This is a brief explanation of neuroplasticity from the work of Michael Merzenich as discussed in Chapter 3 of The Brain that Changes Itself by Norman Doidge. For a more information, please read the book.
Mind-mapping was a process first performed by Wilder Penfield. Using electrodes, he was able to map out areas of the brain associated with sensory input and motor control of various parts of the body. Unfortunately, this led to the belief that mind maps were fixed and the same in every individual. It was Michael Merzenich that showed this was not the case. Mind maps differed from person to person and even within each individual depending on the experiences they had during the course of their lives.
For each brain system to be developed properly from birth, it needs to receive the proper stimulation. For instance, for the eye to see properly, it needs visual stimulation. If you seal that eye shut, the part of the brain associated with vision in that eye fails to develop and that eye becomes blind. I guess this is similar to ambylopia (lazy eye) when the individual relies only on the good eye and the weak eye worsens over time from “disuse”.
The other thing that was discovered was that there are specific times of development for each brain system where it is most sensitive to its environment. Beyond these periods, its plasticity lessens. For example, the critical period of language development begins in infancy and ends between eight years and puberty. Once this period ends, the ability to learn a second language without an accent is limited. Second languages that are learned after the critical period are processed by a part of the brain that is different to the part that processes the native tongue.
Although it has long been accepted that neuroplasticity exists in childhood, it took a while before it was finally accepted that neuroplasticity exists even into adulthood. The interesting thing about neuroplasticity later in life is that it becomes competitive. Everything is fighting for space on the neural cortex of the brain and what eventually gets the greatest representation are the things we focus on. If stimuli activating a certain part of the brain is cut off, the brain real estate is then claimed by other parts. For instance, if one of your fingers was cut off, the part of the brain that represents that finger is then claimed by the other fingers.
Competitive neuroplasticity explains why adults have trouble learning a second language. Although convention states that this difficulty is due to the fact that adults have passed the critical period of language learning, and that the adult brain has become too rigid to change its structure on a large scale, competitive neuroplasticity states otherwise. The older we grow, the more we use our native language and more usage means it takes up more brain real estate, in this case it dominates our linguisitc map space blocking out opportunity for other languages to claim a foot hold. When a child is young, both languages are learned side by side so both are able to claim mind maps of their own. In fact, both languages share a mind map containing a library of sounds from both languages.
Competitive neuroplasticity also explains why bad habits are hard to break. When we establish a habit, it occupies a brain map that could otherwise be used for good habits. The more we repeat the bad habit, the more control it has over the mind map and the harder it becomes to establish a new habit to replace the bad habit. In other words, unlearning is a lot harder than learning and it is this reason that early childhood education is important – we need to get things right early so that bad habits don’t gain control of the brain maps where it will become difficult to unlearn.
It is a little like what a tennis coach once told me, “If you are planning to go for tennis lessons, then you should do so from the start before you’ve picked up bad habits that will be difficult to get rid off.” I guess the same goes for young children and learning. Start them young to avoid the development of bad habits that will be difficult to by-pass later.