| Several recent neuroimaging and electrophysiological studies on animals and humans revealed details of neuroplasticity underlying motor skill learning and long-term motor memory. Advances notwithstanding, characterization of changes in observable behavior was limited to relatively gross measures of task achievement. To complement the understanding of practice-induced neural changes, four longitudinal studies present fine-grained kinematic characterization over extensive practice of 20 daily sessions, including retention after 3-6 months and, in 2 subjects, after 8 years. All experiments involved asymmetric bimanual tasks, performed either in continuous rhythmic fashion or as combination of rhythmic and discrete elements. Experiments 1 and 2 examined the time scales of acquisition and retention of individually preferred patterns using polyrhythmic movements in 3:1 and 3:2 frequency ratios. Experiment 3 explored the time course of generalization to untrained frequency ratios during the practice phase of the 3:1 task. Experiment 4 tested asymmetric learning in a bimanual task involving a discrete and rhythmic movement in each hand.;A range of quantitative measures of the two hands' performance, analyzed in both time and frequency domains, revealed different time scales of change, reflecting the multiplicity of underlying neural processes. All studies showed long-term retention of the acquired asymmetric bimanual skills. Owing to sparse feedback, subjects developed idiosyncratic solutions with remarkable persistence seen after 3 months and even 8 years, suggesting very specific encoding of learnt pattern in the brain. The robustness of the retained pattern was lessened when the polyrhythmic task was paced by a metronome, possibly due to the presence of error information that induced corrective control processes into the self-guided performance. Generalization of the acquired frequency ratios was shown to be a gradual process. It was limited to integer ratios and only with practiced hand assignment. The discrete/rhythmic task showed asymmetric learning in the two hands. The continuous hand's oscillation could not become decoupled from the discrete perturbation.;Taken together, the study introduced a novel experimental paradigm for self-guided rather than error-based skill learning. The comprehensive kinematic characterization complements neuroscientific studies highlighting robustness, specificity, and long duration of neuroplasticity. First steps are presented to complement the behavioral paradigm with electrophysiological data. |
