Dyscalculia and dyslexia in a 17-year-old boy after right hemisphere injury in infancy is reported from the Division of Neurosurgery and Department of Pediatrics, University of Maryland, Baltimore; and Cognitive Neuroscience Section, National Institutes of Health, Bethesda, MD. Social behavior was normal, but math and spelling abilities were impaired and his attention span was short. A functional MRI showed predominantly left hemisphere activation involving frontal and posterior parietal regions while the patient performed calculations. In normal subjects this test produced bilateral activation of the supramarginal gyrus. These MRI findings were consistent with early interhemisperic transfer of right parietal visuospatial skills to the left parietal region. Dyscalculia and dyslexia with normal IQ suggest an acquired left parietal dysfunction caused by competition for left hemisphere representation between verbal and visuospatial functions. [1]
COMMENT. The authors conclude that interhemispheric reorganization of function and language may be bidirectional and not only a left hemisphere feature of language development. The MRI showed an intact left hemisphere following the injury. Visuospatial functions normally subserved by the right parietal area were probably transferred to the left parietal region, causing a crowding effect and disproportionate impairment of reading and math skills in relation to his other cognitive abilities.