Neurophysiological heterogeneity and the definition of dyslexia: preliminary evidence for plasticity.

Developments in the field of quantified electroencephalography have enhanced visualization of brain function in the learning disabilities. Optimal utilization of these techniques requires that populations under study be unambiguously defined. Evidence from the literature demonstrates that brain electrical activity of children with reading disability is more extensive and differs from that seen in children with "dyslexia-pure". Preliminary data are presented demonstrating that electrophysiological change seen in children with dyslexia-plus (dyslexia and attentional deficit disorder) could not be predicted by knowledge of electrophysiologic change in children with dyslexia-pure alone and attentional deficit disorder alone. Data from our laboratory are summarized to show that within dyslexia-pure the anomic, dysphonemic and global Denckla subtypes differ electrophysiologically from one another. Of particular interest is the demonstration that regions of electrophysiological difference among these subtypes may reflect compensatory mechanisms rather than pathological change. Finally, a case study is presented demonstrating advantageous effects of remediation upon brain electrical function. As both spontaneous and environmentally induced change in brain function can be documented, developmental dyslexia in its broadest terms appears to represent a more dynamic or plastic process than previously appreciated.