Normal Activation of Frontotemporal Language Cortex in Dyslexia, as Measured With Oxygen 15 Positron Emission Tomography

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Abstract
Objective: To assess the ability of dyslexic men to activate left middle to anterior language cortex normally. Design: Positron emission tomography using oxygen 15—labeled water as a tracer during rest and during a syntax task involving sentence comprehension. Setting: Research hospital. Patients or Other Participants: Fifteen right-handed, severely dyslexic men (mean [±SD] age, 27±5 years) and 20 matched controls. Interventions: None. Main Outcome Measure: Cerebral blood flow. Results: During rest, dyslexics showed reduced blood flow (relative to controls) in one left parietal region near the angular/supramarginal gyri, but otherwise normal flow. During syntactic processing, dyslexics and controls showed similar, significant activation of left middle to anterior temporal and inferior frontal cortex. Conclusions: These results, together with the previously reported failure of dyslexics to activate left temporoparietal cortex during phonologic processing, argue for dysfunction of left cortical language areas restricted to posterior language regions in dyslexia.