Biology subjects

Nozaki, D.

Publications and source records attributed to Nozaki, D..

12 recordsLinked to original sources

bioRxiv2026

Heart rate deceleration reflects expectation violation during reaching

Heart rate (HR) deceleration occurs following movement error and has been interpreted as an autonomic response to adverse behavioral outcomes. However, movement errors not only represent adverse movement outcomes but may also violate expectations. The present study employed a reaching movement paradigm using a robotic manipulandum in male and female human participants to dissociate the contributions of movement outcome and expectation violation to HR responses. We confirmed that HR deceleration occurred following visuomotor perturbations that induce movement errors, consistent with previous studies. However, when contextual cues predicted upcoming movement outcomes, HR deceleration emerged during movement preparation rather than following movement error, suggesting the involvement of expectation in HR responses. Moreover, across varying levels of expectation for different movement outcomes, HR deceleration was associated with unexpected movement outcomes rather than with the negative valence of movement outcomes. By altering target width to permit successful movements despite visuomotor rotations, we further found that HR deceleration was more strongly associated with task error than with sensory prediction error. Together, these findings indicate that HR responses during movement are more closely associated with violations of movement expectation than with movement error itself. These findings provide a new perspective on autonomic responses during sensorimotor processing and suggest that HR may serve as a physiological marker of expectation-related processing during movement.

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

neuroscience↗

bioRxiv2026

Fast corrective responses in redundant motor control are shaped by intrinsic constraints of movement patterns

In real-world motor tasks, body movements unfold in a high-dimensional space, whereas task errors are defined in a lower-dimensional space. How such low-dimensional errors propagate across redundant motor degrees of freedom to generate rapid corrective responses remains poorly understood. To address this question, we developed a redundant bimanual task in which participants manipulated a virtual stick with both hands to move its tip to a visual target. Visual perturbations either displaced the stick tip (end-effector relevant errors) or altered the tilt angle of the stick without affecting the tip position (end-effector irrelevant errors), allowing us to dissociate errors defined in task space from those arising in redundant dimensions. Participants rapidly corrected both types of perturbations using highly stereotyped movement patterns. Corrections to end-effector relevant errors consistently involved coordinated changes across redundant dimensions, and even perturbations that did not affect task success elicited systematic corrective responses. Together, these results demonstrate that fast corrective responses in redundant motor control are not generated by flexible re-optimization, but are instead shaped by intrinsic coordination constraints that govern how visual errors propagate through the motor system.

neuroscience↗

bioRxiv2026

Sensorimotor adaptation to altered postural dynamics implemented via closed-loop neuromuscular electrical stimulation

Studying sensorimotor adaptation in whole-body motor tasks such as locomotion and postural control remains challenging because well-controlled mechanical perturbations typically require large, specialized apparatus that constrains natural movement. Here, we introduced a novel perturbation system that alters musculoskeletal dynamics using closed-loop neuromuscular electrical stimulation (NMES) and examined how the human postural control system adapts to these altered dynamics during quiet standing. By applying NMES to the tibialis anterior as a function of anterior-posterior body sway, we imposed artificial postural dynamics. Analyses of postural sway revealed robust, systematic adaptation, with distinct patterns across perturbation types. These findings demonstrate that closed-loop NMES can impose controllable, movement-specific dynamics without mechanical constraints, while also revealing the adaptability of human postural control to externally imposed sway dynamics.

neuroscience↗

bioRxiv2026

Visuomotor learning is determined by the tonic component of feedback responses

When a movement error occurs, the motor system updates its commands to improve performance on subsequent trials. A prominent feedback error learning hypothesis proposes that the feedback response that corrects movement within a trial serves as a teaching signal for the learning response, observed as changes in motor commands on the next trial. However, how the temporal pattern of the feedback response influences the learning response remains unclear. Here, we introduce an experimental paradigm that directly compares the temporal patterns of feedback and learning responses across different patterns of visual error. We show that although the feedback response closely tracks the temporal pattern of the visual error, this temporal pattern is not transferred to the learning response. Instead, the amplitude of the feedback response during the holding period, which reflects the temporal history of the visual error, strongly predicts the magnitude of the learning response. These findings suggest that information reflected in the tonic component of feedback responses is closely linked to the scaling of subsequent motor-command updates.

neuroscience↗

bioRxiv2025

Adaptation to transient and local electrical muscle stimulation elicits persistent and global changes in walking kinematics

It is generally assumed that motor commands altered by adaptation to a novel environment revert to their original state once the environment returns to baseline. However, this assumption--based mainly on simple movements such as reaching--may not hold for complex actions. In redundant systems, de-adaptation can cause motor commands and resulting kinematics to settle into states distinct from the original. Here, we examined adaptation and de-adaptation in treadmill walking while modulating lower-limb dynamics using closed-loop neuromuscular electrical stimulation (NMES) applied bilaterally to the tibialis anterior. Adaptation to a localized ankle perturbation induced global kinematic changes across the ankle, knee, and hip joints. After perturbation removal, joint kinematics did not fully return to baseline; instead, features of the adapted gait persisted for eight minutes. These findings highlight the distinctive nature of motor adaptation in redundant systems and demonstrate the potential of NMES-based perturbations for inducing implicit modifications in movement patterns.

neuroscience↗

bioRxiv2025

Successive failure triggered by motor exploration in a reinforcement-based reaching task

Motor exploration, a key process in reinforcement-based motor learning, is triggered by suboptimal performance and leads to increased movement variability. Consequently, failure in one trial may increase the likelihood of failure in subsequent trials. If this pattern emerges, successive failures (SFs) are not merely events to be avoided but part of the trial-and-error process of identifying optimal movements, which can facilitate motor learning. This study investigated whether and how SFs occur above chance levels during a motor learning task with binary success/failure feedback and explored the relationship between SFs and motor learning outcomes. Thirty-three healthy young adults participated in the study, performing a reaching task to pass through a target without visual feedback of their hand position. Binary feedback was provided after each trial, indicating whether the hand trajectory overlapped with the target. The results showed that the probability of two SFs was significantly higher than the square of the overall failure probability, indicating that failure streaks occurred above chance levels. A computational model, in which motor variability comprised constant motor noise and exploratory variability regulated by recent reward history (where variability increased following failure), successfully explained SF emergence. However, the learning index, defined as the difference in failure probability between the first and latter halves of the experiment, was unrelated to SF emergence. Additionally, failure streaks disappeared when participants were asked to reach one of seven randomly selected targets in each trial, suggesting that introducing environmental variability can help alleviate SFs.

neuroscience↗

bioRxiv2024

Shifts in neural tuning systematically alter sensorimotor learning ability

Sensorimotor learning can change the tuning of neurons in motor-related brain areas and rotate their preferred directions (PDs). These PD rotations are commonly interpreted as reflecting motor command changes; however, cortical neurons that display PD rotations also contribute to sensorimotor learning. Sensorimotor learning should, therefore, alter not only motor commands but also the tuning of neurons responsible for this learning, and thus impact subsequent learning ability. Here, we investigate this possibility with computational modeling and by directly measuring adaptive responses during sensorimotor learning in humans. Modeling shows that the PD rotations induced by sensorimotor learning, predict specific anisotropic changes in PD distributions that in turn predict a specific spatial pattern of changes in learning ability. Remarkably, experiments in humans then reveal large, systematic changes in learning ability in a spatial pattern that precisely reflects these model-predicted changes. We find that this pattern defies conventional wisdom and implements Newtons method, a learning rule where the step size is inversely proportional rather than proportional to the learning gradients amplitude, limiting overshooting in the adaptive response. Our findings indicate that PD rotation provides a mechanism whereby the motor system can simultaneously learn how to move and learn how to learn.

neuroscience↗

bioRxiv2023

Motor control and adaptation in a redundant motor task manipulating a stick with both hands

The remarkable ability of the motor system to adapt to novel environments has traditionally been investigated using kinematically non-redundant tasks, such as planar reaching movements. This limitation prevents the study of how the motor system achieves adaptation by altering the movement patterns of our redundant body. To address this issue, we developed a redundant motor task in which participants reached for targets with the tip of a virtual stick held with both hands. Despite the redundancy of the task, participants consistently employed a stereotypical strategy of flexibly changing the tilt angle of the stick depending on the direction of tip movement. Thus, this baseline relationship between tip-movement direction and stick-tilt angle constrained both the physical and visual movement patterns of the redundant system. Our task allowed us to systematically investigate how the motor system implicitly changed both the tip-movement direction and the stick-tilt angle in response to imposed visual perturbations. Both types of perturbations, whether directly affecting the task (tip-movement direction) or not (stick-tilt angle around the tip), drove adaptation, and the patterns of implicit adaptation were guided by the baseline relationship. Consequently, tip-movement adaptation was associated with changes in stick-tilt angle, and intriguingly, even seemingly ignorable stick-tilt perturbations significantly influenced tip-movement adaptation, leading to tip-movement direction errors. These findings provide a new understanding that the baseline relationship plays a crucial role not only in how the motor system controls movement of the redundant system, but also in how it implicitly adapts to modify movement patterns.

neuroscience↗

bioRxiv2022

Divisively normalized neuronal processing of uncertain visual feedback for visuomotor learning

When encountering a visual error during a reaching movement, the motor system improves the motor command for the subsequent trial. The degree of improvement is well-known to be degraded with visual error uncertainty, which is considered evidence that the motor system optimally estimates the error. However, it remains unclear how such statistical computation is accomplished. Here, we propose an alternative motor learning scheme implemented with a divisive normalization (DN) mechanism. This scheme assumes that when an uncertain visual error is provided by multiple cursors, the motor system processes the error conveyed by each cursor and integrates the information using DN. The DN scheme can reproduce the patterns of learning response when 1, 2, or 3 cursors are concurrently displayed and predict how the increase in the visual error uncertainty degrades the learning response. Our proposed scheme provides a novel view of how the motor learning system updates the motor command according to uncertain visual error information.

neuroscience↗

bioRxiv2022

Looking for a sign forecasting failure in actions: reaching errors triggered by a slowdown of movement and specific brain activity in preceding trials

Even experts can sometimes fail while performing fully learned movements. Do such failures suddenly arise, or are there any forecasting signs? It has been reported that the kinematics of the early phase of movements can predict the failure, and brain activity patterns specific to failures are observed just before the movement onset. The presence of abnormal brain activity patterns long before (> 30 s) a failure in a cognitive task leads us to question if signs of a failure in action could exist in trials preceding the failure. Here, we examined this question using a reaching movement adaptation paradigm conventionally used to test motor learning dynamics. Firstly, the presence of a behavioral sign that preceded failures was observed: the peak velocity of the reaching movement significantly decreased in the preceding two trials. Secondly, specific theta and alpha band activity of EEG were observed in the failure trials and the trials preceding the failure. These results suggest that a failure in actions does not occur suddenly, and some signs preceding failures can be observed in the prior trials. Our approach may pave the way to investigate how we prevent failures and improve motor performance.

neuroscience↗

bioRxiv2019

Divisively normalized integration of multisensory error information develops motor memories specific to vision and proprioception

Both visual and proprioceptive information contribute to accurate limb movement, but the mechanism of integration of these different modality signals for movement control and learning remains controversial. Here, we aimed to elucidate the mechanism of integration by examining motor adaptation when various combinations of visual and proprioceptive perturbations were applied during reaching movements. We found that the movement corrections by adaptation were explained by a mechanism known as a divisive normalization, which was previously reported to be the mechanism underlying the integration of multisensory signals in neurons. Furthermore, we found evidence that the motor memory for each sensory modality was formed separately and the outputs from these memories were integrated. These results provide a novel view of the utilization of different sensory modality signals in motor control and adaptation.

neuroscience↗