Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

The isochrony principle is a well-known phenomenon whereby the speed of human arm movement is regulated to increase as its trajectory distance increases. However, the relationship between the trajectory planning and the isochrony phenomenon has never been sufficiently explained. One computational study derived the algorithm for estimating the optimal movement segmentation and its duration based on the framework of the minimum commanded torque change criterion. By extending this finding, we can consider the hypothesis that the human arm trajectory is generated based on the minimum commanded torque change criterion to ensure that the duration average of the commanded torque changes (DCTCs) are equivalent between certain movement segmentations, rather than to satisfy the isochrony phenomenon. To test this hypothesis, we measured the behavioral performance of hand movement tasks in which subjects write eight-shaped and double-elliptical-shaped trajectories including two similar shaped arcs of different sizes (hereafter called large and small loops). Our results indicate that the human arm movement is planned in such a manner that the DCTCs for the large and small loops are equivalent during writing of the double-elliptical-shaped trajectories regardless of the arc size. A similar tendency was also observed for the data during the eight-shaped movements, although the ratio of the DCTCs slightly changed depending on the arc size conditions. Thus, our study provides experimental evidence that the isochrony phenomenon is ensured through the computational process of trajectory planning.

DOI： 10.1016/j.humov.2018.07.001

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)  

Action selection is typically influenced by the history of previously selected actions (the immediate motor history), which is apparent when a selected action is switched from a previously selected one to a new one. This history dependency of the action selection is even observable during a mental hand rotation task. Thus, we hypothesized that the history-dependent interaction of actions might share the same neural mechanisms among different types of action switching tasks. An alternative hypothesis is that the history dependency of the mental hand rotation task might involve a distinctive neural mechanism from the general action selection tasks so that the reported observation with the mental hand rotation task in the previously published literature might lack generality. To refute this possibility, we compared neural activity during action switching in the mental hand rotation with the general action switching task which is triggered by a simple visual stimulus. In the experiment, to focus on temporal changes in whole brain oscillatory activity, we recorded electroencephalographic (EEG) signals while 25 healthy subjects performed the two tasks. For analysis, we examined functional connectivity reflected in EEG phase synchronization and analyzed temporal changes in brain activity when subjects switched from a previously selected action to a new action. Using a clustering-based method to identify functional connectivity reflected in time-varying phase synchronization, we identified alpha-power inter-parietal synchronization that appears only during switching of the selected action, regardless of the hand laterality in the presented image. Moreover, the current study revealed that for both tasks the extent of this alpha-power inter-parietal synchronization was altered by the history of the selected actions. These findings suggest that alpha-power inter-parietal synchronization is engaged as a form of switching-specific functional connectivity, and that switching-related activity is independent of the task paradigm.

DOI： 10.3389/fnhum.2018.00259

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Institute of Electrical and Electronics Engineers Inc.  

In the study of brain computer interface using electroencephalogram (EEG), the area of motor imagery of individual finger movement has been extensively examined. The objective of this study is to predict which finger is moving or being imaged through the use of EEG.We measured EEG activity while subjects performed either motor execution or motor imagery of individual finger movements with their right hand. Event related spectral perturbation was used as indicator of brain activity, which represents frequency power fluctuation from the baseline interval. The frequency bands and (8-15 , 16-31, and 32-128 Hz, respectively) were used for analysis. Additionally, a feature consisting of a combination of those three bands was also explored using principal component analysis. These four kinds of features were classified by a linear discriminant analysis using ten-fold cross validation. Result indicated that the combined feature of the three frequency bands could classify most combinations of finger in both motor execution and motor imagery. The results suggest that EEG during the performance of motor imagery of individual finger movement is discriminable depending on the subject.

DOI： 10.1109/SMC.2017.8123088

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Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Springer Verlag  

The isochrony principle is a well-known phenomenon, whereby the speed of human arm movement is regulated to increase as its planned trajectory distance increases. The isochrony principle is observed in many studies, but its relationship with the motor planning process has never been explained. To address this issue, we attempt to explain the relationship between the isochrony principle and trajectory planning based on observable physiological information. Assuming that electromyography (EMG) reflects the temporal aspect of motor commanded signals, we directly evaluated the EMG changes during cyclic arm movement to consider the physiological mechanism underlying the isochrony phenomenon. Our presented result suggested the tendency that duration-average of the EMG change is equal, regardless of the differences in the movement distance. Its tendency suggest experimental evidence that human arm trajectory is planned to ensure constant EMG changes, rather than for equalization of movement durations.

DOI： 10.1007/978-3-319-70136-3_1

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

While motor imagery has been known as a powerful tool for neuro-rehabilitation in stroke patients, whether this technique is also effective for other brain disorders is unclear. For instance, patients with Parkinson's disease or attention-deficit hyperactivity disorder who are impaired at real motor switching may benefit therapeutically from training that consists of switching their imagined motor movements, and eventually recover from the dysfunction. However, despite its importance little is known about exactly how switching mental images of one's actions is processed in the brain. Therefore, we set out to clarify this issue by measuring brain activity reflected in electroencephalograms as subjects switched an imagined hand rotation from one hand to the other during a motor-imagery task. By comparing electroencephalogram signals from repeated mental imaging of hand movements, we found a switch-specific decrease in the beta-band activity in parietal and frontal regions around 0.6 s after stimulus presentation. Further, we found rotation-related negativity in the parietal cortex at the same time as the decreased beta-band power. These results suggest that the parietal area is dynamically involved in the switching of imagined hand motion, and that frontal areas may have an important role in inhibiting mental imagery of the deselected hand's motion.

DOI： 10.1109/EMBC.2014.6943843

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Event date： 2023.9.4 - 2023.9.6

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