Effects of task difficulty and old age on motor learning and its neural mechanisms

Athletes, patients, and musicians of all ages practice to learn new motor skills or re-learn motor skills lost over time or due to clinical conditions. According to the optimal challenge point framework, practicing a motor skill at a certain, optimal difficulty level enhances its retention. However, the presence of an optimal challenge point for motor learning, as well as its underlying neural mechanisms, are still under debate. Furthermore, it is unclear how task difficulty interacts with age-related declines. Therefore, the main objective of this thesis was to determine the effects of task difficulty and old age on motor learning and practice-related neural plasticity. Together, the results from this thesis suggest that predictions from the optimal challenge point framework are only applicable when a certain error threshold is crossed. While task difficulty does not affect motor skill retention in younger adults, practicing a motor task at a high difficulty level hinders motor skill retention as well as neural plasticity in older adults. In addition, both task difficulty and age affect the strategy to improve in a redundant space-time motor task like mirror star tracing. The findings in this thesis stress the importance of adding task difficulty as a variable to dose motor learning in sports as well as clinical rehabilitation and give a basis for future research aiming to optimize motor learning in clinical settings. In conclusion, this thesis provides evidence that both task difficulty and old age affect motor skill acquisition and retention, as well as the underlying neural plasticity