Short, but interesting article in Scientific American:
Spine Tuning: Finding Physical Evidence of How Practice Rewires the Brain
In kindergarten, several of my friends and I were very serious about learning to tie our shoes. I remember sitting on the edge of the playground, looping laces into bunny ears and twisting them into a knot over and over again until I had it just right. A few years later, whistling became my new challenge. On the car ride to school or walking between classes, I puckered my lips and blew, shifting my tongue like rudder to direct the air. Finally, after weeks of nothing but tuneless wooshing, I whistled my first note.
Although I had no inkling of it at the time, my persistence rewired my brain. Just about everything we do modifies connections between brain cells—learning and memory are dependent on this flexibility. When we improve a skill through practice, we strengthen connections between neurons involved in that skill. In a recent study, scientists peeked into the brains of living mice as the rodents learned some new tricks. Mice who repeated the same task day after day grew more clusters of mushroomlike appendages on their neurons than mice who divided their attention among different tasks. In essence, the scientists observed a physical trace of practice in the brain.