Brain MR images were compared in 16 right-handed men (mean age, 24 years; range 18 to 40) with dyslexia and 14 control subjects using a voxel-based analysis, at Stanford University School of Medicine, CA. Evidence of decreases in gray matter in dyslexics was most notable in the left temporal lobe, especially the left posterior superior temporal gyrus (STG), the temporoparietooccipital juncture bilaterally, and the frontal lobe, caudate, thalamus, and cerebellum. Morphological variations in brain structure affecting several brain regions may explain the neuroanatomical basis of dyslexia. [1]

COMMENT. This study confirms previous MR evidence of decreases in the left temporal lobe volume in dyslexic subjects, and further localizes the deficit to the STG and left inferior, middle, and mesial temporal regions. The decreases are global in distribution and affect subcortical as well as cortical gray matter and also, the cerebellum.

In a Yale University study [2], the influence of age, sex and overall brain size on the measurement of MRI brain volume changes in dyslexia was stressed. Analyses that controlled for these variables failed to confirm smaller left hemisphere structures previously reported in dyslexia. Studies involving changes in the corpus callosum are reported from other centers, (see Progress in Pediatric Neurology III, PNB Publ, 1997;pp269-270; and Ped Neur Briefs Jan 2001;15:1; for further comment on the neurological basis of developmental dyslexia).