Functional Modulation of Primary Motor Cortex During Action Selection

Primary motor cortex plays an important role in the planning and execution of movement, and motor cortical functions depend on cortical excitability. Here, we review how one can use transcranial magnetic stimulation (TMS) to study the functional changes occurring in M1 during the preparation and selection of actions. Specifically, we emphasise the idea that the brain is organised in a hierarchical way in which the boundaries between perception, cognition and action are weak and these processes occur in parallel. This, in turn, predicts that the motor system should be dynamically influenced by information about forthcoming actions we want to perform; this information is flexible and dynamic, and should be conveyed to the motor system through different routes, depending on the current context in which our actions occur. Using TMS, one can read out dynamic changes in M1 excitability in an effector-specific way, and study how such changes relate to the information that guides our actions. In humans, this provides unique insight into the physiological underpinnings and mechanism of action through which we prepare and select our movements in an ever-changing and uncertain world.