Optimizing motor memory in healthy adults

Motor learning is an important component of daily life: humans are constantly adjusting their movements and acquiring new skills in order to meet the demands of their environment. Motor learning also contributes to neurorehabilitation, so it is therefore important to understand the neural mechanisms underlying motor learning so that these mechanisms can be exploited to promote neurorehabilitation after central nervous system injury. This dissertation focuses on three distinct methods of improving motor learning in healthy adults. In Chapter 2, we tested the effects of perturbation schedule on retention of a locomotor adaptation. The results of this work demonstrated that introducing a perturbation slowly and incrementally versus introducing a perturbation abruptly produces similar behavioral expression of locomotor memories across days. In Chapter 3, we tested whether administering 200 mg of caffeine immediately after practicing a novel motor skill enhances retention of that skill 24 hours later. However, we found that post-practice caffeine administration did not significantly improve retention of the motor skill. In combination with previous reports, these results suggest that the effects of post-practice caffeine administration are likely task-specific. In Chapter 4, we examined the interactions between hand use, practice-dependent plasticity and motor learning. We found that experimentally immobilizing the left hand for 8 hours facilitates subsequent practice-dependent changes in corticospinal excitability in a topographically-specific manner. In contrast, immobilization did not facilitate practice-dependent changes in TMS-evoked thumb movements, nor did it promote learning or retention of a ballistic motor skill. Although it is thought that practice-dependent changes in corticospinal excitability are an important and potentially causal contributor to motor memory, the results of this work indicate that experimentally enhancing practice-dependent changes in corticospinal excitability is not sufficient to promote motor learning. In sum, although none of the experimental interventions tested here substantially improved motor learning, these experiments highlight the influence of various mechanisms on motor learning in the intact nervous system.