Neural networks for Braille reading by the blind

Abstract

To explore the neural networks used for Braille reading, we measured regional cerebral blood flow with PET during tactile tasks performed both by Braille readers blinded early in life and by sighted subjects. Eight proficient Braille readers were studied during Braille reading with both right and left index fingers. Eight-character, non-contracted Braille-letter strings were used, and subjects were asked to discriminate 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 subjects using the right index finger. The tasks included a non-discrimination task and three discrimination tasks (angle, width and character). Irrespective of reading finger (right or left), Braille reading by the blind activated the inferior parietal lobule, primary visual cortex, superior occipital gyri, fusiform gyri, ventral premotor area, superior parietal lobule, cerebellum and primary sensorimotor area bilaterally, also the right dorsal premotor cortex, right middle occipital gyrus and right prefrontal area. During non-Braille discrimination tasks, in blind subjects, the ventral occipital regions, including the primary 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 findings suggest that the tactile processing pathways usually linked in the secondary somatosensory area are rerouted in blind subjects to the ventral occipital cortical regions originally reserved for visual shape discrimination.

Cortical plasticity in an early blind musician: an fMRl study

“…This is not surprising in that the task was exclusively auditory and would therefore be unlikely to activate cells that are typically involved in multisensory integration. However, data have shown that in early blind individuals these regions become dominated by nonvisual systems and do not require visual stimulation to be activated [7,13,15,17,30]. This is clearly the case in subject ML.…”

Tactile Acuity is Enhanced in Blindness

“…Functional imaging studies have shown activation of extrastriate cortical areas in early and, to a lesser extent, late blind subjects performing tactile tasks (Cohen et al, 1999;Sadato et al, 2002). According to several studies, primary visual cortex is activated only in early blind subjects (Sadato et al, 1996(Sadato et al, , 1998(Sadato et al, , 2002Cohen et al, 1999) (but see Büchel et al, 1998;Burton et al, 2002), yet tactile stimuli activated both striate and extrastriate cortex in sighted adults blindfolded for 5 d (PascualLeone and Hamilton, 2001). In several studies, the functional relevance of tactile occipital activation was confirmed through the use of disruptive transcranial magnetic stimulation (Cohen et al, 1997(Cohen et al, , 1999Pascual-Leone and Hamilton, 2001).…”

“…Occipital cortical areas that normally subserve vision are activated in congenitally blind subjects performing auditory (Weeks et al, 2000) or tactile (Sadato et al, 1996(Sadato et al, , 1998(Sadato et al, , 2002Cohen et al, 1999;Melzer et al, 2001) spatial discrimination tasks (crossmodal plasticity). In addition, within the primary somatosensory cortex of Braille readers, the representation of the reading finger is enlarged (unimodal plasticity) (Pascual-Leone and Torres, 1993).…”

Evaluation of headache intensity in migrainous patients with visual handicap through the tactile analogical scale (TAS)

“…So cerebral function, when it is analysed through photon emission computed tomography (SPECT), positron emission tomography (PET) and functional resonance nuclear magnetic (fRNM), demonstrated a recruiting of the occipital cortex for other neurones commands, including other sensitive forms as tactile and auditory [14][15][16][17][18] . The metabolic activity of the visual cortex in blind people does not show any difference in the cerebral blood flow, glucose metabolism and oxygen consumption in relation to the control group with no visual deficiency, demonstrating electrical activity in the area [19][20][21] .…”

“…The lost of the visual inputs to the occiptal cortex also influences the trigeminal nociceptive discrimination 12 . It permits to draw a conclusion that the visual cortex is involved in other tasks that are not just visual, as reading in Braille, tactile and trigeminal nociceptive discrimination 12,14,35 .…”