Neuro

SIMPOSIO SATÉLITE: DISLEXIA

SIMPOSIO SATÉLITE: DISLEXIA

Dislexia del desarrollo
A.M. Galaburda, L. Cestnick
DEVELOPMENTAL DYSLEXIA Summary. Developmental dyslexia makes up an important proportion of the known learning disorders. Until the late 1970s most research on dyslexia was carried out by educators and educational psychologists, but soon after the publication of some dyslexic caseswith focal disorders of neuronal migration to the cerebral cortex, interest in the neurobiological and neurocognitive underpinnings of dyslexia grew, especially in Europe and North America. There are at least two types of developmental dyslexia –phonological and surface. Surface dyslexia refers to a disorder in which the difficulty lies in reading irregular words, whereas phonological dyslexia ischaracterized by difficulty with pseudowords. Phonological dyslexia is the more common of the two types. Surface dyslexia does not present a major problem in a language such as Spanish, where the number of irregular words is indeed very small. Still, in languages such as English, where irregular words are common, the phonological type of developmental dyslexia is much more common. Phonologicdyslexics have problems with phonological awareness, that is, the conscious knowledge and manipulation of speech sounds, which is the most proximate explanation for their difficulty in reading pseudowords. Many, but not all, phonologic dyslexics also have problems processing rapidly changing sounds, even if not linguistic, and some slow sounds, too. The same group tends to have visual problems,especially involving the so-called magnocellular pathway of the visual system, which, among others, has the role of analyzing movement. Accompanying these perceptual and cognitive deficits, phonologic dyslexics also show abnormal brain activation to phonological tasks, as shown in functional magnetic resonance studies (figure). In addition, dyslexic brains show focal malformations, ectopias andmicrogyria, of the cerebral cortex, involving mainly the left perisylvian region and the word form area in the temporo-occipital junction. There are also changes in the composition of neurons in the lateral and medial geniculate nuclei of the thalamus. Experimental studies indicate that the thalamic changes are a consequence of the focal malformations, and that they are responsible for the sound processingdeficits. None of these discoveries have changed the therapeutic modalities in this condition, but it is hoped that this will be the next area of progress. [REV NEUROL 2003; 36 (Supl 1): S3-9] Key words. Developmental dyslexia. Learning disorders. Magnocellular visual pathway. Phonological dyslexia. Surface dyslexia.

INTRODUCCIÓN La dislexia del desarrollo (DDD) es un trastorno del lenguaje queafecta principalmente la habilidad de leer y escribir [88], a pesar de que también afecta a otros aspectos del lenguaje. La dislexia es quizás el trastorno del aprendizaje mejor conocido de todos, tanto por el público general como por los médicos. Los niños que sufren dislexia tienen problemas en el ritmo y velocidad del aprendizaje del lenguaje escrito, así como también en la adquisición de unnivel adecuado de desempeño. La dislexia se nota por primera vez cuando el niño ingresa en el jardín de infancia o en el primer año de la escuela primaria, o cuando por primera vez se encuentra frente al desafío de la lectoescritura. En un porcentaje de casos, el problema se manifiesta a los 2-3 años, cuando el niño disléxico también puede demostrar una lentitud o una anomalía en el desarrollo dellenguaje verbal. Tales trastornos consisten en un retardo de la adquisición de la palabra, o en dificultades de la pronunciación. Sin embargo, en la mayoría de los casos no existen rasgos anticipatorios, y la única amenaza se deriva desde el conocimiento de que hay otros miembros de la familia que se han diagnosticado de disléxicos, hecho por sí mismo que aumenta las posibilidades de que el niño...