Right frontotemporal activation by tonal memory in dyslexia, an O15 PET Study

A prior study documented the failure of dyslexic men to activate left temporoparietal cortex during phonologic processing. Because of reports of an anomalous right planum temporale in developmental dyslexia, the functional implications of which are unknown, this study examined the ability of dyslexics to activate right temporal cortex. Regional cerebral blood flow was measured in 15 right-handed dyslexic men during rest and during a tonal memory task expected to activate right-sided cortex in controls. A matched control sample (n = 18) showed significant activation of several right frontotemporal regions as well as of left temporal cortex. In contrast, severely dyslexic men activated fewer right frontotemporal regions, while making many more errors than controls, but showed normal activation of left mid to anterior temporal cortex. These results support hypothesized underlying deficits in rapid temporal processing and possible involvement of right (in addition to left) temporal cortex in severe dyslexia.