How Brain Mapping Came About
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
Brain maps were first made vivid in human beings by the neurosurgeon Dr. Wilder Penfield at the Montreal Neurological Institute in the 1930s. For Penfield, "mapping" a patient's brain meant finding where in the brain different parts of the body were represented and their activities processed — a solid localizationist project. Localizationists had discovered that the frontal lobes were the seat of the brain's motor system, which initiates and coordinates the movement of our muscles.
The three lobes behind the frontal lobe, the temporal, parietal, and occipital lobes, comprise the brain's sensory system, processing the signals sent to the brain from our sense receptors — eyes, ears, touch receptors, and so on.
Penfield spent years mapping the sensory and motor parts of the brain, while performing brain surgery on cancer and epilepsy patients who could be conscious during the operation, because there are no pain receptors in the brain. Both the sensory and motor maps are part of the cerebral cortex, which lies on the brain's surface and so is easily accessible with a probe. Penfield discovered that when he touched a patient's sensory brain map with an electric probe, it triggered sensations that the patient felt in his body. He used the electric probe to help him distinguish the healthy tissue he wanted to preserve from the unhealthy tumors or pathological tissue he needed to remove.
Normally, when one's hand is touched, an electrical signal passes to the spinal cord and up to the brain, where it turns on cells in the map that make the hand feel touched. Penfield found he could also make the patient feel his hand was touched by turning on the hand area of the brain map electrically. When he stimulated another part of the map, the patient might feel his arm being touched; another part, his face. Each time he stimulated an area, he asked his patients what they'd felt, to make sure he didn't cut away healthy tissue. After many such operations he was able to show where on the brain's sensory map all parts of the body's surface were represented.
He did the same for the motor map, the part of the brain that controls movement. By touching different parts of this map, he could trigger movements in a patient's leg, arm, face, and other muscles.
One of the great discoveries Penfield made was that sensory and motor brain maps, like geographical maps, are topographical, meaning that areas adjacent to each other on the body's surface are generally adjacent to each other on the brain maps. He also discovered that when he touched certain parts of the brain, he triggered long-lost childhood memories or dreamlike scenes — which implied that higher mental activities were also mapped in the brain.
The Penfield maps shaped several generations' view of the brain. But because scientists believed that the brain couldn't change, they assumed, and taught, that the maps were fixed, immutable, and universal — the same in each of us — though Penfield himself never made either claim.
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.