NEURAL NETWORKS FOR BRAILLE READING BY THE BLIND

To explore the neural networks used for Braille reading, we measured r egional cerebral blood flow with PET during tactile tasks performed bo th by Braille readers blinded early in life and by sighted subjects. E ight proficient Braille readers were studied during Braille reading wi th both right and left index fingers. Eight-character, non-contracted Braille-letter strings mere used, and subjects were asked to discrimin ate between words and non-words. To compare the behaviour of the brain of the blind and the sighted directly, non-Braille tactile tasks were performed by six different blind subjects and 10 sighted control subj ects using the right index finger. The tasks included a non-discrimina tion task and three discrimination tasks (angle, width and character). Irrespective of reading finger (right or left), Braille reading by th e blind activated the inferior parietal lobule, primary visual cortex, superior occipital gyri, fusiform gyri, ventral premotor area, superi or parietal lobule, cerebellum and primary sensorimotor area bilateral ly, also the right dorsal premotor cortex, right middle occipital gyru s and right prefrontal area. During non-Braille discrimination tasks, in blind subjects, the ventral occipital regions, including the primar y visual cortex and fusiform gyri bilaterally were activated while the secondary somatosensory area was deactivated. The reverse pattern was found in sighted subjects where the secondary somatosensory area was activated while the ventral occipital regions were suppressed. These f indings suggest that the tactile processing pathways usually linked in the secondary somatosensory al:ea are rerouted in blind subjects to t he ventral occipital cortical regions originally reserved for visual s hape discrimination.