NEURAL MECHANISMS OF MOTOR IMAGERY AND THE NATURE OF IMAGERY-BASED SKILL ACQUISITION
Motor imagery (MI), the mental rehearsal of movement, is an effective adjunct to physical practice (PP) for driving skill acquisition. While considered analogous to PP, in that a simulation of movement occurs without overt execution, the mechanisms underlying MI are not well understood. This thesis interrogated the mechanisms of MI-based skill acquisition via three research questions: 1) how does expertise modulate MI-related brain activity?; 2) how does the modality of practice (MI vs. PP) modulate performance and MI-based brain activity?; and 3) does MI rely on effector independent encoding to drive skill acquisition? Expertise modulated brain activation during MI similar to PP, in that novice performance during MI was associated with widespread and bilateral activity. Directly comparing MI-related brain activation and performance following MI- or PP-based training showed that refinement of the motor program is less robust in MI owing to a difference in the mechanism underlying learning, suggesting MI is less effective relative to PP for facilitating skill acquisition. By examining resultant patterns of MI-related brain activation and performance of MI-based training applied prior to or following PP-based training, MI was shown to facilitate effector independent encoding, reflected in improvements in the global aspects of movement, central to early stages of skill acquisition. This finding suggests a role for MI as scaffolding for skill acquisition to be facilitated through PP. Evidence generated indicates that, while MI shares neural representations of motor skills, skill acquisition through MI occurs through an alternate mechanism relative to PP, and encoding of information is different between modalities. These findings have implications for how the mechanisms of MI are probed in future work: prior expertise with tasks being performed, and the use of transfer tasks to directly probe effector independent encoding should be considered in lines of questioning related to the mechanisms underlying MI-based skill acquisition. Further, the findings have potential application for how MI is applied in practice: MI is most effective when applied prior to PP, a finding that may explain inconsistencies in its effectiveness in driving skill acquisition noted in the literature.