Electrophysiological testing of dyslexia.

We enlarged our previous study (Kubová Z. et al. Physiol Res 1995;44:87-89) giving an evidence about magnocellular pathway involvement (delayed motion-onset visual evoked potentials (M-VEPs)) in 70% of dyslexic children. In the new group presented here, only 48% of 25 dyslexics displayed prolonged latencies of cortical responses to motion stimuli. However, there was no correlation of this defect with the used quantification of the reading skills (reading quotients). No significant EEG frequency spectrum changes were found. 10 subjects from the former group, who were re-examined 4 years after the previous study at the mean age of 14 years, exhibited significant shortening of the M-VEP latencies compared to the original values. Also in control subjects a distinct improvement in magnocellular pathway function was proved (in M-VEP re-examination after 4 years). These results document rather late maturation of the magnocellular pathway, which is evident mainly in dyslexic children. In both groups of dyslexics an effect of colour in moving stimuli was also tested to verify the reported effect of light wavelengths onto the magnocellular pathway function. However, no latency differences among grey, green, pink, yellow and blue stimuli were observed.