Neuronal correlates of mental rotation performance in children with developmental dyslexia

People with developmental dyslexia have been shown to have both behavioral and physiological differences when compared with healthy individuals, specifically when looking at the parietal cortex. Reading and writing deficits are well documented, but other cognitive deficits in dyslexia are not as well known. To investigate spatial deficits in children with developmental dyslexia we used a mental rotation test with three types of stimuli (letters, animals, and objects that look like letters) while simultaneously recording electroencephalographs. Behaviorally, it was found that dyslexic children took more time than nondyslexic children to solve the 'letter' and 'object' stimuli and that the dyslexic children had a slower mental rotation speed when solving 'letter' stimuli. The electroencephalographic data demonstrated more negative amplitude modulations for the dyslexic group in the left hemisphere at the time epochs: 200-300, 600-700, 700-800, 800-900, and 900-1000 ms and in the right hemisphere for the time epoch 600-700 and 900-100 ms. In addition, hemispheric group differences were found on the basis of stimuli for the time epoch 600-700 ms in which the processing of letters was lateralized to the left hemisphere for both groups, but the object stimuli was lateralized to the left for nondyslexic and to the right for dyslexic children. These differences support the idea that the behavioral differences found between dyslexic and nondyslexic children may be because of both differences in the early processing of the stimuli and perhaps in the mental rotation itself.