Wednesday, September 03, 2008

We can use our visual cortex for touch

Merabet et al. perform the fascinating experiment of simply blindfolding normal subject for five days, during which intensive tactile training is carried out that improves the subjects' ability to read Braille characters. fMRI measurements reveal an increase in visual cortex responses to tactile stimulation during this period, suggesting that a non-visual input to the visual cortex is being unmasked.
...This increase in signal was no longer present 24 hours after blindfold removal. Finally, reversible disruption of occipital cortex function on the fifth day (by repetitive transcranial magnetic stimulation; rTMS) impaired Braille character recognition ability in the blindfold group but not in non-blindfolded controls. This disruptive effect was no longer evident once the blindfold had been removed for 24 hours.

Overall, our findings suggest that sudden and complete visual deprivation in normally sighted individuals can lead to profound, but rapidly reversible, neuroplastic changes by which the occipital cortex becomes engaged in processing of non-visual information. The speed and dynamic nature of the observed changes suggests that normally inhibited or masked functions in the sighted are revealed by visual loss. The unmasking of pre-existing connections and shifts in connectivity represent rapid, early plastic changes, which presumably can lead, if sustained and reinforced, to slower developing, but more permanent structural changes, such as the establishment of new neural connections in the blind.

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