The act of playing a musical instrument calls upon multiple interconnected brain abilities. For example, balance, when I stand as I usually do to play the flute; vision, to interpret a printed language ('code') on a music stand; motor control, activation of a practiced and primed finely tuned system to receive and execute the instructions of the code; memory, to call up a Bach Sonata from its book shelf in the temporal lobe with a connection that sends instructions to the motor system; coordination, between tongue and both hands fitted precisely into a tempo and rhythm; deep-breathing and breath control, to last through an entire phrase; expression and emotion (phrasing, dynamics, style), layered on to the sounds to fit the character and 'message' of the composition; critical listening system to evaluate my own sounds--pitch, tone quality, fit into an ensemble, pace, tempo--in a feedback loop that makes instant corrections to all the functions mentioned above as needed; and so forth. All instruments demand similar and other abilities.
Whew! That is a major workout for the brain! And it's less expensive and (for me) more interesting than most 'cognitive exercises' I can purchase on the internet or pursue at a local AARP gathering or occupational therapy department. To cap it off, playing music with others is my favorite 'social activity.'
Researchers in 2003 followed older participants to study the relative contribution of various specific activities--like board games, puzzles, group discussions--for 5 years. Those participants who frequently played a musical instrument were less likely to have developed dementia compared to those who rarely played. This protective effect of playing music was stronger than that from the other activities. Physical activities (walking, swimming, etc) did not appear to confer any protective benefit in the development of dementia in this particular study. (They have in others.)
Another group of scientists in 2007 examined the beneficial effects piano lessons in old age. They compared naïve participants randomly allocated to an experimental group (6 months of intensive piano lessons) to a control group that did not have lessons. The experimental group received a half-hour lesson each week and was required to practice independently for a minimum of 3 hours each week. After this period of musical training, the piano players showed improvements on tests of working memory, perceptual speed, and motor skills, while the control group did not.
More recently (2010) researchers in this field concluded:
"To minimize the deleterious effects of aging on brain function, elderly individuals need to engage in demanding multisensory, cognitive, and motor activities on an intensive basis. Accordingly, a training program that is designed specifically to facilitate brain plasticity, or engage multiple brain regions (especially the frontal and prefrontal areas), may counteract some of the negative consequences underlying disuse associated with aging. One activity that has the potential to stimulate and preserve cognition is music making." (here, with a good review of this topic)These observations even provide another argument for early music education. If you have ever played an instrument, it is far easer to take it up again, even when you are elderly, than it is to start cold for the first time in later life.