Influence of performance feedback on motor cortex excitability and motor learning

Primary motor cortex (Ml ) plays a role in motor learning, although the exact nature of that involvement remains unclear. Refinement of the relationship between plastic change of Ml and learning is of clinical importance in terms of understanding and facilitating functional recovery/improvement for stroke and psychiatric disorders with movement dysfunction ( Schizophrenia, for example). In order to optimise symptom improvement for these individuals, it is important to determine which movement characteristics and practice environment variables are effective in facilitating cortical change; aspects which remain unclear. Results of prior research indicate that the depth of processing that occurs as a result of the complexity of the motor task may be one such factor which influences cortical plasticity and learning success. This possibility was investigated in the present thesis by manipulating learning conditions (augmented feedback) and the biomechanical complexity of tasks. Transcranial magnetic stimulation (TMS) protocols were used to measure cortical excitability. A low-complexity thumb-abduction force task was examined in Experiment 1. Although performance of this task improved during acquisition, no evidence of cortical change (measured as cortical excitability) was evident. Furthermore, performance was examined at a post-24 hour retention test, where it was found that performance improvements had not been retained. Again, cortical change was not evident. In Experiment 2, the cognitive complexity of a similar task was increased, and varied between-groups according to the frequency with which augmented performance feedback was available during acquisition. Again, performance improvements during acquisition were not accompanied by cortical change, despite the group receiving more frequent feedback performing better than the reduced frequency feedback group. Performance again deteriorated at retention testing, indicating that learning did not occur. These experiments provide evidence to suggest that improvements in the performance of the force production tasks of varying complexity may not be strongly dependent on modulations of MI cortical excitability. A waveform tracking task of increased biomechanical and cognitive complexity was examined in Experiment 3. Acquisition conditions again varied between-groups according to feedback frequency. Performance improvements following acquisition were maintained to 24 hour-retention testing for the reduced feedback frequency group, evidencing learning. Furthermore, this skill maintenance was accompanied by increased excitability at retention relative to the end of acquisition. This suggests that Ml may play a role in the offline consolidation and retention of acquired complex motor skill. The nature of Ml modulation associated with the practice, acquisition and retention of a novel motor skill appears to vary with the nature and complexity of task requirements. This may have implications for structuring motor learning programs aimed at optimising cortical change and symptom improvement in movement disorders.