Improvement of the working memory and naming by transcranial direct current stimulation

Comparative Neurological and Behavioral Assessment of Central and Peripheral Stimulation Technologies for Induced Pain and Cognitive Tasks

Pain is a multifaceted, multisystem disorder that adversely affects neuro-psychological processes. This study compares the effectiveness of central stimulation (transcranial direct current stimulation-tDCS over F3/F4) and peripheral stimulation (transcutaneous electrical nerve stimulation-TENS over the median nerve) in pain inhibition during a cognitive task in healthy volunteers and to observe potential neuro-cognitive improvements. Eighty healthy participants underwent a comprehensive experimental protocol, including cognitive assessments, the Cold Pressor Test (CPT) for pain induction, and tDCS/TENS administration. EEG recordings were conducted pre- and post-intervention across all conditions. The protocol for this study was categorized into four groups: G1 (control), G2 (TENS), G3 (anodal-tDCS), and G4 (cathodal-tDCS). Paired t-tests (p < 0.05) were conducted to compare Pre-Stage, Post-Stage, and neuromodulation conditions, with t-values providing insights into effect magnitudes. The result showed a reduction in pain intensity with TENS (p = 0.002, t-value = -5.34) and cathodal-tDCS (p = 0.023, t-value = -5.08) and increased pain tolerance with TENS (p = 0.009, t-value = 4.98) and cathodal-tDCS (p = 0.001, t-value = 5.78). Anodal-tDCS (p = 0.041, t-value = 4.86) improved cognitive performance. The EEG analysis revealed distinct neural oscillatory patterns across the groups. Specifically, G2 and G4 showed delta-power reductions, while G3 observed an increase. Moreover, G2 exhibited increased theta-power in the occipital region during CPT and Post-Stages. In the alpha-band, G2, G3, and G4 had reductions Post-Stage, while G1 and G3 increased. Additionally, beta-power increased in the frontal region for G2 and G3, contrasting with a reduction in G4. Furthermore, gamma-power globally increased during CPT1, with G1, G2, and G3 showing reductions Post-Stage, while G4 displayed a global decrease. The findings confirm the efficacy of TENS and tDCS as possible non-drug therapeutic alternatives for cognition with alleviation from pain.

Effect of Home-Based Transcranial Direct Current Stimulation on Cognitive Function in Patients with Mild Cognitive Impairment: A Two-Week Intervention

PURPOSE

Repeated transcranial direct current stimulation (tDCS) is expected to have the potential to improve cognitive function in patients with mild cognitive impairment (MCI). We aimed to evaluate the efficacy and safety of at-home tDCS for elderly patients with MCI.

MATERIALS AND METHODS

Patients aged 60-80 years, who maintained normal daily living but reported objective memory impairments, were enrolled. Active or sham stimulations were applied to the dorsal frontal cortex (left: anode; right: cathode) at home for 2 weeks. Changes in cognitive function were assessed using visual recognition tasks and the Mini-Mental State Exam (MMSE), and safety and efficacy were assessed using self-reports and a remote monitoring application.

RESULTS

Of the 19 participants enrolled, 12 participants were included in the efficacy analysis. Response times and MMSE scores significantly improved after active stimulation compared to the sham stimulation; however, there were no significant differences in the proportion of correct responses. The mean compliance of the efficacy group was 97.5%±4.1%. Three participants experienced burns, but no permanent sequelae remained.

CONCLUSION

This preliminary result suggests that home-based tDCS may be a promising treatment option for MCI patients; however, it requires more attention and technological development to address safety concerns.

CLINICAL TRIAL REGISTRATION

Clinical Research Information Service (CRIS), KCT0002721.

Facilitation of working memory capacity by transcranial direct current stimulation: a secondary analysis from the augmenting cognitive training in older adults (ACT) study

Aging is a public health concern with an ever-increasing magnitude worldwide. An array of neuroscience-based approaches like transcranial direct current stimulation (tDCS) and cognitive training have garnered attention in the last decades to ameliorate the effects of cognitive aging in older adults. This study evaluated the effects of 3 months of bilateral tDCS over the frontal cortices with multimodal cognitive training on working memory capacity. Two hundred ninety-two older adults without dementia were allocated to active or sham tDCS paired with cognitive training. These participants received repeated sessions of bilateral tDCS over the bilateral frontal cortices, combined with multimodal cognitive training. Working memory capacity was assessed with the digit span forward, backward, and sequencing tests. No baseline differences between active and sham groups were observed. Multiple linear regressions indicated more improvement of the longest digit span backward from baseline to post-intervention (p = 0.021) and a trend towards greater improvement (p = 0.056) of the longest digit span backward from baseline to 1 year in the active tDCS group. No significant between-group changes were observed for digit span forward or digit span sequencing. The present results provide evidence for the potential for tDCS paired with cognitive training to remediate age-related declines in working memory capacity. These findings are sourced from secondary outcomes in a large randomized clinical trial and thus deserve future targeted investigation in older adult populations.

Evidence and sources of placebo effects in transcranial direct current stimulation during a single session of visuospatial working memory practice

Transcranial direct current stimulation (tDCS) can be used to non-invasively augment cognitive training. However, the benefits of tDCS may be due in part to placebo effects, which have not been well-characterized. The purpose of this study was to determine whether tDCS can have a measurable placebo effect on cognitive training and to identify potential sources of this effect. Eighty-three right-handed adults were randomly assigned to one of three groups: control (no exposure to tDCS), sham tDCS, or active tDCS. The sham and active tDCS groups were double-blinded. Each group performed 20 min of an adapted Corsi Block Tapping Task (CBTT), a visuospatial working memory task. Anodal or sham tDCS was applied during CBTT training in a right parietal-left supraorbital montage. After training, active and sham tDCS groups were surveyed on expectations about tDCS efficacy. Linear mixed effects models showed that the tDCS groups (active and sham combined) improved more on the CBTT with training than the control group, suggesting a placebo effect of tDCS. Participants' tDCS expectations were significantly related to the placebo effect, as was the belief of receiving active stimulation. This placebo effect shows that the benefits of tDCS on cognitive training can occur even in absence of active stimulation. Future tDCS studies should consider how treatment expectations may be a source of the placebo effect in tDCS research, and identify ways to potentially leverage them to maximize treatment benefit.

Anodal transcranial direct current stimulation (atDCS) and functional transcranial Doppler sonography (fTCD) in healthy elderly and patients with MCI: modulation of age-related changes in word fluency and language lateralization

Introduction: In addition to age-related changes in language, hemispheric lateralization of language functions steadily declines with age. Also, performance on word fluency tasks declines and is sensitive to the expression of dementia-related changes. The aim of this study is to evaluate the effect of anodal tDCS combined with a word fluency training on language lateralization and word fluency performance in healthy elderly subjects and in persons with mild cognitive impairment (MCI). Methods: The effect of anodal tDCS over the left inferio frontal gyrus (IFG) was measured in a group of healthy elderly up to the age of 67 years (YG, Ø = 63.9 ± 3.02), a group of healthy elderly aged 68 years and older (OG, Ø = 78.1, ± 4.85), and a group of patients with MCI (Ø = 81.18, ± 7.35) by comparing performance in phonological and semantic word fluency tasks before and after 3 days of tDCS. Half of the experimental participants received sham stimulation. In addition, language lateralization was determined using a lateralization index (LI) measured with functional transcranial Doppler sonography (fTCD) before and after the stimulation period. Results: Anodal tDCS was associated with significantly higher scores in phonological but not semantic word fluency in both YG and OG. In MCI patients, no difference was measured between the tDCS and sham groups in either word fluency task. fTCD showed significantly increased left lateralization in all three groups after the training phase. However, this effect was independent of tDCS and the degree of lateralization could not be predicted by word fluency performance in any of the groups. Discussion: Phonological word fluency can be increased with atDCS in healthy elderly people by stimulating the IFG in a 3-day training. When cognitive decline has reached a certain stage, as is the case with MCI, this paradigm does not seem to be effective enough.

Home-based, Remotely Supervised, 6-Week tDCS in Patients With Both MCI and Depression: A Randomized Double-Blind Placebo-Controlled Trial

As depressive symptom is considered a prodrome, a risk factor for progression from mild cognitive impairment (MCI) to dementia, improving depressive symptoms should be considered a clinical priority in patients with MCI undergoing transcranial direct current stimulation (tDCS) intervention. We aimed to comprehensively evaluate the efficacy of the home-based and remotely monitored tDCS in patients with both MCI and depression, by integrating cognitive, psychological, and electrophysiological indicators. In a 6-week, randomized, double blind, and sham-controlled study, 37 community-dwelling patients were randomly assigned to either an active or a sham stimulation group, and received 30 home-based sessions of 2 mA tDCS for 30 min with the anode located over the left and cathode over the right dorsolateral prefrontal cortex. We measured depressive symptoms, neurocognitive function, and resting-state electroencephalography. In terms of effects of both depressive symptoms and cognitive functions, active tDCS was not significantly different from sham tDCS. However, compared to sham stimulation, active tDCS decreased and increased the activation of delta and beta frequencies, respectively. Moreover, the increase in beta activity was correlated with the cognitive enhancement only in the active group. It was not possible to reach a definitive conclusion regarding the efficacy of tDCS on depression and cognition in patients with both MCI and depression. Nevertheless, the relationship between the changes of electrophysiology and cognitive performance suggests potential neuroplasticity enhancement implicated in cognitive processes by tDCS.

The Effects of Transcranial Direct Current Stimulation (tDCS) on the Cognitive Functions: A Systematic Review and Meta-analysis

Previous studies have investigated the effect of transcranial direct current stimulation (tDCS) on cognitive functions. However, these studies reported inconsistent results due to differences in experiment design, measurements, and stimulation parameters. Nonetheless, there is a lack of meta-analyses and review studies on tDCS and its impact on cognitive functions, including working memory, inhibition, flexibility, and theory of mind. We performed a systematic review and meta-analysis of tDCS studies published from the earliest available data up to October 2021, including studies reporting the effects of tDCS on cognitive functions in human populations. Therefore, these systematic review and meta-analysis aim to comprehensively analyze the effects of anodal and cathodal tDCS on cognitive functions by investigating 69 articles with a total of 5545 participants. Our study reveals significant anodal tDCS effects on various cognitive functions. Specifically, we observed improvements in working memory reaction time (RT), inhibition RT, flexibility RT, theory of mind RT, working memory accuracy, theory of mind accuracy and flexibility accuracy. Furthermore, our findings demonstrate noteworthy cathodal tDCS effects, enhancing working memory accuracy, inhibition accuracy, flexibility RT, flexibility accuracy, theory of mind RT, and theory of mind accuracy. Notably, regarding the influence of stimulation parameters of tDCS on cognitive functions, the results indicated significant differences across various aspects, including the timing of stimulation (online vs. offline studies), population type (clinical vs. healthy studies), stimulation duration (< 15 min vs. > 15 min), electrical current intensities (1-1.5 m.A vs. > 1.5 m.A), stimulation sites (right frontal vs. left frontal studies), age groups (young vs. older studies), and different cognitive tasks in each cognitive functioning aspect. In conclusion, our results demonstrate that tDCS can effectively enhance cognitive task performance, offering valuable insights into the potential benefits of this method for cognitive improvement.

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.

Inhibitory Control in Young Healthy Adults - a tDCS Study

Inhibitory control plays a role in the behavior selection and detection of conflicts. Defects in inhibitory control are an integral part of many neuropsychiatric disorders and the possibilities of influencing it are the subject of active study. Studies have shown and confirmed the activation of the dorsolateral prefrontal cortex (DLPFC) during the Stroop task and other tests involving response inhibition. Non-invasive brain stimulation is an emerging and actively developing group of methods used in cognitive research. In the present study, we used non-invasive, painless, and delicate transcranial direct stimulation (tDCS) for the study of inhibitory control, and to explore the effect of impulsivity on response inhibition ability in young healthy participants. We conducted a cross-over study with cross-hemispheric application of 2 mA tDCS with electrodes placed on the right - cathode, and left - anode - DLPFC. Participants performed a classic Stroop test before and after stimulation. Impulsivity was measured via the personal impulsiveness questionnaire. There was no significant difference in interference score alteration between active and sham stimulations, anodal and sham tDCS both induced slight improvement in Stroop test results. Individual impulsivity in healthy participants showed no influence on their results. Our study adds to the picture and helps to deepen knowledge about the impact of different stimulation parameters on cognitive functions.

Frontal two-electrode transcranial direct current stimulation protocols may not affect performance on a combined flanker Go/No-Go task

Transcranial direct current stimulation (tDCS) has been tested to modulate cognitive control or response inhibition using various electrode montages. However, electrode montages and current polarities have not been systematically compared when examining tDCS effects on cognitive control and response inhibition. In this randomized, sham-controlled study, 38 healthy volunteers were randomly grouped into receiving one session of sham, anodal, and cathodal each in an electrode montage that targeted either the dorsolateral prefrontal cortex (DLPFC) or the fronto-medial (FM) region. Participants performed a combined flanker Go/No-Go task during stimulation. No effect of tDCS was found in the DLPFC and FM groups neither using anodal nor cathodal stimulation. No major adverse effects of tDCS were identified using either montage or stimulation type and the two groups did not differ in terms of the reported sensations. The present study suggests that single-session tDCS delivered in two two-electrode montages might not affect cognitive control or response inhibition, despite using widely popular stimulation parameters. This is in line with the heterogeneous findings in the field and calls for further systematic research to exclude less reliable methods from those with more pronounced effects, identify the determinants of responsiveness, and develop optimal ways to utilize this technique.

Simultaneous fMRI and tDCS for Enhancing Training of Flight Tasks

There is a gap in our understanding of how best to apply transcranial direct-current stimulation (tDCS) to enhance learning in complex, realistic, and multifocus tasks such as aviation. Our goal is to assess the effects of tDCS and feedback training on task performance, brain activity, and connectivity using functional magnetic resonance imaging (fMRI). Experienced glider pilots were recruited to perform a one-day, three-run flight-simulator task involving varying difficulty conditions and a secondary auditory task, mimicking real flight requirements. The stimulation group (versus sham) received 1.5 mA high-definition HD-tDCS to the right dorsolateral prefrontal cortex (DLPFC) for 30 min during the training. Whole-brain fMRI was collected before, during, and after stimulation. Active stimulation improved piloting performance both during and post-training, particularly in novice pilots. The fMRI revealed a number of tDCS-induced effects on brain activation, including an increase in the left cerebellum and bilateral basal ganglia for the most difficult conditions, an increase in DLPFC activation and connectivity to the cerebellum during stimulation, and an inhibition in the secondary task-related auditory cortex and Broca's area. Here, we show that stimulation increases activity and connectivity in flight-related brain areas, particularly in novices, and increases the brain's ability to focus on flying and ignore distractors. These findings can guide applied neurostimulation in real pilot training to enhance skill acquisition and can be applied widely in other complex perceptual-motor real-world tasks.

Efficacy of stretching exercises versus transcranial direct current stimulation (tDCS) on task performance, kinematic and electroencephalography (EEG) spectrum in subjects with slump posture: a study protocol

BACKGROUND

Slump sitting is a common posture in workplaces. There is limited evidence that poor posture impacts the mental state. This study aims to investigate whether slump posture results in more mental fatigue during computer typing, compared with normal posture and also to compare the effectiveness of stretching exercises with tDCS in fatigue monitoring.

METHODS

The sample size for this study is set at 36 participants with slump posture and 36 participants with normal posture. In the first step, to find out the differences between normal and poor posture, they will be asked to perform the typewriting task for 60 min. During the first and last 3 min of typing, mental fatigue as the primary outcome using EEG signals and further measures including kinematic behavior of neck, visual analog fatigue scale, and musculoskeletal discomfort will be assessed. Post-experiment task performance will be calculated based on typing speed and typing errors. In the next step, to compare the effect of tDCS and stretching exercises on the outcome measures, the slump posture group will receive these interventions in two separate sessions before the typing task.

DISCUSSION

With the assumption of showing significant differences in terms of outcome measures between slump and normal posture groups and also by showing the possible changes of the measures, by using either tDCS as a central modality or stretching exercises as a peripheral modality; the findings may provide evidence to indicate that poor posture has adverse effect on mental state and to introduce the effective method to overcome mental fatigue and promote work productivity.

TRIAL REGISTRATION

Registered on the Iranian Registry of Clinical Trials on 21 September 2022, IRCT Identifier: IRCT20161026030516N2.

Differential Effects of Transcranial Static Magnetic Stimulation Over Left and Right Dorsolateral Prefrontal Cortex on Brain Oscillatory Responses During a Working Memory Task

Transcranial static magnetic stimulation (tSMS) is known to influence behavioral and neural activities. However, although the left and right dorsolateral prefrontal cortex (DLPFC) are associated with different cognitive functions, there remains a lack of knowledge on a difference in the effects of tSMS on cognitive performance and related brain activity between left and right DLPFC stimulations. To address this knowledge gap, we examined how differently tSMS over the left and right DLPFC altered working memory performance and electroencephalographic oscillatory responses using a 2-back task, in which subjects monitor a sequence of stimuli and decide whether a presented stimulus matches the stimulus presented two trials previously. Fourteen healthy adults (five females) performed the 2-back task before, during (20 min after the start of stimulation), immediately after, and 15 min after three different stimulation conditions: tSMS over the left DLPFC, tSMS over the right DLPFC, and sham stimulation. Our preliminary results revealed that while tSMS over the left and right DLPFC impaired working memory performance to a similar extent, the impacts of tSMS on brain oscillatory responses were different between the left and right DLPFC stimulations. Specifically, tSMS over the left DLPFC increased the event-related synchronization in beta band whereas tSMS over the right DLPFC did not show such an effect. These findings support evidence that the left and right DLPFC play different roles in working memory and suggest that the neural mechanism underlying the impairment of working memory by tSMS can be different between left and right DLPFC stimulations.

Underpinning the neurological source of executive function following cross hemispheric tDCS stimulation

Transcranial direct current stimulation (tDCS) is a promising technique for enhancement of executive functions in healthy as well as neurologically disturbed patients. However, the evidence regarding the neuropsychological and behavioral change with neurophysiological shifts as well as the mechanism of tDCS action as evidenced by activation of neuronal sources important for executive functions have remained unaddressed. The study thereby endeavors to (1) determine the neuropsychological, behavioral, and neurophysiological change induced with five sessions of bilateral tDCS stimulation and (2) identify putative neuronal sources related to the executive functions responsible for neuropsychological and behavioral change. For this single blinded study, a total of 40 healthy participants, randomly allocated to active (n = 19) or sham (n = 21) groups completed five sessions of 2 mA tDCS stimulation administered over Dorso-Lateral Prefrontal Cortex (DLPFC) (F3 as anode, F4 as cathode). Repeated measure analysis was performed on neuropsychological (Everyday Memory Questionnaire and Mindful Attention Awareness Scale), and behavioral assessment (n-Back and Stroop tests) to investigate within and between group differences. Pre and post neurophysiological (Electroencephalogram) results showed that bilateral tDCS stimulation activates cortical regions responsible for executive functions including updation (working memory) and inhibition (interference control or attention). Multiple sessions of bilateral tDCS stimulation results in a significant increase in theta, alpha, and beta-band activity in the DLPFC, cingulate and parietal cortex. This study provides evidence that tDCS can be used for performance enhancement of executive functions in able-bodied people.

Transcutaneous auricular vagus stimulation (taVNS) improves human working memory performance under sleep deprivation stress

Many human activities require high cognitive performance over long periods, while impairments induced by sleep deprivation influence various aspects of cognitive abilities, including working memory (WM), attention, and processing speed. Based on previous research, vagal nerve stimulation can modulate cognitive abilities, attention, and arousal. Two experiments were conducted to assess the efficacy of transcutaneous auricular vagus nerve stimulation (taVNS) to relieve the deleterious effects of sleep deprivation. In the first experiment, 35 participants completed N-back tasks at 8:00 a.m. for two consecutive days in a within-subject study. Then, the participants received either taVNS or earlobe stimulation (active control) intervention in two sessions at random orders after 24 h of sustained wakefulness. Then, they completed the N-back tasks again. In the second experiment, 30 participants completed the psychomotor vigilance task (PVT), and 32 completed the N-back tasks at 8:00 a.m. on the first and second days. Then, they received either taVNS or earlobe stimulation at random orders and finished the N-back and PVT tasks immediately after one hour. In Experiment 1, taVNS could significantly improve the accuracy rate of participants in spatial 3-back tasks compared to active control, which was consistent with experiment 2. However, taVNS did not specifically enhance PVT performance. Therefore, taVNS could be a powerful intervention for acute sleep deprivation as it can improve performance on high cognitive load tasks and is easy to administer.

Enhancement of Visuospatial Working Memory by Transcranial Direct Current Stimulation on Prefrontal and Parietal Cortices

Introduction

Previous studies have reported dorsolateral prefrontal cortex (DLPFC) and posterior parietal cortex (PPC) activation during the performance of spatial working memory (SWM), therefore this study aims to compare the effect of transcranial direct current stimulation (tDCS) between these two areas.

Methods

Fifty-four healthy right-handed students (27 women, 27 men; age=24.3±0.2 years) were randomly assigned to an anodal group (n=27) and a sham group (n=27), each of these groups was divided into F4 (representing right DLPFC) or P4 (representing right PPC) subgroups, respectively. A computerized Corsi block tapping (CBT) task was used to measure SWM. The tDCS intervention consisted of five daily sessions with a direct current of 1.5 mA for 15 minutes on the F4 or P4 area of the brain at 24-hour intervals.

Results

Significant enhancement of the SWM span as well as a faster response was observed after anodal tDCS in both the anterior and posterior direction. Moreover, stimulation of the left DLPFC induced a faster reaction time compared to the right PPC.

Conclusion

Stimulation DLPFC and PPC, as an element of the frontoparietal network, showed SWM enhancement, with the DLPFC being more affected. Our finding provides new evidence to compare the effect of stimulation on the two main activated cortical areas during visual SWM.

Modulation of auditory temporal processing, speech in noise perception, auditory-verbal memory, and reading efficiency by anodal tDCS in children with dyslexia

Dyslexia is a neurodevelopmental disorder that is prevalent in children. It is estimated that 30-50% of individuals diagnosed with dyslexia also manifest an auditory perceptual deficit characteristic of auditory processing disorder (APD). Some studies suggest that defects in basic auditory processing can lead to phonological defects as the most prominent cause of dyslexia. Thus, in some cases, there may be interrelationships between dyslexia and some of the aspects of central auditory processing. In recent years, transcranial direct current stimulation (tDCS) has been used as a safe method for the modulation of central auditory processing aspects in healthy adults and reading skills in children with dyslexia. Therefore, the objectives of our study were to investigate the effect of tDCS on the modulation of different aspects of central auditory processing, aspects of reading, and the relationship between these two domains in dyslexic children with APD. A within-subjects design was employed to investigate the effect of two electrode arrays (the anode on the left STG (AC)/cathode on the right shoulder and anode on the left STG/cathode on the right STG) on auditory temporal processing; speech-in-noise perception, short-term auditory memory; and high-frequency word, low-frequency word, pseudoword, and text reading. The results of this clinical trial showed the modulation of the studied variables in central auditory processing and the accuracy and speed of reading variables compared to the control and sham statuses in both electrode arrays. Our results also showed that the improvement of the accuracy and speed of text reading, as well as the accuracy of pseudoword reading were related to the improvement of speech in noise perception and temporal processing. The results of this research can be effective in clarifying the basis of the neurobiology of dyslexia and, in particular, the hypothesis of the role of basic auditory processing and subsequently the role of the auditory cortex in dyslexia. These results might provide a framework to facilitate behavioral rehabilitation in dyslexic children with APD.

Does Executive Function Training Impact on Communication? A Randomized Controlled tDCS Study on Post-Stroke Aphasia

New approaches in aphasia rehabilitation have recently identified the crucial role of executive functions (EFs) in language recovery, especially for people with severe aphasia (PWSA). Indeed, EFs include high-order cognitive abilities such as planning and problem solving, which enable humans to adapt to novel situations and are essential for everyday functional communication. In a randomized double-blind crossover design, twenty chronic Italian PWSA underwent ten days of transcranial direct current stimulation (tDCS) (20 min, 2 mA) over the right dorsolateral prefrontal cortex (DLPFC). Two conditions were considered, i.e., anodal and sham, while performing four types of cognitive training (alertness, selective attention, visuo-spatial working memory, and planning), all of which were related to executive functions. After anodal tDCS, a greater improvement in selective attention, visuospatial working memory and planning abilities was found compared to the sham condition; this improvement persisted one month after the intervention. Importantly, a significant improvement was also observed in functional communication, as measured through the Communication Activities of Daily Living Scale, in noun and verb naming, in auditory and written language comprehension tasks and in executive function abilities. This evidence emphasizes, for the first time, that tDCS over the right DLPFC combined with executive training enhances functional communication in severe aphasia.

Transcranial Direct Current Stimulation Combined With Listening to Preferred Music Alters Cortical Speech Processing in Older Adults

Emerging evidence suggests transcranial direct current stimulation (tDCS) can improve cognitive performance in older adults. Similarly, music listening may improve arousal and stimulate subsequent performance on memory-related tasks. We examined the synergistic effects of tDCS paired with music listening on auditory neurobehavioral measures to investigate causal evidence of short-term plasticity in speech processing among older adults. In a randomized sham-controlled crossover study, we measured how combined anodal tDCS over dorsolateral prefrontal cortex (DLPFC) paired with listening to autobiographically salient music alters neural speech processing in older adults compared to either music listening (sham stimulation) or tDCS alone. EEG assays included both frequency-following responses (FFRs) and auditory event-related potentials (ERPs) to trace neuromodulation-related changes at brainstem and cortical levels. Relative to music without tDCS (sham), we found tDCS alone (without music) modulates the early cortical neural encoding of speech in the time frame of ∼100-150 ms. Whereas tDCS by itself appeared to largely produce suppressive effects (i.e., reducing ERP amplitude), concurrent music with tDCS restored responses to those of the music+sham levels. However, the interpretation of this effect is somewhat ambiguous as this neural modulation could be attributable to a true effect of tDCS or presence/absence music. Still, the combined benefit of tDCS+music (above tDCS alone) was correlated with listeners' education level suggesting the benefit of neurostimulation paired with music might depend on listener demographics. tDCS changes in speech-FFRs were not observed with DLPFC stimulation. Improvements in working memory pre to post session were also associated with better speech-in-noise listening skills. Our findings provide new causal evidence that combined tDCS+music relative to tDCS-alone (i) modulates the early (100-150 ms) cortical encoding of speech and (ii) improves working memory, a cognitive skill which may indirectly bolster noise-degraded speech perception in older listeners.

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.

Transcranial Magnetic Stimulation and Working Memory Training to Address Language Impairments in Aphasia: A Case Study

BACKGROUND

Traditionally, people with aphasia (PWA) are treated with impairment-based language therapy to improve receptive and expressive language skills. In addition to language deficits, PWA are often affected by some level of working memory (WM) impairments. Both language and working memory impairments combined have a negative impact on PWA's quality of life. The aim of this study was to investigate whether the application of intermittent theta-burst stimulation (iTBS) combined with computerized WM training will result in near-ransfer effects (i.e., trained WM) and far-transfer effects (i.e., untrained language tasks) and have a positive effect on the quality of life of PWA.

METHODS

The participant was a 63-year-old Greek-Cypriot male who presented with mild receptive aphasia and short-term memory difficulties. Treatment was carried out using a multiple baseline (MB) design composed of a pretherapy or baseline testing phase, a therapy phase, and a posttherapy/follow-up phase. The treatment program involved iTBS application to the left dorsolateral prefrontal cortex (DLPFC), an area responsible for WM, for 10 consecutive sessions. The participant received a 3-minute iTBS application followed by 30-minute computer-assisted WM training. Outcome measures included a WM screening test, a standardized aphasia test, a nonverbal intelligence test, story-telling speech samples, a procedural discourse task, and a questionnaire addressing quality of life. These measures were performed three times before the treatment, immediately upon completion of the treatment, and once during follow-up testing at 3 months posttreatment.

RESULTS

We found a beneficial effect of iTBS and WM training on naming, reading, WM, reasoning, narrative, communication efficiency, and quality of life (QoL). Implications for Rehabilitation. Noninvasive brain stimulation combined with computerized WM training may be used in aphasia rehabilitation to improve WM and generalize to language improvement.

Combining proactive transcranial stimulation and cardiac biofeedback to substantially manage harmful stress effects

BACKGROUND

Previous studies have identified the dorsolateral prefrontal cortex (dlPFC) as a core region in cognitive emotional regulation. Transcranial direct current stimulations of the dlPFC (tDCS) and heart-rate variability biofeedback (BFB) are known to regulate emotional processes. However, the effect of these interventions applied either alone or concomitantly during an anticipatory stress remains unexplored.

OBJECTIVE

The study investigated the effect of anodal tDCS and BFB, alone or combined, on psychophysiological stress responses and cognitive functioning.

METHODS

Following a stress anticipation induction, 80 participants were randomized into four groups and subjected to a 15-min intervention: neutral video viewing (ctrl), left dlPFC anodal tDCS (tdcs), heart-rate variability biofeedback (bfb), or a combined treatment (bfb + tdcs). Participants were then immediately confronted with the stressor, which was followed by an assessment of executive functions. Psychophysiological stress responses were assessed throughout the experiment (heart rate, heart-rate variability, salivary cortisol).

RESULTS

The tdcs did not modulate stress responses. Compared with both ctrl and tdcs interventions, bfb reduced physiological stress and improved executive functions after the stressor. The main finding revealed that bfb + tdcs was the most effective intervention, yielding greater reduction in psychological and physiological stress responses than bfb.

CONCLUSIONS

Combining preventive tDCS with BFB is a relevant interventional approach to reduce psychophysiological stress responses, hence offering a new and non-invasive treatment of stress-related disorders. Biofeedback may be particularly useful for preparing for an important stressful event when performance is decisive.

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.

Effects of transcranial direct current stimulation combined with listening to preferred music on memory in older adults

Listening to autobiographically-salient music (i.e., music evoking personal memories from the past), and transcranial direct current stimulation (tDCS) have each been suggested to temporarily improve older adults' subsequent performance on memory tasks. Limited research has investigated the effects of combining both tDCS and music listening together on cognition. The present study examined whether anodal tDCS stimulation over the left dorsolateral prefrontal cortex (2 mA, 20 min) with concurrent listening to autobiographically-salient music amplified subsequent changes in working memory and recognition memory in older adults than either tDCS or music listening alone. In a randomized sham-controlled crossover study, 14 healthy older adults (64-81 years) participated in three neurostimulation conditions: tDCS with music listening (tDCS + Music), tDCS in silence (tDCS-only), or sham-tDCS with music listening (Sham + Music), each separated by at least a week. Working memory was assessed pre- and post-stimulation using a digit span task, and recognition memory was assessed post-stimulation using an auditory word recognition task (WRT) during which electroencephalography (EEG) was recorded. Performance on the backwards digit span showed improvement in tDCS + Music, but not in tDCS-only or Sham + Music conditions. Although no differences in behavioural performance were observed in the auditory WRT, changes in neural correlates underlying recognition memory were observed following tDCS + Music compared to Sham + Music. Findings suggest listening to autobiographically-salient music may amplify the effects of tDCS for working memory, and highlight the potential utility of neurostimulation combined with personalized music to improve cognitive performance in the aging population.

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.

Using transcranial Direct Current Stimulation (tDCS) to investigate why faces are and are not special

We believe we are now in a position to answer the question, "Are faces special?" inasmuch as this applies to the face inversion effect (better performance for upright vs inverted faces). Using a double-blind, between-subject design, in two experiments (n = 96) we applied a specific tDCS procedure targeting the Fp3 area while participants performed a matching-task with faces (Experiment 1a) or checkerboards from a familiar prototype-defined category (Experiment 1b). Anodal tDCS eliminated the checkerboard inversion effect reliably obtained in the sham group, but only reduced it for faces (although the reduction was significant). Thus, there is a component to the face inversion effect that we are not affecting with a tDCS procedure that can eliminate the checkerboard inversion effect. We suggest that the reduction reflects the loss of an expertise-based component in the face inversion effect, and the residual is due to a face-specific component of that effect.

The effects of offline and online prefrontal vs parietal transcranial direct current stimulation (tDCS) on verbal and spatial working memory

Working memory (WM) is a limited-capacity system or set of processes that enables temporary storage and manipulation of information essential for complex cognitive processes. The WM performance is supported by a widespread neural network in which fronto-parietal functional connections have a pivotal role. Transcranial direct current stimulation (tDCS) is rapidly emerging as a promising tool for understanding the role of various cortical areas and their functional networks on cognitive performance. Here we comprehensively evaluated the effects of tDCS on WM by conducting three cross-over counterbalanced sham-controlled experiments in which we contrasted the effects and interactions of the anodal (i.e. facilitatory) tDCS across anterior-posterior (i.e. DLPFC vs PPC) and left-right (i.e. the lateralization) axes, and across online and offline protocols using both verbal and spatial WM (3-back) tasks as outcomes. In the offline protocols, left DLPFC stimulation affected neither verbal nor spatial WM, while left PPC stimulation increased spatial WM. When applied offline over right DLPFC, tDCS improved verbal WM task and marginally enhanced spatial WM; while when tDCS was applied over the right PPC, facilitatory effects were observed on verbal WM. In the online protocol, tDCS did not modulate WM regardless of the task modality or stimulation loci. In summary, the study did not replicate the left DLPFC tDCS effect on WM, found in some of the previous studies, but demonstrated positive effects of stimulation of the right DLPFC as well as PPC bilaterally. The observed effects varied across modality of the 3-back task, and tDCS protocol applied. The results of this study argue for moving towards targeting the lesser-explored stimulation sites within the fronto-parietal network, such as PPC, to gain a better understanding of the usefulness of tDCS for WM neuromodulation.

The effect of non-invasive brain stimulation on executive functioning in healthy controls: A systematic review and meta-analysis

In recent years, there has been a heightened interest in the effect of non-invasive brain stimulation on executive functioning. However, there is no comprehensive overview of its effects on different executive functioning domains in healthy individuals. Here, we assessed the state of the field by conducting a systematic review and meta-analysis on the effectiveness of non-invasive brain stimulation (i.e. repetitive transcranial magnetic stimulation and transcranial direct current stimulation) over prefrontal regions on tasks assessing working memory, inhibition, flexibility, planning and initiation performance. Our search yielded 63 studies (n = 1537), and the effectiveness of excitatory and inhibitory non-invasive brain stimulation were assessed per executive functioning task. Our analyses showed that excitatory non-invasive brain stimulation had a small but positive effect on Stop Signal Task and Go/No-Go Task performance, and that inhibitory stimulation had a small negative effect on Flanker Task performance. Non-invasive brain stimulation did not affect performance on working memory and flexibility tasks, and effects on planning tasks were inconclusive.

Noninvasive brain stimulation in children and adults with attention-deficit/hyperactivity disorder: a systematic review and meta-analysis

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) or transcranial direct current stimulation (tDCS) could provide treatment alternatives to stimulant medication for attention-deficit/hyperactivity disorder (ADHD), given some evidence for improvements in cognition and clinical symptoms. However, despite a lack of solid evidence for their use, rTMS and tDCS are already offered clinically and commercially in ADHD. This systematic review and meta-analysis aimed to critically appraise rTMS and tDCS studies in ADHD to inform good research and clinical practice.

METHODS

A systematic search (up to February 2019) identified 18 studies (rTMS 4, tDCS 14; 311 children and adults with ADHD) stimulating mainly the dorsolateral prefrontal cortex (dlPFC). We included 12 anodal tDCS studies (232 children and adults with ADHD) in 3 random-effects meta-analyses of cognitive measures of attention, inhibition and processing speed.

RESULTS

The review of rTMS and tDCS showed positive effects in some functions but not others, and little evidence for clinical improvement. The meta-analyses of 1 to 5 sessions of anodal tDCS over mainly the left or bilateral dlPFC showed trend-level improvements in inhibition and processing speed, but not in attention.

LIMITATIONS

Heterogeneity in stimulation parameters, patient age and outcome measures limited the interpretation of findings.

CONCLUSION

The review and meta-analysis showed limited evidence that 1 to 5 sessions of rTMS and tDCS, mostly of the dlPFC, improved clinical or cognitive measures of ADHD. These findings did not support using rTMS or tDCS of the dlPFC as an alternative neurotherapy for ADHD as yet. Larger, multi-session stimulation studies identifying more optimal sites and stimulation parameters in combination with cognitive training could achieve larger effects.

BRAINSTORMING: A study protocol for a randomised double-blind clinical trial to assess the impact of concurrent brain stimulation (tDCS) and working memory training on cognitive performance in Acquired Brain Injury (ABI)

Background

Acquired Brain Injury (ABI) admissions have an incidence of 385 per 100,000 of the population in the UK, and as brain injury often involves the frontal networks, cognitive domains affected are likely to be executive control, working memory, and problem-solving deficits, resulting in difficulty with everyday activities. The above observations make working memory, and related constructs such as attention and executive functioning attractive targets for neurorehabilitation. We propose a combined home-based rehabilitation protocol involving the concurrent administration of a working memory training program (adaptive N-back task) with non-invasive transcranial direct current stimulation (tDCS) of the right dorsolateral prefrontal cortex to promote long-lasting modification of brain areas underlying working memory function.

Method

Patients with a working memory deficit will be recruited and assigned to two age-matched groups receiving working memory training for 2 weeks: an active group, receiving tDCS (2 mA for 20 min), and a control group, receiving sham stimulation. After the end of the first 2 weeks, both groups will continue the working memory training for three more weeks. Outcome measures will be recorded at timepoints throughout the intervention, including baseline, after the 2 weeks of stimulation, at the end of the working memory training regimen and 1 month after the completion of the training.

Discussion

The aim of the study is to assess if non-invasive tDCS stimulation has an impact on performance and benefits of a working memory training regimen. Specifically, we will examine the impact of brain stimulation on training gains, if changes in gains would last, and whether changes in training performance transfer to other cognitive domains. Furthermore, we will explore whether training improvements impact on everyday life activities and how the home-based training regimen is received by participants, with the view to develop an effective home healthcare tool that could enhance working memory and daily functioning.

Trial registration

This study was registered with clinicaltrials.gov: NCT04010149 on July 8, 2019.

Effect of prefrontal tDCS on resting brain fMRI graph measures in Alcohol Use Disorders: A randomized, double-blind, sham-controlled study

OBJECTIVES

Transcranial Direct Current Stimulation (tDCS) is a promising new adjuvant approach in the treatment of Alcohol Use Disorders (AUDs) that has the potential to ameliorate the aberrations secondary to chronic alcohol use. In this study, using a randomized, double-blind, sham-controlled, parallel-arm design, we examined the effects of prefrontal tDCS on resting-state functional magnetic resonance imaging (rsfMRI) and its correlates with impulsivity and time to first lapse in subjects with AUDs.

METHODS

Patients with AUD as per DSM-5 criteria were randomly allocated to receive a five-day course of either verum-tDCS (n = 12) or sham-tDCS (n = 12). Of them, 21 patients (verum/sham = 11/10) participated in both baseline and post-intervention 10-min rsfMRI sessions. Outside the scanner, subjects also performed the Stop-Signal Task at two time-points (baseline and post-intervention), which provided a measure of changes in impulsivity following tDCS. After completion of the post-intervention scan, all subjects were discharged and were followed-up for 90 days post-discharge or until lapse to first alcohol use.

RESULTS

Graph theoretical analysis of rsfMRI data revealed that verum-tDCS (but not sham) resulted in a significant increase in the global efficiency of brain networks with a concurrent significant reduction in global clustering; network-based statistical analysis identified a significant increase in the functional connectivity of a specific sub-network involving prefrontal regions. Furthermore, increased global efficiency of brain networks following verum tDCS predicted a significantly reduced likelihood of relapse. In addition, a reduction in the global clustering had a significant positive correlation with a reduction in the measure of impulsivity.

CONCLUSIONS

The present study adds further support to the increasing evidence base for the clinical utility of tDCS in AUDs. Importantly, we observed improvement in both whole-brain network efficiency as well as inter-regional connectivity within a specific local prefrontal sub-network that is relevant to the neurobiology of AUDs. Replication and extension of these promising leads from the present study can facilitate clinical translation of tDCS, given its advantages (i.e. safety, cost-effectiveness, administration ease with potential for remotely-supervised / home-based application) for treating patients with AUDs.

Effects of an APOE Promoter Polymorphism on Fronto-Parietal Functional Connectivity During Nondemented Aging

Background: The rs405509 polymorphism ofthe apolipoprotein E (APOE) promoter is related to Alzheimer'sdisease (AD). The T/T allele of rs405509 is known to decrease the transcription of the APOE gene and lead to impairments in specific brain structural networks with aging; thus, it is an important risk factor for AD. However, it remains unknown whether rs405509 affects brain functional connectivity (FC) in aging. Methods: We investigated the effect of the rs405509 genotype (T/T vs. G-allele) on age-related brain FC using functional magnetic resonance imaging. Forty-five elderly TT carriers and 45 elderly G-allele carriers were scanned during a working memory (WM) task. Results: We found that TT carriers showed an accelerated age-related increase in functional activation in the left postcentral gyrus compared with G-allele carriers. Furthermore, the FC between the left postcentral gyrus and some key regions during WM performance, including the right caudal and superior frontal sulcus (SFS), was differentially modulated by age across rs405509 genotype groups. Conclusions: These results demonstrate that the rs405509 T/T allele of APOE causes an age-related brain functional decline in nondemented elderly people, which may be beneficial for understanding the neural mechanisms of rs405509-related cognitive aging and AD pathogenesis.

Effects of theta burst stimulation over the dorsolateral prefrontal cortex on language switching - A behavioral and ERP study

This study investigated the role of the left dorsolateral prefrontal cortex (DLPFC) in language switching using theta burst stimulation (TBS) and electroencephalography in late bilinguals. After a sham-controlled baseline, participants received either excitatory or inhibitory TBS over the left DLPFC before conducting picture naming tasks in pure language blocks and a language switching block, as well as a nonverbal switching task. On the behavioral level, we found no effect of TBS. However, the ERP-analysis revealed an effect of Stimulation for the picture naming tasks, characterized by alterations in the left DLPFC at 20-72 ms, and in networks associated with conflict resolution and self-monitoring at 533-600 ms. As we did not find an interaction between Stimulation and Block (switching vs non-switching), prefrontal stimulation did not specifically modulate interlanguage control. The left DLPFC might rather be involved in enhancingmaintenance of task demands and self-monitoring during language production in both mono- and bilingual contexts.

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.

A Neuroergonomics Approach to Mental Workload, Engagement and Human Performance

The assessment and prediction of cognitive performance is a key issue for any discipline concerned with human operators in the context of safety-critical behavior. Most of the research has focused on the measurement of mental workload but this construct remains difficult to operationalize despite decades of research on the topic. Recent advances in Neuroergonomics have expanded our understanding of neurocognitive processes across different operational domains. We provide a framework to disentangle those neural mechanisms that underpin the relationship between task demand, arousal, mental workload and human performance. This approach advocates targeting those specific mental states that precede a reduction of performance efficacy. A number of undesirable neurocognitive states (mind wandering, effort withdrawal, perseveration, inattentional phenomena) are identified and mapped within a two-dimensional conceptual space encompassing task engagement and arousal. We argue that monitoring the prefrontal cortex and its deactivation can index a generic shift from a nominal operational state to an impaired one where performance is likely to degrade. Neurophysiological, physiological and behavioral markers that specifically account for these states are identified. We then propose a typology of neuroadaptive countermeasures to mitigate these undesirable mental states.

The Effectiveness of Attention Bias Modification with and without Trans Cranial Direct Current Stimulation in Chronic Low Back Pain

Objective: The present study aimed to compare the effect of ABM (attention bias modification) with and without tDCS (transcranial direct current stimulation) on attention bias, pain intensity, and disability due to pain and pain-related psychological consequences, such as depression, anxiety, and stress. Method : Using convenience sampling, 60 individuals who met the criteria for chronic low back pain (LBP) were selected and randomly assigned in to 2 experimental groups and 2 control and sham-tDCS groups. The experimental ABM group received 5 sessions of the dot-probe task, while the second experimental group received 5 sessions of dot-probe task combined with tDCS. Results: The findings indicated that ABM and ABM+tDCS could reduce attention bias and pain-related psychological consequences significantly, compared to the control and sham groups. Also, attention bias and pain outcomes (depression, anxiety, disability due to pain and pain intensity) remained in ABM+tDCS group than in ABM group in a 1-month follow-up. Conclusion: It was found that tDCS + ABM had no additional effects at the end of intervention, but led to more long-lasting effects in 1-month follow-up. Randomized clinical trial registry number: IRCT20171107037306N1.

Effects of transcranial direct current stimulation on cognition and symptoms in Chinese patients with schizophrenia✰

There is preliminary evidence that transcranial direct current stimulation(tDCS) may improve symptoms and cognitive function in schizophrenia, but the generalizability of these results needs further investigation. We present a study of the effects of active vs. sham tDCS on cognition and symptoms in a sample of 45 Chinese patients with schizophrenia who showed significant cognitive deficits and were treated for 10 sessions with active or sham tDCS. Psychiatric symptoms were assessed by PANSS scores, and cognitive symptoms assessed by MATRICS battery and other tests. There were no differences between cognitive or symptom scores between subjects treated with active vs. sham tDCS tested within 1-2 days after the end of the 10th session. However, two weeks later subjects treated with active tDCS showed significantly more improvements on MATRICS Speed of Processing domain. MATRICS Overall Composite and a CogState measure related to accuracy on a 1-back working memory task were improved at two weeks in statistical tests without multiple corrections. The improvement in cognitive test scores 2 weeks after the last tDCS session, suggests longer term effects may be related to changes in neuroplasticity induced by 10 sessions of tDCS. The lack of significant changes in cognition shortly after the completion of 10 tDCS sessions contrasts with our earlier positive findings in U.S. patients with schizophrenia.

Exploring the effects of Transcranial Direct Current Stimulation over the prefrontal cortex on working memory: A cluster analysis approach

BACKGROUND

The interest in the use of anodal transcranial direct current stimulation (tDCS) for the enhancement of cognitive functioning has increased significantly in recent years. However, the efficacy of this technique remains to be established.

OBJECTIVE

The current study explored the effects of anodal vs. sham tDCS over the left dorsolateral prefrontal cortex (DLPFC) during the performance of the digit span backwards task.

METHODS

30 healthy participants received 'offline' anodal tDCS (1.5 mA, 15 min) to the left DLPFC in an intra-individual, cross-over, sham-controlled experimental design. Memory span performance was assessed before (baseline), immediately after tDCS administration (T1) and 10 min post-T1 (T2). We applied cluster analysis in order to characterize individual responses to tDCS, and in order to identify naturally occurring subgroups that may be present.

RESULTS

Analysis of all the subjects showed that anodal tDCS failed to improve memory span performance. Cluster analysis revealed the presence of a subgroup of 'responders' that significantly improved their performance after anodal (vs. sham) tDCS in T1 (47%) and T2 (46%). However, there was no significant improvement in performance after anodal tDCS compared to the best baseline performance.

CONCLUSION

Our findings suggest that tDCS does not improve memory span performance and highlights the need for better ways to optimize methodological approaches in order to account for inter-individual variability and accurately assess the evidential value of tDCS-linked cognitive outcomes.

Transcranial direct current stimulation on prefrontal and parietal areas enhances motor imagery

Considering the potential effect of transcranial direct current stimulation (tDCS) to improve motor imagery the purpose of this study was to investigate the effects of tDCS on prefrontal and postparietal cortex in hand mental rotation (HMR). This investigation was a single-blind, randomized study which 60 healthy right-hand college students (30 males and 30 females, age 24.27±0.19 years) volunteered to attend. Using a simple random method, participants were divided into four groups: anodal: F4 (n=15) and P4 (n=15), sham: F4 (n=15) and P4 (n=15). Participants were asked to perform HMR task before and after five sessions of tDCS. Results showed that there is a significant difference between the pretest and post-test of reaction time (t=10.09, d.f.=29, P=0.005) and accuracy (t=-5.04, d.f.=29, P=0.005) in two sites (F4, P4) in anodal group, also two-way analysis of variance of HMR reaction time showed significant main effect of Group (F=52.458, P=0.000, ηP=0.488) indicating faster response in postanodal Group and Site (F=6.561, P=0.013, ηP=0.107) indicating better response in F4, and in HMR accuracy a significant main effect of Group (F=13.659, P=0.001, ηP=0.199) but not for the main effect of Site (F=0.499, P=0.483, ηP=0.009). According to the findings of the study, it is suggested that tDCS on both prefrontal and postparietal cortex could improve HMR with more effect on prefrontal area.

Modulation of Emotional Conflict Processing by High-Definition Transcranial Direct Current Stimulation (HD-TDCS)

Cognitive control is characterized by selective attention to relevant stimuli while irrelevant, distracting stimuli are inhibited. While the classical color-word Stroop task was implemented to investigate the processes of cognitive control, a variant of it—the face-word Stroop task—allows for directly investigating processes of emotional conflict control. It is thought that the prefrontal cortex (PFC) is especially involved in processes of cognitive control, while the rostral cingulate is mainly associated with the resolution of emotional conflict. In recent years, the role of the dorsolateral PFC (DLPFC) during the performance of the classical Stroop was investigated by means of transcranial direct current stimulation (tDCS) with divergent results. However, investigations to the causal role of the DLPFC during emotional conflict processing are rare. For this purpose, we used a combined high-definition tDCS (HD-tDCS)/electroencephalogram (EEG) setting to investigate the impact of anodal stimulation of the left DLPFC on behavioral and electrophysiological responses during an emotional face-word Stroop task. In two separate sessions, participants (n = 18) received either sham or anodal HD-tdc stimulation while responding to the emotional expression of the face and ignoring the word. Our results show that anodal stimulation of the left DLPFC increases the behavioral interference effect, that is, the already decelerated reaction times (RTs) to incongruent trials further increase while RTs to congruent trials remain largely unaffected. Furthermore, the stimulation modulates brain response to emotional facial expressions during the face-word Stroop generally—independent of the valence of the emotional expression and the congruency of the combined face-word presentation, the N170 decreases during anodal stimulation. These results reveal that the left DLPFC has a causal role in emotional conflict processing during a face-word Stroop.

Transcranial Direct Current Stimulation over the Left Dorsolateral Prefrontal Cortex Improves Inhibitory Control and Endurance Performance in Healthy Individuals

The dorsolateral prefrontal cortex (DLPFC) is a crucial brain region for inhibitory control, an executive function essential for behavioral self-regulation. Recently, inhibitory control has been shown to be important for endurance performance. Improvement in inhibitory control was found following transcranial direct current stimulation (tDCS) applied over the left DLPFC (L-DLPFC). This study examined the effect tDCS on both an inhibitory control and endurance performance in a group of healthy individuals. Twelve participants received either real tDCS (Real-tDCS) or placebo tDCS (Sham-tDCS) in randomized order. The anodal electrode was placed over the L-DLPFC while the cathodal electrode was placed above Fp2. Stimulation lasted 30min with current intensity set at 2mA. A Stroop test was administered to assess inhibitory control. Heart rate (HR), ratings of perceived exertion (RPE), and leg muscle pain (PAIN) were monitored during the cycling time to exhaustion (TTE) test, while blood lactate accumulation (∆B[La^-]) was measured at exhaustion. Stroop task performance was improved after Real-tDCS as demonstrated by a lower number of errors for incongruent stimuli (p=0.012). TTE was significantly longer following Real-tDCS compared to Sham-tDCS (p=0.029, 17±8 vs 15±8min), with significantly lower HR (p=0.002) and RPE (p<0.001), while no significant difference was found for PAIN (p>0.224). ∆B[La^-] was significantly higher at exhaustion in Real-tDCS (p=0.040). Our findings provide preliminary evidence that tDCS with the anodal electrode over the L-DLPFC can improve both inhibitory control and endurance cycling performance in healthy individuals.

Testing the role of cognitive inhibition in physical endurance using high-definition transcranial direct current stimulation over the prefrontal cortex

The aim of this study was to clarify the role of the prefrontal cortex (PFC) in physical effort regulation. We hypothesized that the PFC would be progressively involved in physical endurance through the engagement of cognitive inhibition, which would be necessary to maintain effort by inhibiting fatigue-related cues. This hypothesis was examined using a double-blind, sham-controlled, within-subjects study (N = 20) using high-definition (HD) transcranial direct current stimulation (tDCS) over the right dorsolateral prefrontal cortex (dlPFC). Participants had to maintain a knee extensor contraction at 30% of their maximal force while simultaneously performing an Eriksen flanker task to evaluate their inhibition performance during the task. Anodal stimulation of the dlPFC influenced response to the cognitive task during exercise, as seen by slower response times and better accuracy. However, it did not lead to any measureable improvement in cognitive inhibition and did not influence endurance time. There was no correlation between cognitive inhibition and the maintenance of physical effort. This result does not indicate a relationship between cognitive inhibition and endurance performance. The contribution of the PFC in physical endurance could be explained through its involvement on decisional processes.

Transcranial direct current stimulation (tDCS) for improving aphasia in adults with aphasia after stroke

BACKGROUND

Stroke is one of the leading causes of disability worldwide and aphasia among survivors is common. Current speech and language therapy (SLT) strategies have only limited effectiveness in improving aphasia. A possible adjunct to SLT for improving SLT outcomes might be non-invasive brain stimulation by transcranial direct current stimulation (tDCS) to modulate cortical excitability and hence to improve aphasia.

OBJECTIVES

To assess the effects of tDCS for improving aphasia in people who have had a stroke.

SEARCH METHODS

We searched the Cochrane Stroke Group Trials Register (June 2018), CENTRAL (Cochrane Library, June 2018), MEDLINE (1948 to June 2018), Embase (1980 to June 2018), CINAHL (1982 to June 2018), AMED (1985 to June 2018), Science Citation Index (1899 to June 2018), and seven additional databases. We also searched trial registers and reference lists, handsearched conference proceedings and contacted authors and equipment manufacturers.

SELECTION CRITERIA

We included only randomised controlled trials (RCTs) and randomised controlled cross-over trials (from which we only analysed the first period as a parallel group design) comparing tDCS versus control in adults with aphasia due to stroke.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and risk of bias, and extracted data. If necessary, we contacted study authors for additional information. We collected information on dropouts and adverse events from the trials.

MAIN RESULTS

We included 21 trials involving 421 participants in the qualitative synthesis. Three studies with 112 participants used formal outcome measures for our primary outcome measure of functional communication - that is, measuring aphasia in a real-life communicative setting. There was no evidence of an effect (standardised mean difference (SMD) 0.17, 95% confidence interval (CI) -0.20 to 0.55; P = 0.37; I² = 0%; low quality of evidence; inverse variance method with random-effects model; higher SMD reflecting benefit from tDCS; moderate quality of evidence). At follow-up, there also was no evidence of an effect (SMD 0.14, 95% CI -0.31 to 0.58; P = 0.55; 80 participants ; 2 studies; I² = 0%; very low quality of evidence; higher SMD reflecting benefit from tDCS; moderate quality of evidence).For our secondary outcome measure, accuracy in naming nouns at the end of intervention, there was evidence of an effect (SMD 0.42, 95% CI 0.19 to 0.66; P = 0.0005; I² = 0%; 298 participants; 11 studies; inverse variance method with random-effects model; higher SMD reflecting benefit from tDCS; moderate quality of evidence). There was an effect for the accuracy in naming nouns at follow-up (SMD 0.87, 95% CI 0.25 to 1.48; P = 0.006; 80 participants; 2 studies; I² = 32%; low quality of evidence); however the results were not statistically significant in our sensitivity analysis regarding the assumptions of the underlying correlation coefficient for imputing missing standard deviations of change scores. There was no evidence of an effect regarding accuracy in naming verbs post intervention (SMD 0.19, 95% CI -0.68 to 1.06; P = 0.67; I² = 0%; 21 participants; 3 studies; very low quality of evidence). We found no studies examining the effect of tDCS on cognition in people with aphasia after stroke. We did not find reported serious adverse events and the proportion of dropouts and adverse events was comparable between groups (odds ratio (OR) 0.54, 95% CI 0.21 to 1.37; P = 0.19; I² = 0%; Mantel-Haenszel method with random-effects model; 345 participants; 15 studies; low quality of evidence).

AUTHORS' CONCLUSIONS

Currently there is no evidence of the effectiveness of tDCS (anodal tDCS, cathodal tDCS and Dual-tDCS) versus control (sham tDCS) for improving functional communication in people with aphasia after stroke (low quality of evidence). However, there is limited evidence that tDCS may improve naming performance in naming nouns (moderate quality of evidence), but not verbs (very low quality of evidence) at the end of the intervention period and possibly also at follow-up. Further methodologically rigorous RCTs with adequate sample size calculation are needed in this area to determine the effectiveness of this intervention. Data on functional communication and on adverse events should routinely be collected and presented in further publications as well as data at follow-up. Further study on the relationship between language/aphasia and cognition may be required, and improved cognitive assessments for patients with aphasia developed, prior to the use of tDCS to directly target cognition in aphasia. Authors should state total values at post-intervention as well as their corresponding change scores with standard deviations.

Effect of home-based transcranial direct current stimulation (tDCS) on cognitive function in patients with mild cognitive impairment: a study protocol for a randomized, double-blind, cross-over study

Background

The possible effect of transcranial direct current stimulation (tDCS) in improving cognitive function is clear from studies involving pre-dementia stage mild cognitive impairment (MCI). However, the application of tDCS in actual clinical practice entails repeated hospital visits almost every day for treatment. The objective of this study is to confirm the possibility of self-application of tDCS at home by elderly patients with declined cognitive function and the significant clinical effect of tDCS administered at home.

Methods/design

This study will be conducted in 20 elderly people aged 60 to 80 years with complaints of subjective memory impairment while maintaining general functions with limited activities of daily living. This study involves a cross-over design that will include 2-week active or sham stimulation of both dorsolateral prefrontal cortexes (left, anode; right, cathode) randomly with a 2-week wash-out phase. Changes in cognitive function will be evaluated using visual recognition tasks and neuropsychological tests. In this study, tDCS will be carried out by each patient at his/her home and its safety and suitability will be evaluated.

Discussion

In this study, patients will apply a portable tDCS, developed for home use, for more than 2 weeks. Such studies can contribute to the use of tDCS as a realistic therapy. In addition, the utility of home-based tDCS will be confirmed by application of tDCS at home by the elderly with declined cognitive function. Furthermore, confirmation of tDCS as a significant therapeutic method can facilitate treatment of Alzheimer’s dementia at an early stage, including MCI.

Trial registration

Clinical Research Information Service (CRIS), KCT0002721. Registered on 9 March 2018.

Electronic supplementary material

The online version of this article (10.1186/s13063-019-3360-1) contains supplementary material, which is available to authorized users.