Developmental dyslexia: a multilevel syndrome

Abstract

The study of developmental dyslexia at several levels, from the physiological to the cognitive, has acquired a new energy in the past few years. A debate exists as to whether the condition represents primarily a disorder of perception or a deficit in cognition and metacognitive processes. Neuroanatomical research can shed some light on this debate. Investigation first in human autopsy brains followed by modelling of the findings in experimental animals indicates that anomalies exist at multiple levels and pathways. Thus areas of the brain concerned with perceptual processing, as well as those involved in cognitive and metacognitive tasks, are anatomically affected in dyslexia. Similarly, at least the visual and auditory pathways are affected by the anatomical changes. Moreover, there appears to be, at least in part, a causal relationship between the involvement at different levels and pathways, such that during development—a time of great plasticity—changes at one level or pathway propagate to affect other levels and pathways. It may be inferred from this research that dyslexia represents a complex interaction of both low-level and high-level processing deficits affecting language and perhaps visual performance. Although treatment aimed at correcting deficits at one level or pathway may be helpful, it is suggested that the best forms of treatment will need to deal with the multiple nature of the disorder. Copyright © 1999 John Wiley & Sons, Ltd.