Cortical activation during Braille reading is influenced by early visual experience in subjects with severe visual disability: A correlational fMRI study

Functional magnetic resonance imaging was performed on blind adults resting and reading Braille. The strongest activation was found in primary somatic sensory/motor cortex on both cortical hemispheres. Additional foci of acti vation were situated in the parietal, temporal, and occipital lobes where v isual information is processed in sighted persons. The regions were differe ntiated most in the correlation of their time courses of activation with re sting and reading. Differences in magnitude and expanse of activation were substantially less significant. Among the traditionally visual areas, the s trength of correlation was greatest in posterior parietal cortex and modera te in occipitotemporal, lateral occipital, and primary visual cortex. It wa s low in secondary visual cortex as well as in dorsal and ventral inferior temporal cortex and posterior middle temporal cortex. Visual experience inc reased the strength of correlation in all regions except dorsal inferior te mporal and posterior parietal cortex. The greatest statistically significan t increase, i.e., similar to 30%, was in ventral inferior temporal and post erior middle temporal cortex. In these regions, words are analyzed semantic ally, which may be facilitated by visual experience. In contrast, visual ex perience resulted in a slight, insignificant diminution of the strength of correlation in dorsal inferior temporal cortex where language is analyzed p honetically. These findings affirm that posterior temporal regions are enga ged in the processing of written language. Moreover, they suggest that this function is modified by early visual experience. Furthermore, visual exper ience significantly strengthened the correlation of activation and Braille reading in occipital regions traditionally involved in the processing of vi sual features and object recognition suggesting a role for visual imagery. (C) 2001 Wiley-Liss, Inc.