The Brain That Changes Itself (15)

The competitive nature of plasticity affects us all. There is an endless war of nerves going on inside each of our brains. If we stop exercising our mental skills, we do not just forget them: the brain map space for those skills is turned over to the skills we practice instead. if you ever ask yourself, "How often must I practice French, or guitar, or math to keep on top of it?" you are asking a question about competitive plasticity. You are asking how frequently you must practice one activity to make sure its brain map space is not lost to another.

所以辞了职脑袋也不能闲着呀。刘冬梅同志！

Competitive plasticity in adults even explains some of our limitations. Think of the difficult most adults have in learning a second language. The conventional view now is that the difficulty arises because the critical period for language learning has ended, leaving us with a brain too rigid to change tis structure on a large scale. But the discovery of competitive plasticity suggests there is more to it. As we age, the more we use our native language, the more it comes to dominate our linguistic map space. Thus it is also because our brain is plastic --- and because plasticity is imputative --- that it is so hard to learn a new language and end the tyranny of the mother tongue.

But why, if there is true, is it easier to learn a second language when we are young? Is there not competition the too? Not really. If two languages are learned at the same time, during the critical period, both get a foothold. Brain scans, says Merzenich, show that in a bilingual child all th sounds of its two languages share a single large map, a library of sounds from both languages.

Competitive plasticity also explains why our bad habits are so difficult to brake or "unlearn." most of us think of the brain as a container and learning as putting something in it. When we try to break a bad habit, we think the solution is to put something new into the container. But when we learn a bad habit, it takes over a brain map, and each time we repeat it, it claims more control of that map and prevents the use of that space for "good" habits. That is why "unlearning" is other a lot harder than learning, and why early childhood educate is so important --- it's best to get it right early, before the "bad habit" gets a competitive advantage.