Veering Away from Localizationism
Excerpted from the book: The Brain That Changes Itself
Stories of Personal Triumph from the Frontiers of Brain Science
By Norman Doidge, MD, Penguin Publishing, December, 2007
Up until the 1960s, scientists and physicians thought the adult brain to be “hard-wired” and incapable of change. the scientific mind-set at the time assumed that the brain's structure is like a complex machine, made up of parts, each of which performs a specific mental function and exists in a genetically predetermined or hardwired location — hence the name.
Serious localizationism was first proposed in 1861, when Paul Broca, a surgeon, had a stroke patient who lost the ability to speak and could utter only one word. No matter what he was asked, the poor man responded, "Tan, tan." When he died, Broca dissected his brain and found damaged tissue in the left frontal lobe.
Soon afterward another physician, Carl Wernicke, connected damage in another brain area farther back to a different problem: the inability to understand language. Wernicke proposed that the damaged area was responsible for the mental representations of words and comprehension. It came to be known as "Wernicke's area."
In 1868 Jules Cotard studied children who had early massive brain disease, in which the left hemisphere (including Broca's area) wasted away. Yet these children could still speak normally. This meant that even if speech tended to be processed in the left hemisphere, as Broca claimed, the brain might be plastic enough to reorganize itself, if necessary.
Over the next hundred years localizationism became more specific as new research refined the brain map.
Dr. Paul Bach-y-Rita was a visionary neuroscientist and an early pioneer of the theory of neuroplasticity. He is the father of sensory substitution. He came to doubt localizationism while in Germany in the early 1960s. He had joined a team that was studying how vision worked by inserting an electrodes into the visual processing area of a cat's brain. The team fully expected that when they showed the cat an image, the electrode would discharge an electric spike, showing it was processing that image. And it did.
But when the cat's paw was accidentally stroked, the visual area also fired, indicating that it was processing touch as well. And they found that the visual area was also active when the cat heard sounds.
Bach-y-Rita began to think that the localizationist idea of "one function, one location" couldn't be right. The "visual" part of the cat's brain was processing at least two other functions, touch and sound. He began to conceive of much of the brain as "polysensory" — that its sensory areas were able to process signals from more than one sense. p. 19
Bach-y-Rita realized that the areas that process these electrical impulses are far more homogeneous than neuroscientists appreciated, a belief that was reinforced when the neuroscientist Vernon Mountcastle discovered that the visual, auditory, and sensory cortices all have a similar six-layer processing structure.
To Bach-y-Rita, this meant that any part of the cortex should be able to process whatever electrical signals were sent to it, and that our brain modules were not so specialized after all.
If this post strikes a chord with you, we take brain plasticity possibilities a step further in Impossible Dream, the extraordinary story of triumph over disability told from the first-person perspective of a young woman living with autism.