LAUSR

Introduction A large number of researches have investigated the mechanisms of implicit and explicit motor sequence learning. The functional changes in motor circuits, which involve the primary motor cortex (M1), are thought to play an important role in memory formation of implicit knowledge. However, it is unclear what functions in the motor circuits contribute to formation of implicit knowledge in the M1. The corticospinal neuromuscular system organizes the modular architectures for generating a variety of movements. Therefore, we hypothesized that performance improvement through implicit learning results from reorganization of the modular architectures. Objectives We used transcranial magnetic stimulation (TMS), data-grove system, and principal component analysis (PCA) to test the hypothesis. Materials and methods Seventeen healthy subjects learned a sequence of serial reaction time task (SRTT) implicitly, and explicitly. Before and after a training session, both TMS-evoked finger joint movements and voluntary finger joint movements during the SRTT were recorded. Results PCA extracted a set of principal components (PCs) from TMS-evoked finger joint movements before (pre-PCs) and after (post-PCs) the training session, respectively. To test an idea that post-PCs contain large amount of information on the learned task, we reconstructed the voluntary movements during SRTT in post-training session by linear combination of a selected subset of the PCs. We found that the quality of the movements reconstructed by the post-PCs was superior to that of the pre-PCs in the implicit condition. By contrast, in the explicit condition, there was no significant difference in the reconstruction quality between the pre-PCs and post-PCs. Conclusion Our results suggest that the implicit knowledge is acquired through learning-specific reorganization of the modular architectures in the corticospinal neuromuscular system. On the other hand, the reorganization of the modular architectures does not relate to acquiring the explicit knowledge.