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Transcranial direct current stimulation effects on neural processing in post-stroke aphasia.

ABSTRACT: Non-invasive transcranial direct current stimulation (tDCS) can enhance recovery after stroke. However, fundamental knowledge about how tDCS impacts neural processing in the lesioned human brain is currently lacking. In the present study, it was investigated how tDCS modulates brain function in patients with post-stroke language impairment (aphasia). In a cross-over, randomized trial, patients named pictures of common objects during functional magnetic resonance imaging (fMRI). Concurrently, excitatory (anodal-) or sham-tDCS (1 mA, 20 min, or 30 s, respectively) was administered to the left primary motor cortex, a montage with demonstrated potential to improve aphasic language. By choosing stimuli that could reliable be named by the patients, the authors aimed to derive a pure measure of stimulation effects that was independent of treatment or performance effects and to assess how tDCS interacts with the patients' residual language network. Univariate fMRI data analysis revealed reduced activity in domain-general regions mediating high-level cognitive control during anodal-tDCS. Independent component functional network analysis demonstrated selectively increased language network activity and an inter-correlated shift from higher to lower frequency bands, indicative of increased within-network communication. Compared with healthy controls, anodal-tDCS resulted in overall "normalization" of brain function in the patients. These results demonstrate for the first time how tDCS modulates neural processing in stroke patients. Such information is crucial to assure that behavioral treatments targeting specific neural circuits overlap with regions that are modulated by tDCS, thereby maximizing stimulation effects during therapy. Hum Brain Mapp 38:1518-1531, 2017. © 2016 Wiley Periodicals, Inc.

SUBMITTER: Darkow R

PROVIDER: S-EPMC6866985 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Background: Intensive speech-language therapy (SLT) can promote recovery from chronic post-stroke aphasia, a major consequence of stroke. However, effect sizes of intensive SLT are moderate, potentially reflecting a physiological limit of training-induced progress. Transcranial direct current stimulation (tDCS) is an easy-to-use, well-tolerated and low-cost approach that may enhance effectiveness of intensive SLT. In a recent phase-II randomized controlled trial, 26 individuals with chronic post-stroke aphasia received intensive SLT combined with anodal-tDCS of the left primary motor cortex (M1), resulting in improved naming and proxy-rated communication ability, with medium-to-large effect sizes. Aims: The proposed protocol seeks to establish the incremental benefit from anodal-tDCS of M1 in a phase-III randomized controlled trial with adequate power, ecologically valid outcomes, and evidence-based SLT. Methods: The planned study is a prospective randomized placebo-controlled (using sham-tDCS), parallel-group, double-blind, multi-center, phase-III superiority trial. A sample of 130 individuals with aphasia at least 6 months post-stroke will be recruited in more than 18 in- and outpatient rehabilitation centers. Outcomes: The primary outcome focuses on communication ability in chronic post-stroke aphasia, as revealed by changes on the Amsterdam-Nijmegen Everyday Language Test (A-scale; primary endpoint: 6-month follow-up; secondary endpoints: immediately after treatment, and 12-month follow-up). Secondary outcomes include measures assessing linguistic-executive skills, attention, memory, emotional well-being, quality of life, health economic costs, and adverse events (endpoints: 6-month follow-up, immediately after treatment, and 12-month follow-up). Discussion: Positive results will increase the quality of life for persons with aphasia and their families while reducing societal costs. After trial completion, a workshop with relevant stakeholders will ensure transfer into best-practice guidelines and successful integration within clinical routine. Clinical Trial Registration: www.ClinicalTrials.gov, identifier: NCT03930121.

Project description:Importance:Aphasia is a debilitating language disorder for which behavioral speech therapy is the most efficient treatment, but therapy outcomes are variable and full recovery is not always achieved. It remains unclear if adjunctive brain stimulation (anodal transcranial direct current stimulation [A-tDCS]) applied during aphasia therapy can improve outcomes. Objective:To examine the futility of studying A-tDCS as an adjunctive intervention during speech therapy to improve speech production (naming) for individuals with long-term poststroke aphasia. Design, Setting, and Participants:Double-blinded, prospective randomized clinical trial using a futility design to test adjunctive A-tDCS during speech therapy. The setting was an outpatient clinic. Enrollment of individuals began in August 2012 and was completed in March 2017, and the duration of follow-up was 6 months. Analyses began in April 2017. The study recruited from a volunteer sample, and 89 patients were screened. Patients with long-term (>6 months) aphasia due to 1 previous left hemisphere stroke were enrolled. In comparing A-tDCS and sham tDCS, patients were matched based on site (University of South Carolina or Medical University of South Carolina), baseline age, type of aphasia, and aphasia severity. Interventions:Outpatient speech therapy for 3 weeks (15 sessions, 45 minutes each) combined with either A-tDCS vs sham tDCS applied to preserved left temporal lobe regions. Main Outcomes and Measures:The primary outcome was the ability to name common objects, assessed twice before and after therapy. Results:A total of 74 patients were enrolled. Participants had a mean (SD) age of 60 (10) years, had 15 (2) years of education, and were 44 (40) months from stroke onset. There were 52 men (70%) and 62 non-Hispanic white individuals (84%). Most were retired or not employed (59 [80%]). Broca aphasia was the most common aphasia type (39 [52.7%]). The adjusted mean (SE) change from pretreatment baseline in correct naming was 13.9 (2.4) words (95% CI, 9.0-18.7) for A-tDCS and 8.2 (2.2) words (95% CI, 3.8-12.6) for sham tDCS, with mean (SE) A-tDCS difference of 5.7 (3.3) words (95% CI, -0.9 to 12.3), indicating a relative 70% increase in correct naming for A-tDCS relative to sham. The futility hypothesis P value was .90, indicating failure to reject the null hypothesis and, therefore, providing no evidence that further study of A-tDCS is futile. No serious adverse events were associated with A-tDCS. Conclusions and Relevance:Our findings provide motivation to proceed with another trial to study the effect of A-tDCS on the outcome of aphasia treatment in individuals poststroke. Anodal tDCS during speech therapy is feasible and potentially transformative for aphasia treatment and should be further studied. Trial Registration:ClinicalTrials.gov Identifier: NCT01686373.

Project description: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.

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Transcranial direct current stimulation effects on neural processing in post-stroke aphasia.

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