Regional cerebral blood flow in severe developmental dyslexia
J. M. Rumsey, K. F. Berman, M. B. Denckla, S. D. Hamburger, M. J. Kruesi and D. R. Weinberger
Child Psychiatry Branch, National Institute of Mental Health, Bethesda, MD 20892.
Regional cerebral blood flow was measured under three task conditions in 14
men with severe developmental dyslexia and their control subjects using a
xenon 133 inhalation technique. No group differences in overall level or in
pattern of gray matter flow were seen under relatively undemanding
cognitive conditions. Despite minimal group differences in performance, the
dyslexic group showed an increased hemispheric asymmetry (left greater than
right) on a semantic classification task and a reduced anteroposterior
difference on a line orientation task relative to controls. The exaggerated
asymmetry suggests the possibility of less efficient information processing
or inadequate bihemispheric integration. The reduced anteroposterior
gradient may reflect a deficit in the ability of frontal systems to respond
adequately to cognitive demands.
