Standard EEG and dyslexia in children--new evidence for specific correlates?
Contrary to the current assumption that there are no specific correlates of dyslexia in the standard clinical EEG, we have often noted a spontaneous "intermittent left parietal alpha desynchronization" (ILPAD) when visually evaluating the standard EEGs of children with delayed speech and language development and/or dyslexia. Visual evaluations of EEGs, as well as computer-assisted frequency analysis of three pairs of matched groups (healthy and hyperkinetic children with vs. without relatively "low levels" of verbal performance, as well as children with other child psychiatric disorders with vs. without dyslexia), revealed that healthy children did not display the ILPAD phenomenon. It was seen neither in healthy children with a homogeneous performance profile ("high level" of verbal performance) nor in those with a relatively "low level" of verbal performance. However, the ILPAD phenomenon was evident mainly in children with psychiatric disorders who suffered from dyslexia. Its intermittent occurrence prevented its detection by means of the usual computer-supported analyses of EEG power spectra. Nevertheless, auditory cognitive loading was accompanied by a decrease in alpha power in both healthy and hyperkinetic children with "high" or "low" levels of verbal performance. In a further group of 8-year-old children with dyslexia, but otherwise healthy, the ILPAD phenomenon was also observed if their CNS maturation as reflected in the EEG was normal for their age. These results seemed to indicate at least a deficit-specificity of the ILPAD phenomenon, which is interpreted as an electrophysiological correlate of a "brain-electrical developmental deviation" with regard to the "functions of communication": speech, language, reading and spelling.