Reorganization of finger covariation patterns represented in the corticospinal system by learning of a novel movement irrelevant to common daily movements

How dexterous finger movements are acquired by the nervous system is a fundamental question in the neuroscience field. Previous studies have demonstrated that finger movements can be decomposed into finger covariation patterns, and these patterns are represented in the corticospinal system. However, it remains unclear how such covariation patterns represented in the corticospinal system develop during the acquisition of novel finger movements. In this study, each subject learned to perform a novel finger movement, which was mapped to a region outside the movement subspace spanned by common finger movements seen in daily life, through a custom task. After subjects practiced the task, we detected changes in the finger covariation patterns derived from artificially (transcranial magnetic stimulation) evoked finger joint movements. The artificially evoked movement-derived patterns seen after the training period were associated with both the novel and common finger movements. Regarding the patterns extracted from the artificially evoked movements, the number required to explain most of the variance in the data was unchanged after the training period. Our results indicate that novel finger movements are acquired through the reorganization of preexisting finger covariation patterns represented in the corticospinal system rather than the development of new patterns. These findings might have implications for the basic mechanism responsible for the development of movement repertories in the nervous system. NEW & NOTEWORTHY Various types of finger movements involve common finger covariation patterns, and these patterns are represented in the corticospinal system. Here we examined how a novel finger covariation pattern is acquired in that system through training of a novel finger movement that is irrelevant to common finger movements. Using transcranial magnetic stimulation, we found that the preexisting patterns that contribute to finer control of finger movements are rapidly reorganized to encode the novel pattern through the training.