Some blind people read Braille by running a single finger, like a record stylus, over the stipples representing the alphabet. Others use three fingers, like three styluses playing adjacent grooves. Now researchers have found that the brains of three-finger readers, instead of treating sensory input from each finger as coming from a distinct channel, appear to blur all the input together--like listening to three revolutions of a 45-rpm record simultaneously and still being able to comprehend the lyrics. The findings, reported in the current issue of Nature, suggest that the brain can be far more flexible in how it processes sensory information than previously thought.
A team of researchers at the University of Konstanz and the University of Munich in Germany, and at the University of Alabama, Birmingham, used magnetic field detectors coupled with magnetic resonance imaging to see which areas of the brain lit up in four blind Braille readers who use three fingers to read, six who use one finger, and five sighted individuals. In the one-finger readers and sighted individuals, each finger's sensory input mapped to nerve firing in a distinct region of the cerebral cortex--just what the researchers expected. But in three-finger readers, sensory signals were processed in a larger, more amorphous region. "The same people show an inability to determine which finger has been touched," says Alabama co-author Edward Taub.
This smearing of sensory input might be an advantage to three-finger readers. "As in vision, the more rapidly a reader reads, the more sensory information can be processed simultaneously," Taub says. Experts say that the findings are an important step toward better understanding neuronal "plasticity" and learning. "This is an advent of a tremendously powerful line of experiments," says Michael Merzenich of the University of California, San Francisco, who has done similar work in monkeys. These experiments, he says, have "very quickly changed the classical view of the brain as a fixed computer."