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      Developmental dyslexia: dysfunction of a left hemisphere reading network

      review-article
      Frontiers in Human Neuroscience
      Frontiers Media S.A.
      brain, developmental dyslexia, fMRI, meta-analysis, neuroimaging, reading

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          Abstract

          This mini-review summarizes and integrates findings from recent meta-analyses and original neuroimaging studies on functional brain abnormalities in dyslexic readers. Surprisingly, there is little empirical support for the standard neuroanatomical model of developmental dyslexia, which localizes the primary phonological decoding deficit in left temporo-parietal (TP) regions. Rather, recent evidence points to a dysfunction of a left hemisphere reading network, which includes occipito-temporal (OT), inferior frontal, and inferior parietal regions.

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          Most cited references33

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          Perisylvian language networks of the human brain.

          Early anatomically based models of language consisted of an arcuate tract connecting Broca's speech and Wernicke's comprehension centers; a lesion of the tract resulted in conduction aphasia. However, the heterogeneous clinical presentations of conduction aphasia suggest a greater complexity of perisylvian anatomical connections than allowed for in the classical anatomical model. This article re-explores perisylvian language connectivity using in vivo diffusion tensor magnetic resonance imaging tractography. Diffusion tensor magnetic resonance imaging data from 11 right-handed healthy male subjects were averaged, and the arcuate fasciculus of the left hemisphere reconstructed from this data using an interactive dissection technique. Beyond the classical arcuate pathway connecting Broca's and Wernicke's areas directly, we show a previously undescribed, indirect pathway passing through inferior parietal cortex. The indirect pathway runs parallel and lateral to the classical arcuate fasciculus and is composed of an anterior segment connecting Broca's territory with the inferior parietal lobe and a posterior segment connecting the inferior parietal lobe to Wernicke's territory. This model of two parallel pathways helps explain the diverse clinical presentations of conduction aphasia. The anatomical findings are also relevant to the evolution of language, provide a framework for Lichtheim's symptom-based neurological model of aphasia, and constrain, anatomically, contemporary connectionist accounts of language.
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            The Interactive Account of ventral occipitotemporal contributions to reading

            The ventral occipitotemporal cortex (vOT) is involved in the perception of visually presented objects and written words. The Interactive Account of vOT function is based on the premise that perception involves the synthesis of bottom-up sensory input with top-down predictions that are generated automatically from prior experience. We propose that vOT integrates visuospatial features abstracted from sensory inputs with higher level associations such as speech sounds, actions and meanings. In this context, specialization for orthography emerges from regional interactions without assuming that vOT is selectively tuned to orthographic features. We discuss how the Interactive Account explains left vOT responses during normal reading and developmental dyslexia; and how it accounts for the behavioural consequences of left vOT damage.
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              Dyslexia (specific reading disability).

              Converging evidence from a number of lines of investigation indicates that dyslexia represents a disorder within the language system and more specifically within a particular subcomponent of that system, phonological processing. Recent advances in imaging technology, particularly the development of functional magnetic resonance imaging, provide evidence of a neurobiological signature for dyslexia, specifically a disruption of two left hemisphere posterior brain systems, one parieto-temporal, the other occipito-temporal, with compensatory engagement of anterior systems around the inferior frontal gyrus and a posterior (right occipito-temporal) system. Furthermore, good evidence indicates a computational role for the left occipito-temporal system: the development of fluent (automatic) reading. The brain systems for reading are malleable and their disruption in dyslexic children may be remediated by provision of an evidence-based, effective reading intervention. In addition, functional magnetic resonance imaging studies of young adults with reading difficulties followed prospectively and longitudinally from age 5 through their mid twenties suggests that there may be two types of reading difficulties, one primarily on a genetic basis, the other, and far more common, reflecting environmental influences. These studies offer the promise for more precise identification and effective management of dyslexia in children, adolescents and adults.
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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
                01 May 2012
                2012
                : 6
                : 120
                Affiliations
                simpleDepartment of Psychology, Center for Neurocognitive Research, University of Salzburg Salzburg, Austria
                Author notes

                Edited by: Hauke R. Heekeren, Freie Universität Berlin, Germany

                Reviewed by: Arthur M. Jacobs, Freie Universität Berlin, Germany; Bennett A. Shaywitz, Yale University, USA

                *Correspondence: Fabio Richlan, Department of Psychology, Center for Neurocognitive Research, University of Salzburg, Hellbrunnerstr. 34, 5020 Salzburg, Austria. e-mail: fabio.richlan@ 123456sbg.ac.at
                Article
                10.3389/fnhum.2012.00120
                3340948
                22557962
                de25bb54-00e5-4074-93d7-731dcec3c770
                Copyright © 2012 Richlan.

                This is an open-access article distributed under the terms of the Creative Commons Attribution Non Commercial License, which permits non-commercial use, distribution, and reproduction in other forums, provided the original authors and source are credited.

                History
                : 23 February 2012
                : 16 April 2012
                Page count
                Figures: 1, Tables: 0, Equations: 0, References: 41, Pages: 5, Words: 4645
                Categories
                Neuroscience
                Mini Review Article

                Neurosciences
                developmental dyslexia,meta-analysis,brain,fmri,reading,neuroimaging
                Neurosciences
                developmental dyslexia, meta-analysis, brain, fmri, reading, neuroimaging

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