Neurology of developmental dyslexia

Department of Neurology, Beth Israel Hospital, Boston, Massachusetts.
Current Opinion in Neurobiology (Impact Factor: 6.63). 05/1993; 3(2):237-42. DOI: 10.1016/0959-4388(93)90216-L
Source: PubMed


Developmental dyslexia was until recently considered to belong solely in the domain of educational psychology. With the advent of better theories on language and reading, and better methods for assessing the structure and function of living human brains and for determining genetic transmission, dyslexia is now poised to become a focal concern of cognitive neuroscience, neurology, and genetic research. Still unresolved are questions relating to how much a reading disability represents a normal variation or a separate pathological entity, and whether the cognitive disorder is primarily cognitive, or secondary to a disorder in early perception. Recent findings from neuroanatomy, neurophysiology, neuropsychology, and genetics research are reviewed. (This review is an updated version of a review first published in Current Opinion In Neurology and Neurosurgery 1992, 5:71-76.)

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Available from: Albert M Galaburda
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    • "There are some studies, however, that have shown abnormalities in the magnocellular pathway of the brain in dyslexic individuals [5], [6], [7], [8] and some researchers have suggested that visual impairment, rather than a linguistic processing problem, causes dyslexia [8], [9]. The magnocellular deficit theory purports that children with dyslexia have poor binocular coordination (stemming from the failure to develop a dominant eye), which causes problems in obtaining a single, stable perceptual representation of words from the two retinal inputs [9]. "
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    ABSTRACT: Children with developmental dyslexia show reading impairment compared to their peers, despite being matched on IQ, socio-economic background, and educational opportunities. The neurological and cognitive basis of dyslexia remains a highly debated topic. Proponents of the magnocellular theory, which postulates abnormalities in the M-stream of the visual pathway cause developmental dyslexia, claim that children with dyslexia have deficient binocular coordination, and this is the underlying cause of developmental dyslexia. We measured binocular coordination during reading and a non-linguistic scanning task in three participant groups: adults, typically developing children, and children with dyslexia. A significant increase in fixation disparity was observed for dyslexic children solely when reading. Our study casts serious doubts on the claims of the magnocellular theory. The exclusivity of increased fixation disparity in dyslexics during reading might be a result of the allocation of inadequate attentional and/or cognitive resources to the reading process, or suboptimal linguistic processing per se.
    Full-text · Article · Nov 2011 · PLoS ONE
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    • "Moreover, functional magnetic resonance imaging studies devoted to exploring visual processing abilities in individuals with DD revealed little activation in portions of the magnocellular visual system in response to the perception of subtle changes in motion (Eden et al., 1996). Irregular brain morphology has also been detected in regions associated with executive functions and in subcortical areas (Galaburda, 1993; Hynd et al., 1995; Riccio & Hynd, 1996). Finally, observations made with magnetic resonance spectroscopy (Rae et al., 1998), positron emission tomography (Nicolson et al., 1999) and "
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    ABSTRACT: The reduced verbal long-term memory capacities often reported in dyslexics are generally interpreted as a consequence of their deficit in phonological coding.The present study was aimed at evaluating whether the learning deficit exhibited by dyslexics was restricted only to the verbal component of the long-term memory abilities or also involved visual-object and visual-spatial domain. A further goal of the present study was to investigate the predictive value of non-verbal long-term memory abilities with respect to word and non-word reading in dyslexic children.In accordance with these aims, performances of 60 dyslexic children were compared with that of 65 age-matched normal readers on verbal, visual-spatial and visual-object task.Results documented a generalized impairment of episodic long-term memory capacities in dyslexic children and the results did not vary as a function of children's age.Furthermore, in addition to verbal measures, also individual differences in non-verbal long-term memory tasks turn out to be good predictors of reading difficulties in dyslexics.Our findings indicate that the long-term memory deficit in dyslexia is not limited to the dysfunction of phonological components but also involves visual-object and visual-spatial aspect, thus suggesting that dyslexia is associated to multiple cognitive deficits.
    Full-text · Article · Aug 2010 · Dyslexia
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    • "The volume of visual area 17 in the rat is asymmetric across the hemispheres and this asymmetry is negatively correlated with the density of callosal terminations in this area (Rosen, Galaburda, & Sherman, 1990). One model postulates that brain symmetry is due to faulty pruning mechanisms that leave more interhemispheric connections and more neurons in the right perisylvian region (Galaburda, 1993, 1995). It may also result from abnormalities in neuron number caused by either increased progenitor proliferation or decreased normal developmental apoptosis that occurs during neurogenesis (Geschwind & Miller, 2001). "
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    ABSTRACT: The corpus callosum is the largest commissure in the brain and acts as a "bridge" of nerve fibres connecting the two cerebral hemispheres. It plays a crucial role in interhemispheric integration and is responsible for normal communication and cooperation between the two hemispheres. Evolutionary pressures guiding brain size are accompanied by reduced interhemispheric and enhanced intrahemispheric connectivity. Some lines of evidence suggest that the speed of transcallosal conduction is limited in large brains (e.g., in humans), thus favouring intrahemispheric processing and brain lateralisation. Patterns of directional symmetry/asymmetry of transcallosal transfer time may be related to the degree of brain lateralisation. Neural network modelling and electrophysiological studies on interhemispheric transmission provide data supporting this supposition.
    Full-text · Article · Sep 2009 · Laterality
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