Dyscalculia and dyslexia after right hemisphere injury in infancy
H. S. Levin, J. Scheller, T. Rickard, J. Grafman, K. Martinkowski, M. Winslow and S. Mirvis
Division of Neurosurgery, University of Maryland Medical System, Baltimore, USA.
OBJECTIVE: To use the findings from neuropsychological evaluation and
functional magnetic resonance imaging (fMRI) to assess interhemispheric
reorganization of function after early unilateral brain injury. DESIGN AND
METHODS: The study focused on one case of early brain injury that resulted
in both dyscalculia and dyslexia. Brain injury was studied using both
structural and fMRI. Intellectual function was evaluated using the Wechsler
Intelligence Scale for Children, Third Edition, while visuospatial skills
were assessed using the Block Design subtest of the Wechsler Intelligence
Scale for Children, Third Edition, and Judgment of Line Orientation
subtest. The Selective Reminding Test and the Recurring Figures Test were
used to evaluate memory and orientation; language and speech skills were
evaluated using the Boston Naming Test, Controlled Oral Word Association,
Gates-MacGinitie Reading Test, and color naming. Various methods were used
to study arithmetic skills, including the Wide Range Achievement
Test-Revised and the Peabody Individual Achievement Test. The control group
for fMRI consisted of nine normal subjects. SETTING: Neuropsychological
laboratory in primary care hospital. PATIENT: A 17-year-old boy who had
sustained a closed head injury associated with a partially depressed, right
parietal skull fracture, and right temporal hemorrhage in a motor vehicle
crash at age 7 months (November 9, 1977). Subsequent social behavior was
normal, but the patient had difficulty throughout school in mathematics and
spelling and was characterized as having a "short attention span."
INTERVENTION: None. MAIN OUTCOME MEASURES: Standardized tests of arithmetic
and reading supplemented by an assessment of calculation and quantitative
skills. While performing calculations, fMRI disclosed predominantly left
hemisphere activation involving the frontal and posterior parietal regions,
whereas this task produced bilateral activation of the supramarginal gyrus
in seven of nine normal subjects. RESULTS: Neuropsychological findings
confirmed the presence of dyscalculia and dyslexia despite normal
intellectual functioning. Visuospatial skills ranged from the low normal to
average level. The fMRI findings were consistent with early
interhemispheric transfer of visuospatial skills normally committed to the
right parietal area to the left parietal region. The patient's dyscalculia
and reading ability raise a question of acquired left parietal dysfunction
as a consequence of the competition between verbal and visuospatial
functions for left hemisphere representation. CONCLUSION: Interhemispheric
reorganization of function may be bidirectional rather than a feature
unique to the left hemisphere substrate for language.