Skill learning: Motor cortex rules for learning and memory

A key unresolved issue for systems neurobiology concerns the neural sites and mechanisms of motor skill learning. Sherrington and colleagues [1] noted nearly 100 years ago that neural mechanisms in the primary motor cortex seemingly exhibit a form of plasticity, based on observations of ‘instability’ in responses evoked by cortical stimulation. Seminal work in the following decades also suggested that the motor cortex has a role in plasticity [2,3], though none of these studies could readily address whether the primary motor cortex actually contributes to skill learning. Technical and theoretical advances in studying behavioral aspects of motor learning and motor cortex function have now yielded ample evidence that the primary motor cortex in mammals indeed makes a fundamental contribution to learning. A recent study [4] has highlighted the extent to which neurons in the primary motor cortex may mediate skill acquisition and retention. This work, discussed in detail later in this article, demonstrates that neurons in the motor cortex change their discharge properties when monkeys adapt their arm movements to changes in applied forces. First, however, it is useful to review organizational principles of motor representations and prior work that support a role for the motor cortex in skill acquisition.