Deconstructing skill learning and its physiological mechanisms.

Acquiring complex motor skills involves learning a number of distinct motor components. Two fundamental elements that constitute a skill are the internal representation (i.e., the calibration of a sensorimotor map) and the sequence of movements needed to execute the task. Learning each of these likely rely on different neural substrates such as the cerebellum and primary motor cortex (M1), and physiological mechanisms. However, the specific neurophysiological processes underlying the acquisition of these components remains poorly understood. Here we used non-invasive brain stimulation to identify distinct physiological contributions arising from the cerebellum and M1 associated with learning the internal representation and the sequence of movements to execute a skill. Experiment one evaluated neurophysiological markers of the cerebellum and M1 while participants learned a sensorimotor map. Participants learned to calibrate the appropriate motor outputs to interact with a new device, prior to learning a new motor skill. We found that plastic changes in the cerebellum, but not in M1, are linked to learning the internal representation. Experiment two assessed the same neurophysiological markers while participants learned a sequence of movements, independent of acquiring a novel sensorimotor map. Here, both M1 LTP-like plasticity and cerebellar plasticity mediated movement sequence learning. Our findings indicate that learning the different components that will constitute a motor skill engages multiple nodes of a brain network in a concerted manner. In addition, it calls into question the expectation that targeting specific brain regions, such as M1, with brain stimulation to augment complex skill learning will have positive results.