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

Abstract

Visual cortex activity in the blind has been shown in Braille literate people, which raise the question of whether Braille literacy influences cross-modal reorganization. We used fMRI to examine visual cortex activation during semantic and phonological tasks with auditory presentation of words in two late-onset blind individuals who lacked Braille literacy. Multiple visual cortical regions were activated in the Braille naive individuals. Positive BOLD responses were noted in lower tier visuotopic (e.g., V1, V2, VP, and V3) and several higher tier visual areas (e.g., V4v, V8, and BA 37). Activity was more extensive and cross-correlation magnitudes were greater during the semantic compared to the phonological task. These results with Braille naive individuals plausibly suggest that visual deprivation alone induces visual cortex reorganization. Cross-modal reorganization of lower tier visual areas may be recruited by developing skills in attending to selected non-visual inputs (e.g., Braille literacy, enhanced auditory skills). Such learning might strengthen remote connections with multisensory cortical areas. Of necessity, the Braille naive participants must attend to auditory stimulation for language. We hypothesize that learning to attend to non-visual inputs probably strengthens the remaining active synapses following visual deprivation, and thereby, increases cross-modal activation of lower tier visual areas when performing highly demanding non-visual tasks of which reading Braille is just one example. KeywordsBlindness; Human; Magnetic resonance imaging; Visual cortex/*physiology Imaging studies (i.e., PET and fMRI) have shown activity in visual cortex of blind people when they read Braille [1,8,18]. 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]. In addition, a recent study described visual cortex activation during a tactile discrimination task in two Braille naive, late-onset blind individuals [17]. The activated regions in these late-onset blind individuals involved higher tier visual areas that included a

Crossmodal reorganization in the early deaf switches sensory, but not behavioral roles of auditory cortex

“…Consistent with this finding is the observation that the posterior auditory field, also known for its involvement in auditory localization behaviors (18), is necessary for enhanced visual localization abilities in congenitally deaf cats (11). Furthermore, in early-blind individuals, lexigraphical regions of visual cortex are activated by Braille reading (19) and the nonvisual spatial properties of medial occipital cortex are retained (29). Thus, for a given cortical region, functional specificity is preserved following deafness/blindness despite substitutions among the input modalities.…”

“…One clue might be the observation that the posterior auditory field of hearing animals is involved in auditory localization (18) whereas the same region in congenitally deaf animals underlies their improvement in visual localization of peripheral targets (11). Similarly, following early blindness, the lexigraphic components of Braille reading provide activation of visual cortex (19). Therefore, it seems possible that the behavioral role of a crossmodally reorganized area is related to its role in hearing/sighted individuals.…”

Practice makes perfect: the neural substrates of tactile discrimination by Mah-Jong experts include the primary visual cortex

“…These results suggest that vibrotactile inputs probably activate the visual cortex through some latent pathway common to both blind and sighted subjects [21]. Burton et al [22] also suggested that the learning effect may be important in the V1 activation in the blind. Using fMRI in late-onset but Braille naïve blind individuals, and auditory-presented phonological tasks, they found task-related activation in both lower tier and higher tier visual areas.…”

“…In contrast, cross-modal reorganization of the lower tier visual areas, which are not cross-modally responsive in sighted people, may be recruited particularly through regularly attending to selected non-visual inputs. Such learning might be needed to strengthen the more remote connections with multisensory cortical areas [22]. Cross-modal reorganization of lower tier visual areas may thus be triggered in sighted subjects by learning skills such as Mah-Jong discrimination.…”

Recognition memory for vibrotactile rhythms: An fMRI study in blind and sighted individuals

“…In blind but not sighted people, language tasks activate regions in occipital and temporal cortex that correspond to visually activated areas in sighted (Kujala et al 1995a; Sadato et al 1996; Büchel et al 1998a, 1998b; Melzer et al 2001; Burton et al 2002a, 2002b, 2003, 2006; Röder et al 2002; Amedi et al 2003; Burton 2003; Burton and McLaren 2006). The functional reorganization of these regions in the blind possibly aids in semantic word generation and word memory retrieval (Amedi et al 2003).…”