Does the brain control muscles or movements?

One of the major scientific questions about the brain is how it can translate the simple intent to perform an action—say, reach for a glass—into the dynamic, coordinated symphony of muscle movements required for that action. The neural instructions for such actions originate in the brain’s primary motor cortex, and the puzzle has been whether the neurons in this region encode the details of individual muscle activities or the high-level commands that govern kinetics—the direction and velocity of desired movements.