Fields or flows? A comparative metaanalysis of transcranial magnetic and direct current stimulation to treat post-stroke aphasia

Effectiveness of Transcranial Direct Current Stimulation as an Adjuvant to Aphasia Treatment Following Stroke: Evidence From Systematic Reviews and Meta-Analyses

PURPOSE

Transcranial direct current stimulation (tDCS) is a neuromodulation tool to amplify neural excitability and enhance outcomes associated with speech-language therapy (SLT). Stimulation currents to the left and right hemispheres vary in applying anodal (excitatory), cathodal (inhibitory), or bihemispheric signals. Several systematic reviews (SRs) and meta-analyses (MAs) have summarized the large literature examining tDCS for aphasia rehabilitation. The purpose of this project was to appraise the quality of SRs and MAs of tDCS for aphasia and examine the weight of the evidence for language outcomes in individuals with aphasia beyond SLT alone.

METHOD

We searched four databases for SRs/MAs examining effects of tDCS for poststroke aphasia. We identified 16 reviews, with nine that incorporated MA to quantify results. Two reviewers reliably coded articles for methodological rigor using the AMSTAR 2 (A MeaSurement Tool to Assess Systematic Reviews, Version 2). We then summarized findings of the 16 reviews.

RESULTS

The AMSTAR 2 appraisal criteria suggest that critical weaknesses were noted among all reviews except those by Elsner et al. (2015, 2019). Reviews summarized three to 48 studies, as some included only randomized crossover trials and others included all trial designs. All SRs and one MA reported improvements following tDCS stimulation for general aphasia abilities and measures of repetition and speech fluency. Five recent MAs reported significant naming improvements following tDCS using all stimulation arrays. No tDCS effects were noted for comprehension measures.

CONCLUSIONS

As the tDCS literature matured, the conclusions of MAs merged with earlier SRs reporting statistically positive benefits over SLT alone. Most consistent results are reported for naming measures, leaving some to question the clinical significance of tDCS effects for functional measures of aphasia recovery. Although the tDCS literature is expansive, important questions remain before the technique can be confidently recommended for clinical practice.

Asynchronous, online spaced-repetition training alleviates word-finding difficulties in aphasia

Word-finding difficulties for naming everyday objects are often prevalent in aphasia. Traditionally, treating these difficulties has involved repeated drilling of troublesome items with a therapist. Spaced repetition schedules can improve the efficiency of such training. However, spaced repetition in a therapy environment can be both difficult to implement and time-consuming. The current study evaluated the potential utility of automated, asynchronous, online spaced repetition training for the treatment of word-finding difficulties in individuals with aphasia. Twenty-one participants completed a two-week training study, completing approximately 60 minutes per day of asynchronous online drilling. The training items were identified using a pretest, and word-finding difficulties were evaluated both at the end of training (i.e., a post-test) and four weeks later (i.e., a retention test). The trained items were separated into three different spaced-repetition schedules: (1) Short-spacing; (2) Long-spacing; and (3) Adaptive-spacing. At the retention-test, all trained items outperformed non-trained items in terms of accuracy and reaction time. Further, preliminary evidence suggested a potential reaction time advantage for the adaptive-spacing condition. Overall, online, asynchronous spaced repetition training appears to be effective in treating word-finding difficulties in aphasia. Further research will be required to determine if different spaced repetition schedules can be leveraged to enhance this effect.

Long-term effects of transcranial direct current stimulation (tDCS) combined with speech language therapy (SLT) on post-stroke aphasia patients: A systematic review and network meta-analysis of randomized controlled trials

BACKGROUND

Transcranial direct current stimulation (tDCS) is a noninvasive neuromodulation tool for improving language performance in patients with aphasia after stroke. However, it remains unclear whether it has long-term effects. After consulting a large number of relevant studies, it was found that there are no definitive conclusions about the long-term effects of tDCS on post-stroke aphasia patients.

OBJECTIVE

To determine whether tDCS has long-term effects on post-stroke aphasia patients (PAPs) and which type of tDCS has the most beneficial treatment effects on language performance (especially naming ability).

METHODS

A network meta-analysis was conducted by searching for randomized controlled trials (RCTs) published until April 2023 in the following databases: Web of Science, Embase, Medline (from OVID and PubMed), PsycInfo and PsycARTICLES (from OVID). We only included RCTs published in English. PAPs treated by tDCS combined with speech-language therapy were selected. Sham tDCS was the control group. Naming ability or other language performance must be assessed at follow-up states. Two reviewers independently used checklists to assess the primary outcome (the long-term effects on naming ability) and the secondary outcome (other language performance, such as communication). Cochrane Collaboration guidelines were used to assess the risk of bias.

RESULTS

Seven studies with 249 patients were included for data synthesis. For primary outcomes (naming nous), there was no obvious evidence to show a difference between interventions (C-tDCS vs. S-tDCS SMD = 0.06, 95% CI = -1.01, 1.12; A-tDCS vs. S-tDCS SMD = 0.00, 95% CI = -0.66, 0.65; D-tDCS vs. S-tDCS SMD = 0.77, 95% CI = -0.71, 2.24; A-tDCS vs. C-tDCS SMD = -0.06, 95% CI = -1.31,1.19; D-tDCS vs. C-tDCS SMD = 0.71, 95% CI = -1.11,2.53; D-tDCS vs. A-tDCS SMD = 0.77, 95% CI = -0.84, 2.39). In addition, no evidence showed differences in communication ability (C-tDCS vs. S-tDCS SMD = 0.08 95% CI = -1.77, 1.92; A-tDCS vs. S-tDCS SMD = 1.23 95% CI = -1.89, 4.34; D-tDCS vs. S-tDCS SMD = 0.70; 95% CI = -1.93, 3.34; A-tDCS vs. C-tDCS SMD = 1.15 95% CI = -2.48, 4.77; D-tDCS vs. C-tDCS SMD = 0.62 95% CI = -2.59, 3.84; D-tDCS vs. A-tDCS SMD = -0.52 95% CI = -4.60, 3.56).

CONCLUSION

It seems that tDCS has no long-term effects on post-stroke aphasia patients in naming nouns and communication in terms of the results of our network meta-analysis. However, the results should be interpreted with caution. In the future, more RCTs with long follow-up times should be included in the research to conduct subgroup or meta-regression analyses to obtain a sufficient effect size.

Targeted neurorehabilitation strategies in post-stroke aphasia

BACKGROUND

Aphasia is a debilitating language impairment, affecting millions of people worldwide. About 40% of stroke survivors develop chronic aphasia, resulting in life-long disability.

OBJECTIVE

This review examines extrinsic and intrinsic neuromodulation techniques, aimed at enhancing the effects of speech and language therapies in stroke survivors with aphasia.

METHODS

We discuss the available evidence supporting the use of transcranial direct current stimulation (tDCS), repetitive transcranial magnetic stimulation, and functional MRI (fMRI) real-time neurofeedback in aphasia rehabilitation.

RESULTS

This review systematically evaluates studies focusing on efficacy and implementation of specialized methods for post-treatment outcome optimization and transfer to functional skills. It considers stimulation target determination and various targeting approaches. The translation of neuromodulation interventions to clinical practice is explored, emphasizing generalization and functional communication. The review also covers real-time fMRI neurofeedback, discussing current evidence for efficacy and essential implementation parameters. Finally, we address future directions for neuromodulation research in aphasia.

CONCLUSIONS

This comprehensive review aims to serve as a resource for a broad audience of researchers and clinicians interested in incorporating neuromodulation for advancing aphasia care.

Repetitive transcranial magnetic stimulation (rTMS) combined with multi-modality aphasia therapy for chronic post-stroke non-fluent aphasia: A pilot randomized sham-controlled trial

Repetitive transcranial magnetic stimulation (rTMS) shows promise in improving speech production in post-stroke aphasia. Limited evidence suggests pairing rTMS with speech therapy may result in greater improvements. Twenty stroke survivors (>6 months post-stroke) were randomized to receive either sham rTMS plus multi-modality aphasia therapy (M-MAT) or rTMS plus M-MAT. For the first time, we demonstrate that rTMS combined with M-MAT is feasible, with zero adverse events and minimal attrition. Both groups improved significantly over time on all speech and language outcomes. However, improvements did not differ between rTMS or sham. We found that rTMS and sham groups differed in lesion location, which may explain speech and language outcomes as well as unique patterns of BOLD signal change within each group. We offer practical considerations for future studies and conclude that while combination therapy of rTMS plus M-MAT in chronic post-stroke aphasia is safe and feasible, personalized intervention may be necessary.

Timing of transcranial direct current stimulation (tDCS) combined with speech and language therapy (SLT) for aphasia: study protocol for a randomized controlled trial

BACKGROUND

Studies suggest that language recovery in aphasia may be improved by pairing speech-language therapy with transcranial direct current stimulation. However, results from many studies have been inconclusive regarding the impact transcranial direct current stimulation may have on language recovery in individuals with aphasia. An important factor that may impact the efficacy of transcranial direct current stimulation is its timing relative to speech-language therapy. Namely, online transcranial direct current stimulation (paired with speech-language therapy) and offline transcranial direct current stimulation (prior to or following speech-language therapy) may have differential effects on language recovery in post-stroke aphasia. Transcranial direct current stimulation provided immediately before speech-language therapy may prime the language system whereas stimulation provided immediately after speech-language therapy may aid in memory consolidation. The main aim of this study is to investigate the differential effects of offline and online transcranial direct stimulation on language recovery (i.e., conversation) in post-stroke aphasia.

METHODS/DESIGN

The study is a randomized, parallel-assignment, double-blind treatment study. Participants will be randomized to one of four treatment conditions and will participate in 15 treatment sessions. All groups receive speech-language therapy in the form of computer-based script practice. Three groups will receive transcranial direct current stimulation: prior to speech-language therapy, concurrent with speech-language therapy, or following speech-language therapy. One group will receive sham stimulation (speech-language therapy only). We aim to include 12 participants per group (48 total). We will use fMRI-guided neuronavigation to determine placement of transcranial direct stimulation electrodes on participants' left angular gyrus. Participants will be assessed blindly at baseline, immediately post-treatment, and at 4 weeks and 8 weeks following treatment. The primary outcome measure is change in the rate and accuracy of the trained conversation script from baseline to post-treatment.

DISCUSSION

Results from this study will aid in determining the optimum timing to combine transcranial direct current stimulation with speech-language therapy to facilitate better language outcomes for individuals with aphasia. In addition, effect sizes derived from this study may also inform larger clinical trials investigating the impact of transcranial direct current stimulation on functional communication in individuals with aphasia.

TRIAL REGISTRATION

ClinicalTrials.gov NCT03773406. December 12, 2018.

Differential Effects of Speech and Language Therapy and rTMS in Chronic Versus Subacute Post-stroke Aphasia: Results of the NORTHSTAR-CA Trial

Background & objective

Contralesional 1-Hz repetitive transcranial magnetic stimulation (rTMS) over the right pars triangularis combined with speech-language therapy (SLT) has shown positive results on the recovery of naming in subacute (5–45 days) post-stroke aphasia. NORTHSTAR-CA is an extension of the previously reported NORTHSTAR trial to chronic aphasia (>6 months post-stroke) designed to compare the effectiveness of the same rTMS protocol in both phases.

Methods

Sixty-seven patients with left middle cerebral artery infarcts (28 chronic, 39 subacute) were recruited (01-2014 to 07-2019) and randomized to receive rTMS (N = 34) or sham stimulation (N = 33) with SLT for 10 days. Primary outcome variables were Z-score changes in naming, semantic fluency and comprehension tests and adverse event frequency. Intention-to-treat analyses tested between-group effects at days 1 and 30 post-treatment. Chronic and subacute results were compared.

Results

Adverse events were rare, mild, and did not differ between groups. Language outcomes improved significantly in all groups irrespective of treatment and recovery phase. At 30-day follow-up, there was a significant interaction of stimulation and recovery phase on naming recovery (P <.001). Naming recovery with rTMS was larger in subacute (Mdn = 1.91/IQR = .77) than chronic patients (Mdn = .15/IQR = 1.68/P = .015). There was no significant rTMS effect in the chronic aphasia group.

Conclusions

The addition of rTMS to SLT led to significant supplemental gains in naming recovery in the subacute phase only. While this needs confirmation in larger studies, our results clarify neuromodulatory vs training-induced effects and indicate a possible window of opportunity for contralesional inhibitory stimulation interventions in post-stroke aphasia.

NORTHSTAR trial registration

https://clinicaltrials.gov/ct2/show/NCT02020421.

Application of tDCS in children with cerebral palsy: A mini review

Cerebral palsy (CP) refers to a group of diseases characterized by persistent central dyskinesia, postural development disorder and activity limitation syndromes caused by nonprogressive brain injury in the developing fetus or infant, which is often accompanied by sensory, cognitive and attention disorders. The routine rehabilitation methods for children with CP mainly include physical therapy, occupational therapy, speech therapy and other methods. In recent years, noninvasive brain stimulation (NIBS), as a relatively new intervention method, has been widely used because of its potential to regulate cortical excitability and plasticity. Transcranial direct current stimulation (tDCS) is an NIBS technique that is easier and more convenient to perform. It does not require patients to remain stationary for a long time or have a significant impact on treatment results due to children's frequent activities. Compared with other NIBS techniques, tDCS has greater flexibility and no strict restrictions on patients' activities; it also helps the therapist conduct occupational therapy or speech therapy while a child receives tDCS, which markedly reduces the treatment time and avoids burnout due to a long treatment duration. Thus, tDCS is a better and more convenient intervention for CP children and warrants further exploration. Accordingly, this article reviews tDCS application in children with CP and discusses tDCS application prospects for such children to promote its expansion in clinical practice.

Transcranial Direct-Current Stimulation and Behavioral Training, a Promising Tool for a Tailor-Made Post-stroke Aphasia Rehabilitation: A Review

Aphasia is an acquired language disorder resulting from damage to portions of the brain which are responsible for language comprehension and formulation. This disorder can involve different levels of language processing with impairments in both oral and written comprehension and production. Over the last years, different rehabilitation and therapeutic interventions have been developed, especially non-invasive brain stimulation (NIBS) techniques. One of the most used NIBS techniques in aphasia rehabilitation is the Transcranial Direct-Current Stimulation (tDCS). It has been proven to be effective in promoting a successful recovery both in the short and the long term after a brain injury. The main strength of tDCS is its feasibility associated with relatively minor side effects, if safely and properly administered. TDCS requires two electrodes, an anode and a cathode, which are generally placed on the scalp. The electrode montage can be either unipolar or bipolar. The main aim of this review is to give an overview of the state of the art of tDCS for the treatment of aphasia. The studies described included patients with different types of language impairments, especially with non-fluent aphasia and in several cases anomia. The effects of tDCS are variable and depend on several factors, such as electrode size and montage, duration of the stimulation, current density and characteristics of the brain tissue underneath the electrodes. Generally, tDCS has led to promising results in rehabilitating patients with acquired aphasia, especially if combined with different language and communication therapies. The selection of the appropriate approach depends on the patients treated and their impaired language function. When used in combination with treatments such as Speech and Language Therapy, Constraint Induced Aphasia Therapy or Intensive Action Treatment, tDCS has generally promoted a better recovery of the impaired functions. In addition to these rehabilitation protocols, Action Observation Therapy, such as IMITAF, appeared to contribute to the reduction of post-stroke anomia. The potential of combining such techniques with tDCS would would therefore be a possibility for further improvement, also providing the clinician with a new action and intervention tool. The association of a tDCS protocol with a dedicated rehabilitation training would favor a generalized long-term improvement of the different components of language.

New Treatment Strategy Using Repetitive Transcranial Magnetic Stimulation for Post-Stroke Aphasia

Repetitive transcranial magnetic stimulation (rTMS) for post-stroke aphasia (PSA) has been suggested to promote improvement of language function when used in combination with rehabilitation. However, many challenges remain. In some reports examined by category of language function, only naming has good evidence of improvement, and the improvement effect on other language modalities is low. Therefore, it is necessary to establish methods that contribute to the improvement of language functions other than naming. Therapeutic methods for PSA based on the mechanism of rTMS are mainly inhibitory stimulation methods for language homologous areas. However, the mechanisms of these methods are controversial when inferred from the process of recovery of language function. Low-frequency rTMS applied to the right hemisphere has been shown to be effective in the chronic phase of PSA, but recent studies of the recovery process of language function indicate that this method is unclear. Therefore, it has been suggested that evaluating brain activity using neuroimaging contributes to confirming the effect of rTMS on PSA and the elucidation of the mechanism of functional improvement. In addition, neuroimaging-based stimulation methods (imaging-based rTMS) may lead to further improvements in language function. Few studies have examined neuroimaging and imaging-based rTMS in PSA, and further research is required. In addition, the stimulation site and stimulation parameters of rTMS are likely to depend on the time from onset to intervention. However, there are no reports of studies in patients between 90 and 180 days after onset. Therefore, research during this period is required. New stimulation methods, such as multiple target methods and the latest neuroimaging methods, may contribute to the establishment of new knowledge and new treatment methods in this field.

Novel Advances to Post-Stroke Aphasia Pharmacology and Rehabilitation

Aphasia is one of the most common clinical features of functional impairment after a stroke. Approximately 21–40% of stroke patients sustain permanent aphasia, which progressively worsens one’s quality of life and rehabilitation outcomes. Post-stroke aphasia treatment strategies include speech language therapies, cognitive neurorehabilitation, telerehabilitation, computer-based management, experimental pharmacotherapy, and physical medicine. This review focuses on current evidence of the effectiveness of impairment-based aphasia therapies and communication-based therapies (as well as the timing and optimal treatment intensities for these interventions). Moreover, we present specific interventions, such as constraint-induced aphasia therapy (CIAT) and melodic intonation therapy (MIT). Accumulated data suggest that using transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) is safe and can be used to modulate cortical excitability. Therefore, we review clinical studies that present TMS and tDCS as (possible) promising therapies in speech and language recovery, stimulating neuroplasticity. Several drugs have been used in aphasia pharmacotherapy, but evidence from clinical studies suggest that only nootropic agents, donepezil and memantine, may improve the prognosis of aphasia. This article is an overview on the current state of knowledge related to post-stroke aphasia pharmacology, rehabilitation, and future trends.

Functional Magnetic Resonance Imaging of Language Following Constraint-Induced Aphasia Therapy Primed with Intermittent Theta Burst Stimulation in 13 Patients with Post-Stroke Aphasia

Background

Aphasia is a debilitating consequence of stroke. This study aimed to investigate the role of functional magnetic resonance imaging (fMRI) activation changes during overt language tasks in promoting language improvements following constraint-induced aphasia therapy (CIAT) primed with intermittent theta burst stimulation (iTBS) in 13 patients with aphasia following ischemic stroke.

Material/Methods

Participants with post-stroke aphasia participated in CIAT primed with iTBS on 10 consecutive weekdays. They also underwent language testing and fMRI while performing overt language tasks at baseline (N=13), immediately post-treatment (N=13), and after 3 months (N=12). Outcome measures were compared between time points, and relationships between changes in language ability and fMRI activation were examined.

Results

We observed improvements in naming (p<0.001), aphasia symptoms (p=0.038), apraxia of speech symptoms (p=0.040), perception of everyday communicative ability (p=0.001), and the number of spoken words produced during fMRI (p=0.028). Pre- to post-treatment change in naming was negatively correlated with change in right postcentral gyrus activation related to noun-verb associations (rho=−0.554, p=0.0497). Change in aphasia symptoms from immediately after to 3 months post-treatment was negatively correlated with change in bilateral supplementary motor area activation related to verbal encoding (rho=−0.790, p=0.0022).

Conclusions

Aphasia improvements coupled with fMRI activation changes over time provide support for treatment-induced neuroplasticity with CIAT primed with iTBS. However, a larger randomized sham-controlled study is warranted to confirm our findings and further our understanding of how iTBS can potentiate beneficial effects of language therapy in post-stroke aphasia.

A systematic review of repetitive transcranial magnetic stimulation in aphasia rehabilitation: Leads for future studies

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive tool that induces neuromodulation in the brain. Several studies have shown that rTMS improves language recovery in patients with post-stroke aphasia.

OBJECTIVE

This systematic review summarizes the role of rTMS in aphasia rehabilitation.

METHODS

We searched MEDLINE via PubMed and Scopus on 30October, 2020, for English articles (1996-2020). Eligible studies involved post-stroke aphasia rehabilitation with rTMS. In some of these studies, rTMS was also combined with speech therapy.

RESULTS

In total, seven meta-analyses and 59studies (23randomized clinical trials) were included in this systematic review. The methods used in these studies were heterogeneous. Only six studies did not find that rTMS had a significant effect on language performance.

CONCLUSIONS

The evidence from the peer-reviewed literature suggests that rTMS is an effective tool in post-stroke aphasia rehabilitation. However, the precise mechanisms that underlie the effects of rTMS and the reorganization of language networks in patients who have had a stroke remain unclear. We discuss these crucial challenges in the context of future studies.

High definition transcranial direct current stimulation modulates abnormal neurophysiological activity in post-stroke aphasia

Recent findings indicate that measures derived from resting-state magnetoencephalography (rsMEG) are sensitive to cortical dysfunction in post-stroke aphasia. Spectral power and multiscale entropy (MSE) measures show that left-hemispheric areas surrounding the stroke lesion (perilesional) exhibit pathological oscillatory slowing and alterations in signal complexity. In the current study, we tested whether individually-targeted high-definition transcranial direct current stimulation (HD-tDCS) can reduce MEG abnormalities and transiently improve language performance. In eleven chronic aphasia survivors, we devised a method to localize perilesional areas exhibiting peak MSE abnormalities, and subsequently targeted these areas with excitatory/anodal-tDCS, or targeted the contralateral homolog areas with inhibitory/cathodal-tDCS, based on prominent theories of stroke recovery. Pathological MEG slowing in these patients was correlated with aphasia severity. Sentence/phrase repetition accuracy was assessed before and after tDCS. A delayed word reading task was administered inside MEG to assess tDCS-induced neurophysiological changes in relative power and MSE computed on the pre-stimulus and delay task time windows. Results indicated increases in repetition accuracy, decreases in contralateral theta (4–7 Hz) and coarse-scale MSE (slow activity), and increases in perilesional low-gamma (25–50 Hz) and fine-scale MSE (fast activity) after anodal-tDCS, indicating reversal of pathological abnormalities. RsMEG may be a sensitive measure for guiding therapeutic tDCS.

Efficacy of Noninvasive Brain Stimulation (tDCS or TMS) Paired with Language Therapy in the Treatment of Primary Progressive Aphasia: An Exploratory Meta-Analysis

Noninvasive brain stimulation techniques, such as transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS), paired with behavioral language therapy, have demonstrated the capacity to enhance language abilities in primary progressive aphasia (PPA), a debilitating degenerative neurological syndrome that leads to declines in communication abilities. The aim of this meta-analysis is to systematically evaluate the efficacy of tDCS and TMS in improving language outcomes in PPA, explore the magnitude of effects between stimulation modalities, and examine potential moderators that may influence treatment effects. Standard mean differences for change in performance from baseline to post-stimulation on language-related tasks were evaluated. Six tDCS studies and two repetitive TMS studies met inclusion criteria and provided 22 effects in the analysis. Random effect models revealed a significant, heterogeneous, and moderate effect size for tDCS and TMS in the enhancement of language outcomes. Findings demonstrate that naming ability significantly improves due to brain stimulation, an effect found to be largely driven by tDCS. Future randomized controlled trials are needed to determine long-term effectiveness of noninvasive brain stimulation techniques on language abilities, further delineate the efficacy of tDCS and TMS, and identify optimal parameters to enable the greatest gains for persons with PPA.

Transcranial direct current stimulation (tDCS) for improving aphasia after stroke: a systematic review with network meta-analysis of randomized controlled trials

BACKGROUND

Transcranial Direct Current Stimulation (tDCS) is an emerging approach for improving aphasia after stroke. However, it remains unclear what type of tDCS stimulation is most effective. Our aim was to give an overview of the evidence network regarding the efficacy and safety of tDCS and to estimate the effectiveness of the different stimulation types.

METHODS

This is a systematic review of randomized controlled trials with network meta-analysis (NMA). We searched the following databases until 4 February 2020: Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE, CINAHL, AMED, Web of Science, and four other databases. We included studies with adult people with stroke. We compared any kind of active tDCS (anodal, cathodal, or dual, that is applying anodal and cathodal tDCS concurrently) regarding improvement of our primary outcome of functional communication, versus control, after stroke.

PROSPERO ID

CRD42019135696.

RESULTS

We included 25 studies with 471 participants. Our NMA showed that tDCS did not improve our primary outcome, that of functional communication. There was evidence of an effect of anodal tDCS, particularly over the left inferior frontal gyrus, in improving our secondary outcome, that of performance in naming nouns (SMD = 0.51; 95% CI 0.11 to 0.90). There was no difference in safety between tDCS and its control interventions, measured by the number of dropouts and adverse events.

CONCLUSION

Comparing different application/protocols of tDCS shows that the anodal application, particularly over the left inferior frontal gyrus, seems to be the most promising tDCS treatment option to improve performance in naming in people with stroke.

Theta Burst Transcranial Magnetic Stimulation of Fronto-Parietal Networks: Modulation by Mental State

Transcranial magnetic stimulation (TMS) treats neuropsychiatric disorders, but effects of stimulation are highly state-dependent and in most therapeutic applications, mental state is not controlled. This exploratory proposal will test the broad hypothesis that when TMS, specifically intermittent theta burst stimulation (iTBS), is applied during a controlled mental state, network changes will be facilitated, compared to stimulation when mental state is uncontrolled. We will focus on the dorsolateral prefrontal cortex (dlPFC) and the associated fronto-parietal network (FPN), which subserves cognitive control, an important neural and behavioral target of therapeutic TMS. After a baseline functional magnetic resonance imaging (fMRI) session, iTBS will be administered to 40 healthy subjects in three sessions over three days in a within-subjects, cross-over design: (1) dlPFC stimulation by iTBS alone, (2) dlPFC stimulation by iTBS while simultaneously performing a cognitive task, and (3) vertex (control) iTBS stimulation. Immediately after each iTBS session, we will measure blood oxygenation level-dependent (BOLD) activation during a cognitive control task (“n-back” task) and during the resting state, using BOLD connectivity and arterial spin labeling (ASL). We will test hypotheses that persisting neural changes and performance enhancement induced by iTBS to the dlPFC, compared to iTBS to the vertex, will affect the FPN, and these effects will be modulated by whether or not subjects receive iTBS when they are engaged in a cognitive control task. Demonstrating this interaction between iTBS and mental state will lay critical groundwork for future studies to show how controlling mental state during TMS can improve therapeutic effects.

Impact of Combined Transcranial Direct Current Stimulation and Speech-language Therapy on Spontaneous Speech in Aphasia: A Randomized Controlled Double-blind Study

OBJECTIVE

Aphasia recovery depends on neural reorganization, which can be enhanced by speech-language therapy and noninvasive brain stimulation. Several studies suggested that transcranial direct current stimulation (tDCS) associated with speech-language therapy may improve verbal performance evaluated by analytic tests, but none focused on spontaneous speech. We explored the effect of bihemispheric tDCS on spontaneous speech in patients with poststroke aphasia.

METHODS

In this multicentric controlled randomized cross-over double-blind study, we included 10 patients with poststroke aphasia (4 had aphasia >6 months and 6 with aphasia <6 months). We combined the sessions of speech-language therapy and bihemispheric tDCS (2 mA, 20 min). After three baseline speech evaluations (1/week), two different conditions were randomly consecutively proposed: active and sham tDCS over 3 weeks with 1 week of washout in between. The main outcome measure was the number of different nouns used in 2 min to answer the question "what is your job."

RESULTS

There was no significant difference between conditions concerning the main outcome measure (p = .47) nor in the number of verbs, adjectives, adverbs, pronouns, repetitions, blank ideas, ideas, utterances with grammatical errors or paraphasias used. Other cognitive functions (verbal working memory, neglect, or verbal fluency) were not significantly improved in the tDCS group. No adverse events occurred.

CONCLUSION

Our results differed from previous studies using tDCS to improve naming in patients with poststroke aphasia possibly due to bihemispheric stimulation, rarely used previously. The duration of the rehabilitation period was short given the linguistic complexity of the measure. This negative result should be confirmed by larger studies with ecological measures.

Repetitive transcranial magnetic stimulation in stroke rehabilitation: review of the current evidence and pitfalls

Acute brain ischemia causes changes in several neural networks and related cortico-subcortical excitability, both in the affected area and in the apparently spared contralateral hemisphere. The modulation of these processes through modern techniques of noninvasive brain stimulation, namely repetitive transcranial magnetic stimulation (rTMS), has been proposed as a viable intervention that could promote post-stroke clinical recovery and functional independence. This review provides a comprehensive summary of the current evidence from the literature on the efficacy of rTMS applied to different clinical and rehabilitative aspects of stroke patients. A total of 32 meta-analyses published until July 2019 were selected, focusing on the effects on motor function, manual dexterity, walking and balance, spasticity, dysphagia, aphasia, unilateral neglect, depression, and cognitive function after a stroke. Only conventional rTMS protocols were considered in this review, and meta-analyses focusing on theta burst stimulation only were excluded. Overall, both HF-rTMS and LF-rTMS have been shown to be safe and well-tolerated. In addition, the current literature converges on the positive effect of rTMS in the rehabilitation of all clinical manifestations of stroke, except for spasticity and cognitive impairment, where definitive evidence of efficacy cannot be drawn. However, routine use of a specific paradigm of stimulation cannot be recommended yet due to a significant level of heterogeneity of the studies in terms of protocols to be set and outcome measures that have to be used. Future studies need to preliminarily evaluate the most promising protocols before going on to multicenter studies with large cohorts of patients in order to achieve a definitive translation into daily clinical practice.

Repetitive transcranial magnetic stimulation in stroke rehabilitation: review of the current evidence and pitfalls

Acute brain ischemia causes changes in several neural networks and related cortico-subcortical excitability, both in the affected area and in the apparently spared contralateral hemisphere. The modulation of these processes through modern techniques of noninvasive brain stimulation, namely repetitive transcranial magnetic stimulation (rTMS), has been proposed as a viable intervention that could promote post-stroke clinical recovery and functional independence. This review provides a comprehensive summary of the current evidence from the literature on the efficacy of rTMS applied to different clinical and rehabilitative aspects of stroke patients. A total of 32 meta-analyses published until July 2019 were selected, focusing on the effects on motor function, manual dexterity, walking and balance, spasticity, dysphagia, aphasia, unilateral neglect, depression, and cognitive function after a stroke. Only conventional rTMS protocols were considered in this review, and meta-analyses focusing on theta burst stimulation only were excluded. Overall, both HF-rTMS and LF-rTMS have been shown to be safe and well-tolerated. In addition, the current literature converges on the positive effect of rTMS in the rehabilitation of all clinical manifestations of stroke, except for spasticity and cognitive impairment, where definitive evidence of efficacy cannot be drawn. However, routine use of a specific paradigm of stimulation cannot be recommended yet due to a significant level of heterogeneity of the studies in terms of protocols to be set and outcome measures that have to be used. Future studies need to preliminarily evaluate the most promising protocols before going on to multicenter studies with large cohorts of patients in order to achieve a definitive translation into daily clinical practice.

From Broca and Wernicke to the Neuromodulation Era: Insights of Brain Language Networks for Neurorehabilitation

Communication in humans activates almost every part of the brain. Of course, the use of language predominates, but other cognitive functions such as attention, memory, emotion, and executive processes are also involved. However, in order to explain how our brain "understands," "speaks," and "writes," and in order to rehabilitate aphasic disorders, neuroscience has faced the challenge for years to reveal the responsible neural networks. Broca and Wernicke (and Lichtheim and many others), during the 19th century, when brain research was mainly observational and autopsy driven, offered fundamental knowledge about the brain and language, so the Wernicke-Geschwind model appeared and aphasiology during the 20th century was based on it. This model is still useful for a first approach into the classical categorization of aphasic syndromes, but it is outdated, because it does not adequately describe the neural networks relevant for language, and it offers a modular perspective, focusing mainly on cortical structures. During the last three decades, neuroscience conquered new imaging, recording, and manipulation techniques for brain research, and a new model of the functional neuroanatomy of language was developed, the dual stream model, consisting of two interacting networks ("streams"), one ventral, bilaterally organized, for language comprehension, and one dorsal, left hemisphere dominant, for production. This new model also has its limitations but helps us to understand, among others, why patients with different brain lesions can have similar language impairments. Furthermore, interesting aspects arise from studying language functions in aging brains (and also in young, developing brains) and in cognitively impaired patients and neuromodulation effects on reorganization of brain networks subserving language. In this selective review, we discuss methods for coupling new knowledge regarding the functional reorganization of the brain with sophisticated techniques capable of activating the available supportive networks in order to provide improved neurorehabilitation strategies for people suffering from neurogenic communication disorders.

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.

Semantic discrimination impacts tDCS modulation of verb processing

Motor cortex activation observed during body-related verb processing hints at simulation accompanying linguistic understanding. By exploiting the up- and down-regulation that anodal and cathodal transcranial direct current stimulation (tDCS) exert on motor cortical excitability, we aimed at further characterizing the functional contribution of the motor system to linguistic processing. In a double-blind sham-controlled within-subjects design, online stimulation was applied to the left hemispheric hand-related motor cortex of 20 healthy subjects. A dual, double-dissociation task required participants to semantically discriminate concrete (hand/foot) from abstract verb primes as well as to respond with the hand or with the foot to verb-unrelated geometric targets. Analyses were conducted with linear mixed models. Semantic priming was confirmed by faster and more accurate reactions when the response effector was congruent with the verb's body part. Cathodal stimulation induced faster responses for hand verb primes thus indicating a somatotopical distribution of cortical activation as induced by body-related verbs. Importantly, this effect depended on performance in semantic discrimination. The current results point to verb processing being selectively modifiable by neuromodulation and at the same time to a dependence of tDCS effects on enhanced simulation. We discuss putative mechanisms operating in this reciprocal dependence of neuromodulation and motor resonance.

Transcranial Direct Current Stimulation in Post-stroke Chronic Aphasia: The Impact of Baseline Severity and Task Specificity in a Pilot Sample

Emerging evidence suggests that transcranial direct current stimulation (tDCS) can improve aspects of language production in persons with chronic non-fluent aphasia due to left hemisphere stroke. However, to date, studies exploring factors that predict response to tDCS in this or any patient population remain sparse, as are studies that investigate the specific aspects of language performance that are most responsive to stimulation. The current study explored factors that could predict recovery of language fluency and which aspects of language fluency could be expected to improve with the identified factor(s). We report nine patients who demonstrated deficits in fluency as assessed using the Cookie Theft picture description task of the Boston Diagnostic Aphasia Examination. In the treatment condition, subjects received a 2.0 mA current through 5 cm × 5 cm electrodes for 20 min at a site previously shown to elicit a patient-dependent optimal response to tDCS. They were then tested 2-weeks and 2-months after treatment. In the sham condition, a subset of these subjects were tested on the same protocol with sham instead of real tDCS. The current study assessed language fluency improvements in measures of production at the word-level and sentence level, grammatical accuracy, and lexical selection as a function of baseline aphasia severity. A more severe baseline language profile was associated with larger improvements in fluency at the word-level after real tDCS but not sham stimulation. These improvements were maintained at the 2-week follow-up. The results suggest that for at least some outcome measures, baseline severity may be an important factor in predicting the response to tDCS in patients with chronic non-fluent aphasia. Moving forward, the ability to identify patient factors that can predict response could help refine strategies for the administration of therapeutic tDCS, focusing attention on those patients most likely to benefit from stimulation.

Non-invasive Brain Stimulation in the Treatment of Post-stroke and Neurodegenerative Aphasia: Parallels, Differences, and Lessons Learned

Numerous studies over the span of more than a decade have shown that non-invasive brain stimulation (NIBS) techniques, namely transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS), can facilitate language recovery for patients who have suffered from aphasia due to stroke. While stroke is the most common etiology of aphasia, neurodegenerative causes of language impairment—collectively termed primary progressive aphasia (PPA)—are increasingly being recognized as important clinical phenotypes in dementia. Very limited data now suggest that (NIBS) may have some benefit in treating PPAs. However, before applying the same approaches to patients with PPA as have previously been pursued in patients with post-stroke aphasia, it will be important for investigators to consider key similarities and differences between these aphasia etiologies that is likely to inform successful approaches to stimulation. While both post-stroke aphasia and the PPAs have clear overlaps in their clinical phenomenology, the mechanisms of injury and theorized neuroplastic changes associated with the two etiologies are notably different. Importantly, theories of plasticity in post-stroke aphasia are largely predicated on the notion that regions of the brain that had previously been uninvolved in language processing may take on new compensatory roles. PPAs, however, are characterized by slow distributed degeneration of cellular units within the language system; compensatory recruitment of brain regions to subserve language is not currently understood to be an important aspect of the condition. This review will survey differences in the mechanisms of language representation between the two etiologies of aphasia and evaluate properties that may define and limit the success of different neuromodulation approaches for these two disorders.