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May 1997

A Positron Emission Tomographic Study of Impaired Word Recognition and Phonological Processing in Dyslexic Men

Author Affiliations

From the Child Psychiatry Branch (Dr Rumsey and Mss Nace and Wise and Mr Donohue) and the Laboratory of Psychology and Psychopathology (Dr Maisog), National Institute of Mental Health, Bethesda, Md; and the Division of Neuropharmacologic Drug Products, Food and Drug Administration, Rockville, Md (Dr Andreason).

Arch Neurol. 1997;54(5):562-573. doi:10.1001/archneur.1997.00550170042013

Background:  Developmental dyslexia is characterized by impaired word recognition, which is thought to result from deficits in phonological processing. Improvements during the course of development are thought to disproportionately involve orthographic components of reading; phonological deficits persist into adulthood.

Objective:  To localize the neural correlates of impaired word recognition and phonological processing in men with developmental dyslexia.

Methods:  Regional cerebral blood flow was measured with oxygen 15 positron emission tomography in 17 men with dyslexia and in 14 matched controls during the performance of phonological and orthographic tasks—pronunciation (reading aloud) and lexical decision making—designed to activate posterior and anterior perisylvian cortices, respectively.

Results:  Altered patterns of activation (reduced activation, unusual deactivation) were seen in dyslexic men in mid- to posterior temporal cortex bilaterally and in inferior parietal cortex, predominantly on the left, during both pronunciation and decision making. In contrast, dyslexic men demonstrated essentially normal activation of left inferior frontal cortex during both phonological and orthographic decision making.

Conclusion:  These, along with prior findings, are compatible with a hypothesis of bilateral involvement of posterior temporal and parietal cortices in dyslexia.

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