Biology subjects

Ushiyama, J.

Publications and source records attributed to Ushiyama, J..

10 recordsLinked to original sources

bioRxiv2026

Vestibular signals enhance the temporal precision of predictive movements to musical rhythms

Humans exhibit head movements synchronized with musical rhythms, frequently observed during instrument playing or dancing (e.g., hip hop). We conjectured that vestibular input from head movements could aid motor execution anticipatory of musical rhythms, known as sensorimotor synchronization (SMS). To examine this, we applied subthreshold galvanic vestibular stimulation (GVS) simultaneously with musical beats while healthy adults performed SMS to those beats. We designed a GVS waveform where the current rose steeply before each beat onset, which was expected to trigger intense vestibular afferent firing before the beats (as actual head movements would). Participants flexed their index finger in synchrony with the beats of syncopated auditory rhythms. In GVS trials, the SMS timing variability was significantly lower than in trials without GVS, suggesting that vestibular input stabilizes SMS to musical beats. Additionally, a control experiment using a waveform with a gradually increasing current revealed no significant difference in SMS variability between trials with and without GVS. This study provides causal evidence that the vestibular system is involved in synchronized movement to music. In addition, the results suggest that a specific parameter of the GVS waveform could influence predictive motor execution anticipatory of upcoming auditory events.

neuroscience↗

bioRxiv2026

Loud acoustic stimulation reveals an online reticulospinal contribution to long-latency reflexes in humans

The long-latency reflex (LLR), the fastest feedback response that recruits supraspinal pathways, is an important model for understanding how descending motor pathways shape rapid corrective responses in humans. While the corticospinal tracts contribution to the LLR has been well established, that of the reticulospinal tract, the other major descending motor pathway, remains purely speculative. To address this online contribution to the generation of the LLR, we used loud acoustic stimulation (LAS), which can strongly engage brainstem circuits including the pontomedullary reticular formation. By delivering LAS at nine timings (0-80 ms in 10-ms steps) relative to perturbation onset, we tested whether LAS selectively facilitates the LLR but not the short-latency reflex (SLR), and whether the facilitated epoch shifts systematically with LAS timing. In twelve healthy participants, elbow extension perturbations were applied to evoke stretch reflexes in the biceps brachii muscle. LAS produced significant supralinear facilitation in the LLR but not in the SLR. Moreover, at LAS timings of 50 ms or more after perturbation onset, LLR facilitation shifted progressively later with LAS, remaining at an approximately fixed delay of 30 ms after LAS onset. This fixed delay indicates that LAS-evoked descending input from the same origin facilitates the ongoing LLR. Together with the lack of significant SLR facilitation, this temporal pattern supports an online reticulospinal contribution to the human LLR, alongside the established corticospinal contribution. This approach provides a new, non-invasive means to investigate the physiological role of the reticulospinal tract in human motor control. Key PointsO_LIThe long-latency reflex is a rapid muscle response to sudden stretch. Unlike faster spinal reflexes, it is shaped by commands descending from the brain and adjusts to the task. C_LIO_LIThough the corticospinal tract is known to shape this reflex, whether the reticulospinal tract also contributes to the reflex has not been tested in humans. C_LIO_LIWe stretched the arm and, at various delays, played a loud sound that engages the brainstem origin of the reticulospinal tract. The sound significantly enhanced the long-latency reflex, whereas no significant enhancement was detected in the faster spinal reflex. C_LIO_LIWhen the sound came 50 milliseconds or more after the stretch, the enhancement followed the sound at a stable delay, indicating that sound-evoked descending signals interacted with the ongoing reflex response. C_LIO_LIThese findings support a real-time contribution of the reticulospinal tract to the human long-latency reflex and provide a non-invasive way to study this pathway. C_LI

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bioRxiv2025

Chronotype-specific impacts of sleep-wake schedule on behavioral, physiological and psychological parameters

Diurnal variations in human performance are known to be associated with chronotype, which reflects individual differences in preferred sleep-wake cycles. Early chronotypes (ECs) exhibit superior motor and cognitive functions in the morning, whereas late chronotypes (LCs) tend to perform better in the evening. However, previous studies have examined these patterns under socially imposed nighttime sleep schedules, without considering individuals preferred sleep timing. Thus, it remains unclear whether these chronotype-dependent performance peaks persist when individuals follow their preferred sleep schedules. To address this question, we measured subjective states, sleep pressure (using electroencephalography), and motor and cognitive functions at 1.5 and 12.5 hours after awakening under two conditions: the Clock-Time condition (10:30 PM-6:30 AM sleep aligned with social rhythms) and the Self-Time condition (8 hours of sleep aligned with individual preferences). The results revealed distinct chronotype-specific patterns. ECs exhibited increases in fatigue and sleepiness dependent on awake duration, showing typical sleep pressure accumulation. LCs were more affected by sleep timing and showed atypical patterns of sleep pressure accumulation compared with ECs. Motor ability tended to improve in the afternoon in both chronotypes, irrespective of sleep-wake schedule, whereas cognitive performance peaked at different stages of wakefulness - earlier for ECs and later for LCs - independent of the time of day. These findings suggest that chronotype-aligned sleep-wake schedules could help optimize fatigue management, cognitive performance, and motor control. Diurnal variations in performance cannot be attributed to clock time alone but emerge from the combined effects of chronotype, awake duration, and sleep-wake regulation. Statement of SignificanceThis study provides new insights into the ways in which chronotype and sleep-wake schedules jointly shape behavioral, physiological, and psychological dynamics across the day. Whereas previous research has largely emphasized circadian rhythms, our findings underscore the critical role of actual sleep timing in modulating daily function ing. This integrative perspective extends current understanding of the ways in which individual differences in biological timing and social constraints interact to influence human health and performance. Importantly, the results highlight the need for future studies to disentangle circadian and sleep-wake schedule effects, which could inform personalized strategies for optimizing well-being, productivity, and clinical interventions in disorders related to sleep and circadian misalignment.

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bioRxiv2025

Inter- and intra-individual differences in temporal modulation patterns of the β-band sensorimotor rhythm and its relationship to corticomuscular coherence during intermittent voluntary contraction

The {beta}-band sensorimotor rhythm (SMR), recorded using electroencephalography, generally begins to decrease in amplitude with motor preparation reflecting cortical desynchronization, and subsequently becomes coupled with electromyogram signals during voluntary contraction, thus forming corticomuscular coherence (CMC). However, it remains unclear how the time-resolved modulation of {beta}-band SMR varies among individuals, potentially relating to individual differences in CMC. Additionally, it is also unclear how the nervous system modulates {beta}-band SMR to meet varying task demands within individuals. Here, we explored how time-resolved modulation patterns of {beta}-band SMR relate to CMC from two perspectives: inter-individual differences (Experiment 1), and intra-individual variability depending on task demands (Experiment 2). In Experiment 1, participants repeated a steady-force maintenance task. The degree of {beta}-band SMR modulation (i.e., rebound from desynchronization to synchronization) during contractions varied greatly among individuals and was positively correlated with CMC magnitude. This suggests that even under steady-force maintenance, the motor control strategy used while regulating {beta}-band SMR varies greatly among individuals. In Experiment 2, participants who showed significant CMC in Experiment 1 performed four tasks with varying target trajectories. Even within individuals, the degree of {beta}-band SMR modulation was reduced in parallel with the CMC magnitude as force adjustment was required. This finding suggests that, when confronted with more challenging task demands, our nervous system suppresses the SMR modulation and decouples from muscles. Overall, the way in which our nervous system regulates {beta}-band SMR is assumed to represent a strategy for flexible adaptation to diverse motor environments.

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bioRxiv2024

Switching on Behavioral and Neural Rhythmicity to Retrieve Memories When the Number of Retained Items Exceeds Four

Even when we experience difficulty in recalling memories, we nevertheless manage to retrieve the target items. However, the neural mechanisms that enable such difficult memory retrieval are unknown. Here, we report an intriguing phenomenon where our nervous system "switches on" behavioral/neural rhythmicity to retrieve memory when the number of candidate items exceeds four. In our experiments, participants learned and retrieved 2-5 color/letter pairs. Analyses of hundreds of reaction times revealed a significant tendency for memory recall to occur at discrete times corresponding to theta-alpha (4-13 Hz) cycles, but only when the number of memorized pairs exceeded four. Electrophysiological data localized theta-alpha rhythmicity around parietal electrodes, a region associated with the long-term memory system. Our findings suggest that neural rhythmicity facilitates memory retrieval when the number of candidate items exceeds four, which is known as the "magical number" corresponding to the limit of human cognitive capacity.

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bioRxiv2024

The flow state is not accompanied by frontal-midline theta activity: An EEG investigation of more than 700 video gameplay sessions

People sometimes experience a "flow state"--characterized by hyperfocus, time distortion, and loss of self-awareness--during sports or video gameplay. Previous neuropsychological studies using simple laboratory tasks have reported that the flow state is associated with activation in the frontal lobe, reflected in theta (4-7 Hz) band rhythmic neural activity in medial prefrontal regions (frontal-midline theta [FMT] activity). However, the findings of previous studies might be problematic because they did not appropriately capture the neural activity associated with the flow state for the following reasons: 1) they used unfamiliar and unmotivating tasks; 2) they defined the neural basis of the flow state as neural activity occurring during tasks of optimal difficulty, disregarding trial-to-trial variations in subjective experience of the flow state; 3) the duration of the experiment or the number of trials was not sufficient to capture the rare experience of flow; or 4) they ignored individual differences in neural activities related to flow experiences. Thus, we examined the relationship between the flow state and FMT activity, recorded via scalp electroencephalography, in an experimental paradigm that addressed these four issues. First, participants played their favorite competitive video games, which they had been routinely playing. Second, task difficulty was kept as uniform as possible across trials by employing rank matching to directly examine the correlation between subjective flow level and FMT activity across trials. Third, to address the concern regarding the low frequency of the flow experience, more than 100 trials were completed over 10 days by each participant. Lastly, we adopted a within-participant statistical approach to examine individual differences in the nature of the flow experience. The results showed no correlation between FMT activity and the degree of subjective flow in six out of seven participants, contrary to previous reports. Our results challenge the conventional view that frontal lobe activity, as reflected in FMT activity, is instrumental in entering into the flow state.

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bioRxiv2022

Overflow of Working Memory from an Easily Accessible Active State

Working memory is a system that realizes short-term memory retention and is essential to everyday activities. Recently, it has been suggested that working memory items can be maintained in both an active state with sustained neural activity and a latent state without any explicit neural activity. However, how easily we can retrieve memories in each state and how much information can be retained in the active state remains unknown. Here, we addressed these questions by adopting a novel experimental paradigm for measuring the reaction time required to recall a letter of the alphabet when presented with a corresponding color, based on memorized color/letter pairs. The results demonstrated that when participants retained only two pairs of items, they could recall both pairs similarly quickly. However, when there were two or more memorized pairs, the most recent or internally attended pairs were recalled more quickly than the other pairs. These results suggest that memories in the "active" state are accessed first and memories that have overflowed into the "latent" state are accessed afterward. Additionally, the capacity of the easily accessible active state is extremely limited (to approximately two chunks of information) compared with the traditionally considered working memory capacity (four to seven chunks). These results provide robust behavioral support for the co-existence of multiple states in working memory and underscore the need for a more detailed classification of the working memory capacity. SIGNIFICANCE STATEMENTWe sometimes cannot quickly retrieve what we are sure we remember. Regarding working memory retrieval, we observed a phenomenon that the most recently encoded memory was retrieved quickly whereas others were retrieved afterward, showing an "overflow" of memory items from an easily accessible active state. This observation has two critical implications: 1) when maintaining multiple items in working memory, not all items are functionally the same, and there is a dissociation between easily accessible active items and items that have overflowed to a latent state; 2) the number of items that can be maintained in the active state is two, which is remarkably smaller than the traditionally considered working memory capacity of four, necessitating the update of working memory models.

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bioRxiv2021

The presence of corticomuscular coherence during unipedal stance

Standing in unipedal stance requires higher effort to maintain posture balance within narrow base-of-support. Although changes in cortical activity are known to occur as standing task difficulty increased, it is unclear whether it indicates a change in cortical control of muscle activity. To elucidate this point, this study examined corticomuscular coherence (CMC) between the sensorimotor cortex and ankle joint muscles during three tasks such as bipedal stance, unipedal stance, and isometric contraction tasks. For twenty-one healthy participants, we measured the maximal peak of CMC (CMCmax) between electroencephalograms overlying the foot representation area and surface electromyograms from the tibialis anterior (TA), medial gastrocnemius (MG), lateral gastrocnemius (LG), and soleus (SOL), respectively, for each task. We also measured the center of pressure (COP) during both stance tasks. Although there was no significant CMC during bipedal stance in all participants, most participants (n = 14) showed significant CMC for all muscles during unipedal stance with larger COP fluctuation in most participants. Indeed, there was significant difference in CMCmax between unipedal and bipedal stance tasks. The greater CMC would indicate increased cortical control of muscle activity to compensate for postural instability during unipedal stance.

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bioRxiv2021

Gymnasts' ability for general motor imagery evaluated by bioelectric sensorimotor rhythms

Previous psychological studies using questionnaires have consistently reported that athletes have superior motor imagery ability, both for sports-specific and sports non-specific movements. However, regarding motor imagery of sports non-specific movements, no physiological studies have demonstrated differences in neural activity between athletes and non-athletes. The purpose of the present study was to examine differences in bioelectric sensorimotor rhythms during kinesthetic motor imagery (KMI) of sports non-specific movements between gymnasts and non-gymnasts. We selected gymnasts as an example population because they are likely to have particularly superior motor imagery ability due to frequent usage of motor imagery including KMI as part of daily practice. Healthy young participants (16 gymnasts and 16 non-gymnasts) performed repeated motor execution and KMI of sports non-specific movements (wrist dorsiflexion and shoulder abduction of the dominant hand). Scalp electroencephalogram (EEG) was recorded over the contralateral sensorimotor cortex. During motor execution and KMI, sensorimotor EEG power is known to decrease in the - (8-15 Hz) and {beta}-bands (16-35 Hz), referred to as event-related desynchronization (ERD). We calculated the maximal peak of ERD both in the - (ERDmax) and {beta}-bands ({beta}ERDmax) as a measure of changes in corticospinal excitability. ERDmax was significantly greater in gymnasts, who subjectively evaluated their KMI as being more vivid, for both KMI tasks. On the other hand, {beta}ERDmax was greater in gymnasts only for shoulder abduction KMI. These findings suggest gymnasts signature of flexibly modulating sensorimotor rhythm with no movements, which may be the basis of their superior ability of KMI for sports non-specific movements. New & NoteworthyKinesthetic motor imagery of sports non-specific movements was compared between gymnasts and non-gymnasts (i.e., healthy controls) from both physiological and psychological approaches. The EEG sensorimotor rhythms during kinesthetic motor imagery were more desynchronized in gymnasts who subjectively imaged their own movements as being more vivid. The work reveals novel ability in gymnasts to flexibly control their sensorimotor rhythms with no actual movements, which would be the basis of their superior ability of motor imagery.

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bioRxiv2021

Rhythmic Accessibility to Sequential Working Memory in a Theta Phase-Dependent Manner

Working memory is active short-term memory storage that is easily accessible for later utilization. There is emerging evidence that memorized items are represented rhythmically on the specific phase of the theta-band (4-7 Hz) neural oscillation. However, it is still unknown how this process impacts the accessibility to the active memory storage. Here we show that simply memorizing sequential information causes theta-band fluctuation in our behaviour (i.e., reaction time, RT). We measured RTs to a visual probe that appeared at sequentially memorized locations after a random interval. Consequently, RTs to the probes fluctuated in the theta range as a function of the random interval, and the behavioural rhythmicity supported the hypothesis of the phase-dependent coding of sequential working memory. The current results demonstrate that our behaviour fluctuates unconsciously in the theta-range when recalling sequential memory, suggesting that accessibility to sequential working memory is rhythmic rather than stable, possibly reflecting theta-phase dependent coding.

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