Controlling complex movements is a profoundly challenging problem for the nervous system, and working out how neurons in the motor system solve this problem is an equally challenging problem for neuroscience. The difficulty is that even such apparently simple acts as reaching to a nearby object involve the coordinated action of the muscles controlling the position of several joints. This poses a question: does the activity of neurons represent low-level dynamic aspects of movement such as movement forces and muscle activations, or does it reflect high-level kinematic parameters such as the direction and velocity of hand movements? Signals in spinal motoneurons, plainly, correspond to single-muscle actions; neurons in premotor areas seem to specify movement goals rather than details (Pesaran et al., 2006). But at the level of primary motor cortex (M1), the question of ‘‘muscles or movements’’ remains open and is the subject of active study.