Functional relevance of cross-modal plasticity in blind humans

Abstract

Functional imaging studies of people who were blind from an early age have revealed that their primary visual cortex can be activated by Braille reading and other tactile discrimination tasks. Other studies have also shown that visual cortical areas can be activated by somatosensory input in blind subjects but not those with sight. The significance of this cross-modal plasticity is unclear, however, as it is not known whether the visual cortex can process somatosensory information in a functionally relevant way. To address this issue, we used transcranial magnetic stimulation to disrupt the function of different cortical areas in people who were blind from an early age as they identified Braille or embossed Roman letters. Transient stimulation of the occipital (visual) cortex induced errors in both tasks and distorted the tactile perceptions of blind subjects. In contrast, occipital stimulation had no effect on tactile performance in normal-sighted subjects, whereas similar stimulation is known to disrupt their visual performance. We conclude that blindness from an early age can cause the visual cortex to be recruited to a role in somatosensory processing. We propose that this cross-modal plasticity may account in part for the superior tactile perceptual abilities of blind subjects.

Cross-modal associations between vision, touch, and audition influence visual search through top-down attention, not bottom-up capture

“…There is growing evidence for early sensory interactions between vision and touch, and it has been suggested that the reorganization of the visual cortex of blind individuals that occurs in the absence of visual input reinforces preexisting connections between the somatosensory and visual cortices (see a review by Pascual-Leone, Amedi, & Fregni, 2005). Consistent with this suggestion, studies have demonstrated that the visual cortex of blind individuals is activated during tasks such as Braille reading (Cohen et al, 1997;Sadato et al, 1996) and haptic object recognition (Amedi, Raz, Azulay, Malach, & Zohary, 2010). Moreover, the existence of networks between vision and touch in normally sighted individuals is supported by neuroimaging studies; visual areas have been shown to be activated during tactile orientation discrimination (Sathian & Zangaladze, 2002;Sathian, Zangaladze, Epstein, & Grafton, 1999), haptic object recognition (Amedi, Jacobson, Hendler, Malach, & Zohary, 2002;Amedi et al, 2010;Deibert, Kraut, Kremen, & Hart, 1999;James, Humphrey, Gati, Servos, Menon, & Goodale, 2002;Pietrini et al, 2004), and Braille reading in sighted subjects following 5 days of complete visual deprivation (Merabet et al, 2008).…”

Correlation between vividness of visual imagery and echolocation ability in sighted, echo-naïve people

“…Specifically, as laid out in the introduction, blind people typically show better echolocation F o r P e e r R e v i e w 13 performance than sighted people (see Teng and Whitney 2011, for a summary). Furthermore, blind people also show increased activation in calcarine cortex for non-visual stimuli, such as touch and sound (for reviews see Bavelier and Neville 2002;Merabet and Pascual-Leone 2010), and TMS studies show that CC in the blind brain is functionally relevant for performance in non-visual tasks (Cohen et al 1997) . In addition, within a group of blind people a positive correlation has been observed between age at onset of vision loss and echolocation ability such that people who lost sight earlier in life are better at echolocation (Teng et al 2012).…”

Plasticity in the developing brain: Implications for rehabilitation

“…Sadato et al [1996] used positron emission tomography (PET) to demonstrate that Braille reading in these subjects activated the somatosensory cortex assigned to the Braille reading fingers, as well as the primary visual cortex. They also showed that transient inactivation of the occipital cortex with transcranial magnetic stimulation (TMS) impaired tactile discrimination in the blind subjects but did not affect sensation in nonblind individuals [Cohen et al, 1997]. A case has been reported in which an individual with early blindness learned to read Braille proficiently but then lost this ability following bilateral occipital stroke although her primary somatosensory perception remained intact [Hamilton et al, 2000].…”