The motor system is responsible for directing and controlling movement and ranges from simple reflex arcs (withdrawal of a limb from a painful stimulus) to highly sophisticated volitional motor acts (playing the piano). Historically, movements have been conceptualised as being either ‘closed-loop’ (directly guided and modified by sensory inputs providing feedback) or ‘open-loop’ (triggered by a decision to move which acts as the input, with no initial feedback). In reality, almost all movements rely on some degree of sensory feedback and there is also a degree of volition in some apparently ‘closed-loop’ movements, making this dichotomy an oversimplification.