significantly improved by noisy GVS in both groups. Accordingly, the EEG power of theta, alpha, beta, and gamma bands significantly increased in the left parietal lobe after noisy GVS during walking and standing in both groups. GVS post-stimulation effect changed EEG activities in the left and right precentral gyrus, and the right parietal lobe. After stimulation, EEG activity changes were greater in healthy subjects than in patients. Our findings reveal noisy GVS as a non-invasive therapeutic alternative to improve postural stability in patients with BVH. This novel approach provides insight to clinicians and researchers on brain activities during noisy GVS in standing and walking conditions in both healthy and BVH patients.

Efficacy of transcranial direct current stimulation in ameliorating negative symptoms and cognitive impairments in schizophrenia: A systematic review and meta-analysis

AIMS

Negative symptoms and cognitive impairments in schizophrenia patients are associated with the patients' functional outcomes and quality of life. However, pharmacotherapy has little effect on such symptoms. This study aimed to systematically evaluate the efficacy of transcranial direct current stimulation (tDCS) in ameliorating negative symptoms and cognitive impairments in schizophrenia patients.

METHODS

A literature search was performed in the PubMed, Embase, PsycINFO and Cochrane Library databases through March 23, 2020. Studies were included if they met all the following criteria: (1) subjects were exclusively patients with schizophrenia, schizoaffective disorder or psychosis, (2) active tDCS and shame stimulation were conducted in two parallel groups, (3) sufficient data were present, and (4) the study design was based on a randomized controlled trial. Two authors conducted the search strategy, publication assessment and data extraction independently, and a third person was consulted when any disagreement emerged.

RESULTS

A total of 14 studies were included (12 studies included negative symptoms and 7 studies included cognitive impairments). The overall meta-analysis showed no significant difference between active and sham tDCS in ameliorating negative symptoms in schizophrenia patients (SMD: -0.14, 95% CI: -0.33- 0.05). Subgroup analysis including studies with a high stimulation frequency, twice daily, revealed a significant difference in therapeutic effects between active tDCS and sham stimulation (SMD: -0.31, 95% CI: -0.58 to -0.05). With respect to cognitive impairments, there was a trend indicating that active tDCS might improve cognitive impairment (SMD: -0.21, 95% CI: -0.46- 0.04), but the overall meta-analysis failed to obtain statistically significant results.

CONCLUSION

Our meta-analysis indicates that tDCS is a potential strategy for improving negative symptoms, but the therapeutic benefit for negative symptoms requires a high stimulation frequency (twice a day).

An Integrative Clustering Approach to tDCS Individual Response Variability in Cognitive Performance: Beyond a Null Effect on Working Memory

Despite the growing interest in the use of transcranial direct current stimulation (tDCS) for the modulation of human cognitive function, there are contradictory findings regarding the cognitive benefits of this technique. Inter-individual response variability to tDCS may play a significant role. We explored the effects of anodal versus sham tDCS over the left prefrontal cortex (LPFC) on working memory performance, taking into account the inter-individual variability. Twenty-nine healthy volunteers received an 'offline' anodal tDCS (1.5 mA, 15 min) to the left prefrontal cortex (F3 electrode site) in an intra-individual, cross-over, sham-controlled experimental design. n-back and Sternberg task performance was assessed before (baseline), immediately after tDCS administration (T1) and 5 min post-T1 (T2). We applied an integrative clustering approach to characterize both the group and individual responses to tDCS, as well as identifying naturally occurring subgroups that may be present within the total sample. Anodal tDCS failed to improve working memory performance in the total sample. Cluster analysis identified a subgroup of 'responders' who significantly improved their performance after anodal (vs. sham) stimulation, although not to a greater extent than the best baseline or sham condition. The proportion of 'responders' ranged from 15% to 59% across task conditions and behavioral outputs. Our findings show a high inter-individual variability of the tDCS response, suggesting that the use of tCDS may not be an effective tool to improve working memory performance in healthy subjects. We propose that the use of clustering methods is more suitable in identifying 'responders' and for evaluating the efficacy of this technique.

The Effects of Bi-Anodal tDCS Over the Prefrontal Cortex Regions With Extracephalic Reference Placement on Insight Levels and Cardio-Respiratory and Autonomic Functions in Schizophrenia Patients and Exploratory Biomarker Analyses for Treatment Response

BACKGROUND

We previously showed the efficacy of bi-anodal transcranial direct current stimulation (tDCS) over the prefrontal cortex (PFC) regions with extracephalic reference placement in improving negative symptoms in schizophrenia. In this ancillary investigation, the effects of this intervention on insight levels, other clinical outcomes, and cardio-respiratory and autonomic functions were examined and the potential of biomarkers for treatment response was explored.

METHODS

Schizophrenia patients were randomly allocated to receive 10 sessions of bi-anodal tDCS over the PFC regions with extracephalic reference placement (2 mA, 20 minutes, twice daily for 5 weeks) or sham stimulation. We examined, in 60 patients at baseline, immediately after stimulation and at follow-up visits, the insight levels, other clinical outcomes, blood pressure, respiratory rate, heart rate, and heart rate variability.

RESULTS

Insight levels as assessed by the abbreviated version of the Scale to Assess Unawareness in Mental Disorder in schizophrenia awareness of the disease, positive and negative symptoms dimensions, and beliefs about medication compliance as assessed by Medication Adherence Rating Scale were significantly enhanced by active stimulation relative to sham. No effects were observed on cognitive insight, other clinical outcomes, or cardio-respiratory and autonomic functions. Heart rate variability indices as biomarkers were not associated with the clinical response to the intervention.

CONCLUSIONS

Our results provide evidence for bi-anodal tDCS over the PFC regions with extracephalic reference placement in heightening the levels of insight into the disease and symptoms, as well as beliefs about medication compliance in schizophrenia, without impacting other clinical outcomes and cardio-respiratory/autonomic functions.

The Effects of Transcranial Electrical Stimulation on Human Motor Functions: A Comprehensive Review of Functional Neuroimaging Studies

Transcranial electrical stimulation (tES) is a promising tool to enhance human motor skills. However, the underlying physiological mechanisms are not fully understood. On the other hand, neuroimaging modalities provide powerful tools to map some of the neurophysiological biomarkers associated with tES. Here, a comprehensive review was undertaken to summarize the neuroimaging evidence of how tES affects human motor skills. A literature search has been done on the PubMed database, and 46 relative articles were selected. After reviewing these articles, we conclude that neuroimaging techniques are feasible to be coupled with tES and offer valuable information of cortical excitability, connectivity, and oscillations regarding the effects of tES on human motor behavior. The biomarkers derived from neuroimaging could also indicate the motor performance under tES conditions. This approach could advance the understanding of tES effects on motor skill and shed light on a new generation of adaptive stimulation models.

A systematic review of EEG source localization techniques and their applications on diagnosis of brain abnormalities

In recent years, multiple noninvasive imaging modalities have been used to develop a better understanding of the human brain functionality, including positron emission tomography, single-photon emission computed tomography, and functional magnetic resonance imaging, all of which provide brain images with millimeter spatial resolutions. Despite good spatial resolution, time resolution of these methods are poor and values are about seconds. Scalp electroencephalography recordings can be used to perform the inverse problem in order to specify the location of the dominant sources of the brain activity. In this paper, EEG source localization method, diagnosis of brain abnormalities using common EEG source localization methods, investigating the effect of the head model on EEG source imaging results have been studied. In this review we present enough evidence that provides motivation for consideration in the future research using EEG source localization methods.

Effects of Transcranial Direct Current Stimulation on Baseline and Slope of Prefrontal Cortex Hemodynamics During a Spatial Working Memory Task

Background: Transcranial direct current stimulation (tDCS) has been shown to be an inexpensive, safe, and effective way of augmenting a variety of cognitive abilities. Relatively recent advances in neuroimaging technology have provided the ability to measure brain activity concurrently during active brain stimulation rather than after stimulation. The effects on brain activity elicited by tDCS during active tDCS reported by initial studies have been somewhat conflicted and seemingly dependent on whether a behavioral improvement was observed. Objective: The current study set out to address questions regarding behavioral change, within and between-participant designs as well as differentiating the effects on hemodynamic amplitude and baseline during active tDCS stimulation. Methods: We tested the effects of transcranial direct current stimulation (tDCS) on anterior hemodynamics in prefrontal cortex during performance on a spatial memory task. Prefrontal cortex activity was measured with functional near infrared spectroscopy (fNIRS), a wearable and portable neuroimaging technique that utilizes near infrared light to measure cortical oxygenated and deoxygenated hemoglobin changes non-invasively. There were two groups, one group (n = 10) received only sham stimulation and the other group (n = 11) received sham followed by anodal stimulation to right ventral lateral prefrontal cortex. Results: Analyses revealed an increase in spatial memory performance following tDCS stimulation. This augmented performance was accompanied by changes to oxygenation (HbO-HbR) at the onset of the hemodynamic response in bilateral dorsolateral prefrontal cortex and left ventral medial prefrontal cortex. In these regions we also observed that stimulation improved neural processing efficiency, by reducing oxygenation and increasing performance from block to block. During and following tDCS stimulation, it was also observed that in bilateral dorsolateral prefrontal cortex the relationship between performance and oxygenation inverted, from a negative relationship to a positive relationship. Conclusion: The results suggest that tDCS is predominately a mechanism for changing neurons propensity for activity as opposed to their strength of activity. tDCS not only alters the efficiency of task relevant processing, but also the nature in which hemodynamic resources are used during augmented task performance.

Biomarkers and neuromodulation techniques in substance use disorders

Addictive disorders are a severe health concern. Conventional therapies have just moderate success and the probability of relapse after treatment remains high. Brain stimulation techniques, such as transcranial Direct Current Stimulation (tDCS) and Deep Brain Stimulation (DBS), have been shown to be effective in reducing subjectively rated substance craving. However, there are few objective and measurable parameters that reflect neural mechanisms of addictive disorders and relapse. Key electrophysiological features that characterize substance related changes in neural processing are Event-Related Potentials (ERP). These high temporal resolution measurements of brain activity are able to identify neurocognitive correlates of addictive behaviours. Moreover, ERP have shown utility as biomarkers to predict treatment outcome and relapse probability. A future direction for the treatment of addiction might include neural interfaces able to detect addiction-related neurophysiological parameters and deploy neuromodulation adapted to the identified pathological features in a closed-loop fashion. Such systems may go beyond electrical recording and stimulation to employ sensing and neuromodulation in the pharmacological domain as well as advanced signal analysis and machine learning algorithms. In this review, we describe the state-of-the-art in the treatment of addictive disorders with electrical brain stimulation and its effect on addiction-related neurophysiological markers. We discuss advanced signal processing approaches and multi-modal neural interfaces as building blocks in future bioelectronics systems for treatment of addictive disorders.

Causal underpinnings of working memory and Stroop interference control: Testing the effects of anodal and cathodal tDCS over the left DLPFC

By means of transcranial direct current stimulation applied to the left dorsolateral prefrontal cortex, we investigated the causal role of increased or decreased excitability of this brain region for two facets of executive functions: working memory and Stroop interference control. We tested 1) whether anodal tDCS of the left DLPFC enhances working memory 15 minutes after termination of stimulation and in the absence of direct task practice under stimulation; 2) whether anodal tDCS of the left DLPFC enhances interference control, as evidenced by Stroop performance and Stroop sequence effects; and 3) whether cathodal tDCS leads to compromised executive functioning compared to anodal stimulation. In a between-subject design with 88 healthy psychology students, we compared the impact of anodal and cathodal stimulation against a sham condition, on performance on a Stroop task (during active stimulation) and on an n-back task (completed 15 minutes after active stimulation ended). We found significantly enhanced accuracy in the n-back task after anodal stimulation compared with sham, as well as speeded reactions in the Stroop tasks independent of trial type. By contrast, we found no modulation of Stroop interference effects or Stroop sequence effects. No inhibitory effects of cathodal stimulation were observed. These results support the causal role of the left DLPFC in working memory but lend no support to its involvement in Stroop interference control.

Examining bi-anodal transcranial direct current stimulation (tDCS) over bilateral dorsolateral prefrontal cortex coupled with bilateral extracephalic references as a treatment for negative symptoms in non-acute schizophrenia patients: A randomized, double-blind, sham-controlled trial

No studies have examined the efficacy of bi-anodal transcranial direct current stimulation (tDCS) over bilateral dorsolateral prefrontal cortex (DLPFC) coupled with bilateral extracephalic references in treating negative symptoms of non-acute schizophrenia patients. This study aimed to investigate the therapeutic effects of the new approach of tDCS on negative symptoms, other schizophrenia symptoms, cognitive deficits and psychosocial functioning in a double-blind, randomized, sham-controlled trial. Patients with non-acute schizophrenia (N = 60) in randomized order received sham treatment or bilaterally provided tDCS (2 mA, twice-daily sessions for five consecutive days) with the anode over the DLPFC and the reference (cathode) over the ipsilateral forearm. The negative symptoms as measured by a dimensional approach of Positive and Negative Syndrome Scale (PANSS) were rapidly reduced by bimodal tDCS relative to sham stimulation (F = 24.86, Cohen's d = 0.661, p = 6.11 × 10^-6). The beneficial effect on negative symptoms lasted for up to 3 months. The authors also observed improvement with tDCS of psychosocial functioning as measured by the global score of Personal and Social Performance scale (PSP) and psychopathological symptoms especially for disorganization and cognitive symptoms as measured by the PANSS. No effects were observed on other schizophrenia symptom dimensions and the performance on a series of neurocognitive tests. Our results show promise for bi-anodal tDCS over bilateral DLPFC using bilateral extracephalic references in treating negative symptoms and other selected manifestations of schizophrenia. Further studies with electrophysiological or imaging evaluation help unravel the exact mechanism of action of this novel stimulation parameter of tDCS in schizophrenia patients. (ClinicalTrials.gov ID:NCT03701100).

Assessing neurophysiological changes associated with combined transcranial direct current stimulation and cognitive-emotional training for treatment-resistant depression

Transcranial direct current stimulation (tDCS), a form of non-invasive brain stimulation, is a promising treatment for depression. Recent research suggests that tDCS efficacy can be augmented using concurrent cognitive-emotional training (CET). However, the neurophysiological changes associated with this combined intervention remain to be elucidated. We therefore examined the effects of tDCS combined with CET using electroencephalography (EEG). A total of 20 participants with treatment-resistant depression took part in this open-label study and received 18 sessions over 6 weeks of tDCS and concurrent CET. Resting-state and task-related EEG during a 3-back working memory task were acquired at baseline and immediately following the treatment course. Results showed an improvement in mood and working memory accuracy, but not response time, following the intervention. We did not find significant effects of the intervention on resting-state power spectral density (frontal theta and alpha asymmetry), time-frequency power (alpha event-related desynchronisation and theta event-related synchronisation) or event-related potentials (P2 and P3 components). We therefore identified little evidence of neurophysiological changes associated with treatment using tDCS and concurrent CET, despite significant improvements in mood and near-transfer effects of cognitive training to working memory accuracy. Further research incorporating a sham-controlled group may be necessary to identify the neurophysiological effects of the intervention.

Neural Correlates of Working Memory Deficits in Different Adult Outcomes of ADHD: An Event-Related Potential Study

BACKGROUND

We investigated working memory (WM) processing in a longitudinal sample of young adults with persistent and remittent childhood-onset ADHD to investigate the neural correlates of working memory with adult outcomes of ADHD.

METHODS

Forty-seven young Chinese adults who had been diagnosed with ADHD during childhood underwent follow-up assessments for an average of 9 years. The ADHD sample consisted of 25 ADHD persisters (mean age =18.38 ± 0.5 years) and 22 remitters (mean age = 18.78 ± 1.10 years), who were compared with 25 sex ratio- and IQ-matched healthy adults (mean age = 19.60 ± 1.22 years) in a verbal n-back task.

RESULTS

No differences in behavioral measures were observed across the three groups. Compared with the healthy controls, the ADHD persisters and remitters had larger N1 amplitudes and smaller P2 amplitudes, while no significant differences between the persistence and remission groups were observed. The P3 amplitudes of the remission and control groups were higher than that of the persistence group, but there was no significant difference between the remitters and healthy controls.

CONCLUSION

The P3 amplitudes reflecting postdecisional processing and/or WM updating were sensitive to ADHD remission, as they might improve concurrently with ADHD symptoms. These results indicate that the N1, P2, and P3 components of WM processing might be potential biomarkers for different ADHD outcomes.

Neural and behavioral changes driven by observationally-induced hypoalgesia

Observing successful pain treatment in others can induce anticipatory neural processes that, in turn, relieve pain. Previous studies have suggested that social learning and observation influence placebo hypoalgesia. Here, we used electroencephalography (EEG) to determine the neurophysiological changes associated with pain relief acquired through the observation. Thirty-one participants observed a demonstrator undergo painful heat stimulations paired with a "control" cream and non-painful ones paired with a "treatment" cream, which actually were both Vanicreams. After their observation, the participants then received the same creams and stimulations. We found that the treatment cream led to lower self-reported pain intensity ratings than the control cream. Anticipatory treatment cues elicited smaller P2 in electrodes F1, Fz, FC1, and FCz than the control condition. The P2 component localization indicated a higher current density in the right middle frontal gyrus, a region associated with attentional engagement. In placebo responders, the sensorimotor cortex activity captured in electrodes C3, Cz, and C4 indicated that hypoalgesia was positively correlated with resting state peak alpha frequency (PAF). These results suggest that observationally-induced placebo hypoalgesia may be driven by anticipatory mechanisms that modulate frontal attentional processes. Furthermore, resting state PAF could serve as a predictor of observationally-induced hypoalgesia.

Significant group-level hotspots found in deep brain regions during transcranial direct current stimulation (tDCS): A computational analysis of electric fields

OBJECTIVE

Transcranial direct current stimulation (tDCS) is a neuromodulation scheme that delivers a small current via electrodes placed on the scalp. The target is generally assumed to be under the electrode, but deep brain regions could also be involved due to the large current spread between the electrodes. This study aims to computationally evaluate if group-level hotspots exist in deep brain regions for different electrode montages.

METHODS

We computed the tDCS-generated electric fields (EFs) in a group of subjects using interindividual registration methods that permitted the projection of EFs from individual realistic head models (n = 18) to a standard deep brain region.

RESULTS

The spatial distribution and peak values (standard deviation of 14%) of EFs varied significantly. Nevertheless, group-level EF hotspots appeared in deep brain regions. The caudate had the highest field peaks in particular for F3-F4 montage (70% of maximum cortical EF), while other regions reach field peaks of 50%.

CONCLUSIONS

tDCS at deeper regions may include not only modulation via underlying cortical or subcortical circuits but also modulation of deep brain regions.

SIGNIFICANCE

The presented EF atlas in deep brain regions can be used to explain tDCS mechanism or select the most appropriate tDCS montage.

Neural Activity and Decoding of Action Observation Using Combined EEG and fNIRS Measurement

In a social world, observing the actions of others is fundamental to understanding what they are doing, as well as their intentions and feelings. Studies of the neural basis and decoding of action observation are important for understanding action-related processes and have implications for cognitive, social neuroscience, and human-machine interaction (HMI). In the current study, we first investigated temporal-spatial dynamics during action observation using a combined 64-channel electroencephalography (EEG) and 48-channel functional near-infrared spectroscopy (fNIRS) system. We measured brain activation while 16 healthy participants observed three action tasks: (1) grasping a cup with the intention of drinking; (2) grasping a cup with the intention of moving it; and (3) touching a cup with an unclear intention. The EEG and fNIRS source analysis results revealed the dynamic involvement of both the mirror neuron system (MNS) and the theory of mind (ToM)/mentalizing network during action observation. The source analysis results suggested that the extent to which these two systems were engaged was determined by the clarity of the intention of the observed action. Based on the difference in neural activity observed among different action-observation tasks in the first experiment, we conducted a second experiment to classify the neural processes underlying action observation using a feature classification method. We constructed complex brain networks based on the EEG and fNIRS data. Fusing features from both EEG and fNIRS complex brain networks resulted in a classification accuracy of 72.7% for the three action observation tasks. This study provides a theoretical and empirical basis for elucidating the neural mechanisms of action observation and intention understanding, and a feasible method for decoding the underlying neural processes.

High-definition tDCS to the right temporoparietal junction modulates slow-wave resting state power and coherence in healthy adults

The right temporoparietal junction (rTPJ) is a multisensory integration hub that is increasingly utilized as a target of stimulation studies exploring its rich functional network roles and potential clinical applications. While transcranial direct current stimulation (tDCS) is frequently employed in such studies, there is still relatively little known regarding its local and network neurophysiological effects, particularly at important nonmotor sites such as the rTPJ. The current study applied either anodal, cathodal, or sham high-definition tDCS to the rTPJ of 53 healthy participants and used offline EEG to assess the impacts of stimulation on resting state (eyes open and eyes closed) band power and coherence. Temporoparietal and central region delta power was increased after anodal stimulation (the latter trend only), whereas cathodal stimulation increased frontal region delta and theta power. Increased coherence between right and left temporoparietal regions was also observed after anodal stimulation. All significant effects occurred in the eyes open condition. These findings are discussed with reference to domain general and mechanistic theories of rTPJ function. Low-frequency oscillatory activity may exert long-range inhibitory network influences that enable switching between and integration of endogenous/exogenous processing streams.

NEW & NOTEWORTHY Through the novel use of high-definition transcranial direct current stimulation (tDCS) and EEG, we provide evidence that both anodal and cathodal stimulation of the right temporoparietal junction selectively modulate slow-wave power and coherence in distributed network regions of known relevance to proposed temporoparietal junction functionality. These results also provide direct evidence of the ability of tDCS to modulate oscillatory activity at a long-range network level, which may have explanatory power in terms of both neurophysiological and behavioral effects.

Behavioural and electrophysiological modulations induced by transcranial direct current stimulation in healthy elderly and Alzheimer's disease patients: A pilot study

OBJECTIVE

To investigate whether anodal and cathodal transcranial direct current stimulation (tDCS) can modify cognitive performance and neural activity in healthy elderly and Alzheimer's disease (AD) patients.

METHODS

Fourteen healthy elderly and twelve AD patients performed a working memory task during an electroencephalogram recording before and after receiving anodal, cathodal, and sham tDCS over the left dorsolateral prefrontal cortex. Behavioural performance, event-related potentials (P200, P300) and evoked cortical oscillations were studied as correlates of working memory.

RESULTS

Anodal tDCS increased P200 and P300 amplitudes in healthy elderly. Cathodal tDCS increased P200 amplitude and frontal theta activity between 150 and 300 ms in AD patients. Improved working memory after anodal tDCS correlated with increased P300 in healthy elderly. In AD patients, slight tendencies between enhanced working memory and increased P200 after cathodal tDCS were observed.

CONCLUSIONS

Functional neural modulations were promoted by anodal tDCS in healthy elderly and by cathodal tDCS in AD patients.

SIGNIFICANCE

Interaction between tDCS polarity and the neural state (e.g., hyper-excitability exhibited by AD patients) suggests that appropriate tDCS parameters (in terms of tDCS polarity) to induce behavioural improvements should be chosen based on the participant's characteristics. Future studies using higher sample sizes should confirm and extend the present findings.

Pre-stimulus Brain Activity Is Associated With State-Anxiety Changes During Single-Session Transcranial Direct Current Stimulation

Transcranial direct current stimulation is a promising neuromodulation method for treating depression. However, compared with pharmacological treatment, previous studies have reported that a relatively limited proportion of patients respond to tDCS treatment. In addition, the neurophysiological mechanisms underlying tDCS treatment remain unclear, making it difficult to identify response predictors for tDCS treatment based on neurophysiological function. Because treatment effects are achieved by repetitive application of tDCS, studying the immediate effects of tDCS in depressive patients could extend understanding of its treatment mechanisms. However, immediate changes in a single session of tDCS are not well documented. Thus, in the current study, we focused on the immediate impact of tDCS and its association with pre-stimulus brain activity. To address this question, we applied anodal tDCS to the left dorsolateral prefrontal cortex (DLPFC) or dorsomedial prefrontal cortex (DMPFC) in 14 patients with major depressive disorder (MDD) and 19 healthy controls (HCs), at an intensity of 1.0 mA for 20 min in a single session. To evaluate anxiety, the state trait anxiety inventory was completed before and after tDCS. We recorded resting electroencephalography before tDCS, and calculated electrical neuronal activity in the theta and alpha frequency bands using standardized low-resolution electromagnetic tomography. We found that, during application of left DLPFC tDCS to patients with MDD, the anxiety reduction effect of tDCS was related to higher baseline theta-band activity in the rostral anterior cingulate cortex (rACC) and no medication with benzodiazepine used as hypnotic. For DMPFC stimulation in MDD, the anxiety reduction effect was associated with lower baseline alpha-band activity in the left inferior parietal lobule. In contrast, in HCs, the anxiety reduction effect was associated with higher baseline alpha activity in the precuneus during DMPFC stimulation. The current results suggest that the association between pre-tDCS brain activity and the anxiety reduction effect of tDCS depends on psychopathology (depressed or non-depressed) as well as the site of stimulation (DMPFC or left DLPFC) and insomnia. Furthermore, the results suggest that tDCS response might be associated with baseline resting state electrophysiological neural activity.

Top 100 cited noninvasive neuromodulation clinical trials

INTRODUCTION

Introduction: Transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS) are noninvasive neuromodulation techniques used as therapeutic and research tools for several neuropsychiatric conditions. Given the exponential scientific growth of this field, we aimed to systematically review the most cited clinical trials using TMS or tDCS.

AREAS COVERED

A de-novo keyword search strategy identified and characterized the 100 most-cited trials. Total citation count for the most cited trials was 13,204. Articles were published between 2008 and 2014 in 50 different journals with a median impact factor of 6.52 (IQR 3.37). Almost half of the top cited papers were investigating mechanisms of action in healthy subjects. Most studies were feasibility trials and only five were pivotal trials, including the ones used for recent FDA approval. Seven articles were interlinked with another article by at least 25 citations and eight authors had collaborated with at least one other author.

EXPERT OPINION

Although there has been a significant increase in interest for rTMS and tDCS, most of the cited clinical trials are still small feasibility studies, what reinforced the need for more robust clinical trials (larger samples sizes and effects sizes) to better define clinical effectiveness.

Anodal tDCS modulates cortical activity and synchronization in Parkinson's disease depending on motor processing

Background

Transcranial direct current stimulation (tDCS) may alleviate motor symptoms in Parkinson's disease (PD). However, the neurophysiological effects of tDCS on cortical activation, synchronization, and the relation to clinical motor symptoms and motor integration need characterization.

Objective

We aimed to explore the effect of tDCS over the left sensorimotor area on clinical motor outcome, right hand fine motor performance as well as cortical activity and synchronization in the high beta range.

Methods

In this double-blind randomized sham-controlled clinico-neurophysiological study we investigated ten idiopathic PD patients and eleven matched healthy controls (HC) on two days during an isometric precision grip task and at rest before and after ‘verum’ and ‘sham’ anodal tDCS (20 min; 1 mA; anode [C3], cathode [Fp2]). We measured clinical outcome, fine motor performance, and analysed both cortical frequency domain activity and corticocortical imaginary coherence.

Results

tDCS improved PD motor symptoms. Neurophysiological features indicated a motor-task-specific modulation of activity and coherence from 22 to 27 Hz after ‘verum’ stimulation in PD. Activity was significantly reduced over the left sensorimotor and right frontotemporal area. Before stimulation, PD patients showed reduced coherence over the left sensorimotor area during motor task compared to HC, and this increased after ‘verum’ stimulation in the motor task. The activity and synchronization modulation were neither observed at rest, after sham stimulation nor in healthy controls.

Conclusion

Verum tDCS modulated the PD cortical network specifically during fine motor integration. Cortical oscillatory features were not in general deregulated in PD, but depended on motor processing.

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tDCS improved motor function in Parkinson's disease.

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tDCS modulated cortical beta activity and synchronization in Parkinson's disease.

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the Parkinson's disease motor network may be susceptible to cortical stimulation.

•

tDCS may reverse pathologic cortical network states.

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.

Neurobiological effects of transcranial direct current stimulation in younger adults, older adults and mild cognitive impairment

Transcranial direct current stimulation (tDCS) has been investigated as a way to improve motor and cognitive functioning, with largely variable results. Currently, relatively little is known about the neurobiological effects, and possible drivers of variability, in either healthy or clinical populations. Therefore, this study aimed to characterise the neurobiological effects to tDCS in younger adults, older adults and adults with mild cognitive impairment (MCI), and their relationship to cognitive performance. 20 healthy younger adults, 20 healthy older adults and 9 individuals with MCI participated in the study. All completed neuropsychological tasks and TMS-EEG, prior to and following delivery of 20 min of anodal tDCS to the left dorsolateral prefrontal cortex (DLPFC). EEG was also recorded during the 2-Back working memory task. Following tDCS, younger adults demonstrated alterations in early TMS-Evoked Potentials (TEPs), namely P30 and P60. Both younger and older adults exhibited a larger task-related N250 amplitude after stimulation, with contrasting relationships to cognitive performance. The MCI group showed no change in TEPs or ERPs over time. Comparisons between the groups revealed differences in the change in amplitude of early TEP (P60) and ERP (N100) peaks between younger and older adults. Our findings indicate that tDCS was able to modulate cortical activity in younger and older healthy adults, but in varying ways. These findings suggest that varied response to tDCS may be related to factors such as age and the presence/absence of cognitive impairment, and these factors should be considered when assessing the effectiveness of tDCS in healthy and pathological aging.

A systematic review on the therapeutic effectiveness of non-invasive brain stimulation for the treatment of anxiety disorders

The interest in the use of non-invasive brain stimulation for enhancing neural functions and reducing symptoms in anxiety disorders is growing. Based on the DSM-V classification for anxiety disorders, we examined all available research using repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) for the treatment of specific phobias, social anxiety disorder, panic disorder, agoraphobia, and generalized anxiety disorder. A systematic literature search conducted in PubMed and Google Scholar databases provided 26 results: 12 sham-controlled studies and 15 not sham-controlled studies. With regard to the latter sub-group of studies, 9 were case reports, and 6 open label studies. Overall, our work provides preliminary evidence that both, excitatory stimulation of the left prefrontal cortex and inhibitory stimulation of the right prefrontal cortex can reduce symptom severity in anxiety disorders. The current results are discussed in the light of a model for the treatment for anxiety disorders via non-invasive brain stimulation, which is based on up-/downregulation mechanisms and might serve as guide for future systematic investigations in the field.

The effect of nicotine patches on craving in the brain: A functional MRI study on heavy smokers

BACKGROUND

Smoking is a common phenomenon and kills over 6 million people every year. Many smokers try to quit smoking by using nicotine replacement therapy (NRT). Most of the time, relapse occurs in less than six months after finishing the program of NRT. We performed a single blinded study in which our aim was to figure out what the effect of the nicotine patch is on craving in the brain of smokers deprived from smoking.

METHODS

Five heavy smokers (Fagerström Test for Nicotine Dependence ≥4) underwent a functional magnetic resonance imaging (fMRI) in 4 random conditions: smoking (S); smoking deprivation (SD); SD combined with a NP (SD + NP); SD combined with a placebo patch (SD + PP). Visual stimulation provoked craving in block design by randomly displaying images of smoking related scenes. After image preprocessing, a fixed-effect analysis was performed to compare average group activations. The Questionnaire for Smoking Urges (QSU) was obtained before and after each scan.

RESULTS

The fMRI results showed higher activation in areas involved in craving in S compared with SD + NP, SD + PP, and SD. In the SD + NP, limbic circuit and attention area were higher activated compared with SD and SD + PP. The SD + PP and SD showed higher activation in the frontal cortex and limbic system compared with S and SD + NP. Nonsmokers showed higher limbic activation compared with SD.The QSU increased significantly after the fMRI experiment in S (P = .036).The SD had higher QSU scores compared with the S before (P = .002), and also after (P = .022) the fMRI experiment. The NP showed lower scores than the SD before the experiment (P = .046).

CONCLUSION

The fMRI experiment revealed lower activity in areas associated with attention when subjects were nicotine deprived (SD + PP and SD). Areas involved with craving showed less activity when nicotine is present (S and SD + NP). The QSU showed a significant difference between SD and when nicotine is present (S and SD + NP).

Cathodal tDCS Over Motor Cortex Does Not Improve Tourette Syndrome: Lessons Learned From a Case Series

Introduction: Current pathophysiological hypotheses of Gilles de la Tourette Syndrome (GTS) refer to temporally abnormal neuronal activation in cortico-striato-thalamo-cortical (CSTC) networks. Modifying cortical activity by non-invasive brain-stimulation appears to be a new treatment option in GTS. Background: Previous studies suggested therapeutic effects of cathodal transcranial direct current stimulation (tDCS) to pre-supplementary motor areas (SMA), however, treatment modalities concerning electrode placement, current intensity and stimulation-rate have not been systematically explored. Aim of this study was to assess efficacy of an alternative stimulation regime on GTS symptoms in a pilot study. To test a treatment protocol with tDCS twice a day, we administered 10 sessions over 5 days of bilateral cathodal tDCS (30 min, 2 mA) over the pre-SMA in three patients with severe GTS. Tic severity as well as obsessive-compulsive (OC) symptoms and affective scales were rated before and after tDCS treatment. Discussion: Only one out of three patients showed a 34.5% reduction in tic severity. The two other patients showed an increase in tic severity. All patients showed a mild increase in positive affect and a reduction in negative affect, OC symptom changes were heterogeneous. Our results do not support earlier findings of extensive therapeutic effects of cathodal tDCS on tics in patients with GTS and show that prediction of stimulation effects on a targeted brain area remains inaccurate. Concluding Remarks: Future research will have to focus on the determination of most effective stimulation modes regarding site, polarity and frequency of tDCS in GTS patients.

Interrogating the Relationship Between Schizotypy, the Catechol-O-Methyltransferase (COMT) Val158Met Polymorphism, and Neuronal Oscillatory Activity

The COMT Val158Met polymorphism affects the availability of synaptic dopamine in the prefrontal cortex and has been widely studied as a genetic risk factor for psychosis. Schizotypy is associated with an increased risk of psychosis, with some studies implicating similar neurobiological mechanisms to schizophrenia. The present study sought to interrogate the link between the COMT Val158Met polymorphism and schizotypy using electroencephalogram (EEG) to identify neurophysiological mechanisms underpinning psychosis risk. Neurotypical (N = 91) adults were genotyped for the COMT Val158Met polymorphism, completed the Schizotypal Personality Questionnaire (SPQ), and had eyes open resting-state EEG recorded for 4 min. SPQ suspiciousness subscale scores were higher for individuals homozygous for Val/Val and Met/Met versus Val/Met genotypes. Delta, theta, alpha-2, beta-1, and beta-2 amplitudes were lower for Val/Val than Met/Met individuals. Lower theta amplitudes were correlated with higher total SPQ scores (P = 0.050), and multiple regression revealed that higher delta, and lower theta and beta-2 amplitudes (but not COMT genotype) best predicted total SPQ scores (P = 0.014). This study demonstrates the importance of COMT genotype in determining trait suspiciousness and EEG oscillatory activity. It also highlights relationships between dopaminergic alterations, EEG and schizotypy that are dissimilar to those observed in schizophrenia.

The Efficacy of Transcranial Current Stimulation Techniques to Modulate Resting-State EEG, to Affect Vigilance and to Promote Sleepiness

Transcranial Current Stimulations (tCSs) are non-invasive brain stimulation techniques which modulate cortical excitability and spontaneous brain activity by the application of weak electric currents through the scalp, in a safe, economic, and well-tolerated manner. The direction of the cortical effects mainly depend on the polarity and the waveform of the applied current. The aim of the present work is to provide a broad overview of recent studies in which tCS has been applied to modulate sleepiness, sleep, and vigilance, evaluating the efficacy of different stimulation techniques and protocols. In recent years, there has been renewed interest in these stimulations and their ability to affect arousal and sleep dynamics. Furthermore, we critically review works that, by means of stimulating sleep/vigilance patterns, in the sense of enhancing or disrupting them, intended to ameliorate several clinical conditions. The examined literature shows the efficacy of tCSs in modulating sleep and arousal pattern, likely acting on the top-down pathway of sleep regulation. Finally, we discuss the potential application in clinical settings of this neuromodulatory technique as a therapeutic tool for pathological conditions characterized by alterations in sleep and arousal domains and for sleep disorders per se.

Changing Brain Networks Through Non-invasive Neuromodulation

Background/Objective: Non-invasive neuromodulation techniques, such as repetitive Transcranial Magnetic Stimulation (rTMS) and transcranial Direct Current Stimulation (tDCS), have increasingly been investigated for their potential as treatments for neurological and psychiatric disorders. Despite widespread dissemination of these techniques, the underlying therapeutic mechanisms and the ideal stimulation site for a given disorder remain unknown. Increasing evidence support the possibility of non-invasive neuromodulation affecting a brain network rather than just the local stimulation target. In this article, we present evidence in a clinical setting to support the idea that non-invasive neuromodulation changes brain networks.

Method: This article addresses the idea that non-invasive neuromodulation modulates brain networks, rather than just the local stimulation target, using neuromodulation studies in tinnitus and major depression as examples. We present studies that support this hypothesis from different perspectives.

Main Results/Conclusion: Studies stimulating the same brain region, such as the dorsolateral prefrontal cortex (DLPFC), have shown to be effective for several disorders and studies using different stimulation sites for the same disorder have shown similar results. These findings, as well as results from studies investigating brain network connectivity on both macro and micro levels, suggest that non-invasive neuromodulation affects a brain network rather than just the local stimulation site targeted. We propose that non-invasive neuromodulation should be approached from a network perspective and emphasize the therapeutic potential of this approach through the modulation of targeted brain networks.

Motor facilitation during observation of implied motion: Evidence for a role of the left dorsolateral prefrontal cortex

The phenomenon of motor resonance (the increase in motor cortex excitability during observation of actions) has been previously described. Transcranial magnetic stimulation (TMS) studies have demonstrated a similar effect during perception of implied motion (IM). The left dorsolateral prefrontal cortex (DLPFC) seems to be activated during action observation. Furthermore, the role of this brain area in motor resonance to IM is yet to be investigated. Fourteen healthy volunteers were enrolled into the study. We used transcranial direct current stimulation (tDCS) to stimulate DLPFC aiming to investigate whether stimulation with different polarities would affect the amplitude of motor evoked potential collected during observation of images with and without IM. The results of our experiment indicated that Cathodal tDCS over the left DLPFC prevented motor resonance during observation of IM. On the contrary, anodal and sham tDCS did not significantly modulate motor resonance to IM. The current study expands the understanding of the neural circuits engaged during observation of IM. Our results are consistent with the hypothesis that action understanding requires the interaction of large networks and that the left DLPFC plays a crucial role in generating motor resonance to IM.

The Effects of Transcranial Direct Current Stimulation (tDCS) on Psychomotor and Visual Perception Functions Related to Driving Skills

Objective: It could be demonstrated that anodal transcranial direct current stimulation (tDCS) of the left dorsolateral prefrontal cortex (DLPFC) enhances accuracy in working memory tasks and reaction time in healthy adults and thus may also have an influence on complex everyday tasks like driving a car. However, no studies have applied tDCS to psychomotor skills related to a standard driving test so far.

Methods: 10 female and 5 male healthy adults without any medication and history of psychiatric or neurological illness were randomly assigned to two groups receiving active and sham stimulation in a double blind, cross-over study design. Standardized computerized psychomotor tests according to the German guidelines for road and traffic safety were administered at baseline. Then they performed the same tests during an anodal or sham tDCS of the left DLPFC in two separated sessions.

Results: No significant improvements in skills related to driving performance like visual perception, stress tolerance, concentration, and vigilance could be shown after left anodal prefrontal tDCS. Side effects were low and did not differ between active and sham stimulation.

Conclusions: The findings of our study indicate that left prefrontal tDCS may not alter driving skills affording more automated action patterns but as shown in previous studies may have an influence on driving behavior requiring executive control processes. This however has to be proved in future studies and within greater samples.

The Effects of Theta and Gamma tACS on Working Memory and Electrophysiology

A single blind sham-controlled study was conducted to explore the effects of theta and gamma transcranial alternating current stimulation (tACS) on offline performance on working memory tasks. In order to systematically investigate how specific parameters of tACS affect working memory, we manipulated the frequency of stimulation (theta frequency vs. gamma frequency), the type of task (n-back vs. change detection task) and the content of the tasks (verbal vs. figural stimuli). A repeated measures design was used that consisted of three sessions: theta tACS, gamma tACS and sham tACS. In total, four experiments were conducted which differed only with respect to placement of tACS electrodes (bilateral frontal, bilateral parietal, left fronto-parietal and right-fronto parietal). Healthy female students (N = 72) were randomly assigned to one of these groups, hence we were able to assess the efficacy of theta and gamma tACS applied over different brain areas, contrasted against sham stimulation. The pre-post/sham resting electroencephalogram (EEG) analysis showed that theta tACS significantly affected theta amplitude, whereas gamma tACS had no significant effect on EEG amplitude in any of the frequency bands of interest. Gamma tACS did not significantly affect working memory performance compared to sham, and theta tACS led to inconsistent changes in performance on the n-back tasks. Active theta tACS significantly affected P3 amplitude and latency during performance on the n-back tasks in the bilateral parietal and right-fronto parietal protocols.

Concurrent measurement of cerebral hemodynamics and electroencephalography during transcranial direct current stimulation

Transcranial direct current stimulation (tDCS) is currently being used for research and treatment of some neurological and neuropsychiatric disorders, as well as for improvement of cognitive functions. In order to better understand cerebral response to the stimulation and to redefine protocols and dosage, its effects must be monitored. To this end, we have used functional diffuse correlation spectroscopy (fDCS) and time-resolved functional near-infrared spectroscopy (TR-fNIRS) together with electroencephalography (EEG) during and after stimulation of the frontal cortex. Twenty subjects participated in two sessions of stimulation with two different polarity montages and twelve also underwent a sham session. Cerebral blood flow and oxyhemoglobin concentration increased during and after active stimulation in the region under the stimulation electrode while deoxyhemoglobin concentration decreased. The EEG spectrum displayed statistically significant power changes across different stimulation sessions in delta (2 to 4 Hz), theta (4 to 8 Hz), and beta (12 to 18 Hz) bands. Results suggest that fDCS and TR-fNIRS can be employed as neuromonitors of the effects of transcranial electrical stimulation and can be used together with EEG.

Does Transcranial Direct Current Stimulation Combined with Peripheral Electrical Stimulation Have an Additive Effect in the Control of Hip Joint Osteonecrosis Pain Associated with Sickle Cell Disease? A Protocol for a One-Session Double Blind, Block-Randomized Clinical Trial

Chronic pain in Sickle Cell Disease (SCD) is probably related to maladaptive plasticity of brain areas involved in nociceptive processing. Transcranial Direct Current Stimulation (tDCS) and Peripheral Electrical Stimulation (PES) can modulate cortical excitability and help to control chronic pain. Studies have shown that combined use of tDCS and PES has additive effects. However, to date, no study investigated additive effects of these neuromodulatory techniques on chronic pain in patients with SCD. This protocol describes a study aiming to assess whether combined use of tDCS and PES more effectively alleviate pain in patients with SCD compared to single use of each technique. The study consists of a one-session double blind, block-randomized clinical trial (NCT02813629) in which 128 participants with SCD and femoral osteonecrosis will be enrolled. Stepwise procedures will occur on two independent days. On day 1, participants will be screened for eligibility criteria. On day 2, data collection will occur in four stages: sample characterization, baseline assessment, intervention, and post-intervention assessment. These procedures will last ~5 h. Participants will be divided into two groups according to homozygous for S allele (HbSS) (n = 64) and heterozygous for S and C alleles (HbSC) (n = 64) genotypes. Participants in each group will be randomly assigned, equally, to one of the following interventions: (1) active tDCS + active PES; (2) active tDCS + sham PES; (3) sham tDCS + active PES; and (4) sham tDCS + sham PES. Active tDCS intervention will consist of 20 min 2 mA anodic stimulation over the primary motor cortex contralateral to the most painful hip. Active PES intervention will consist of 30 min sensory electrical stimulation at 100 Hz over the most painful hip. The main study outcome will be pain intensity, measured by a Visual Analogue Scale. In addition, electroencephalographic power density, cortical maps of the gluteus maximus muscle elicited by Transcranial Magnetic Stimulation (TMS), serum levels of Brain-derived Neurotrophic Factor (BDNF), and Tumor Necrosis Factor (TNF) will be assessed as secondary outcomes. Data will be analyzed using ANOVA of repeated measures, controlling for confounding variables.

Anodal Transcranial Direct Current Stimulation Promotes Frontal Compensatory Mechanisms in Healthy Elderly Subjects

Recent studies have demonstrated that transcranial direct current stimulation (tDCS) is potentially useful to improve working memory. In the present study, young and elderly subjects performed a working memory task (n-back task) during an electroencephalogram recording before and after receiving anodal, cathodal, and sham tDCS over the left dorsolateral prefrontal cortex (DLPFC). We investigated modulations of behavioral performance and electrophysiological correlates of working memory processes (frontal and parietal P300 event-related potentials). A strong tendency to modulated working memory performance was observed after the application of tDCS. In detail, young, but not elderly, subjects benefited from additional practice in the absence of real tDCS, as indicated by their more accurate responses after sham tDCS. The cathodal tDCS had no effect in any group of participants. Importantly, anodal tDCS improved accuracy in elderly. Moreover, increased accuracy after anodal tDCS was correlated with a larger frontal P300 amplitude. These findings suggest that, in elderly subjects, improved working memory after anodal tDCS applied over the left DLPFC may be related to the promotion of frontal compensatory mechanisms, which are related to attentional processes.

Prefrontal transcranial direct current stimulation (tDCS) as treatment for major depression: study design and methodology of a multicenter triple blind randomized placebo controlled trial (DepressionDC)

Transcranial direct current stimulation (tDCS) has been proposed as novel treatment for major depressive disorder (MDD) based on clinical pilot studies as well as randomized controlled monocentric trials. The DepressionDC trial is a triple-blind (blinding of rater, operator and patient), randomized, placebo controlled multicenter trial investigating the efficacy and safety of prefrontal tDCS used as additive treatment in MDD patients who have not responded to selective serotonin reuptake inhibitors (SSRI). At 5 study sites, 152 patients with MDD receive a 6-weeks treatment with active tDCS (anode F3 and cathode F4, 2 mA intensity, 30 min/day) or sham tDCS add-on to a stable antidepressant medication with an SSRI. Follow-up visits are at 3 and 6 months after the last tDCS session. The primary outcome measure is the change of the Montgomery-Asberg Depression Rating Scale (MADRS) scores at week 6 post-randomisation compared to baseline. Secondary endpoints also cover other psychopathological domains, and a comprehensive safety assessment includes measures of cognition. Patients undergo optional investigations comprising genetic testing and functional magnetic resonance imaging (fMRI) of structural and functional connectivity. The study uses also an advanced tDCS technology including standard electrode positioning and recording of technical parameters (current, impedance, voltage) in every tDCS session. Aside reporting the study protocol here, we present a novel approach for monitoring technical parameters of tDCS which will allow quality control of stimulation and further analysis of the interaction between technical parameters and clinical outcome. The DepressionDC trial will hopefully answer the important clinical question whether prefrontal tDCS is a safe and effective antidepressant intervention in patients who have not sufficiently responded to SSRIs.

TRIAL REGISTRY

ClinicalTrials.gov Identifier NCT0253016.

No effect of transcranial direct current stimulation of the dorsolateral prefrontal cortex on short-term memory

INTRODUCTION

Short-term memory refers to the capacity for holding information in mind for a short period of time with conscious memorization. It is an important ability for daily life and is impaired in several neurological and psychiatric disorders. Anodal transcranial direct current stimulation (tDCS) applied to the dorsolateral prefrontal cortex (DLPFC) was reported to enhance the capability of short-term memory in healthy subjects. However, results were not consistent and what is the possible impact factor is not known. One important factor that may significantly influence the effect of tDCS is the timing of tDCS administration.

AIMS

In order to explore whether tDCS impact short-term memory and the optimal timing of tDCS administration, we applied anodal tDCS to the left DLPFC to explore the modulatory effect of online and off-line tDCS on digit span as well as visual short-term memory performance in healthy subjects.

RESULTS

Results showed tDCS of the left DLPFC did not influence intentional digit span memory performance, whether before the task or during the task. In addition, tDCS of the DLPFC administered before the task showed no effect on visual short-term memory, while there was a trend of increase in false alarm when tDCS of the DLPFC administered during the task.

CONCLUSIONS

These results did not provide evidence for the enhancement of short-term memory by tDCS of the left DLPFC in healthy subjects, but it suggested an importance of administration time for visual short-term memory. Further studies are required to taking into account the baseline performance of subjects and time-dependence feature of tDCS.

Effects of Transcranial Direct Current Stimulation, Transcranial Pulsed Current Stimulation, and Their Combination on Brain Oscillations in Patients with Chronic Visceral Pain: A Pilot Crossover Randomized Controlled Study

OBJECTIVE

Chronic visceral pain (CVP) syndromes are persistently painful disorders with a remarkable lack of effective treatment options. This study aimed at evaluating the effects of different neuromodulation techniques in patients with CVP on cortical activity, through electreocephalography (EEG) and on pain perception, through clinical tests.

DESIGN

A pilot crossover randomized controlled study.

SETTINGS

Out-patient.

SUBJECTS

Adults with CVP (>3 months).

METHODS

Participants received four interventions in a randomized order: (1) transcranial pulsed current stimulation (tPCS) and active transcranial direct current stimulation (tDCS) combined, (2) tPCS alone, (3) tDCS alone, and (4) sham condition. Resting state quantitative electroencephalography (qEEG) and pain assessments were performed before and after each intervention. Results were compared with a cohort of 47 healthy controls.

RESULTS

We enrolled six patients with CVP for a total of 21 visits completed. Compared with healthy participants, patients with CVP showed altered cortical activity characterized by increased power in theta, alpha and beta bands, and a significant reduction in the alpha/beta ratio. Regarding tES, the combination of tDCS with tPCS had no effect on power in any of the bandwidths, nor brain regions. Comparing tPCS with tDCS alone, we found that tPCS induced higher increase in power within the theta and alpha bandwidths.

CONCLUSION

This study confirms that patients with CVP present abnormal EEG-indexed cortical activity compared with healthy controls. Moreover, we showed that combining two types of neurostimulation techniques had no effect, whereas the two interventions, when applied individually, have different neural signatures.

The absence of resting-state high-gamma cross-frequency coupling in patients with tinnitus

Tinnitus is a psychoacoustic phantom perception of currently unknown neuropathology. Despite a growing number of post-stimulus tinnitus studies, uncertainty still exists regarding the neural signature of tinnitus in the resting-state brain. In the present study, we used high-gamma cross-frequency coupling and a Granger causality analysis to evaluate resting-state electroencephalographic (EEG) data in healthy participants and patients with tinnitus. Patients with tinnitus lacked robust frontal delta-phase/central high-gamma-amplitude coupling that was otherwise clearly observed in healthy participants. Since low-frequency phase and high-frequency amplitude coupling reflects inter-regional communication during cognitive processing, and given the absence of frontal modulation in patients with tinnitus, we hypothesized that tinnitus might be related to impaired prefrontal top-down inhibitory control. A Granger causality analysis consistently showed abnormally pronounced functional connectivity of low-frequency activity in patients with tinnitus, possibly reflecting a deficiency in large-scale communication during the resting state. Moreover, different causal neurodynamics were characterized across two subgroups of patients with tinnitus; the T1 group (with higher P300 amplitudes) showed abnormal frontal-to-auditory cortical information flow, whereas the T2 group (with lower P300 amplitudes) exhibited abnormal auditory-to-frontal cortical information control. This dissociation in resting-state low-frequency causal connectivity is consistent with recent post-stimulus observations. Taken together, our findings suggest that maladaptive neuroplasticity or abnormal reorganization occurs in the auditory default mode network of patients with tinnitus. Additionally, our data highlight the utility of resting-state EEG for the quantitative diagnosis of tinnitus symptoms and the further characterization of tinnitus subtypes.

Single-session transcranial direct current stimulation induces enduring enhancement of visual processing speed in patients with major depression

Attentional deficits are considered key cognitive symptoms in major depressive disorder (MDD) arising from abnormal activation patterns within dorsolateral prefrontal cortex (dlPFC) alertness networks. Altering these activity patterns with transcranial direct current stimulation (tDCS) might thus ameliorate alertness-dependent cognitive deficits in MDD patients. In a double-blind, randomized, sham-controlled study, we investigated the effect of a single session of anodal tDCS (2 mA) applied to the left dlPFC on different parameters of visual attention based on Bundesen's theory of visual attention (Psychol Rev 97(4):523-547, 1990) in a group of 20 patients with MDD and a control group of 20 healthy participants. The parametric attention assessment took place before, immediately after and 24 h after tDCS intervention. It revealed a selective impairment in visual processing speed as a primary functional deficit in MDD at baseline assessment. Furthermore, a significant stimulation condition × time point interaction showed that verum tDCS over the left dlPFC resulted in a processing speed enhancement 24 h post-stimulation in MDD patients. In healthy control participants, we did not find similar tDCS-induced effects. Our results suggest that even a single session of tDCS over the dlPFC can induce enduring neurocognitive benefits that indicate an amelioration of cortical under-arousal in MDD patients in a time frame beyond that of immediate, excitability increases that are directly induced by the current.