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      Induction of neuroplasticity and recovery in post-stroke aphasia by non-invasive brain stimulation

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          Abstract

          Stroke victims tend to prioritize speaking, writing, and walking as the three most important rehabilitation goals. Of note is that two of these goals involve communication. This underscores the significance of developing successful approaches to aphasia treatment for the several hundred thousand new aphasia patients each year and over 1 million stroke survivors with chronic aphasia in the U.S. alone. After several years of growth as a research tool, non-invasive brain stimulation (NBS) is gradually entering the arena of clinical aphasiology. In this review, we first examine the current state of knowledge of post-stroke language recovery including the contributions from the dominant and non-dominant hemispheres. Next, we briefly discuss the methods and the physiologic basis of the use of inhibitory and excitatory repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS) as research tools in patients who experience post-stroke aphasia. Finally, we provide a critical review of the most influential evidence behind the potential use of these two brain stimulation methods as clinical rehabilitative tools.

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          Most cited references 70

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          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.
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            A comprehensive review of the effects of rTMS on motor cortical excitability and inhibition.

            Repetitive transcranial magnetic stimulation (rTMS) procedures are being widely applied in therapeutic and investigative studies. Numerous studies have investigated the effects of rTMS on cortical excitability and inhibition, yielding somewhat contradictory results. The purpose of this study was to comprehensively review this literature to guide the selection of methodology in therapeutic studies. We conducted a comprehensive review of all identified studies that investigated effects of low and/or high frequency rTMS on motor cortical excitability or inhibition. Low frequency rTMS appears to produce a transient reduction in cortical excitability as assessed by motor evoked potential (MEP) size and produces no substantial effect on cortical inhibition. High frequency rTMS appears to produce a persistent increase in MEP size and a reduction in cortical inhibition measured with paired pulse methods although few studies have investigated frequencies greater than 5Hz. A number of novel stimulation paradigms have significant potential for altering cortical excitability but require further investigation. Although commonly applied forms of rTMS have effects on cortical excitability, more substantial effects may be obtained through the use of novel stimulation paradigms or innovative approaches to the stimulation of areas connected to a potential target site. Further research is required, however, before these paradigms can be more widely adopted.
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              Aphasia in acute stroke: incidence, determinants, and recovery.

              Knowledge of the frequency and remission of aphasia is essential for the rehabilitation of stroke patients and provides insight into the brain organization of language. We studied prospectively and consecutively an unselected and community-based sample of 881 patients with acute stroke. Assessment of aphasia was done at admission, weekly during the hospital stay, and at a 6-month follow-up using the aphasia score of the Scandinavian Stroke Scale. Thirty-eight percent had aphasia at the time of admission; at discharge 18% had aphasia. Sex was not a determinant of aphasia in stroke, and no sex difference in the anterior-posterior distribution of lesions was found. The remission curve was steep: Stationary language function in 95% was reached within 2 weeks in those with initial mild aphasia, within 6 weeks in those with moderate, and within 10 weeks in those with severe aphasia. A valid prognosis of aphasia could be made within 1 to 4 weeks after the stroke depending on the initial severity of aphasia. Initial severity of aphasia was the only clinically relevant predictor of aphasia outcome. Sex, handedness, and side of stroke lesion were not independent outcome predictors, and the influence of age was minimal.
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                Author and article information

                Journal
                Front Hum Neurosci
                Front Hum Neurosci
                Front. Hum. Neurosci.
                Frontiers in Human Neuroscience
                Frontiers Media S.A.
                1662-5161
                24 December 2013
                2013
                : 7
                Affiliations
                1Department of Neurology, University of Pennsylvania Philadelphia, PA, USA
                2Laboratory for Cognition and Neural Stimulation, Center for Cognitive Neuroscience, University of Pennsylvania Philadelphia, PA, USA
                3Department of Neurology, University of Alabama at Birmingham Birmingham, AL, USA
                Author notes

                Edited by: Edward Taub, University of Alabama at Birmingham, USA

                Reviewed by: Victor W. Mark, University of Alabama at Birmingham, USA; Gitendra Uswatte, University of Alabama at Birmingham, USA

                *Correspondence: Roy H. Hamilton, Department of Neurology, Center for Cognitive Neuroscience, University of Pennsylvania, 518 Goddard Building, 3710 Hamilton Walk, Philadelphia, PA 19104, USA e-mail: roy.hamilton@ 123456uphs.upenn.edu

                This article was submitted to the journal Frontiers in Human Neuroscience.

                Article
                10.3389/fnhum.2013.00888
                3870921
                Copyright © 2013 Shah, Szaflarski, Allendorfer and Hamilton.

                This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

                Page count
                Figures: 2, Tables: 1, Equations: 0, References: 89, Pages: 17, Words: 13939
                Categories
                Neuroscience
                Review Article

                Neurosciences

                tms, rtms, fmri, tdcs, rehabilitation, aphasia

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