Cerebral brain metabolism in adult dyslexic subjects assessed with positron emission tomography during performance of an auditory task.

Ten dyslexic adults (aged 33.5 +/- 7.3 years, nine men, one woman) and 10 age-, sex- and handedness-matched control subjects (aged 33.6 +/- 5.8 years) performed an auditory syllable discrimination task during 18-fluoro-2-deoxyglucose uptake, and then underwent positron emission tomographic scans. A second normal control group performed an analogous visual discrimination task. Dyslexic subjects experienced greater difficulty and made significantly more errors in performing the auditory task. There were no differences in brain metabolic rates in lateral cortical areas (frontal, parietal, temporal, and occipital lobes). A significant difference emerged in the medial temporal lobe, with dyslexic subjects having significantly higher absolute and relative brain metabolism along an anterior-posterior gradient than normal adults. These data support the hypothesis of altered cerebral processing of auditory stimuli in patients with dyslexia.