Reading embossed capital letters: An fMRI study in blind and sighted individuals

Abstract

Reading Braille activates visual cortex in blind people [Burton et al., J Neurophysiol 2002;87:589-611; Sadato et al., Nature 1996;380:526-528; Sadato et al., Brain 1998;121:1213-1229]. Because learning Braille requires extensive training, we had sighted and blind people read raised block capital letters to determine whether all groups engage visual cortex similarly when reading by touch. Letters were passively rubbed across the right index finger at 30 mm/s using an MR-compatible drum stimulator. Age-matched sighted, early blind (lost sight 0-5 years), and late blind (lost sight >5.5 years) volunteers performed three tasks: stating an identified letter, stating a verb containing an identified letter, and feeling a moving smooth surface. Responses were voiced immediately after the drum stopped moving across the fingertip. All groups showed increased activity in visual areas V1 and V2 during both letter identification tasks. Blind compared to sighted participants showed greater activation increases predominantly in the parafoveal-peripheral portions of visuotopic areas and posterior parts of BA 20 and 37. Sighted participants showed suppressed activity in most of the same areas except for small positive responses bilaterally in V1, left V5/MT+, and bilaterally in BA 37/20. Blind individuals showed suppression of the language areas in the frontal cortex, while sighted individuals showed slight positive responses. Early blind showed a more extensive distribution of activity in superior temporal sulcal multisensory areas. These results show cross-modal reorganization of visual cortex and altered response dynamics in nonvisual areas that plausibly reflect mechanisms for adaptive plasticity in blindness.

Touch, sound and vision in human superior temporal sulcus

“…Previous studies have reported somatosensory responses in human STS (Burton et al, 2006;Disbrow et al, 2001;Golaszewski et al, 2002). The present results are the first to show that these responses are co-localized with auditory and visual responses.…”

“…Previous human fMRI studies examining responses to somatosensory, auditory and visual stimulation have found regions responsive to all three modalities in parietal and frontal cortex, but not in the STS (Bremmer et al, 2001;Downar et al, 2000). Some studies of somatosensory processing have reported activity in STS (Burton et al, 2006;Disbrow et al, 2001;Golaszewski et al, 2002) but it is unclear if somatosensory, auditory and visual responses occur in human STSms as they do in macaque STP.…”

Tactile Spatial Acuity Enhancement in Blindness: Evidence for Experience-Dependent Mechanisms

“…This happens in blindfolded sighted participants (Merabet et al, 2007(Merabet et al, , 2008 and blind participants (Sadato et al, 1996(Sadato et al, , 1998(Sadato et al, , 2002(Sadato et al, , 2004Cohen et al, 1999;Burton et al, 2002Burton et al, , 2006Ptito et al, 2005;Stilla et al, 2008). Several lines of evidence suggest a functional role for cross-modal plasticity: a congenitally blind Braille reader developed alexia for Braille after suffering a bilateral occipital stroke , occipital transcranial magnetic stimulation (TMS) impairs blind participants' tactile performance (Cohen et al, 1997(Cohen et al, , 1999Kupers et al, 2007), and occipital TMS elicits sensations on the fingers in some participants (Ptito et al, 2008).…”

“…We discuss our findings with respect to two possible neural mechanisms: experience-driven enlargement of somatosensory cortical representations (Pascual-Leone and Torres, 1993;Sterr et al, 1998 and recruitment of occipital cortical areas for tactile tasks (Sadato et al, 1996(Sadato et al, , 1998(Sadato et al, , 2002(Sadato et al, , 2004Cohen et al, 1999;Burton et al, 2002Burton et al, , 2006Ptito et al, 2005;Stilla et al, 2008).…”

Visual cortex activation in late-onset, Braille naive blind individuals: An fMRI study during semantic and phonological tasks with heard words

“…Braille literate blind people also exhibit visual cortical activity during a variety of non-Braille tactile [6,7,16] and auditory tasks [2,5,21], which raises the question of whether Braille literacy influences visual cortex cross-modal plasticity. However, sensory deprivation alone may be sufficient to induce visual cortex reorganization because short-term visual deprivation in sighted people made visual cortex more excitable [3] and responsive during discrimination of Braille letters or auditory pitch [12].…”