The brains of experts - due to predispositions and/or training?

Here is how Golestant et al. frame their interesting study on the brains of expert Phoneticians - who typically spend one to four years of formal training learning to identify speech sounds and to transcribe them into an international phonetic alphabet. (Remember, you can view any of the brain structures they mention by simply entering their name in Google Image Search.) The work suggests that morphological brain differences at birth might well influence career choices. We tend to enjoy and get reinforcement for doing things we are good at. (I've always wondered about a brain correlate for my ability, from a young age, to sight read any piece of sheet music put in front of me.)

Expertise has been shown to have both functional and structural correlates in the human brain. For example, expert golfers show a different pattern of neural activity than novice golfers when planning shots, and London taxi drivers have a larger posterior hippocampal volume than matched controls. It can be difficult to establish, however, the extent to which these effects relate to preexisting differences between the novice and expert groups, or whether these effects mainly arise from training-induced plasticity. Here we investigate brain anatomy in expert phoneticians...to distinguish experience-dependent plasticity from brain structural features that existed before the onset of expertise training.

From their abstract:

...We found a positive correlation between the size of left pars opercularis and years of phonetic transcription training experience, illustrating how learning may affect brain structure. Phoneticians were also more likely to have multiple or split left transverse gyri in the auditory cortex than nonexpert controls, and the amount of phonetic transcription training did not predict auditory cortex morphology. The transverse gyri are thought to be established in utero; our results thus suggest that this gross morphological difference may have existed before the onset of phonetic training, and that its presence confers an advantage of sufficient magnitude to affect career choices. These results suggest complementary influences of domain-specific predispositions and experience-dependent brain malleability, influences that likely interact in determining not only how experience shapes the human brain but also why some individuals become engaged by certain fields of expertise.