The second chapter discusses the "plasticity" of the human brain, meaning whether or not the adult brain can "change" itself, or whether the brain is "wired up" in childhood in such a way that it is unable to physically modify its neural passageways later on. Apparently, for most of history, the brain was thought to be unchangeable after childhood, but in the second half of the 20th century, researchers began to discover that the brain does indeed "rewire" itself, even in adults. For example, if a person loses a limb, the part of the brain that previously was used to control that limb, accept sensory input from that limb, etc. is soon re-purposed for other tasks. That's most likely the reason that blind people often develop sharper sense of hearing, smell, etc. than sighted people; their brains have reused the visual cortex for something else. In fact, there have been experimental therapies used on people who have lost the use of some part of their bodies due to strokes or other head injuries that indicate that if you perform repetitive tasks with that part of the body often enough, you can begin to regain your use of it. Your brain is sensing that you need some power for that body part, and it's sending reinforcements out to work on it. A part of your brain that you are not using for something else is being given the chance to come into use.
What really stuck with me, though, was a section that started with "It's not just repeated physical actions that can rewire our brains. Purely mental activity can also alter our neural circuitry, sometimes in far-reaching ways." It goes on to tell about a study of London cab drivers that showed that people who spend their days performing the spatially-intense task of driving have larger posterior hippocampuses (the part of the brain that handles spatial representations of the person's surroundings). The part of their brains that they constantly stimulate begins to develop. Then it talks about another study in which people with no experience playing piano were taught to play a simple melody, and then one group was told to practice the melody on a piano for a certain amount of time per day, and another group was told to think about playing the song, sitting at a piano, for the same amount of time. Both groups experienced the same kinds of changes in their brains. "Their brains had changed in response to actions that took place purely in their imagination—in response, that is, to their thoughts," Carr reports. "We become, neurologically, what we think."
That the human brain can be physically changed should not be too much of a surprise to any Christian. Romans 12:2 says "Do not be conformed to this world, but be transformed by the renewal of your mind, that by testing you may discern what is the will of God, what is good and acceptable and perfect." Obviously, the way to find out the will of God is to spend time in the Word of God and in prayer, so that verse tells us that our mind can be "transformed" and "renewed" if we do so. By the repetitive action of reading God's Word, studying it, thinking about it, going over and over its basic teachings, submitting our lives to God in prayer and worship, even science tells us that we can "change our minds" and make them work in a certain way. Wouldn't it be great if your mind could operate in such a way that God's thoughts became your thoughts? That's not the way it is naturally, you know. But by spending time with God, using our brains to think about His ways, we can "become what we think." If you approach God with an open heart, He will pour His life into you, and you will be transformed. Your mind will begin to think in terms of God's ways. You might even find things that are not of God less desirable, as His desires become yours. Get into the habit! You'll be glad you did!
I have stored up your word in my heart,
that I might not sin against you. (Psalm 119:11 ESV)