Functional neuroimaging studies of reading and reading disability (developmental dyslexia)

Converging evidence from a number of neuroimaging studies, including our ow n, suggest that fluent word identification in reading is related to the fun ctional integrity of two consolidated left hemisphere (LH) posterior system s: a dorsal (temporo-parietal) circuit and a ventral (occipitotemporal) cir cuit. This posterior system is functionally disrupted in developmental dysl exia. Reading disabled readers, relative to nonimpaired readers, demonstrat e heightened reliance on both inferior frontal and right hemisphere posteri or regions, presumably in compensation for the LH posterior difficulties, W e propose a neurobiological account suggesting that for normally developing readers the dorsal circuit predominates at first, and is associated with a nalytic processing necessary for learning to integrate orthographic feature s with phonological and lexical-semantic features of printed words. The ven tral circuit constitutes a fast, late-developing, word identification syste m which underlies fluent word recognition in skilled readers, (C) 2000 Wile y-Liss, Inc.