In 1993 a small study reported that ten minutes of listening to a Mozart sonata gave a short boost on a spatial reasoning task. The press turned it into Mozart makes babies smarter, and a market for classical CDs appeared almost overnight.
What the study measured
Later studies could not repeat the result. The original finding was narrow: one composer, ten minutes, passive listening, and an effect that faded within the hour. It was never about playing an instrument, and never about intelligence in general.
Listening is not the same as playing
The useful part is the difference it points to. Listening is something that happens to you. Learning to play is something you do, with your eyes, ears and hands working together. That is where the real research on piano and the brain begins.
Frequently asked questions
Is the Mozart effect real?
Not as it was reported. The original result was small and short-lived, and other researchers could not reproduce it.
Does listening to classical music help the brain at all?
Music can improve mood and focus for some people, but that is different from making you smarter.
So does playing an instrument help?
Trials with older adults found some gains after piano lessons, and they are modest. The articles linked below go through them.