So if, as scientists' findings suggest, the visual cortex need not be devoted solely to sight, how does the brain adapt after injury or new environmental influences? Does the brain forge new connections that did not exist before, or are the connections already there lying dormant, pressed into service by the circumstances?

Pascual-Leone's current work with his colleagues at Beth Israel Deaconess aims to answer those questions. For the past few years, they have been studying sighted subjects who volunteer to be blindfolded for five days and learn certain nonvisual tasks, including rudimentary Braille. In every case, before subjects donned the blindfold,functional MRI (fMRI) scans revealed little activity in their visual cortices during tactile tasks. After the subjects wore the blindfolds for two days, however, the scans showed bright patches of activity in the visual brain when the subjects used their fingers for tactile or Braille-reading tasks. By day five, the visual cortex glowed steadily during these same tasks. Yet two hours after the blindfolds were removed and the subjects' eyes had readjusted, scans of the visual area of their brains were as dark as they'd been on day one. Once the blindfolds were removed, touching, handling objects, and Braille-reading no longer activated ''sight" in the seeing.