Different activation patterns in the visual cortex of late and congenitally blind subjects

In a PET study we demonstrate that congenitally blind subjects show taskspecific activation of extrastriate visual areas and parietal association areas during Braille reading, compared with auditory word processing

C Buchel


Scholarcy highlights

  • Blindness due to ocular or anterior visual pathway pathology permits the study of cortical reorganization after sensory deprivation in man
  • Visual experience is important for early organization of the visual cortex, suggesting that early reorganization depends upon the age of onset of deprivation
  • We have studied sighted subjects, and congenitally and late blind subjects with H215O-PET, comparing Braille reading, visual reading and auditory word processing to address two issues. Has visual cortex that has been deprived of visual input shifted its allegiance sufficiently to be activated by other sensory modalities and, related to this, does the age of onset of blindness influence such reorganization? Comparing two sensory modalities directly with each other, allowed us to demonstrate modality specific activations
  • Comparison of late blind, congenitally blind and sighted subjects raises the issue of differences in structural anatomy of the visual cortex
  • The spatially normalized, smoothed grey matter segmented T1weighted MRI images were submitted to a voxel-based ANCOVA testing for significant differences in grey matter density using SPM96. This analysis revealed no significant differences at this macroscopic level of structural anatomy, in the occipital cortex, between the three groups at P Ͻ 0.05 for either degree of smoothing
  • There were no significant differences in activations between late and congenitally blind subjects when we looked for greater activations in auditory processing, relative to Braille reading
  • It is very unlikely that the discrepancy of primary visual cortex activations can be attributed to the different tasks, as late and congenitally blind subjects in our study were involved in the same task
  • Taking earlier data together with our findings, we conclude that differential activation of extrastriate visual areas during Braille reading, relative to auditory processing, supports taskspecific crossmodal responses in extrastriate cortex

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