Acute working memory improvement after tDCS in antidepressant-free patients with major depressive disorder

Influence of noninvasive brain stimulation on connectivity and local activation: a combined tDCS and fMRI study

The effect of transcranial direct current stimulation (tDCS) on neurobiological mechanisms underlying executive function in the human brain remains elusive. This study aims at examining the effect of anodal and cathodal tDCS over the left dorsolateral prefrontal cortex (DLPFC) in comparison with sham stimulation on resting-state connectivity as well as functional activation and working memory performance. We hypothesized perturbed fronto-parietal resting-state connectivity during stimulation and altered working memory performance combined with modified functional working memory-related activation. We applied tDCS with 1 mA for 21 min over the DLPFC inside an fMRI scanner. During stimulation, resting-state fMRI was acquired and task-dependent fMRI during working memory task performance was acquired directly after stimulation. N = 36 healthy subjects were studied in a within-subject design with three different experimental conditions (anodal, cathodal and sham) in a double-blind design. Seed-based functional connectivity analyses and dynamic causal modeling were conducted for the resting-state fMRI data. We found a significant stimulation by region interaction in the seed-based ROI-to-ROI resting-state connectivity, but no effect on effective connectivity. We also did not find an effect of stimulation on task-dependent signal alterations in working memory activation in our regions of interest and no effect on working memory performance parameters. We found effects on measures of seed-based resting-state connectivity, while measures of effective connectivity and task-based connectivity did not show any stimulation effect. We could not replicate previous findings of tDCS stimulation effects on behavioral outcomes. We critically discuss possible methodological limitations and implications for future studies.

Stress priming transcranial direct current stimulation (tDCS) enhances updating of emotional content in working memory

Transcranial direct current stimulation (tDCS) targeting the prefrontal cortex has emerged as a valuable tool in psychiatric research. Understanding the impact of affective states, such as stress at the time of stimulation, on the efficacy of prefrontal tDCS is crucial for advancing tDCS interventions. Stress-primed tDCS, wherein stress is used as a priming agent, has the potential to modulate neural plasticity and enhance cognitive functions, particularly in emotional working memory. However, prior research using stress-primed tDCS focused solely on non-emotional working memory performance, yielding mixed results. In this sham-controlled study, we addressed this gap by investigating the effects of stress-primed bifrontal tDCS (active versus sham) on both non-emotional and emotional working memory performance. The study was conducted in 146 healthy individuals who were randomly assigned to four experimental groups. The Trier Social Stress Test (TSST) or a control variant of the test was used to induce a stress versus control state. The results showed that stress priming significantly enhanced the effects of tDCS on the updating of emotional content in working memory, as evidenced by improved accuracy. Notably, no significant effects of stress priming were found for non-emotional working memory performance. These findings highlight the importance of an individual's prior affective state in shaping their response to tDCS, especially in the context of emotional working memory.

Non-invasive brain stimulation for patients and healthy subjects: Current challenges and future perspectives

Non-invasive brain stimulation (NIBS) techniques have a rich historical background, yet their utilization has witnessed significant growth only recently. These techniques encompass transcranial electrical stimulation and transcranial magnetic stimulation, which were initially employed in neuroscience to explore the intricate relationship between the brain and behaviour. However, they are increasingly finding application in research contexts as a means to address various neurological, psychiatric, and neurodegenerative disorders. This article aims to fulfill two primary objectives. Firstly, it seeks to showcase the current state of the art in the clinical application of NIBS, highlighting how it can improve and complement existing treatments. Secondly, it provides a comprehensive overview of the utilization of NIBS in augmenting the brain function of healthy individuals, thereby enhancing their performance. Furthermore, the article delves into the points of convergence and divergence between these two techniques. It also addresses the existing challenges and future prospects associated with NIBS from ethical and research standpoints.

Effects of transcranial direct current stimulation and transcranial random noise stimulation on working memory and task-related EEG in major depressive disorder

OBJECTIVE

To compare effects of transcranial direct current stimulation (tDCS) and transcranial random noise stimulation with a direct-current offset (tRNS + DC-offset) on working memory (WM) performance and task-related electroencephalography (EEG) in individuals with Major Depressive Disorder (MDD).

METHODS

Using a sham-controlled, parallel-groups design, 49 participants with MDD received either anodal tDCS (N = 16), high-frequency tRNS + DC-offset (N = 16), or sham stimulation (N = 17) to the left dorsolateral prefrontal cortex (DLPFC) for 20-minutes. The Sternberg WM task was completed with concurrent EEG recording before and at 5- and 25-minutes post-stimulation. Event-related synchronisation/desynchronisation (ERS/ERD) was calculated for theta, upper alpha, and gamma oscillations during WM encoding and maintenance.

RESULTS

tDCS significantly increased parieto-occipital upper alpha ERS/ERD during WM maintenance, observed on EEG recorded 5- and 25-minutes post-stimulation. tRNS + DC-offset did not significantly alter WM-related oscillatory activity when compared to sham stimulation. Neither tDCS nor tRNS + DC-offset improved WM performance to a significantly greater degree than sham stimulation.

CONCLUSIONS

Although tDCS induced persistent effects on WM-related oscillatory activity, neither tDCS nor tRNS + DC-offset enhanced WM performance in MDD.

SIGNIFICANCE

This reflects the first sham-controlled comparison of tDCS and tRNS + DC-offset in MDD. These findings directly contrast with evidence of tRNS-induced enhancements in WM in healthy individuals.

Neural Mechanism Underlying Task-Specific Enhancement of Motor Learning by Concurrent Transcranial Direct Current Stimulation

The optimal protocol for neuromodulation by transcranial direct current stimulation (tDCS) remains unclear. Using the rotarod paradigm, we found that mouse motor learning was enhanced by anodal tDCS (3.2 mA/cm2) during but not before or after the performance of a task. Dual-task experiments showed that motor learning enhancement was specific to the task accompanied by anodal tDCS. Studies using a mouse model of stroke induced by middle cerebral artery occlusion showed that concurrent anodal tDCS restored motor learning capability in a task-specific manner. Transcranial in vivo Ca2+ imaging further showed that anodal tDCS elevated and cathodal tDCS suppressed neuronal activity in the primary motor cortex (M1). Anodal tDCS specifically promoted the activity of task-related M1 neurons during task performance, suggesting that elevated Hebbian synaptic potentiation in task-activated circuits accounts for the motor learning enhancement. Thus, application of tDCS concurrent with the targeted behavioral dysfunction could be an effective approach to treating brain disorders.

Using multisession tDCS stimulation as an early intervention on memory bias processing in subthreshold depression

Transcranial direct current stimulation (tDCS) as an intervention tool has gained promising results in major depression disorder. However, studies related to subthreshold depression's (SD) cognitive deficits and neuromodulation approaches for the treatment of SD are still rare. We adopted Beck's cognitive model of depression and tested the tDCS stimulation effects on attentional and memory deficits on SD. First, this was a single-blinded, randomized, sham-controlled clinical trial to determine a 13-day tDCS modulation effect on 49 SD (27: Stimulation; 22: Sham) and 17 healthy controls. Second, the intervention effects of the consecutive and single-session tDCS were compared. Furthermore, the attentional and memory biases were explored in SD. Anodal tDCS was administrated over left dorsolateral prefrontal cortex for 13 consecutive days. Attentional and memory bias were assessed through a modified Sternberg task and a dot-probe task on the 1st, 2nd, and 15th day while their EEG was being recorded. After the 13-day tDCS stimulation (not after single-session stimulation), we found reduced memory bias (Stimulation vs. Sham, p = .02, r²  = .09) and decreased mid-frontal alpha power (p < .01, r²  = .13). In contrast, tDCS did not affect any attentional related behavioral or neural indexes (all ps > .15). Finally, reduced depressive symptoms (e.g., BDI score) were found for both groups. The criteria of SD varied across studies; the efficacy of this protocol should be tested in elderly patients. Our study suggests memory bias of SD can be modulated by the multisession tDCS and alpha power could serve as a neural index for intervention.

Electric Field Strength From Prefrontal Transcranial Direct Current Stimulation Determines Degree of Working Memory Response: A Potential Application of Reverse-Calculation Modeling?

BACKGROUND

Transcranial direct current stimulation (tDCS) for working memory is an enticing treatment, but there is mixed evidence to date.

OBJECTIVES

We tested the effects of electric field strength from uniform 2 mA dosing on working memory change from prestimulation to poststimulation. Second, we statistically evaluated a reverse-calculation method of individualizing tDCS dose and its effect on normalizing electric field at the cortex.

MATERIALS AND METHODS

We performed electric field modeling on a data set of 28 healthy older adults (15 women, mean age = 73.7, SD = 7.3) who received ten sessions of active 2 mA tDCS (N = 14) or sham tDCS (N = 14) applied over bilateral dorsolateral prefrontal cortices (DLPFC) in a triple-blind design. We evaluated the relationship between electric field strength and working memory change on an N-back task in conditions of above-median, high electric field from active 2 mA (N = 7), below-median, low electric field from active 2 mA (N = 7), and sham (N = 14) at regions of interest (ROI) at the left and right DLPFC. We then determined the individualized reverse-calculation dose to produce the group average electric field and measured the electric field variance between uniform 2 mA doses vs individualized reverse-calculation doses at the same ROIs.

RESULTS

Working memory improvements from pre- to post-tDCS were significant for the above-median electric field from active 2 mA condition at the left DLPFC (mixed ANOVA, p = 0.013). Furthermore, reverse-calculation modeling significantly reduced electric field variance at both ROIs (Levene's test; p < 0.001).

CONCLUSIONS

Higher electric fields at the left DLPFC from uniform 2 mA doses appear to drive working memory improvements from tDCS. Individualized doses from reverse-calculation modeling significantly reduce electric field variance at the cortex. Taken together, using reverse-calculation modeling to produce the same, high electric fields at the cortex across participants may produce more effective future tDCS treatments for working memory.

Enhancing Visuospatial Working Memory Performance Using Intermittent Theta-Burst Stimulation Over the Right Dorsolateral Prefrontal Cortex

Noninvasive brain stimulation provides a promising approach for the treatment of neuropsychiatric conditions. Despite the increasing research on the facilitatory effects of this kind of stimulation on the cognitive processes, the majority of the studies have used the standard stimulation approaches such as the transcranial direct current stimulation and the conventional repetitive transcranial magnetic stimulation (rTMS) which seem to be limited in robustness and the duration of the transient effects. However, a recent specialized type of rTMS, theta-burst stimulation (TBS), patterned to mimic the natural cross-frequency coupling of the human brain, may induce robust and longer-lasting effects on cortical activity. Here, we aimed to investigate the effects of the intermittent TBS (iTBS), a facilitatory form of TBS, over the right DLPFC (rDLPFC), a brain area implicated in higher-order cognitive processes, on visuospatial working memory (VSWM) performance. Therefore, iTBS was applied over either the rDLPFC or the vertex of 24 healthy participants, in two separate sessions. We assessed VSWM performance using 2-back and 4-back visuospatial tasks before iTBS (at the baseline (BL), and after the iTBS. Our results indicate that the iTBS over the rDLPFC significantly enhanced VSWM performance in the 2-back task, as measured by the discriminability index and the reaction time. However, the 4-back task performance was not significantly modulated by iTBS. These findings demonstrate that the rDLPFC plays a critical role in VSWM and that iTBS is a safe and effective approach for investigating the causal role of the specific brain areas.

Early Auditory Processing Predicts Efficient Working Memory Functioning in Schizophrenia

Early auditory processing (EAP) deficits have been consistently documented in individuals diagnosed with schizophrenia (SZ). However, a relationship between EAP and executive attention has not been confirmed in SZ versus healthy controls (HC). The current study aimed to demonstrate that unlike HC, in SZ patients, auditory change-detection event-related potentials (ERPs) are significantly associated with executive working memory (WM) functioning. Additionally, correlational analyses investigated the relationships between patients’ auditory ERPs, WM performance, and schizophrenia symptom severity scores. We examined verbal WM accuracy associated with “executive-control” prefrontal cortex mechanisms and EAP ERPs under midline prefrontal electrodes in 12 SZ patients versus 12 demographically matched HC. Mismatch negativity (MMN) amplitudes and latencies in SZ patients were not significantly different from HC, however, their verbal WM performance was significantly impaired versus HC. Importantly, prolonged MMN latencies in the SZ group were correlated with better WM accuracy. In the HC group, WM accuracy was unrelated to MMN latencies. Patients’ MMN parameters were unrelated to schizophrenia symptom-domain severity. However, patients’ WM RTs and accuracy were significantly related to illness severity and negative symptom severity, respectively. Therefore, inefficient sensory excitation related to EAP timing may underlie poor executive verbal WM functioning and might indirectly exacerbate the severity of negative symptoms in SZ. Treatments targeting prefrontal cortex dysfunction in schizophrenia are discussed.

Korean Medication Algorithm for Depressive Disorder 2021, Fourth Revision: An Executive Summary

Objective

In the 19 years since the Korean College of Neuropsychopharmacology and the Korean Society for Affective Disorders developed the Korean Medication Algorithm Project for Depressive Disorder (KMAP-DD) in 2002, four revisions have been conducted.

Methods

To increase survey efficiency in this revision, to cover the general clinical practice, and to compare the results with previous KMAP-DD series, the overall structure of the questionnaire was maintained. The six sections of the questionnaire were as follows: 1) pharmacological treatment strategies for major depressive disorder (MDD) with/without psychotic features; 2) pharmacological treatment strategies for persistent depressive disorder and other depressive disorder subtypes; 3) consensus for treatment-resistant depression; 4) the choice of an antidepressant in the context of safety, adverse effects, and comorbid physical illnesses; 5) treatment strategies for special populations (children/adolescents, elderly, and women); and 6) non-pharmacological biological therapies. Recommended first-, second-, and third-line strategies were derived statistically.

Results

There has been little change in the four years since KMAP-DD 2017 due to the lack of newly introduced drug or treatment strategies. However, shortened waiting time between the initial and subsequent treatments, increased preference for atypical antipsychotics (AAPs), especially aripiprazole, and combination strategies with AAPs yield an active and somewhat aggressive treatment trend in Korea.

Conclusion

We expect KMAP-DD to provide clinicians with useful information about the specific strategies and medications appropriate for treating patients with MDD by bridging the gap between clinical real practice and the evidence-based world.

Application of Transcranial Direct Current Stimulation in Psychiatry

Transcranial direct current stimulation (tDCS) is a neuromodulation technique, which noninvasively alters cortical excitability via weak polarizing currents between two electrodes placed on the scalp. Since it is comparably easy to handle, cheap to use and relatively well tolerated, tDCS has gained increasing interest in recent years. Based on well-known behavioral effects, a number of clinical studies have been performed in populations including patients with major depressive disorder followed by schizophrenia and substance use disorders, in sum with heterogeneous results with respect to efficacy. Nevertheless, the potential of tDCS must not be underestimated since it could be further improved by systematically investigating the various stimulation parameters to eventually increase clinical efficacy. The present article briefly explains the underlying physiology of tDCS, summarizes typical stimulation protocols and then reviews clinical efficacy for various psychiatric disorders as well as prevalent adverse effects. Future developments include combined and more complex interactions of tDCS with pharmacological or psychotherapeutic interventions. In particular, using computational models to individualize stimulation protocols, considering state dependency and applying closed-loop technologies will pave the way for tDCS-based personalized interventions as well as the development of home treatment settings promoting the role of tDCS as an effective treatment option for patients with mental health problems.

Identifying regions in prefrontal cortex related to working memory improvement: A novel meta-analytic method using electric field modeling

Altering cortical activity using transcranial direct current stimulation (tDCS) has been shown to improve working memory (WM) performance. Due to large inter-experimental variability in the tDCS montage configuration and strength of induced electric fields, results have been mixed. Here, we present a novel meta-analytic method relating behavioral effect sizes to electric field strength to identify brain regions underlying largest tDCS-induced WM improvement. Simulations on 69 studies targeting left prefrontal cortex showed that tDCS electric field strength in lower dorsolateral prefrontal cortex (Brodmann area 45/47) relates most strongly to improved WM performance. This region explained 7.8 % of variance, equaling a medium effect. A similar region was identified when correlating WM performance and electric field strength of right prefrontal tDCS studies (n = 18). Maximum electric field strength of five previously used tDCS configurations were outside of this location. We thus propose a new tDCS montage which maximizes the tDCS electric field strength in that brain region. Our findings can benefit future tDCS studies that aim to affect WM function.

The effects of stress and transcranial direct current stimulation (tDCS) on working memory: A randomized controlled trial

Recent reviews of transcranial direct current stimulation (tDCS) show limited support for its initially cited enhancing effects on working memory (WM). They highlight the need for additional research, assessing the specific circumstances that optimize stimulation outcome. Social stress is an attractive candidate in this regard, as it affects WM and is mediated by prefrontal cortex activity; tDCS that targets these neuronal networks may, therefore, interact with social stress to affect WM. Our objective was to explore the interaction between social stress and tDCS on WM performance in a healthy cohort, 69 female participants were randomized to four experimental conditions (i.e., 2 × 2 design): stimulation (dlPFC tDCS vs. sham stimulation) and stress manipulation (Trier Social Stress Test [TSST] procedure vs. a friendly control TSST). Participants' attention, WM (assessed using an n-back task), and subjective/objective indicators of stress were assessed. A significant Stimulation × Stress Manipulation interaction was found, F(1, 65) = 6.208, p = .015, suggesting that active tDCS may increase WM performance in the no-stress conditions, while decreasing it under stress. Follow-up analyses of variance, however, were not significant (i.e., ps=.083 / .093), and Bayesian analyses were inconclusive. In conclusion, stress seems to be a crucial factor in determining the effects of tDCS, and tDCS may have an enhancing effect on WM at lower levels of stress, while being detrimental at higher stress levels (i.e., reversing the direction of effect). Possible theoretical underpinnings of the findings are discussed, while acknowledging the need for further research.

Using Neuroscience to Augment Behavioral Interventions for Depression

Depression is both prevalent and costly, and many individuals do not adequately respond to existing psychopharmacological and behavioral interventions. The current article describes the use of neuroscience in augmenting behavioral interventions for depression in two primary areas: anhedonia and cognitive deficits/biases. Neuroscience research has increased our understanding of the neural bases of reward processing and regulation of positive affect, and anhedonia among depressed samples can be related to deficits in each of these domains. Treatments that specifically target reward processing and regulation of positive affect in order to reduce anhedonia represent a recent advance in the field. Depression is also associated with aberrant processes relating to working memory, autobiographical memory, attentional bias, and interpretive bias. Neuroscience findings have increasingly been leveraged to augment the efficacy of cognitive-training and bias-modification interventions in these domains. The use of neuroscience to inform the development and augmentation of behavioral interventions for depression is a promising avenue of continued research.

Decreased integration of the frontoparietal network during a working memory task in major depressive disorder

BACKGROUND

Working memory deficits are a common feature in major depressive disorder and are associated with poor functional outcomes. Intact working memory performance requires the recruitment of large-scale brain networks. However, it is unknown how the disrupted recruitment of distributed regions belonging to these large-scale networks at the whole-brain level brings about working memory impairment seen in major depressive disorder.

METHODS

We used graph theory to examine the functional connectomic metrics (local and global efficiency) at the whole-brain and large-scale network levels in 38 patients with major depressive disorder and 41 healthy controls during a working memory task. Altered connectomic metrics were studied in a moderation model relating to clinical symptoms and working memory accuracy in patients, and a machine learning method was employed to assess whether these metrics carry enough illness-specific information to discriminate patients from controls.

RESULTS

Global efficiency of the frontoparietal network was reduced in major depressive disorder (false discovery rate corrected, p = 0.014); this reduction predicted worse working memory performance in patients with less severe illness burden indexed by Brief Psychiatric Rating Scale (β =-0.43, p = 0.035, t =-2.2, 95% confidence interval = [-0.043,-0.002]). We achieved a classification accuracy and area under the curve of 73.42% and 0.734, respectively, to discriminate patients from controls based on connectomic metrics, and the global efficiency of the frontoparietal network contributed most to the diagnostic classification.

CONCLUSIONS

We report a putative mechanistic link between the global efficiency of the frontoparietal network and impaired n-back performance in major depressive disorder. This relationship is more pronounced at lower levels of symptom burden, indicating the possibility of multiple pathways to cognitive deficits in severe major depressive disorder.

Is tDCS a potential first line treatment for major depression?

Transcranial direct current stimulation (tDCS) is a novel treatment option for major depression which could be provided as a first-line treatment. tDCS is a non-invasive form of transcranial stimulation which changes cortical tissue excitability by applying a weak (0.5-2 mA) direct current via scalp electrodes. Anodal and cathodal stimulation leads to depolarisation and hyperpolarisation, respectively, and cumulative effects are observed with repeated sessions. The montage in depression most often involves anodal stimulation to the left dorsolateral prefrontal cortex. Rates of clinical response, remission, and improvements in depressive symptoms following a course of active tDCS are greater in comparison to a course of placebo sham-controlled tDCS. In particular, the largest treatment effects are evident in first episode and recurrent major depression, while minimal effects have been observed in treatment-resistant depression. The proposed mechanism is neuroplasticity at the cellular and molecular level. Alterations in neural responses have been found at the stimulation site as well as subcortically in prefrontal-amygdala connectivity. A possible mediating effect could be cognitive control in emotion dysregulation. Additional beneficial effects on cognitive impairments have been reported, which would address an important unmet need. The tDCS device is portable and can be used at home. Clinical trials are required to establish the efficacy, feasibility and acceptability of home-based tDCS treatment and mechanisms.

Left prefrontal transcranial direct-current stimulation reduces symptom-severity and acutely enhances working memory in schizophrenia

Recent studies indicated that left dorsolateral prefrontal cortex (DLPFC) transcranial direct current stimulation (tDCS) may improve clinical status and cognitive functioning in schizophrenia patients. The current study examined the effects of left prefrontal anodal tDCS on symptom-severity and on working memory performance in schizophrenia (SZ) patients. We conducted a double-blind, randomized sham-controlled parallel-group trial. Following baseline clinical and WM assessments, 19 chronic SZ patients were randomly assigned to receive 10 sessions of either active left dorsolateral prefrontal cortex (DLPFC) tDCS or sham DLPFC-tDCS across five consecutive days, followed by post-tDCS assessments every four weeks across 12 weeks. Active tDCS significantly alleviated symptom-severity versus baseline and versus sham tDCS. WM-performance improved versus baseline in the active tDCS group. Patients' symptom alleviation was maintained for four weeks after tDCS intervention. Patients' Post-tDCS WM scores were comparable to healthy controls' WM scores. The present findings highlight the benefits of left-prefrontal tDCS interventions and support the association between DLPFC dysfunction and symptom-severity in schizophrenia.

Could tDCS Be a Potential Performance-Enhancing Tool for Acute Neurocognitive Modulation in eSports? A Perspective Review

Competitive sports involve physical and cognitive skills. In traditional sports, there is a greater dependence on the development and performance of both motor and cognitive skills, unlike electronic sports (eSports), which depend much more on neurocognitive skills for success. However, little is known about neurocognitive functions and effective strategies designed to develop and optimize neurocognitive performance in eSports athletes. One such strategy is transcranial direct current stimulation (tDCS), characterized as a weak electric current applied on the scalp to induce prolonged changes in cortical excitability. Therefore, our objective is to propose anodal (a)-tDCS as a performance-enhancing tool for neurocognitive functions in eSports. In this manuscript, we discussed the neurocognitive processes that underlie exceptionally skilled performances in eSports and how tDCS could be used for acute modulation of these processes in eSports. Based on the results from tDCS studies in healthy people, professional athletes, and video game players, it seems that tDCS is applied over the left dorsolateral prefrontal cortex (DLPFC) as a potential performance-enhancing tool for neurocognition in eSports.

Cognitive outcomes of the bipolar depression electrical treatment trial (BETTER): a randomized, double-blind, sham-controlled study

Bipolar depression is associated with marked cognitive deficits. Pharmacological treatments for this condition are limited and may aggravate depressive and cognitive symptoms. Therefore, therapeutic interventions that preserve adequate cognitive functioning are necessary. Our previous results demonstrated significant clinical efficacy of transcranial direct current stimulation (tDCS) in the Bipolar Depression Electrical Treatment Trial (BETTER). Here, cognitive outcomes of this study are reported. We randomized 59 patients with bipolar disorder I or II in an acute depressive episode to receive active (12 2 mA, 30-min, anodal-left, cathodal-right prefrontal cortex tDCS sessions) or sham tDCS. Patients were on stable pharmacological regimen for at least 2 weeks. A battery of 12 neuropsychological assessments in five cognitive domains (attention and processing speed, memory, language, inhibitory control, and working memory and executive function) was performed at baseline, after two weeks and at endpoint (week 6). No significant differences between groups over 6 weeks of treatment were observed for any cognitive outcomes. Moreover, no decrease in cognitive performance was observed. Our findings warrant further replication in larger studies. Trial Registration: clinicaltrials.gov Identifier: NCT02152878.

Effects of Transcranial Direct Current Stimulation on Information Processing Speed, Working Memory, Attention, and Social Cognition in Multiple Sclerosis

Multiple Sclerosis (MS) is a chronic inflammatory disease of the central nervous system. Cognitive impairment occurs in 40-65% of patients and could drastically affect their quality of life. Deficits could involve general cognition (e.g., attention and working memory) as well as social cognition. Transcranial direct current stimulation (tDCS), is a novel brain stimulation technique that has been assessed in the context of several neuropsychiatric symptoms, including those described in the context of MS. However, very rare trials have assessed tDCS effects on general cognition in MS, and none has tackled social cognition. The aim of this work was to assess tDCS effects on general and social cognition in MS. Eleven right-handed patients with MS received two blocks (bifrontal tDCS and sham, 2 mA, 20 min, anode/cathode over left/right prefrontal cortex) of 5 daily stimulations separated by a 3-week washout interval. Working memory and attention were, respectively, measured using N-Back Test (0-Back, 1-Back, and 2-Back) and Symbol Digit Modalities Test (SDMT) at the first and fifth day of each block and 1 week later. Social cognition was evaluated using Faux Pas Test and Eyes Test at baseline and 1 week after each block. Interestingly, accuracy of 1-Back test improved following sham but not active bifrontal tDCS. Therefore, active bifrontal tDCS could have impaired working memory via cathodal stimulation of the right prefrontal cortex. No significant tDCS effects were observed on social cognitive measures and SDMT. Admitting the small sample size and the learning (practice) effect that might arise from the repetitive administration of each task, the current results should be considered as preliminary and further investigations in larger patient samples are needed to gain a closer understanding of tDCS effects on cognition in MS.

Effects of bilateral transcranial direct current stimulation on working memory and global cognition in older patients with remitted major depression: A pilot randomized clinical trial

OBJECTIVES

To assess the effects of a 10-day course of bilateral anodal transcranial direct current stimulation (tDCS) of the dorsolateral prefrontal cortex (DLPFC) on working memory and global cognition in elderly participants with remitted major depressive disorder at 14 days (primary outcome) and 90 days (secondary outcome) post intervention.

DESIGN

Randomized double blind controlled trial (clinicaltrials.gov # NCT02212366).

SETTING

Community dwelling outpatient setting.

PARTICIPANTS

Sixty or older with previous single or recurrent episodes of major depression currently in full remission.

INTERVENTION

A 10 day course of active or sham bilateral DLPFC anodal tDCS.

MEASUREMENTS

(a) Working memory assessed by a computerized N back task, and (b) global cognition assessed by a standard paper and pencil neuropsychological test battery.

RESULTS

Thirty-three participants, (mean (SD) age = 66. 5 (5.7) year) were enrolled, out of which 18 (mean (SD) age = 66. 3 (5.8) year) were randomized to active tDCS and 15 (mean (SD) age = 66. 7 (5.8) years) to sham tDCS. All randomized participants except one from the sham group -completed the tDCS course. There were no differences between the groups on working memory performance or global cognition at 14 or 90 days post intervention. Both groups showed promising changes in working memory and global cognition over time.

CONCLUSIONS

tDCS was well tolerated in older patients with remitted MDD, however, as compared to the sham group, it did not improve working memory or global cognition. Future studies should investigate tDCS with alternative parameters to enhance cognition in this population.

Transcranial direct current stimulation and working memory: Comparison of effect on learning shapes and English letters

We present the results of a study investigating whether there is an effect of Anodal-Transcranial Direct Current Stimulation (A-tDCS) on working memory (WM) performance. The relative effectiveness of A-tDCS on WM is investigated using a 2-back test protocol using two commonly used memory visual stimuli (shapes and letters). In a double-blinded, randomised, crossover, sham-controlled experiment, real A-tDCS and sham A-tDCS were applied separately to the left dorsolateral prefrontal cortex (L-DLPFC) of twenty healthy subjects. There was a minimal interval of one week between sham and real A-tDCS sessions. For the letters based stimulus experiment, 2-back test recall accuracy was measured for a set of English letters (A-L) which were presented individually in a randomised order where each was separated by a blank interval. A similar 2-back protocol was used for the shapes based stimuli experiment where instead of letters, a set of 12 geometric shapes were used. The working memory accuracy scores measured appeared to be significantly affected by memory stimulus type used and by the application of A-tDCS (repeated measures ANOVA p<0.05). A large effect size (d = 0.98) and statistical significance between sham and real A-tDCS WM scores (p = 0.01) was found when shapes were used as a visual testing stimulus, while low (d = 0.38) effect size and insignificant difference (p = 0.15) was found when letters were used. This results are important as they show that recollection different stimuli used in working memory can be affected differently by A-tDCS application. This highlights the importance of considering using multiple methods of WM testing when assessing the effectiveness of A-tDCS.

Transcranial Direct Current Stimulation and Cognition in Neuropsychiatric Disorders: Systematic Review of the Evidence and Future Directions

Transcranial direct current stimulation (tDCS) has been implemented in neuropsychiatric disorders characterized by cognitive impairment. However, methodological heterogeneity challenges conclusive remarks. Through a critical analysis of previous conflicting findings and in the light of current neurobiological models of pathophysiology, we qualitatively assessed the effects of tDCS in neuropsychiatric disorders that share neurobiological underpinnings, as to evaluate whether stimulation can improve cognitive deficits in patients' cohorts. We performed a systematic review of tDCS studies targeting cognitive functions in mental disorders and pathological cognitive aging. Data from 41 studies, comprising patients with diagnosis of mood disorders, schizophrenia-spectrum disorders, Alzheimer's disease (AD), and mild cognitive impairment (MCI), were included. Results indicate that tDCS has the capacity to enhance processing speed, working memory, and executive functions in patients with mood and schizophrenia-spectrum disorders. The evidence of a positive effect on general cognitive functioning and memory is either inconclusive in AD, or weak in MCI. Future directions are discussed for developing standardized stimulation protocols and for translating the technique therapeutic potential into effective clinical practice.

Evidence-based Umbrella Review of Cognitive Effects of Prefrontal tDCS

Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique, which has been increasingly used as an investigational tool in neuroscience. In social and affective neuroscience research, the prefrontal cortex has been primarily targeted, since this brain region is critically involved in complex psychobiological processes subserving both Șhotș and Școldș domains. Although several studies have suggested that prefrontal tDCS can enhance neuropsychological outcomes, meta-analyses have reported conflicting results. Therefore, we aimed to assess the available evidence by performing an umbrella review of meta-analyses. We evaluated the effects of prefrontal active vs sham tDCS on different domains of cognition among healthy and neuropsychiatric individuals. A MeaSurement Tool to Assess Systematic Reviews 2 was employed to evaluate the quality of meta-analyses, and the GRADE system was employed to grade the quality of evidence of every comparison from each meta-analysis. PubMed/MEDLINE, PsycINFO and the Cochrane Database of Systematic Reviews were searched, and 11 meta-analyses were included resulting in 55 comparisons. Only 16 comparisons reported significant effects favoring tDCS, but 13 of them had either very low or low quality of evidence. Of the remaining 39 comparisons which reported non-significant effects, 38 had either very low or low quality of evidence. Meta-analyses were rated as having critically low and low quality. Among several reasons to explain these findings, the lack of consensus and reproducibility in tDCS research is discussed.

Effects of 1 mA and 2 mA transcranial direct current stimulation on working memory performance in healthy participants

Anodal transcranial current stimulation (tDCS) to the left dorsolateral prefrontal cortex (DLPFC) has been shown to enhance working memory (WM) in neuropsychiatric patients. In healthy populations, however, tDCS obtains inconclusive results, mostly due to heterogeneous study and stimulation protocols. Here, we approached these issues by investigating effects of tDCS intensity on simultaneous WM performance with three cognitive loads by directly comparing findings of two double-blind, cross-over, sham-controlled experiments. TDCS was administrated to the left DLPFC at intensity of 1 mA (Experiment 1) or 2 mA (Experiment 2), while participants completed a verbal n-back paradigm (1-, 2-, 3-back). Analysis showed no overall effects of tDCS on WM, but a significant interaction with cognitive load. The present study suggests that cognitive load rather than tDCS intensity could be a decisive factor for effects on WM. Moreover, it emphasizes the need of thorough investigation on study parameters to develop more efficient stimulation protocols.

Combined and Isolated Effects of Acute Exercise and Brain Stimulation on Executive Function in Healthy Young Adults

Abstract: Acute cognitive enhancement has been sought by healthy young individuals to improve academic and professional performance. Among several methods, physical exercise interventions and transcranial direct current brain stimulation (tDCS) have shown promise in impacting executive functions. Here, we observed a set of new findings about the causal effect of acute aerobic exercise and tDCS across three facets of executive function: Inhibition (as measured by a flanker task) was selectively impacted by acute aerobic exercise but not tDCS, whereas working memory (as measured by an n-back task) was impacted by both acute aerobic exercise and tDCS, with effects emerging on distinct processing components for each manipulation. Sustained attention (as measured by the Mackworth clock task), on the other hand, was not impacted by acute aerobic exercise or tDCS. Interestingly, no effects of combining acute aerobic exercise and tDCS emerged. We argue that understanding the unique and combined contributions of these cognitive enhancement techniques can not only contribute to a deeper mechanistic explanation in healthy individuals but also inform future research with clinical and aging populations.

Neurocognitive effects of transcranial direct current stimulation (tDCS) in unipolar and bipolar depression: Findings from an international randomized controlled trial

OBJECTIVE

Transcranial direct current stimulation (tDCS) has been found to have antidepressant effects and may have beneficial neurocognitive effects. However, prior research has produced an unclear understanding of the neurocognitive effects of repeated exposure to tDCS. The study's aim was to determine the neurocognitive effects following tDCS treatment in participants with unipolar or bipolar depression.

METHOD

The study was a triple-masked, randomized, controlled clinical trial across six international academic medical centers. Participants were randomized to high dose (2.5 mA for 30 min) or low dose (0.034 mA, for 30 min) tDCS for 20 sessions over 4 weeks, followed by an optional 4 weeks of open-label high dose treatment. The tDCS anode was centered over the left dorsolateral prefrontal cortex at F3 (10/20 EEG system) and the cathode over F8. Participants completed clinical and neurocognitive assessments before and after tDCS. Genotype (BDNF Val66Met and catechol-o-methyltransferase [COMT] Val158Met polymorphisms) were explored as potential moderators of neurocognitive effects.

RESULTS

The study randomized 130 participants. Across the participants, tDCS treatment (high and low dose) resulted in improvements in verbal learning and recall, selective attention, information processing speed, and working memory, which were independent of mood effects. Similar improvements were observed in the subsample of participants with bipolar disorder. There was no observed significant effect of tDCS dose. However, BDNF Val66Met and COMT Val158Met polymorphisms interacted with tDCS dose and affected verbal memory and verbal fluency outcomes, respectively.

CONCLUSIONS

These findings suggest that tDCS could have positive neurocognitive effects in unipolar and bipolar depression. Thus, tDCS stimulation parameters may interact with interindividual differences in BDNF and COMT polymorphisms to affect neurocognitive outcomes, which warrants further investigation.

Transcranial direct current stimulation: a roadmap for research, from mechanism of action to clinical implementation

Transcranial direct current stimulation (tDCS) is a promising method for altering the function of neural systems, cognition, and behavior. Evidence is emerging that it can also influence psychiatric symptomatology, including major depression and schizophrenia. However, there are many open questions regarding how the method might have such an effect, and uncertainties surrounding its influence on neural activity, and human cognition and functioning. In the present critical review, we identify key priorities for future research into major depression and schizophrenia, including studies of the mechanism(s) of action of tDCS at the neuronal and systems levels, the establishment of the cognitive impact of tDCS, as well as investigations of the potential clinical efficacy of tDCS. We highlight areas of progress in each of these domains, including data that appear to favor an effect of tDCS on neural oscillations rather than spiking, and findings that tDCS administration to the prefrontal cortex during task training may be an effective way to enhance behavioral performance. Finally, we provide suggestions for further empirical study that will elucidate the impact of tDCS on brain and behavior, and may pave the way for efficacious clinical treatments for psychiatric disorders.

Neural predictors of treatment response to brain stimulation and psychological therapy in depression: a double-blind randomized controlled trial

Standard depression treatments, including antidepressant medication and cognitive behavioural therapy (CBT), are ineffective for many patients. Prefrontal transcranial direct current stimulation (tDCS) has been proposed as an alternative treatment, but has shown inconsistent efficacy for depression, and its mechanisms are poorly understood. We recruited unmedicated patients with major depressive disorder (N = 71 approached; N = 39 randomised) for a mechanistic, double-blind, randomized controlled trial consisting of eight weekly sessions of prefrontal tDCS administered to the left prefrontal cortex prior to CBT. We probed (1) whether tDCS improved the efficacy of CBT relative to sham stimulation; and (2) whether neural measures predicted clinical response. We found a modest and non-significant effect of tDCS on clinical outcome over and above CBT (active: 50%; sham: 31.6%; odds ratio: 2.16, 95% CI = 0.59-7.99), but a strong relationship, predicted a priori, between baseline activation during a working memory task in the stimulated prefrontal region and symptom improvement. Repeating our analyses of symptom outcome splitting the sample according to this biomarker revealed that tDCS was significantly superior to sham in individuals with high left prefrontal cortex activation at baseline; we also show 86% accuracy in predicting clinical response using this measure. Exploratory analyses revealed several other regions where activation at baseline was associated with subsequent response to CBT, irrespective of tDCS. This mechanistic trial revealed variable, but predictable, clinical effects of prefrontal tDCS combined with CBT for depression. We have discovered a potential explanation for this variability: individual differences in baseline activation of the region stimulated. Such a biomarker could potentially be used to pre-select patients for trials and, eventually, in the clinic.

Experimental Pain Is Alleviated by Manual Traction Itself Rather than Subjective Bias in the Knee: A Signal Detection Analysis

BACKGROUND

Manual traction is used for pain relief, but it is not clear whether the pain relief effect of manual traction is due to sensitivity or to subjective bias. The differences between manual traction and touch have also been unclear.

OBJECTIVES

We used signal detection theory to investigate whether manual traction and touch were effective for pain relief, and we compared the pain relief effect between manual traction and touch.

DESIGN

Repeated measures and single blinding.

METHODS

Twenty healthy adult volunteers performed an intensity judgment task immediately before and after each intervention. The intervention was either manual traction or touch for 10 minutes. We measured the intensity judgment task's signal detection measures of hit rates, false alarm rates, sensitivity (d'), and response bias (C) in an Aδ fiber-mediated pain condition and C fiber-mediated pain condition.

RESULTS

Manual traction did not provide a significant level of change, but its effect sizes differed. In our comparison of the effect sizes, manual traction tended to reduce the hit rate and altered the sensitivity value rather than the response bias in Aδ fiber-mediated pain. There was no significant difference in the amount of change in the hit rate between touch and manual traction regarding Aδ fiber-mediated pain and C fiber-mediated pain.

CONCLUSIONS

In terms of effect sizes, manual traction was effective for the pain relief of the first pain by producing a change in pain sensitivity rather than by subjective bias. Manual traction reduced the first pain, whereas touch reduced the first pain and second pain.

The COMT Val158 Met polymorphism does not modulate the after-effect of tDCS on working memory

Transcranial direct current stimulation (tDCS) can alter cortical excitability, neural plasticity, and cognitive-behavioral performance; however, its effects are known to vary across studies. A partial account of this variability relates to individual differences in dopamine function. Indeed, dopaminergic manipulations alter the physiological and cognitive-behavioral effects of tDCS, and gene polymorphisms related to dopamine have predicted individual response to online tDCS (i.e., stimulation overlapping with the critical task). Notably, the role of individual differences in dopamine has not yet been properly assessed in the effect of offline tDCS (i.e., stimulation prior to the critical task). We investigated if and how the COMT Val158 Met polymorphism (rs4680) modulates the after-effect of prefrontal tDCS on verbal working memory (WM). One hundred and thirty-nine participants were genotyped for the COMT Val158 Met polymorphism and received anodal-over-left, cathodal-over-right (AL-CR), cathodal-over-left, anodal-over-right (CL-AR), or sham stimulation over the dorsolateral prefrontal cortex in a between-subjects, pretest-posttest study design. WM was assessed using the N-back task. The results provide no evidence that the COMT polymorphism impacts the after-effect of prefrontal tDCS on WM. Taken together with previous findings on dopamine and tDCS interactions, the results of the present study suggest that (a) indirect markers of dopamine (such as COMT) are differently related to online and offline effects of tDCS, and (b) findings from studies involving pharmacological manipulation should be generalized with caution to findings of inter-individual differences. In sum, we argue that state (i.e., a manipulation of) and trait (i.e., baseline) differences in dopamine may exert different effects on online and offline tDCS.

Improving working memory in schizophrenia: Effects of 1 mA and 2 mA transcranial direct current stimulation to the left DLPFC

Deficits in various cognitive processes, such as working memory, are characteristic for schizophrenia, lowering patients' functioning and quality of life. Recent research suggests that transcranial direct stimulation (tDCS) applied to the dorsolateral prefrontal cortex (DLPFC) may be a potential therapeutic intervention for cognitive deficits in schizophrenia. Here, we examined the effects of online tDCS to the DLPFC on working memory (WM) performance in 40 schizophrenia patients in two separate experiments with a double blind, sham-controlled, cross-over design. Patients underwent single sessions of active and sham tDCS in a randomized order. Stimulation parameters were anode F3, cathode right deltoid muscle, 21 min tDCS duration, 1 mA tDCS in Experiment 1 (N = 20) and 2 mA tDCS in Experiment 2 (N = 20). Primary outcome was the change in WM performance as measured by a verbal n-back paradigm (1- to 3-back). Irrespective of the stimulation intensity, data analysis showed a significant higher WM accuracy during active tDCS than during sham tDCS (p = 0.019), but no main effect of stimulation intensity (p = 0.392). Subsequent separate analyses revealed a significantly improved WM performance only during 1 mA (p = 0.048). TDCS facilitated WM functioning in schizophrenia, with an advantage of 1 mA over 2 mA. Our results support the notion that tDCS may be a potential treatment for cognitive deficits in schizophrenia and emphasize the need for future research on the specific stimulation parameters.

Enhancement of pain inhibition by working memory with anodal transcranial direct current stimulation of the left dorsolateral prefrontal cortex

The aim of this study was to examine whether transcranial direct current stimulation (tDCS) of the dorsolateral prefrontal cortex (DLPFC) enhances pain inhibition by improving working memory (WM). Forty healthy volunteers participated in two tDCS sessions. Pain was evoked by electrical stimulation at the ankle. Participants performed an n-back task (0-back and 2-back). The experimental protocol comprised five counterbalanced conditions (0-back, 2-back, pain, 0-back with pain and 2-back with pain) that were performed twice (pre-tDCS baseline and during tDCS). Compared with the pre-tDCS baseline values, anodal tDCS decreased response times for the 2-back condition (p < 0.01) but not for the 0-back condition (p > 0.5). Anodal tDCS also decreased pain ratings marginally in the 2-back with pain condition, but not the 0-back with pain condition (p = 0.052 and p > 0.2, respectively). No effect was produced by sham tDCS for any condition (p > 0.2). These results indicate that tDCS of the left DLPFC may enhance pain inhibition by improving WM.

Noninvasive brain stimulation over dorsolateral prefrontal cortex for pain perception and executive function in aging

OBJECTIVES

Based on the evidence that the dorsolateral prefrontal cortex (DLPFC) is the main region affected by the aging process, and that tDCS modulates cortical excitability, the aim of the study is to prove the feasibility of tDCS for pain perception and executive function of community-dwelling elderly individuals.

METHODS

We performed a double-blind, single-arm trial, including a sham period. 5 consecutive anodal tDCS was applied over DLPFC of twenty-four elderly for 20 min during each intervention periods (in order of Sham-1 mA-2 mA). First, we classified chronic non-inflammatory pain sites into three domain (Neck and upper extremity, low back, lower extremity). Then, we used visual analogue scale, pain self-efficacy scale, Tampa scale for kinesiophobia, and Global perceived Effect scale to observe the change in pain perception, as well as Trailing Making Test and Timed Up and Go (dual) to observe the change in executive function. The changes in maximal grip strength and 12-item Short Form survey were measured secondarily.

RESULTS

In the results, we observed significant improvement in pain perception and quality of life, while executive function and grip strength did not change significantly.

CONCLUSION

Our findings demonstrated the feasibility of tDCS for aging-related pain perception and suggest that further randomized controlled trials with longer duration are necessary to examine the effects on executive function.

Cognitive Effects of Transcranial Direct Current Stimulation in Healthy and Clinical Populations: An Overview

Transcranial direct current stimulation (tDCS) is a neuromodulatory approach that is affordable, safe, and well tolerated. This review article summarizes the research and clinically relevant findings from meta-analyses and studies investigating the cognitive effects of tDCS in healthy and clinical populations. We recapitulate findings from recent studies where cognitive performance paired with tDCS was compared with performance under placebo (sham stimulation) in single sessions and longitudinal designs where cognitive effects were evaluated following repeated sessions. In summary, the tDCS literature currently indicates that the effects of tDCS on cognitive measures are less robust and less predictable compared with the more consistent effects on motor outcomes. There is also a notable difference in the consistency of single-session and longitudinal designs. In single-session tDCS designs, there are small effects amid high variability confounded by individual differences and potential sham stimulation effects. In contrast, longitudinal studies provide more consistent benefits in healthy and clinical populations, particularly when tDCS is paired with a concurrent task. Yet, these studies are few in number, thereby impeding design optimization. While there is good evidence that tDCS can modulate cognitive functioning and potentially produce longer-term benefits, a major challenge to widespread translation of tDCS is the absence of a complete mechanistic account for observed effects. Significant future work is needed to identify a priori responders from nonresponders for every cognitive task and tDCS protocol.

Cognitive outcomes of TMS treatment in bipolar depression: Safety data from a randomized controlled trial

BACKGROUND

Bipolar depression (BD) is a highly prevalent condition associated with marked cognitive deficits that persist even in the euthymic phase of the illness. Pharmacological treatments for BD might further aggravate cognitive impairment, highlighting the need of developing interventions that present cognitive safety. In this study, we evaluated the cognitive effects of H1-coil (deep) transcranial magnetic stimulation (TMS) in patients with treatment-resistant bipolar depression.

METHODS

Fourty-three patients were randomized to receive 20 sessions of active (55 trains, 18 Hz, 120% resting motor threshold intensity) or sham rTMS within a double-blind, sham-controlled trial. A battery of 20 neuropsychological assessments, grouped in 6 domains (attention and processing speed, working memory and executive function, inhibitory control, language, immediate verbal memory, and long-term verbal memory) was performed at baseline and after 4 and 8 weeks of trial onset. Depressive symptoms were assessed with the 17-item Hamilton Rating Scale for Depression.

RESULTS

Cognitive improvement was shown for all cognitive domains. It occurred regardless of intervention group and depression improvement. For the language domain, greater improvement was observed in the sham group over time. No correlations between depression (at baseline or during treatment) and cognitive improvement were found.

LIMITATIONS

Absence of healthy control group.

CONCLUSION

The results of this exploratory study provide evidence on the cognitive safety of H1-coil TMS for BD patients. Putative pro-cognitive effects of rTMS in BD were not observed and thus should be further investigated.

Prefrontal cortex executive processes affected by stress in health and disease

Prefrontal cortical executive functions comprise a number of cognitive capabilities necessary for goal directed behavior and adaptation to a changing environment. Executive dysfunction that leads to maladaptive behavior and is a symptom of psychiatric pathology can be instigated or exacerbated by stress. In this review we survey research addressing the impact of stress on executive function, with specific focus on working memory, attention, response inhibition, and cognitive flexibility. We then consider the neurochemical pathways underlying these cognitive capabilities and, where known, how stress alters them. Finally, we review work exploring potential pharmacological and non-pharmacological approaches that can ameliorate deficits in executive function. Both preclinical and clinical literature indicates that chronic stress negatively affects executive function. Although some of the circuitry and neurochemical processes underlying executive function have been characterized, a great deal is still unknown regarding how stress affects these processes. Additional work focusing on this question is needed in order to make progress on developing interventions that ameliorate executive dysfunction.

Transcranial Direct Current Stimulation (tDCS): A Promising Treatment for Major Depressive Disorder?

Background: Transcranial direct current stimulation (tDCS) opens new perspectives in the treatment of major depressive disorder (MDD), because of its ability to modulate cortical excitability and induce long-lasting effects. The aim of this review is to summarize the current status of knowledge regarding tDCS application in MDD. Methods: In this review, we searched for articles published in PubMed/MEDLINE from the earliest available date to February 2018 that explored clinical and cognitive effects of tDCS in MDD. Results: Despite differences in design and stimulation parameters, the examined studies indicated beneficial effects of tDCS for MDD. These preliminary results, the non-invasiveness of tDCS, and its good tolerability support the need for further research on this technique. Conclusions: tDCS constitutes a promising therapeutic alternative for patients with MDD, but its place in the therapeutic armamentarium remains to be determined.

Transcranial direct current brain stimulation decreases impulsivity in ADHD

BACKGROUND

Impulsivity is a core deficit in attention deficit hyperactivity disorder (ADHD). Transcranial direct current stimulation (tDCS) of the dorsolateral prefrontal cortex (DLPFC) has been shown to modulate cognitive control circuits and could enhance DLPFC activity, leading to improved impulse control in ADHD.

OBJECTIVE

Hypothesis: We predicted 2.0 mA anodal stimulation (tDCS) versus sham stimulation applied over the left DLPFC would improve Conners Continuous Performance Task (CPT) scores. Our secondary hypothesis predicted that stop signal task (SST) reaction time (SSRT) would decrease with tDCS (versus sham).

METHODS

Thirty-seven participants completed two periods of three tDCS (or sham) sessions two weeks apart in a within-subject, double-blind, counterbalanced order. Participants performed a fractal N-back training task concurrent with tDCS (or sham) stimulation. Participants completed the CPT and SST at the beginning of treatment (baseline), at the end of the treatment, and at a 3-day post-stimulation follow-up.

RESULTS

There was a significant stimulation condition by session interaction for CPT false positive scores (χ² = 15.44, p < 0.001) driven by a decrease in false positive errors from baseline to end of treatment in the tDCS group (β = -0.36, 95% Confidence Interval (CI) -0.54 to -0.18, p < 0.001). This effect did not persist at follow-up (β = -0.13, p > 0.05). There was no significant stimulation condition by session interaction effect on CPT true positive errors or response time (ps > 0.05). No significant change in SSRT performance was observed (p > 0.05).

CONCLUSION

These findings suggest that stimulation of the left DLPFC with tDCS can improve impulsivity symptoms in ADHD, supporting the therapeutic potential for tDCS in adult ADHD patients.

Cognitive effects of transcranial direct current stimulation treatment in patients with major depressive disorder: An individual patient data meta-analysis of randomised, sham-controlled trials

Transcranial direct current stimulation (tDCS) has emerged as a promising new treatment for major depression. While recent randomised, sham-controlled studies found tDCS to have antidepressant effects, it remains to be determined whether a tDCS treatment course may also enhance cognitive function independent of mood effects in depressed patients. This systematic review and individual patient data (IPD) meta-analysis examined cognitive outcomes from randomised, sham-controlled trials of tDCS treatment for major depression. Seven randomised, sham-controlled trials (n = 478 participants, 260 in active and 218 in sham) of tDCS for major depression were included. Results showed no cognitive enhancement after active tDCS compared to sham for the 12 cognitive outcomes investigated. Active relative to sham tDCS treatment was associated with reduced performance gains on a measure of processing speed (β = -0.33, 95% CI -0.58; -0.08, p = 0.011). Active tDCS treatment for depression did not show cognitive benefits independent of mood effects. Rather, tDCS treatment relative to sham stimulation for major depression may instead be associated with a reduced practice effect for processing speed.

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.

Balanced bifrontal transcranial direct current stimulation enhances working memory in adults with high-functioning autism: a sham-controlled crossover study

Background

Working memory (WM) often is impaired in autism spectrum disorder (ASD). Such impairment may underlie core deficits in cognition and social functioning. Transcranial direct current stimulation (tDCS) has been shown to enhance WM in both healthy adults and clinical populations, but its efficacy in ASD is unknown. We predicted that bifrontal tDCS would improve WM performances of adults with high-functioning autism during active stimulation compared to sham stimulation and that such enhancement would generalize to an untrained task.

Methods

Twelve adults with high-functioning ASD engaged in a battery of WM tasks that included backward spatial span, backward digit span, spatial n-back and letter n-back. While engaged, 40 min of 1.5 mA bifrontal stimulation was applied over the left and the right dorsolateral prefrontal cortices (DLPFC). Using a single-blind crossover design, each participant received left anodal/right cathodal stimulation, right anodal/left cathodal stimulation, or sham stimulation, in randomized counterbalanced order on three separate days. Following tDCS, participants again engaged in letter and spatial n-back tasks before taking the Brief Test of Attention (BTA). We used repeated-measures ANOVA to compare overall performance on the WM battery as measured by a composite of z-scores for all five measures. Post hoc ANOVAs, t tests, Friedman’s tests, and Wilcoxon signed-rank tests were used to measure the online and offline effects of tDCS and to assess performances on individual measures.

Results

Compared to sham stimulation, both left DLPFC anodal stimulation (t₁₁ = 5.4, p = 0.0002) and right DLPFC anodal stimulation (t₁₁ = 3.57, p = 0.004) improved overall WM performance. Left anodal stimulation (t₁₁ = 3.9, p = 0.003) and right anodal stimulation (t₁₁ = 2.7, p = 0.019) enhanced performances during stimulation. Enhancement transferred to an untrained task 50 min after right anodal stimulation (z₁₁ = 2.263, p = 0.024). The tasks that showed the largest effects of active stimulation were spatial span backward (z₁₁ = 2.39, p = 0.017) and BTA (z₁₁ = 2.263, p = 0.024).

Conclusions

In adults with high-functioning ASD, active bifrontal tDCS given during WM tasks appears to improve performance. TDCS benefits also transferred to an untrained task completed shortly after stimulation. These results suggest that tDCS can improve WM task performance and could reduce some core deficits of autism.

Trial registration

NCT01602263

Transcranial direct current stimulation can enhance working memory in Huntington's disease

Transcranial direct current stimulation (tDCS) combined with a cognitive task can enhance targeted aspects of cognitive functioning in clinical populations. The movement disorder Huntington's disease (HD) is associated with progressive cognitive impairment. Deficits in working memory (WM) can be apparent early in the disease and impact functional capacity. We investigated whether tDCS combined with cognitive training could improve WM in patients with HD, and if baseline clinical or cognitive measures may predict efficacy. Twenty participants with HD completed this crossover trial, undergoing 1.5mA anodal tDCS over left dorsolateral prefrontal cortex and sham stimulation on separate visits. Participants and assessor were blinded to condition order, which was randomised across participants. All participants completed baseline clinical and cognitive assessments. Pre- and post-stimulation tasks included digit reordering, computerised n-back tests and a Stroop task. During 15min of tDCS/sham stimulation, participants practiced 1- and 2-back WM tasks. Participants exhibited an increase in WM span on the digit re-ordering span task from pre- to post-stimulation after tDCS, but not after sham stimulation. Gains in WM were positively related to motor symptom ratings and negatively associated with verbal fluency scores. Patients with more severe motor symptoms showed greatest improvement, suggesting that motor symptom ratings may help identify patients who are most likely to benefit from tDCS.

CONCLUSIONS

Dorsolateral prefrontal tDCS appears well tolerated in HD and enhances WM span compared to sham stimulation. Our findings strongly encourage further investigation of the extent to which tDCS combined with cognitive training could enhance everyday function in HD. ClinicalTrials.gov; NCT02216474 Brain stimulation in Movement Disorders; https://clinicaltrials.gov/ct2/show/NCT02216474.

Predicting brain stimulation treatment outcomes of depressed patients through the classification of EEG oscillations

Major depressive disorder (MDD) is a mental disorder that is characterized by negative thoughts, mood and behavior. Transcranial direct current stimulation (tDCS) has recently emerged as a promising brain-stimulation treatment for MDD. A standard tDCS treatment involves numerous sessions that run over a few weeks, however, not all participants respond to this type of treatment. This study aims to predict which patients improve in mood and cognition in response to tDCS treatment by analyzing electroencephalography (EEG) of MDD patients that was collected at the start of tDCS treatment. This is achieved through classifying power spectral density (PSD) of resting-state EEG using support vector machine (SVM), linear discriminate analysis (LDA) and extreme learning machine (ELM). Participants were labelled as improved/not improved based on the change in mood and cognitive scores. The obtained classification results of all channel pair combinations are used to identify the most relevant brain regions and channels for this classification task. We found the frontal channels to be particularly informative for the prediction of the clinical outcome of the tDCS treatment. Subject independent results reveal that our proposed method enables the correct identification of the treatment outcome for seven of the ten participants for mood improvement and nine of ten participants for cognitive improvement. This represents an encouraging sign that EEG-based classification may help to tailor the selection of patients for treatment with tDCS brain stimulation.