After-effects of transcranial alternating current stimulation on evoked delta and theta power

Objective

Phase synchronization is suggested to be among the mechanisms that can explain the effects of transcranial alternating current stimulation (tACS). However, little is known about the effects of tACS on event-related oscillatory activity. Therefore the objective was to investigate frequency-related effects of frontal tACS on event-related oscillatory power.

经颅交流电刺激干预神经精神疾病的研究进展

经颅交流电刺激是一种无创的电刺激疗法,有望成为干预大脑相关疾病的一种新的神经调控方法。本文中简要介绍与经颅交流电刺激干预疗效的相关因素、可能的治疗机制、临床应用及其发展前景。     

Parametric effects of transcranial alternating current stimulation on multitasking performance

Background

We have previously demonstrated that transcranial alternating current stimulation (tACS) can generate positive effects on multitasking performance and associated neurophysiological measures when it is applied with anti-phase theta band stimulation across bilateral prefrontal cortex (PFC) and a short (1-min) inter-session interval (ISI). However, it is unclear how altering the phase of stimulation and the duration of the ISI might impact positive tACS effects. Here, we investigated the role of tACS parameters in engendering performance improvements by manipulating these two stimulation parameters (i.e. phase and ISI) in two experiments.

Individual differences in neuroanatomy and neurophysiology predict effects of transcranial alternating current stimulation

BackgroundNoninvasive transcranial electrical stimulation (tES) research has been plagued with inconsistent effects. Recent work has suggested neuroanatomical and neurophysiological variability may alter tES efficacy. However, direct evidence is limited.ObjectiveWe have previously replicated effects of transcranial alternating current stimulation (tACS) on improving multitasking ability in young adults. Here, we attempt to assess whether these stimulation parameters have comparable effects in older adults (aged 60–80 years), which is a population known to have greater variability in neuroanatomy and neurophysiology. It is hypothesized that this variability in neuroanatomy and neurophysiology will be predictive of tACS efficacy.MethodsWe conducted a pre-registered study where tACS was applied above the prefrontal cortex (between electrodes F3-F4) while participants were engaged in multitasking. Participants were randomized to receive either 6-Hz (theta) tACS for 26.67 min daily for three days (80 min total; Long Exposure Theta group), 6-Hz tACS for 5.33 min daily (16-min total; Short Exposure Theta group), or 1-Hz tACS for 26.67 min (80 min total; Control group). To account for neuroanatomy, magnetic resonance imaging data was used to form individualized models of the tACS-induced electric field (EF) within the brain. To account for neurophysiology, electroencephalography data was used to identify individual peak theta frequency.ResultsResults indicated that only in the Long Theta group, performance change was correlated with modeled EF and peak theta frequency. Together, modeled EF and peak theta frequency accounted for 54%–65% of the variance in tACS-related performance improvements, which sustained for a month.ConclusionThese results demonstrate the importance of individual differences in neuroanatomy and neurophysiology in tACS research and help account for inconsistent effects across studies.     

Phase-specific manipulation of rhythmic brain activity by transcranial alternating current stimulation

BackgroundOscillatory phase has been proposed as a key parameter defining the spatiotemporal structure of neural activity. To enhance our understanding of brain rhythms and improve clinical outcomes in pathological conditions, modulation of neural activity by transcranial alternating current stimulation (tACS) emerged as a promising approach. However, the phase-specificity of tACS effects in humans is still critically debated.ObjectiveHere, we investigated the phase-specificity of tACS on visually evoked steady state responses (SSRs) in 24 healthy human participants.MethodsWe used an intermittent electrical stimulation protocol and assessed the influence of tACS on SSR amplitude in the interval immediately following tACS. A neural network model served to validate the plausibility of experimental findings.ResultsWe observed a modulation of SSR amplitudes dependent on the phase shift between flicker and tACS. The tACS effect size was negatively correlated with the strength of flicker-evoked activity. Supported by simulations, data suggest that strong network synchronization limits further neuromodulation by tACS. Neural sources of phase-specific effects were localized in the parieto-occipital cortex within flicker-entrained regions. Importantly, the optimal phase shift between flicker and tACS associated with strongest SSRs was correlated with SSR phase delays in the tACS target region.ConclusionsOverall, our data provide electrophysiological evidence for phase-specific modulations of rhythmic brain activity by tACS in humans. As the optimal timing of tACS application was dependent on cortical SSR phase delays, our data suggest that tACS effects were not mediated by retinal co-stimulation. These findings highlight the potential of tACS for controlled, phase-specific modulations of neural activity.     

Effects on motor learning of transcranial alternating current stimulation applied over the primary motor cortex and cerebellar hemisphere

Transcranial alternating current stimulation (tACS) is a non-invasive method of brain stimulation that modulates oscillatory neural activity in the cortical area under the electrodes. Gamma (γ)-tACS applied over the primary motor cortex (M1) and cerebellar hemisphere is known to improve motor performance; however, it is not yet known whether it affects motor learning. Thus, here we investigated whether γ-tACS applied over the M1 and cerebellar hemisphere affects motor learning. This study involved 30 healthy subjects (14 females, 16 males) performing a visuomotor control task (eight trials) during an administration of either γ-tACS or a sham stimulation (15 subjects per condition) over their right M1 and left cerebellar hemisphere. Each subject performed five trials after 24 h. The motor learning efficiency, motor learning retention and re-motor learning efficiency in each condition were compared. The motor learning retention in the γ-tACS condition was significantly higher than that in the sham condition (p = 0.031). Thus, subjects who were administered γ-tACS maintained their motor performance the next day better than sham-stimulated subjects. There was no significant difference between the conditions in the motor learning efficiency and those in the re-motor learning efficiency. Our results demonstrate that γ-tACS administered over the M1 and cerebellar hemisphere during a motor learning task can enhance motor learning retention.     

Optimized auditory transcranial alternating current stimulation improves individual auditory temporal resolution

Background

Temporal resolution of cortical, auditory processing mechanisms is suggested to be linked to peak frequency of neuronal gamma oscillations in auditory cortex areas (individual gamma frequency, IGF): Individuals with higher IGF tend to have better temporal resolution.

Boosting visual perceptual learning by transcranial alternating current stimulation over the visual cortex at alpha frequency

BackgroundTranscranial alternating current stimulation (tACS) has been widely used to alter ongoing brain rhythms in a frequency-specific manner to modulate relevant cognitive functions, including visual functions. Therefore, it is a useful tool for exploring the causal role of neural oscillations in cognition. Visual functions can be improved substantially by training, which is called visual perceptual learning (VPL). However, whether and how tACS can modulate VPL is still unclear.ObjectiveThis work aims to explore how tACS modulates VPL and the role of neural oscillations in VPL.MethodsA between-subjects design was adopted. Subjects were assigned to six groups and undertook five daily training sessions to execute an orientation discrimination task. During training, five groups received occipital tACS stimulation at 6, 10, 20, 40, and sham 10 Hz respectively, and one group was stimulated at the sensorimotor regions by 10 Hz tACS.ResultsCompared with the sham stimulation, occipital tACS at 10 Hz, but not at other frequencies, accelerated perceptual learning and increased the performance improvement. However, these modulatory effects were absent when 10 Hz tACS was delivered to the sensorimotor areas. Moreover, the tACS-induced performance improvement lasted at least two months after the end of training.ConclusionTACS can facilitate orientation discrimination learning in a frequency- and location-specific manner. Our findings provide strong evidence for a pivotal role of alpha oscillations in boosting VPL and shed new light on the design of effective neuromodulation protocols that can facilitate rehabilitation for patients with neuro-ophthalmological disorders.     

Recovery of motor disability and spasticity in post-stroke after repetitive transcranial magnetic stimulation (rTMS)

Lately it has been indicated that the stimulation of both sides of the motor cortices with different frequencies of rTMS can improve the behaviour of a paretic arm. We studied the effect of rTMS in severe cases of post-stroke after nearly 10 years. They had wide hemispheric lesion and their paresis had not changed for more than 5 years. The majority of patients could not move their fingers on the affected side. In our study we examined whether the active movement could be induced by rTMS even several years after stroke and which hemisphere (affected or unaffected) stimulated by rTMS would be the best location for attenuating the spasticity and for developing movement in the paretic arm.Sixty-four patients (more than 5 years after stroke in a stable state) were followed for 3 months. They were treated with rTMS with 1 Hz at 30% of 2.3 T 100 stimuli per session twice a day for a week. The area to be stimulated was chosen according to the evoked movement by TMS in the paretic arm. That way, four groups were created and compared. In group A, where both hemispheres were stimulated (because of the single stimulation of TMS could induce movement from both sides of hemispheres) the spasticity decreased but the movement could not be influenced. A highly significant improvement in spasticity, in movement induction and in the behaviour of paresis was observed in group B, where before treatment, there was no evoked movement in the paretic arm from stimulating either hemispheres of the brain. For treatment we stimulated the unaffected hemisphere from where the intact arm is moved (ipsilateral to the paretic side). In both groups C (contralateral hemisphere to the paretic arm) and D (ipsilaterally evoked movement in the paretic arm), the spasticity decreased during the first week, but the movement of the paretic arm improved only in group C.It seems that spasticity can be modified by the stimulation either the affected or the unaffected hemisphere, but the induction of movement can be achieved only by the stimulation of an intact motor pathway and its surrounding area (groups B and C). The improvement in paretic extremities can be achieved with rTMS even after years of stroke when the traditional rehabilitation has failed.     

Treatment of depression with transcranial direct current stimulation (tDCS): A Review

Major Depression Disorder (MDD) is usually accompanied by alterations of cortical activity and excitability, especially in prefrontal areas. These are reflections of a dysfunction in a distributed cortico-subcortical, bihemispheric network. Therefore it is reasonable to hypothesize that altering this pathological state with techniques of brain stimulation may offer a therapeutic target. Besides repetitive transcranial magnetic stimulation, tonic stimulation with weak direct currents (tDCS) modulates cortical excitability for hours after the end of stimulation, thus, it is a promising non-invasive therapeutic option. Early studies from the 1960s suggested some efficacy of DC stimulation to reduce symptoms in depression, but mixed results and development of psychotropic drugs resulted in an early abandonment of this technique. In the last years tDCS protocols have been optimized. Application of the newly developed stimulation protocols in patients with major depression has shown promise in few pilot studies. Further studies are needed to identify the optimal parameters of stimulation and the clinical and patient characteristics that may condition response to tDCS.     

Repetitive transcranial magnetic stimulation (rTMS) versus transcranial direct current stimulation (tDCS) in the management of patients with fibromyalgia: A randomized controlled trial

ObjectivesThe aim of this study was to compare the effects of repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) on pain and quality of life in patients with fibromyalgia.MethodsThirty participants were randomized into two groups of 15 patients, to receive 3 sessions of either high-frequency (10 Hz) rTMS or 2 mA, 20 min anodal transcranial direct current stimulation over the left dorsolateral prefrontal cortex (DLPFC) over 1 week. Pain was assessed using a Visual Analog Scale (VAS) before treatment, immediately after treatment, 6 and 12 weeks later. Quality of life was evaluated using the Revised Fibromyalgia Impact Questionnaire (FIQR) and psychiatric symptoms were measured using the Depression Anxiety Stress Scale-21 Item (DASS-21) before treatment, and 6 and 12 weeks after treatment.ResultsFor the VAS there was a significant time-group interaction, showing that the behavior of two groups differed regarding changes of VAS in favor of the RTMS group (df = 1.73, F = 4.80, p = <0.016). Time-group interaction effect on DASS-21 and FIQR was not significant. 66.6% of patients in rTMS group and 26.6% of patients in tDCS group experienced at least a 30% reduction of VAS from baseline to last follow-up (p = 0.028).DiscussionWith the methodology used in this study, both rTMS and tDCS were safe modalities and three sessions of rTMS over DLPFC had greater and longer lasting analgesic effects compared to tDCS in patients with FM. However, considering the limitations of this study, further studies are needed to explore the most effective modality.     

Improving working memory: Exploring the effect of transcranial random noise stimulation and transcranial direct current stimulation on the dorsolateral prefrontal cortex

Objective

The aim of this study was to determine if working memory (WM) performance is significantly improved after the delivery of transcranial random noise stimulation (tRNS) to the left dorsolateral prefrontal cortex (DLPFC), compared to an active comparator or sham.

Methods

Ten participants undertook three experimental sessions in which they received 10 min of anodal tDCS (active comparator), tRNS or sham tDCS whilst performing the Sternberg WM task. Intra-stimulation engagement in a WM task was undertaken as this has been previously shown to enhance the effects of tDCS. Experimental sessions were separated by a minimum of 1 week. Immediately prior to and after each stimulation session the participants were measured on speed and accuracy of performance on an n-back task.

Results

There was significant improvement in speed of performance following anodal tDCS on the 2-back WM task; this was the only significant finding.

Conclusions

The results do not provide support for the hypothesis that tRNS improves WM. However, the study does provide confirmation of previous findings that anodal tDCS enhances some aspects of DLPFC functioning. Methodological limitations that may have contributed to the lack of significant findings following tRNS are discussed.

Significance

Anodal tDCS may have significant implications for WM remediation in psychiatric conditions, particularly schizophrenia.     

The effects of transcranial direct current stimulation on upper-limb function post-stroke: A meta-analysis of multiple-session studies

ObjectiveTo systematically review how patient characteristics and/or transcranial direct current stimulation (tDCS) parameters influence tDCS effectiveness in respect to upper limb function post-stroke.MethodsThree electronic databases were searched for sham-controlled randomised trials using the Fugl-Meyer Assessment for upper extremity as outcome measure. A meta-analysis and nine subgroup-analyses were performed to identify which tDCS parameters yielded the greatest impact on upper limb function recovery in stroke patients.ResultsEighteen high-quality studies (507 patients) were included. tDCS applied in a chronic stage yields greater results than tDCS applied in a (sub)acute stage. Additionally, patients with low baseline upper limb impairments seem to benefit more from tDCS than those with high baseline impairments. Regarding tDCS configuration, all stimulation types led to a significant improvement, but only tDCS applied during therapy, and not before therapy, yielded significant results. A positive dose–response relationship was identified for current/charge density and stimulation duration, but not for number of sessions.ConclusionOur results demonstrate that tDCS improves upper limb function post-stroke. However, its effectiveness depends on numerous factors. Especially chronic stroke patients improved, which is promising as they are typically least amenable to recovery.SignificanceThe current work highlights the importance of several patient-related and protocol-related factors regarding tDCS effectiveness.     

The effect of somatosensory alpha transcranial alternating current stimulation on pain empathy is trait empathy and gender dependent

BackgroundPain empathy enables a person to experience and understand other''s pain state by observing others in pain condition. Such prosocial ability is deficient in many psychopathological disorders. Somatosensory alpha suppression is considered as neural correlates of pain empathy and is hypothesized as a target for enhancement of pain empathy. Researches demonstrated that alpha suppression could be enhanced by transcranial alternating current stimulation (tACS) at alpha frequency non‐invasively.AimsWe applied alpha tACS over the primary somatosensory cortex of healthy subjects to investigate whether alpha tACS is able to enhance the pain empathy performance.ResultsThe results showed that there was no difference of pain empathy performance between alpha tACS and sham tACS either when tACS was applied during the task or before task. While in the alpha tACS group, the pain empathy performance was positively correlated with empathic concern of male subjects, the sub‐component of personal trait empathy.ConclusionsAlpha tACS cannot alter the empathy performance overall, but the modulation effect of alpha tACS on pain empathy is dependent on the gender and trait empathy of subjects.     

Effects of transcranial direct current stimulation coupled with repetitive electrical stimulation on cortical spreading depression

We have recently shown that two techniques of brain stimulation - repetitive electrical stimulation (ES) (that mimics transcranial magnetic stimulation) and transcranial direct current stimulation (tDCS) - modify the velocity of cortical spreading depression (CSD) significantly. Herein we aimed to study the effects of these two techniques combined on CSD. Thirty-two Wistar rats were divided into four groups according to the treatment: sham tDCS/sham ES, sham tDCS/1 Hz ES, anodal tDCS/1 Hz ES, cathodal tDCS/1 Hz ES. Our findings show that 1 Hz ES reduced CSD velocity, and this effect was modified by either anodal or cathodal tDCS. Anodal tDCS induced larger effects than cathodal tDCS. Hereby CSD velocity was actually increased significantly after anodal tDCS/1 Hz ES. Our results show that combining two techniques of brain stimulation can modify significantly the effects of ES alone on cortical excitability as measured by the neurophysiological parameter of cortical spreading depression and therefore provide important insights into the effects of this new approach of brain stimulation on cortical activity.     

Safety aspects of transcranial direct current stimulation concerning healthy subjects and patients

Cortical excitability changes induced by tDCS and revealed by TMS, are increasingly being used as an index of neuronal plasticity in the human cortex. The aim of this paper is to summarize the partially adverse effects of 567 tDCS sessions over motor and non-motor cortical areas (occipital, temporal, parietal) from the last 2 years, on work performed in our laboratories. One-hundred and two of our subjects who participated in our tDCS studies completed a questionnaire. The questionnaire contained rating scales regarding the presence and severity of headache, difficulties in concentrating, acute mood changes, visual perceptual changes and any discomforting sensation like pain, tingling, itching or burning under the electrodes, during and after tDCS. Participants were healthy subjects (75.5%), migraine patients (8.8%), post-stroke patients (5.9%) and tinnitus patients (9.8%). During tDCS a mild tingling sensation was the most common reported adverse effect (70.6%), moderate fatigue was felt by 35.3% of the subjects, whereas a light itching sensation under the stimulation electrodes occurred in 30.4% of cases. After tDCS headache (11.8%), nausea (2.9%) and insomnia (0.98%) were reported, but fairly infrequently. In addition, the incidence of the itching sensation (p=0.02) and the intensity of tingling sensation (p=0.02) were significantly higher during tDCS in the group of the healthy subjects, in comparison to patients; whereas the occurrence of headache was significantly higher in the patient group (p=0.03) after the stimulation. Our results suggest that tDCS applied to motor and non-motor areas according to the present tDCS safety guidelines, is associated with relatively minor adverse effects in healthy humans and patients with varying neurological disorders.     

Modulation of creativity by transcranial direct current stimulation

BackgroundCreativity is the use of original ideas to accomplish something innovative. Previous research supports the notion that creativity is facilitated by an activation of the right and/or a deactivation of the left prefrontal cortex. In contrast, recent brain imaging studies suggest that creativity improves with left frontal activation.ObjectiveThe present study was designed to further elucidate the neural basis of and ways to modulate creativity, based on the modulation of prefrontal cortical activity through the non-invasive brain stimulation technique transcranial direct current stimulation (tDCS).MethodsNinety healthy University students performed three tasks on major aspects of creativity: conceptual expansion (Alternate Uses Task, AUT), associative thinking (Compound Remote Associate Task, CRA), and set shifting ability (Wisconsin Card Sorting Task, WCST). Simultaneously, they received cathodal stimulation of the left and anodal stimulation of the right inferior frontal gyrus (IFG), the reverse protocol, or sham stimulation.ResultsThe main pattern of results was a superior performance with bilateral left cathodal/right anodal stimulation, and an inferior performance in the reversed protocol compared to sham stimulation. As a potential underlying physiological mechanism, resting state EEG beta power, indicative of enhanced cortical activity, in the right frontal area increased with anodal stimulation and was associated with better performance.ConclusionThe findings provide new insights into ways of modulating creativity, whereby a deactivation of the left and an activation of the right prefrontal cortex with tDCS is associated with increased creativity. Potential future applications might include tDCS for patients with mental disorders and for healthy individuals in creative professions.     

Effects of transcranial direct current stimulation on performance and recovery sleep during acute sleep deprivation: a pilot study

BackgroundPrevious studies claimed that transcranial direct current stimulation (tDCS) over the left dorsolateral prefrontal cortex (DLPFC) improves cognition in neuropsychiatric patients with cognitive impairment, schizophrenia, organic hypersomnia, etc, but few studies evaluated the effects of tDCS on cognitive improvement following sleep deprivation. The objective of this study was to determine whether tDCS (anode on the left DLPFC and cathode on the right DLPFC with a 2-mA current for 30 min) improves cognition following sleep deprivation.MethodsSeven participants received active tDCS and eight participants received sham tDCS when their cognition declined during at least 30 h of sleep deprivation. All participants completed the psychomotor vigilance task, Trail Making Tests A and B, digit cancellation test, Stroop color word test, the Brief Visuospatial Memory Test-Revised and a procedural game every 2 h during the sleep deprivation and after recovery sleep.ResultsCompared to the sham stimulation, active tDCS (anode on the left DLPFC and cathode on the right DLPFC at a 2-mA current for 30 min) had beneficial effects on attention, memory, executive function, processing speed, and the ability to inhibit cognitive interference, and improved in subjective drowsiness and fatigue following sleep deprivation. The lasting effect of a single tDCS on cognition during sleep deprivation was greater than 2 h. In all participants, tDCS did not disturb recovery sleep, and cognitive performance recovered to the baseline levels after recovery sleep.ConclusionsThe study results indicate that tDCS can improve cognition following sleep deprivation and does not disturb recovery sleep or cognitive performance after recovery sleep. The possible pathophysiological mechanisms might be related to the modulation of the corticothalamic pathway. We believe that tDCS can be applied in the treatment of sleep disorders involving sleepiness.Trial registration numberChiCTR2000029420.Date of registration2020-1-31.     

Randomized clinical trial comparing of transcranial direct current stimulation (tDCS) and transcutaneous electrical nerve stimulation (TENS) in knee osteoarthritis

BackgroundDue to the limitations of pharmacological and surgical management of knee osteoarthritis (OA), several non-pharmacologic approaches including transcutaneous electrical nerve stimulation (TENS) and transcranial direct current stimulation (tDCS) have been introduced, with promising results.ObjectiveWe aimed to investigate and compare the therapeutic effects of TENS and tDCS for the treatment of patients with knee OA.MethodsIn this double-blinded randomized controlled trial, a total of 40 adult patients with knee OA were randomly allocated to either the TENS or the tDCS group. Patients in either group received 6 sessions of the TENS or tDCS for 2 weeks. Knee strengthening exercises were performed twice daily for the entire treatment period. Patients were evaluated using the visual analogue scale (VAS) and Western Ontario and McMaster Universities (WOMAC).ResultsSignificant improvement was observed in all outcomes in both TENS and tDCS groups at each follow up compared to baseline although the early improvement (first follow-up) in the WOMAC index was not significant in the TENS group. Based on the within-subject analysis, the behavior of two treatment groups did not differ regarding the changes in the course of the VAS, WOMAC score and its subscales, i.e. stiffness, pain and function (p = 0.263, 0.051, 0.198, 0.075, and 0.146, respectively).ConclusionsBased on the results of this study, the effect of tDCS and TENS was not significantly different on pain and function of patients with knee OA.