Biology subjects

Nambu, I.

Publications and source records attributed to Nambu, I..

3 recordsLinked to original sources

bioRxiv2025

Effects of stimulus modality and response type on oddball stimulus discrimination using polarity-considered EEG microstate labeling

ObjectiveBrain-computer interfaces (BCIs) require effective feature extraction and dimensionality reduction from multidimensional brain signals. Electroencephalogram (EEG) microstate analysis offers a fast and noise-resistant approach by classifying the states of brain signals into spatial distribution patterns (templates). Each EEG segment was assigned the template with the highest spatial correlation, reducing the information to a one-dimensional representation. However, prior BCI studies have often ignored the polarity of spatial distributions in these templates. Incorporating polarity during labeling may enhance classification performance. This study investigated the effectiveness of polarity-considered microstate labeling for classifying infrequent stimuli in an auditory-visual oddball task with implications for BCI applications. MethodEEG recordings were analyzed using polarity-considered microstate labeling to classify infrequent stimuli. This study examined the effects of stimulus modality (auditory or visual), modality conditions (unimodal: stimulus and response in the same modality; cross-modal: stimulus and response in different modalities), and response type (key-press task vs. mental counting task) on classification accuracy. Machine learning models were used for classification, including support vector machine, random forest, logistic regression, XGBoost, CatBoost and K-means methods. ResultsPolarity-considered labeling outperformed the non-polarity approach, especially in decision-tree-based models (20.1% improvement in the key-press task and 22.2% improvement in the mental counting task). A significant interaction was observed between stimulus modality and response type, with the highest accuracy achieved when the infrequent stimuli in the key-press task involved cross-modal visual information. ConclusionThe findings suggest that polarity-considered microstate labeling enhances EEG-based classification. This approach has potential applications in BCI, such as in P300 spellers using cross-modal auditory-visual stimuli.

neuroscience↗

bioRxiv2023

Robustness and adaptability of sensorimotor skills in expert piano performance

Skillful execution of sequential actions requires the delicate balance of sensorimotor control, encompassing both robustness and adaptability. Previous studies have characterized behavioral and electrophysiological responses to sensory perturbation during performance of sequential movements such as speech and singing. However, it remains unknown whether and in what manner both motor and neural responses, triggered by sensory perturbation, undergo plastic adaptation as a consequence of extensive sensorimotor experience. Here, we addressed this question by comparing effects of transiently delayed tone production on the spatiotemporal patterns of the subsequent motor actions and event-related potentials (ERPs) during fast and accurate piano performance between expert pianists and musically-untrained individuals (non-musicians). Following the delayed tone production, the inter-keystroke interval was abnormally prolonged in non-musicians but not in pianists. By contrast, the keystroke velocity following the tone delay was increased only in the pianists. A regression model further demonstrated that the change in the inter-keystroke interval following the perturbation covaried with the ERPs of the N180 and P300 components particularly at the frontal and parietal regions. In contrast, the alteration in the keystroke velocity was associated with the P300 component of the temporal region ipsilateral to the moving hand, which suggests enhancement of auditory but not somatosensory feedback gain following auditory perturbation. Together, these findings suggest that distinct neural mechanisms underlie robust and adaptive sensorimotor skills individuals with different levels of proficiency.

neuroscience↗

bioRxiv2018

Cortical activation associated with motor preparation can be used to predict the freely chosen effector of an upcoming movement and reflects response time: An fMRI decoding study

Motor action is prepared in the human brain for rapid initiation at the appropriate time. Recent non-invasive decoding techniques have shown that brain activity for action preparation represents various parameters of an upcoming action. In the present study, we demonstrated that a freely chosen effector can be predicted from brain activity measured using functional magnetic resonance imaging (fMRI) before initiation of the action. Furthermore, the activity was related to response time (RT). We measured brain activity with fMRI while 12 participants performed a finger-tapping task using either the left or right hand, which was freely chosen by them. Using fMRI decoding, we identified brain regions in which activity during the preparatory period could predict the hand used for the upcoming action. We subsequently evaluated the relationship between brain activity and the RT of the upcoming action to determine whether correct decoding was associated with short RT. We observed that activity in the supplementary motor area, dorsal premotor cortex, and primary motor cortex measured before action execution predicted the hand used to perform the action with significantly above-chance accuracy (approximately 70%). Furthermore, in most participants, the RT was shorter in trials for which the used hand was correctly predicted. The present study showed that preparatory activity in cortical motor areas represents information about the effector used for an upcoming action, and that well-formed motor representations in these regions are associated with reduced response times.\n\nHighlightsO_LIBrain activity measured by fMRI was used to predict freely chosen effectors.\nC_LIO_LIM1/PMd and SMA activity predicted the effector hand prior to action initiation.\nC_LIO_LIResponse time was shorter in trials in which effector hand was correctly predicted.\nC_LIO_LIFreely chosen action is represented in the M1/PMd and SMA.\nC_LIO_LIWell-formed preparatory motor representations lead to reduced response time.\nC_LI

neuroscience↗