'Seeing' with our fingers taps brain's visual reserves

People who become blind often develop improved hearing or sense of touch, and their brains borrow sensory processing power from the visual center for other tasks, research based on brain imaging has shown.

But how do those gains in other senses come about? Are new neural connections being formed, or does the brain draw on capacity just waiting to be tapped?

Researchers from Beth Israel Deaconess Medical Center report in PLoS One that when vision is temporarily lost, the brain quickly unmasks connections in the visual cortex that are already there, findings that are important to understanding the brain's adaptability and possible rehabilitation.

"The potential for the brain to reorganize itself is much greater than previously assumed," the authors write.

In the trial led by Dr. Alvaro Pascual-Leone, 32 adults with normal sight were randomly assigned to be completely blindfolded for five days or only while an instructor taught them Braille.

The subjects were tested on their Braille skills on day 1 and day 5, when they also had functional MRIs to record their brain activity. In line with previous research, the 24/7 blindfolded subjects performed better than the people who wore blindfolds only while they were being trained to read Braille.

The MRIs from the always-blindfolded people showed higher activity in their visual cortex on day 5 while their fingers were reading Braille, but once the blindfolds stayed off for a day, those signs of touch stirring activity in the visual cortex disappeared.

Fifteen other study participants -- eight blindfolded, seven not -- also learned Braille, but on the fifth day some received a form of brain stimulation that temporarily blocked activity in the visual cortex. During that disruption, they couldn't read Braille as well. But the next day, their skills returned.

The researchers conclude that the brain can rapidly adapt to blindness, compensating for vision loss by shifting connections used for sight to tasks using touch.

"Enhanced understanding of the mechanisms ... is critical for the fundamental understanding of the adaptation of the human brain to injury and might suggest strategies for neurorehabilitation," the authors conclude.