Biology subjects

Osu, R.

Publications and source records attributed to Osu, R..

12 recordsLinked to original sources

bioRxiv2026

Theta Dual-Brain Stimulation of rTPJ Shapes Joint Agency

Joint agency, the shared feeling of "we are doing this together", has been linked to inter-brain synchrony, but its causal role in shaping this experience remains unclear. We applied dual transcranial alternating current stimulation (dual-tACS) over the right temporo-parietal junction (rTPJ) to 13 dyads performing an alternating tapping task (target ITI = 0.5 s; 180 deg. relative phase), manipulating in- and anti-phase coupling at theta (6 Hz), alpha (10 Hz), and beta (20 Hz). As a result, tapping in the theta anti-phase condition was significantly slower than the memorized reference tempo, whereas the other stimulation conditions did not influence the inter-tap interval. Meanwhile, the relative phase remained close to 180 deg. across all conditions. In the theta condition, anti-phase stimulation produced significantly lower joint agency than in-phase stimulation. Furthermore, mediation analysis suggested that the inter-tap interval may partially account for the effect of theta dual-brain stimulation on joint agency, although this indirect pathway did not reach statistical significance. These findings suggest that anti-phase theta stimulation over the rTPJ lowers joint agency, possibly by reducing coordination efficiency while preserving the overall 180 deg. alternation structure.

neuroscience↗

bioRxiv2026

Large-scale brain network differences during deliberate and spontaneous mind-wandering in a sustained attention task: An electroencephalography source-level connectivity study

Mind-wandering (MW), the shift of attention away from an ongoing task, can be classified as either deliberate or spontaneous, depending on whether these internal thoughts arise intentionally or unintentionally. Previous functional magnetic resonance imaging-based resting state studies have shown that spontaneous MW traits are positively correlated with coupling within the default mode network (DMN), whereas deliberate MW traits are positively correlated with coupling both within the DMN and between the DMN and control-or attention-related networks. However, state-based functional connectivity during each MW episode remains unknown. Addressing this knowledge gap, we investigated how deliberate and spontaneous MW differentially involve state-based large-scale network interactions during a sustained attention task using electroencephalography (EEG), which captures rapid network dynamics. Thirty-one participants performed the gradual-onset continuous performance task using 64-channel EEG. Mental states were classified via experience-sampling probes as on-task, deliberate, or spontaneous MW. EEG data from 1-s pre-probe epochs were analyzed using source estimation and the weighted phase lag index to assess functional connectivity within and across the DMN, control network (CN), dorsal attention network (DAN), and salience network (SN) in the delta, theta, alpha, and beta frequency bands. Relative to both spontaneous MW and the on-task state, deliberate MW was characterized by significantly stronger alpha band functional connectivity. A prominent connectivity cluster was centered on the right frontal operculum-insula of the SN, linking regions across the SN, CN, and DMN. In addition, deliberate MW exhibited enhanced SN-DAN-DMN coupling compared with the on-task state. By contrast, spontaneous MW did not show significant connectivity differences relative to the on-task state in any frequency band. Taken together, these results suggest that alpha band network interactions centered on the SN may contribute to the intentional regulation of internally directed thought during deliberate MW.

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bioRxiv2025

Transcutaneous auricular vagus nerve stimulation during short-term motor practice drives cortical plasticity without behavioral improvement

Transcutaneous auricular vagus nerve stimulation (taVNS) is emerging as a promising non-invasive neuromodulation technique to augment neurorehabilitation, yet its mechanisms in humans remain poorly understood. Animal studies suggest that VNS delivered during motor skill practice drives task-specific plasticity in the primary motor cortex (M1), but direct evidence in humans has been lacking. Here, we provide the first demonstration that taVNS paired with motor skill practice selectively enhances cortical plasticity without boosting motor performance beyond practice alone during short-term training. Thirty-one healthy right-handed adults practiced a novel implicit motor task, rotating two balls with the non-dominant hand for 15 minutes. Participants were randomized to receive taVNS to the left tragus or sham stimulation during practice. Motor performance, M1 hand representation (TMS mapping), and spinal excitability (F-wave) were assessed pre- and post-practice, while pupil diameter was continuously monitored as an index of noradrenergic activity. Motor performance improved similarly in both groups, whereas cortical map expansion was significantly greater in the taVNS group than in the sham group. F-wave amplitude increased only in the sham group, suggesting that taVNS-driven plasticity was restricted to cortical circuits. Moreover, taVNS uniquely elicited pupil dilation during practice, consistent with noradrenergic system engagement. These findings reveal that taVNS can promote task-specific cortical reorganization in humans independent of immediate behavioral improvement. By linking taVNS-induced plasticity to noradrenergic modulation and dissociating cortical from spinal effects, this study provides novel mechanistic insight into how taVNS may lay the neural groundwork for enhanced motor recovery, with critical implications for neurorehabilitation. Significance StatementMotor recovery after stroke depends on the brains ability to reorganize motor circuits. Vagus nerve stimulation (VNS) has been proposed as a powerful approach to enhance such plasticity, but the underlying mechanisms in humans remain unclear. Here we show that non-invasive transcutaneous auricular VNS (taVNS), when paired with motor practice, selectively enhances reorganization of the primary motor cortex without additional behavioral improvement. Importantly, these effects were observed after only 15 minutes of practice, demonstrating that taVNS can induce rapid plastic changes. This provides the first evidence in humans that taVNS promotes task-specific cortical plasticity, underscoring its promise as a neuromodulatory tool for neurorehabilitation.

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bioRxiv2024

Inter-individual variability in motor learning due to differences in effective learning rates between generalist and specialist memory stores

Humans exhibit large interindividual differences in motor learning ability. However, most previous studies have examined properties common across populations, with less emphasis on interindividual differences. We hypothesized here, based on our previous experimental and computational motor adaptation studies, that individual differences in effective learning rates between a generalist memory module that assumes environmental continuity and specialist modules that are responsive to trial-by-trial environmental changes could explain both large population-wise and individual-wise differences in dual tasks adaptation under block and random schedules. Participants adapted to two opposing force fields, either sequentially with alternating training blocks or simultaneously with random sequences. As previously reported, in the block training schedule, all participants adapted to the force field presented in a block but showed large interference in the subsequent opposing force field blocks, such that adapting to the two force fields was impossible. In contrast, in the random training schedule, participants could adapt to the two conflicting tasks simultaneously as a group; however, large interindividual variability was observed. A modified MOSAIC computational model of motor learning equipped with one generalist module and two specialist modules explained the observed behavior and variability for wide parameter ranges: when the predictions errors were large and consistent as in block schedules, the generalist module was selected to adapt quickly. In contrast, the specialist modules were selected when they more accurately predicted the changing environment than the generalist, as during random schedules; this resulted in consolidated memory specialized to each environment, but only when the ratio of learning rates of the generalist to specialists was relatively small. This dynamic selection process plays a crucial role in explaining the individual differences observed in motor learning abilities.

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bioRxiv2023

Effect of prior somatosensory electrical stimulation on the wrist in biasing human hand choice

Hand choice is an unconscious decision frequently made in daily life. A correlation has been found between the state of brain activity before target presentation and hand choice for the target, around which the hand choice probability is in equilibrium. However, whether the neural state before target presentation affects hand choice remains unknown. Therefore, this study aimed to examine whether instantaneous somatosensory electrical stimulation administered to the unilateral wrist at 0, 300, or 600 ms before the target presentation facilitates or inhibits stimulated hand choice for targets around the hand selection equilibrium point. A single electrical stimulation comprised five trains of 1 ms electrical pulses, with a 20 ms inter-pulse interval. The stimulus intensity was set at 80% of the motor threshold. Fourteen right- handed healthy adults (five females, nine males; mean age, 25.1 {+/-} 4.64 years) participated. Unilateral wrist stimulation significantly increased the probability of choosing the stimulated hand and led to a faster reaction time than bilateral wrist stimulation and no-stimulation conditions. The results suggest that prior somatosensory stimulation significantly affects the hand-choice process, effectively promoting selection of the stimulated hand. These findings highlight the potential application of this stimulation method in stroke rehabilitation to facilitate use of the paretic hand. Impact StatementPrior neural stimulation significantly affected the hand-selection process by promoting the selection of the stimulated hand, thus potentially beneficial in rehabilitating the paretic hand of patients with stroke.

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bioRxiv2023

The topology of interpersonal neural network in weak social ties

People often have opportunities to engage in social interactions with strangers, which have been reported to contribute to their well-being. Although strategies for social interaction between strangers differ from those between acquaintances, the differences in neural basis of social interaction have not been fully elucidated. In this study, we examined the geometrical properties of interpersonal neural networks in pairs of strangers and acquaintances during joint tapping using dual electroencephalography (EEG). Twenty-one pairs of participants performed antiphase joint tapping under four different conditions. Intra-brain synchronizations were calculated using the weighted phase lag index (wPLI) for all possible intra-brain pairs of the 29 channels (29C2 = 406), and inter-brain synchronizations were calculated using the phase locking value (PLV) for all possible inter-brain pairs of the 29 channels (29 x 29 = 841) in the theta, alpha, and beta frequency bands. Electrode pairs with larger wPLI and PLV than their surrogates were defined as the nodes (EEG channels) and edges (connections between nodes) of the neural networks. We then calculated the global efficiency, local efficiency, clustering coefficient, and modularity derived from graph theory for the combined intra- and inter-brain networks of each pair. No significant differences in the tapping phase variance were identified between the stranger and acquaintance pairs. However, in the combined intra- and inter-brain theta EEG (4-7 Hz) networks, stranger pairs showed larger local efficiency and cluster coefficients than acquaintance pairs, indicating that the two brains of stranger pairs were more densely connected. Moreover, in the beta EEG bands, the modularity of the two brains was low in the fast condition, indicating that the two brains were coupled when the task demand was high. Our results show that weak social ties promote more extensive social interactions and result in dense brain-to-brain coupling.

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bioRxiv2023

The Effect of Evaluating Self's Emotions on Frontal Alpha Asymmetry

In this research to assess emotions from biometric signals, participants are asked to evaluate the emotions they subjectively experienced in order to confirm whether the assumed emotions were actually elicited. However, the evaluation of emotions is not routinely performed in daily life, and it is possible that this evaluation may alter biological signals. In fMRI studies, evaluation has been shown to activate the amygdala, which is said to be related to emotional expression. However, electroencephalography (EEG) studies do not take into consideration the effects of such evaluations, and it is unclear how these evaluations affect emotion-related brain activity observed in EEG. We hypothesized that emotion evaluations would amplify emotions and c alter Frontal Alpha Asymmetry (FAA), which has been shown to be related to emotional pleasantness and unpleasantness. We suspect this is because in order to evaluate ones emotions, one must pay attention to ones internal state, and this self-focused attention has been found to enhance the subjective emotional experience. We measured a 29-channel EEG when presented with unpleasant and highly arousing images from the International Affective Picture System (IAPS) from 40 healthy male and female participants. The results revealed that FAA was significantly lower in the condition in which participants rated their own emotions compared to the condition in which they did not. Similar to fMRI studies, this result indicates that emotion-related brain activity is amplified on an EEG. This paper provides a cautionary note regarding the use of such evaluations in EEG emotion estimation studies.

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bioRxiv2023

Efficacy of neurofeedback training for improving attentional performance in healthy adults: A systematic review and meta-analysis

This systematic review and meta-analysis examined the NFT effects on attentional performance in healthy adults. Six databases were searched until June 2022 to identify parallel randomized controlled trials (RCTs) evaluating attentional improvements after NFT. Risk of bias was assessed using the Cochrane Collaboration tool. We identified 41 RCTs for qualitative synthesis and 15 RCTs (569 participants) for meta-analysis. The overall NFT effect on attentional performance was significant (standardized mean difference = 0.27, 95% confidence interval = 0.10-0.44). However, no significant pooled effect was found within the trials comparing its effect with sham NFT (8 RCTs). Additionally, variable effects were observed on individual subsets of attentional performance. Further sham-controlled RCTs are required to validate the improvement of attentional performance with NFT.

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bioRxiv2022

Brain Activity During Constraint Relaxation in the Insight Problem-Solving Process: An fNIRS Study

People solve insight problems that they encounter daily with a sudden sense of aha! to reach a solution. Chunk decomposition, which decomposes the factors of the problem, and constraint relaxation, which manipulates filters to organize the information necessary to solve the problem, are important in insight problem-solving. Although there have been many studies on brain activity during chunk decomposition, few have examined brain activity during constraint relaxation. Particularly, no study has observed the changes over time due to constraint relaxation during insight problem-solving. This study used a slot machine task as an insight problem to measure brain activity using functional Near-Infrared Spectroscopy (fNIRS), and eye movements to estimate constraint relaxation. The results showed that the right dorsolateral prefrontal cortex (DLPFC) and right superior temporal gyrus (STG) were activated over time in participants in whom constraint relaxation was induced. The right inferior temporal gyrus (ITG) of participants who were able to solve the insight problem after constraint relaxation was also activated. The analysis of brain activity during constraint relaxation in insight problem-solving may be useful for advancing research on the aha! phenomenon and creativity.

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bioRxiv2021

The Relationship between Stability of Interpersonal Coordination and Inter-Brain EEG Synchronization during Anti-phase Tapping

Inter-brain synchronization is enhanced when individuals perform rhythmic interpersonal coordination tasks, such as playing instruments in music ensembles. Experimentally, synchronization has been shown to correlate with the performance of joint tapping tasks. However, it is unclear whether inter-brain synchronization is related to the stability of interpersonal coordination represented as the standard deviation of relative phase (SDRP). In this study, we simultaneously recorded electroencephalograms of two paired individuals during anti-phase tapping in three speed conditions: slow (reference inter-tap interval [ITI]: 0.5 s), fast (reference ITI: 0.25 s), and free (preferred ITI). We calculated the inter-brain synchronization within six regions of interest: frontal, central, left/right temporal, parietal, and occipital regions. We found that synchronization of the central-temporal regions was positively correlated with SDRP in the theta and alpha bands, while synchronization of the frontal-frontal and frontal-central was positively correlated with SDRP in the beta band. These results demonstrate that inter-brain synchronization occurs only when task requirements are high, and that it increases with the instability of the coordination. This may be explained by the stronger mutual prediction required in unstable coordination than that in stable coordination, which increases inter-brain synchronization.

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bioRxiv2021

Identifying Brain Regions Related to Word Prediction During Listening to Japanese Speech by Combining a LSTM Language Model and MEG

Recently, a neuroscientific approach has revealed that humans understand language while subconsciously predicting the next word from the preceding context. Most studies on human word prediction have investigated the correlations between brain activity while reading or listening to sentences on functional magnetic resonance imaging (fMRI) and the predictive difficulty of each word in a sentence calculated by the N-gram language model. However, because of its low temporal resolution, fMRI is not optimal for identifying the changes in brain activity that accompany language comprehension. In addition, the N-gram language model is a simple computational structure that does not account for the structure of the human brain. Furthermore, it is necessary for humans to retain information prior to the N-1 word in order to form a contextual understanding of a presented story. Therefore, in the present study, we measured brain activity using magnetoencephalography (MEG), which has a higher temporal resolution than fMRI, and calculated the prediction difficulty of words using a long short-term memory language model (LSTMLM), which is based on a neural network inspired by the structure of the human brain and has longer information retention than the N-gram language model. We then identified the brain regions involved in language prediction during Japanese-language speech listening using encoding and decoding analyses. In addition to surprisal-related regions revealed in previous studies, such as the superior temporal gyrus, fusiform gyrus, and temporal pole, we also found relationships between surprisal and brain activity in other regions, including the insula, superior temporal sulcus, and middle temporal gyrus, which are believed to be involved in longer-term, sentence-level cognitive processing.

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bioRxiv2020

Hierarchical motor adaptations negotiate failures during force field learning

Humans have the amazing ability to learn the dynamics of the body and environment to develop motor skills. Traditional motor studies using arm reaching paradigms have viewed this ability as the process of internal model adaptation. However, the behaviors have not been fully explored in the case when reaches fail to attain the intended target. Here we examined human reaching under two force fields types; one that induces failures (i.e., target errors), and the other that does not. Our results show the presence of a distinct failure-driven adaptation process that enables quick task success after failures, and before completion of internal model adaptation, but that can result in persistent changes to the undisturbed trajectory. These behaviors can be explained by considering a hierarchical interaction between internal model adaptation and the failure-driven adaptation of reach direction. Our findings suggest that movement failure is negotiated using hierarchical motor adaptations by humans.

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