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      Inhibitory non-invasive brain stimulation to homologous language regions as an adjunct to speech and language therapy in post-stroke aphasia: a meta-analysis

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          Chronic communication impairment is common after stroke, and conventional speech and language therapy (SLT) strategies have limited effectiveness in post-stroke aphasia. Neurorehabilitation with non-invasive brain stimulation techniques (NIBS)—particularly repetitive transcranial magnetic stimulation (rTMS) or transcranial direct current stimulation (tDCS)—may enhance the effects of SLT in selected patients. Applying inhibitory NIBS to specific homologous language regions may induce neural reorganization and reduce interhemispheric competition. This mini review highlights randomized controlled trials (RCTs) and randomized cross-over trials using low-frequency rTMS or cathodal tDCS over the non-lesioned non-language dominant hemisphere and performs an exploratory meta-analysis of those trials considered combinable. Using a random-effects model, a meta-analysis of nine eligible trials involving 215 participants showed a significant mean effect size of 0.51 (95% CI = 0.24–0.79) for the main outcome “accuracy of naming” in language assessment. No heterogeneity was observed ( I 2 = 0%). More multicenter RCTs with larger populations and homogenous intervention protocols are required to confirm these and the longer-term effects.

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          Meta-analyzing left hemisphere language areas: phonology, semantics, and sentence processing.

          The advent of functional neuroimaging has allowed tremendous advances in our understanding of brain-language relationships, in addition to generating substantial empirical data on this subject in the form of thousands of activation peak coordinates reported in a decade of language studies. We performed a large-scale meta-analysis of this literature, aimed at defining the composition of the phonological, semantic, and sentence processing networks in the frontal, temporal, and inferior parietal regions of the left cerebral hemisphere. For each of these language components, activation peaks issued from relevant component-specific contrasts were submitted to a spatial clustering algorithm, which gathered activation peaks on the basis of their relative distance in the MNI space. From a sample of 730 activation peaks extracted from 129 scientific reports selected among 260, we isolated 30 activation clusters, defining the functional fields constituting three distributed networks of frontal and temporal areas and revealing the functional organization of the left hemisphere for language. The functional role of each activation cluster is discussed based on the nature of the tasks in which it was involved. This meta-analysis sheds light on several contemporary issues, notably on the fine-scale functional architecture of the inferior frontal gyrus for phonological and semantic processing, the evidence for an elementary audio-motor loop involved in both comprehension and production of syllables including the primary auditory areas and the motor mouth area, evidence of areas of overlap between phonological and semantic processing, in particular at the location of the selective human voice area that was the seat of partial overlap of the three language components, the evidence of a cortical area in the pars opercularis of the inferior frontal gyrus dedicated to syntactic processing and in the posterior part of the superior temporal gyrus a region selectively activated by sentence and text processing, and the hypothesis that different working memory perception-actions loops are identifiable for the different language components. These results argue for large-scale architecture networks rather than modular organization of language in the left hemisphere.
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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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              tDCS-enhanced motor and cognitive function in neurological diseases.

               Agnes Flöel (2014)
              Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation tool that is now being widely used in neuroscientific and clinical research in humans. While initial studies focused on modulation of cortical excitability, the technique quickly progressed to studies on motor and cognitive functions in healthy humans and in patients with neurological diseases. In the present review we will first provide the reader with a brief background on the basic principles of tDCS. In the main part, we will outline recent studies with tDCS that aimed at enhancing behavioral outcome or disease-specific symptoms in patients suffering from mild cognitive impairment, Alzheimer's disease, movement disorders, and epilepsy, or persistent deficits after stroke. The review will close with a summary statement on the present use of tDCS in the treatment of neurological disorders, and an outlook to further developments in this realm. tDCS may be an ideal tool to be administered in parallel to intensive cognitive or motor training in neurological disease, but efficacy for the areas of activities and participation still needs to be established in controlled randomized trials. Its use in reducing disease-specific symptoms like dystonia or epileptic seizures is still unclear. Copyright © 2013 Elsevier Inc. All rights reserved.

                Author and article information

                Front Hum Neurosci
                Front Hum Neurosci
                Front. Hum. Neurosci.
                Frontiers in Human Neuroscience
                Frontiers Media S.A.
                28 April 2015
                : 9
                1Center for Stroke Research Berlin, Charité University Medicine Berlin, Germany
                2Department of Neurology, NeuroCure Clinical Research Center, Charité University Medicine Berlin, Germany
                Author notes

                Edited by: Nathalie Tzourio-Mazoyer, Université de Bordeaux, France

                Reviewed by: Monica Baciu, Université Pierre Mendès-France, France; Bernhard Sehm, Max Planck Institute for Human Cognitive and Brain Sciences, Germany

                *Correspondence: Begonya Otal, Center for Stroke Research Berlin, Charité University Medicine, Charitéplatz 1, 10117 Berlin, Germany begonya.otal@ 123456gmail.com
                Copyright © 2015 Otal, Olma, Flöel and Wellwood.

                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: 1, Tables: 1, Equations: 0, References: 46, Pages: 7, Words: 5297
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