Redesigning the Brain - Part 1
In this chapter, Doidge introduces Michael Merzenich to us. His work has produced a cochlear implant for deaf individuals. For others with learning disabilities, he and his team have produced Fast ForWord, a software program. Fast ForWord disguises itself as a children’s game. With as little as 30-60 hours of treatment, big changes have been made. Children with autism have, unexpectedly also been helped.
“Merzenich claims that when learning occurs in a way consistent with the laws that govern brain plasticity, the mental ‘machinery’ of the brain can be improved so that we learn and perceive with greater precision, speed, and retention” p. 47
“The cerebral cortex,” he says of the thin outer layer of the brain, “is actually selectively its processing capabilities to fit each task at hand.” It doesn’t simply learn; it is always “learning how to learn” The brain Merzenich describes is not an inanimate vessel that we fill; rather it is more like a living creature with an appetite, one that can grow and change itself with proper nourishment and exercise.” P. 48
In the 1930s neuroscientists were “localizationists” identifying the frontal cortex as the area for the brain’s motor systems (output), “which initiates and coordinates the movement of our muscles.” P. 28 They also identified three lobes behind the frontal cortex as the parts that process sensory input. These three lobes are temporal, parietal and occipital – receptors for the eyes, ears, touch receptors etc. p. 28 Dr. Wilder Penfield of the Montreal Neurological Institute began mapping the mind in the 1930s. “One of the greatest 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.” P. 49
Since “scientists believed that the brain couldn’t change, they assumed, and taught that the maps were fixed, immutable, and universal – the same for each of us – though Penfield himself never made either claim.” P 49
Years later, Merzenich discovered that brains could change and that the brain maps were not fixed. He was able to use much finer instruments than had using microelectrodes during his graduate studies at John Hopkins. Merzenich and his colleagues laboriously mapped extensively parts of the brain during surgeries – placing microelectrodes are a part of a monkey’s brain and then touching different parts of the body. P. 51
In the 1960s two other scientists were micromapping the visual cortex. David Hubel and Tortsen Wiesel also at John Hopkins were learning how vision is processed using kittens. They learned that newborn kittens need to receive specific visual stimulation from the third to eighth week of life in order to develop normally. In the experiment one eye was sewn shut during the ‘critical period’ That eye was blind for life, but the part of the brain responsible for that eye had already begun to redesign itself for another use. These men received the Nobel Prize for their work. They demonstrated neuroplasticity in the ‘critical period” but remained localizationists, believing that the adult brain was hard wired.
This discovery of a critical period was reinforced with the work of other scientists. Different neural functions had their own critical period. “Language development, for instance, has a critical period that begins in infancy and ends between eight years and puberty. After this critical period closes, a person’s ability to learn a second language without an accent is limited. In fact, second languages learned after the critical period are not processed in the same part of the brain as is the native tongue.” P. 52
Etiologist, Konrad Lorenz learned that goslings could ‘imprint” or bond with a human if exposed to a human during their critical period of fifteen hours and three days. P. 52
These discoveries caused doctors to do surgeries during that critical period to take advantage of this time frame., However, “Merzeninch’s first glimpse of adult plasticity was accidental.” After receiving his doctorate, he and neurosurgeons Ron Paul and Herbert Goodman “decided to observe what happens in the brain when one of the peripheral nerves in the hand is cut and then starts to regenerate.” P. 53
Nervous System has two parts:
1) Central nervous system (the brain and spinal cord) – command and control center (thought to lack plasticity) 2) Peripheral nervous system – brings messages to the spinal cord and brain and carries messages from the central nervous to the muscles and glands. (known to have plasticity – that is it could regenerate or heal itself).
Neurons have three parts:
1) Dendrites – treelike branches that receive input from other neurons. 2) Cell body – dendrites lead to the cell body – sustains life; contains DNA 3) Axon – living cable of varying lengths – carry electrical to neighboring neurons – very high speeds. P. 53
Neurons receive two types of signals:
1) excitatory signals – when received the neuron will send its own signal 2) inhibitory signals – when received the neuron will be less likely to send off a signal p. 53-54
These neurons are separated by a microscopic space called a synapse.
In their experiment they cut the nerves on the hands of several adolescent monkeys. Then they sewed them together, but not closely enough to rejoin in the same place. They expected to see a chaotic brain map after seven months. To their surprise Merzenich said, “What we saw was absolutely astounding. I couldn’t understand it.” “It was topographically arranged as though the brain had unshuffled the signals from the crossed nerves.” P. 55 Merzenich realized that he and all scientist had it all wrong. The brain could normalize structure in response to abnormal input. Neuroplasticity beyond the ‘critical period’ had to explain this.
Merzenich scoured the library to find other evidence that contradicted localization:
1) 1912 – Graham Brown & Charles Sherington – “stimulating one point in the motor cortex might cause an animal to bend its leg at one time and straighten it at another” p. 55 2) 1923 – Karl Lashley – also found the same stimulus could produce a different movement.
He wrote a paper, but it was rejected. He was working in someone else’s lab.
Merzenich became a professor at the University of California of San Francisco in 1971. As a professor in the department of otolaryngology and physiology, he began some experiments under the guise of acceptable research. He was mapping the auditory cortex of different animals. This work contributed to invent and perfect the cochlear implant. Unlike a hearing aid, which amplifies sound in someone who is hard of hearing, the cochlear implant replaces the damaged cochlea in a deaf person. While the artificial cochlea is much simpler than the original, the fact that the brain could modify itself to the artificial one, is another indication that the brain at any age is plastic.
Later, Merzenich and Joh Vass of Vanderbilt University in Nashville cut the median nerve in the hand of adult monkeys. Two months later, the micromapping demonstrated that the radial and ulnar muscles had taken over much of the unused part of the brain previously used by the median nerve. The wrote up their results and used the word “plasticity.” P. 58-59
These experiments help us understand the competitive nature of plasticity. If you don’t use it in the original way, you lose it and some other function takes it over.
Merzenich’s work has much more to teach us so we will continue with this next time.
While many of these men were not Christians, we as Christians can see that we, indeed, “are fearfully and wonderfully made.” Psalm 139