From a study by Sluming V, Brooks J, Howard M, Downes JJ, and Roberts N:
We provide neurobehavioral evidence supporting the transferable benefit of music training to alter brain function and enhance cognitive performance [emphasis added] in a nonmusical visuospatial task in professional orchestral musicians. In particular, orchestral musicians’ performance on a three-dimensional mental rotation (3DMR) task exhibited the behavioral profile normally only attained after significant practice, supporting the suggestion that these musicians already possessed well developed neural circuits to support 3DMR [emphasis added]. Furthermore, functional magnetic resonance imaging revealed that only orchestral musicians showed significantly increased activation in Broca’s area, in addition to the well known visuospatial network [emphasis added], which was activated in both musicians and nonmusicians who were matched on age, sex, and verbal intelligence. We interpret these functional neuroimaging findings to reflect preferential recruitment of Broca’s area, part of the neural substrate supporting sight reading and motor-sequence organization underpinning musical performance, to subserve 3DMR in musicians. Our data, therefore, provide convergent behavioral and neurofunctional evidence supporting the suggestion that development of the sight-reading skills of musical performance alters brain circuit organization which, in turn, confers a wider cognitive benefit, in particular, to nonmusical visuospatial cognition [emphasis added] in professional orchestral musicians.
We know that Broca’s area, intimately involved in language, is used for sight-reading skills. Here we see that musicians have also cross-trained this area of the brain, through sight-reading, to perform three-dimensional mental rotations (think of assembling knockdown furniture, or model planes, or any of the other dozens of similar tasks that require this skill). Although our brains process music in the same way that they process language, it’s quite a surprise to find that these areas then can contribute to performance of seemingly unrelated tasks (or perhaps we don’t understand language well enough to figure out how three-dimensional mental rotation relates to it).
We read about cross-training that occurs in the brain, when, for example, after the onset of blindness, the visual cortex is then co-opted to interpret signals from touch, hearing or smell; or when one part of the brain is damaged, as in head trauma, that causes the loss of language, and another brain takes over the speech functions. Cross-training is usually a desirable thing, as it increases the flexibility of the brain, and allows for far faster skill acquisition and performance.
If you are thinking about taking music lessons to improve your cognitive functioning, then, make sure you get a teacher who teaches you to sight-read (in a recent study, 93% of piano teachers said that they did not teach sight-reading systematically) for maximum benefit.