Neural redeployment replaces the old paradigm of predetermined brain areas with something more flexible. Territory can be reassigned to different tasks. There is nothing special about visual cortex neurons, for example. They are simply neurons that happen to be involved in processing edges or colors in people who have functioning eyes. These exact same neurons can process other types of information in the sightless.

      The old paradigm would assert that the North American acreage labeled as Louisiana was predetermined for French people. The new paradigm is not surprised when the Louisiana Territory gets sold and citizens from around the globe set up shop there.

      Given that the brain has to distribute all its tasks across the finite volume of the cortex, it may be that some disorders arise from suboptimal distributions. One example is autistic savantism, in which a child who has severe cognitive and social deficits might be a virtuoso at, say, memorizing the phone book, or copying down visual scenes, or solving the Rubik’s Cube with stunning speed. The pairing of cognitive disabilities with outstanding talents has attracted many theories; one of relevance here is an unusual distribution of cortical real estate.³⁶ The idea is that atypical feats can be accomplished when the brain devotes an unusually large swath of its real estate to one task (such as memorization, or visual analysis, or puzzles). But these human superpowers come at the expense of other tasks among which brains normally divide their territory, such as all the subtasks that add up to reliable social skills.

BLINDINGLY FAST

      Recent decades have yielded several revelations about brain plasticity, but perhaps the biggest surprise is its rapidity. Some years ago, researchers at McGill University put several adults who had just recently lost their sight into a brain scanner. The participants were asked to listen to sounds. Not surprisingly, the sounds caused activity in their auditory cortex. But the sounds also caused activity in their occipital cortex—activity that would not have been there even a few weeks earlier, when the participants had sight. The activity wasn’t as strong as that seen in people who had been blind for a long while, but it was detectable nevertheless.³⁷

      This demonstrated that the brain can implement changes rapidly when vision disappears. But how rapidly?

      The researcher Alvaro Pascual-Leone began to wonder about the speed at which these major brain changes can take place. He noted that aspiring instructors at a school for the blind were required to blindfold themselves for seven full days to gain firsthand understanding of their students’ living experiences. Most of the instructors become aware of enhanced skills with sounds—orienting to them, judging their distance, and identifying them:

      Several describe becoming able to identify people quickly and accurately as they started talking or even as they simply walked by due to the cadence of their steps. Several learned to differentiate cars by the sounds of their motors, and one described the “joy of telling motorcycles apart by their sound.”³⁸

      This got Pascual-Leone and his colleagues considering what would happen if a sighted person were blindfolded in a laboratory setting for several days. They launched the experiment, and what they found was nothing short of remarkable. They discovered that neural reorganization—the same kind seen in blind subjects—also happens with temporary blindness of sighted subjects. Rapidly.

      In one of their studies, sighted participants were blindfolded for five days, during which time they were put through an intensive Braille-training paradigm.³⁹ At the end of five days, the subjects had become quite good at detecting subtle differences between Braille characters—much better than a control group of sighted participants who underwent the same training without a blindfold.

      But especially striking was what happened to their brains, as measured in the scanner. Within five days, the blindfolded participants had recruited their occipital cortex when they were touching objects. Control subjects, not surprisingly, used only their somatosensory cortex. The blindfolded subjects also showed occipital responses to sounds and words.

      When this new occipital lobe activity was intentionally disrupted in the laboratory by magnetic pulses, the Braille-reading advantage of the blindfolded subjects went away—indicating that the recruitment of this brain area was not an accidental side effect but a critical piece of the improved behavioral performance.

      When the blindfold was removed, the response of the occipital cortex to touch or sound disappeared within a day. At that point, the participants’ brains returned to looking indistinguishable from every other sighted brain out there.

      In another study, the visual areas of the brain were carefully mapped out using more powerful neuroimaging techniques. Participants were blindfolded, put in a scanner, and asked to perform a touching task that required fine discrimination with their fingers. In these conditions, investigators could detect activity emerging in the primary visual cortex after a blindfolding session of a mere forty to sixty minutes.⁴⁰

      The shock of these findings was their sheer speed. The shape shifting of brains is not like the glacial drifting of continental plates, but can instead be remarkably swift. In later chapters, we’ll see that visual deprivation causes the unmasking of already-existing nonvisual input into the occipital cortex, and we’ll come to understand how the brain is always sprung like a mousetrap to implement rapid change. But for now the important point is that the brain’s changes are more brisk than even the most optimistic neuroscientist would have dared to guess at the beginning of this century.