If you practice biceps curls at the gym, you will get bigger muscles that are also stronger. So far, the same seemed true for the brain. Thanks to neuroplasticity, practice triggers neuronal and synaptic growth (i.e., brain volume growth), which correlates with better performance. In this fascinating Scientific American article we learn that as the brain masters a new skill, some brain areas do get bigger but eventually shrink back to normal! The performance gain acquired through practice stays present, in spite of the shrinkage.
Studying the auditory cortex of rats, they found that the expansion of a ‘skill-specific’ brain area with training is only short lived, even when changes in ability are long lasting.