The goal of this proposal is to understand the physiological cerebellar contributions to different forms of motor learning: adaptation and skill learning. The cerebellum (CB) is known to be engaged in adaptive learning by recalibrating movement dynamics to meet predictable demands. Calibrating sensorimotor dynamics can translate to several motor processes and is essential for producing accurate movements. Thus, it seems likely that the CB also contributes to skill learning in this fashion. Starting from the premise that the CB is crucially involved in learning sensorimotor calibrations, we plan to test the cerebellar physiological role during adaptive and skill motor learning. We will use transcranial magnetic stimulation (TMS) to explore the connectivity between the CB and motor cortex (CBI) in healthy participants to gain information about the cerebellar physiological role during motor learning. We predict that CBI will change only in the learning or transferred effector, following a somatotopic specific rule, during adaptation and early on during skill motor learning. Furthermore, the changes during skill learning will be related to learning sensorimotor calibrations, rather than sequence related learning. Specific Aim 1 will test our hypothesis that changes in CBI are somatotopic specific. To do this, Experiment 1 will use a visuomotor adaptation task known to transfer asymmetrically between the arm and hand to determine whether changes in CBI are somatotopic specific or indicate a diffuse cerebellar change. Our preliminary results are consistent with prior studies demonstrating that learning transfers from arm to hand, and that CBI changes for both effectors. In Specific Aim 2, we will test the hypothesis that CBI will be reduced early during skill learning. In experiment 2 we will assess CBI in participants that either learn an isometric finger-pinch sequence skill task or perform a random task where no learning occurs. Our preliminary data shows that CBI changes occur early on for those who learned the task. Since learning the skill task involves two main components, (1) acquiring a sensorimotor mapping to successfully use the sensorimotor pinch force transducer and (2) learning the sequence embedded in the task, we will perform experiment 3. Here, we will disentangle whether CBI changes are related to learning a sensorimotor calibration or learning the sequence of the task. To this end, we will test CBI before and after participants learn a sensorimotor calibration (without a sequence of targets), as well as before and after participants learn the sequence of targets. Our preliminary behavioral data shows that repeated exposure to the sensorimotor mapping improves both the acquisition and overall performance of the skill task. The results from this proposal will further our understanding of the cerebellar role in human motor learning. This is important because neurological patients who frequently experience motor impairment need to use motor learning strategies to improve their recovery. Thus, understanding the contributions of the cerebellum to motor learning and overall function can help develop rehabilitation strategies aimed to enhance behavior.