Researchers at Catholic University of Leuven, Belgium used diffusion tensor imaging tractography, a structural MRI technique, to assess the integrity of white matter tracts involved in reading. Group comparisons of 20 adults with dyslexia and 20 typical reading adults showed a significantly reduced fractional anisotropy (i.e. an index of the amount of anisotropy) in the left arcuate fasciculus of dyslexics, reflecting reduced myelination. Performance on phoneme awareness and speech perception was specifically related to the integrity of the left arcuate fasciculus (dorsal phonological route underlying grapheme-phoneme decoding), whereas orthographic (direct word) processing was related to fractional anisotropy values in the left inferior fronto-occipital fasciculus (ventral orthographic route). Structural anomalies found in the left arcuate fasciculus of dyslexics corroborate the hypothesis of dyslexia as a disorder of network connections. 
COMMENT. Dyslexics have reduced white matter integrity in the component of the left arcuate fasciculus that links Wernicke’s to Broca’s area.