Excitability of both stretch reflex (SR) and motor evoked potential (MEP) elicited in the tibiali... more Excitability of both stretch reflex (SR) and motor evoked potential (MEP) elicited in the tibialis anterior (TA) muscle by transcranial magnetic stimulation were tested in standing humans. The results demonstrated significantly greater values for both SR and MEP in the TA while standing than while in the supine posture, although background electromyographic activity was silent in the two conditions. Taken together with previous reports that both pathways are facilitated in the TA at the early stance phase of human walking, our findings suggest that a common neural mechanism underlies both observations, one that might be functionally relevant for securing ankle joint stabilization during upright standing.
The human sensorimotor control has evolved in the Earth’s environment where all movement is influ... more The human sensorimotor control has evolved in the Earth’s environment where all movement is influenced by the gravitational force. Changes in this environmental force can severely impact the performance of arm movements which can be detrimental in completing certain tasks such as piloting or controlling complex vehicles. For this reason, subjects that are required to perform such tasks undergo extensive training procedures in order to minimize the chances of failure. We investigated whether local gravity simulation of altered gravitational conditions on the arm would lead to changes in kinematic parameters comparable to the full-body experience of microgravity and hypergravity onboard a parabolic flight. To see if this would be a feasible approach for on-ground training of arm reaching movements in altered gravity conditions we developed a robotic device that was able to apply forces at the wrist in order to simulate micro- or hypergravity conditions for the arm while subjects perfo...
The main aim of the study was to evaluate how the brain of a Paralympic athlete with severe disab... more The main aim of the study was to evaluate how the brain of a Paralympic athlete with severe disability due to cerebral palsy has reorganized after continuous training geared to enhance performance. Both corticospinal excitability of upper-limb muscles and electromyographic activity during swimming were investigated for a Paralympic gold medalist in swimming competitions. Transcranial magnetic stimulation (TMS) to the affected and intact hand motor cortical area revealed that the affected side finger muscle cortical representation area shifted towards the temporal side, and cortico-spinal excitability of the target muscle was prominently facilitated, i.e., the maximum motor evoked potential in the affected side, 6.11 ± 0.19 mV was greater than that in the intact side, 4.52 ± 0.39 mV (mean ± standard error). Electromyographic activities during swimming demonstrated well-coordinated patterns as compared with rather spastic activities observed in the affected side during walking on land. These results suggest that the ability of the brain to reorganize through intensive training in Paralympic athletes can teach interesting lessons to the field neurorehabilitation.
Like electroencephalographic (EEG) activity during reaction time tasks, EEG activity during tasks... more Like electroencephalographic (EEG) activity during reaction time tasks, EEG activity during tasks without overt responses may also consist of two components: stimulus-locked and-unlocked components. The extraction of such stimulus-unlocked components has been difficult owing to the unknown delays. Here, we propose a novel method to extract both of the two components from single-channel EEG epochs. In this method, we initially set random values for the delays and extract uncontaminated stimulus-locked and-unlocked components using the preset delays and a discrete Fourier transform. Then, we reconstruct the EEG by overlapping the extracted components with the preset delays, and calculate the residual errors between the reconstructed and original EEG. This procedure is repeated by updating the delays until the residual errors become adequately small. After verifying the performance of this method by two kinds of simulations with artificial and EEG data, we apply the method to EEG during NoGo trials of a Go/NoGo task, and obtain the stimulus-unlocked components, the magnitudes of which are comparable with those of the stimulus-locked components. By applying this method, it is possible to study internal and subjective brain activity, which occurs with variable delays.
We propose a generalized method to estimate waveforms common across trials from electroencephalog... more We propose a generalized method to estimate waveforms common across trials from electroencephalographic (EEG) data. From single/multi-channel EEGs, the proposed method estimates the number of waveforms common across trials, their delays in individual trials, and all of the waveforms. After verifying the performance of this method by a number of simulation tests with artificial EEGs, we apply it to EEGs during a Go/NoGo task. This method can be used in general situations where the number and the delays of EEG waveforms common across trials are unknown.
Direct evidence supporting the contribution of upper limb motion on the generation of locomotive ... more Direct evidence supporting the contribution of upper limb motion on the generation of locomotive motor output in humans is still limited. Here, we aimed to examine the effect of upper limb motion on locomotor-like muscle activities in the lower limb in persons with spinal cord injury (SCI). By imposing passive locomotion-like leg movements, all cervical incomplete ( n = 7) and thoracic complete SCI subjects ( n = 5) exhibited locomotor-like muscle activity in their paralyzed soleus muscles. Upper limb movements in thoracic complete SCI subjects did not affect the electromyographic (EMG) pattern of the muscle activities. This is quite natural since neural connections in the spinal cord between regions controlling upper and lower limbs were completely lost in these subjects. On the other hand, in cervical incomplete SCI subjects, in whom such neural connections were at least partially preserved, the locomotor-like muscle activity was significantly affected by passively imposed upper l...
We demonstrate that both detection of weak visual signals to the right eye and phase synchronizat... more We demonstrate that both detection of weak visual signals to the right eye and phase synchronization of electro-encephalogram (EEG) signals from widely separated areas of the human brain are increased by addition of weak visual noise to the left eye. We found a close relationship between the resulting noise-induced changes in behavioural performance and the similarly resulting changes in phase
Posters recently developed theta burst form of repetitive transcranial magnetic stimulation (TBS)... more Posters recently developed theta burst form of repetitive transcranial magnetic stimulation (TBS). Intermittent TBS (iTBS) and continuous (cTBS) were used to induce LTP-and LTD-like effects, respectively. Short form of cTBS (cTBS150) and iTBS (iTBS150) were used as the intervention. Results: The shorter protocols of cTBS150 and iTBS150 had no aftereffects when given alone. The potentiation effect induced by iTBS was completely erased by cTBS150 given 1 min after iTBS, whereas the depressive effect of cTBS was successfully abolished by iTBS150. The reversal was less effective when the intervention was given 10 min after induction of plasticity. Conclusions: We have shown for the first time that it is possible to reverse LTP/LTD-like effects in the conscious human brain with short bursts of stimulation that on their own have no apparent effect on cortical excitability. Moreover, the reversal of plasticity-like effect is time dependent. All these features are compatible with those of depotentiation and de-depression demonstrated in animal studies.
We demonstrate experimentally that enhanced detection of weak visual signals by addition of visua... more We demonstrate experimentally that enhanced detection of weak visual signals by addition of visual noise is accompanied by an increase in phase synchronization of EEG signals across widely-separated areas of the human brain. In our sensorimotor integration task, observers responded to a weak rectangular gray-level signal presented to their right eyes by pressing and releasing a button whenever they detected
The ability to suddenly stop a planned movement or a movement being performed and restart it afte... more The ability to suddenly stop a planned movement or a movement being performed and restart it after a short interval is an important mechanism that allows appropriate behavior in response to contextual or environmental changes. However, performing such stop-and-restart movements smoothly is difficult at times. We investigated performance (response time) of stop-and-restart movements using a go/stop/re-go task and found consistent stop-and-restart difficulties after short (,100 ms) stop-to-restart intervals (SRSI), and an increased probability of difficulties after longer (.200 ms) SRSIs, suggesting that two different mechanisms underlie stop-and-restart difficulties. Next, we investigated motor evoked potentials (MEPs) in a moving muscle induced by transcranial magnetic stimulation during a go/stop/re-go task. In re-go trials with a short SRSI (100 ms), the MEP amplitude continued to decrease after the re-go-signal onset, indicating that stopand-restart difficulties with short SRSIs might be associated with a neural mechanism in the human motor system, namely, stop-related suppression of corticomotor (CM) excitability. Finally, we recorded electroencephalogram (EEG) activity during a go/stop/re-go task and performed a single-trial-based EEG power and phase time-frequency analysis. Alpha-band EEG phase locking to re-go-signal, which was only observed in re-go trials with long SRSI (250 ms), weakened in the delayed rego response trials. These EEG phase dynamics indicate an association between stop-and-restart difficulties with long SRSIs and a neural mechanism in the human perception system, namely, decreased probability of EEG phase locking to visual stimuli. In contrast, smooth stop-and-restart human movement can be achieved in re-go trials with sufficient SRSI (150-200 ms), because release of stop-related suppression and simultaneous counter-activation of CM excitability may occur as a single task without second re-go-signal perception. These results suggest that skilled motor behavior is subject to various constraints in not only motor, but also perceptual (and attentional), systems.
Plantarflexors such as the soleus (SOL) and medial gastrocnemius (MG) play key roles in controlli... more Plantarflexors such as the soleus (SOL) and medial gastrocnemius (MG) play key roles in controlling bipedal stance; however, how the central nervous system controls the activation levels of these plantarflexors is not well understood. Here we investigated how the central nervous system controls the plantarflexors' activation level during quiet standing in a cosine tuning manner where the maximal activation is achieved in a preferred direction (PD). Further, we investigated how spinal cord injury affects these plantarflexors' activations. Thirteen healthy adults (AB) and thirteen individuals with chronic, incomplete spinal cord injury (iSCI) performed quiet standing trials. Their body kinematics, kinetics as well as electromyography signals from the MG and SOL were recorded. In the AB-group, we found that the plantarflexors followed the cosine tuning manner during quiet standing. That is, MG was most active when the ratio of plantarflexion torque to knee extension torque was ...
How can a human collective coordinate, for example to move a banquet table, when each person is i... more How can a human collective coordinate, for example to move a banquet table, when each person is influenced by the inertia of others who may be inferior at the task? We hypothesized that large groups cannot coordinate through touch alone, accruing to a zero-sum scenario where individuals inferior at the task hinder superior ones. We tested this hypothesis by examining how dyads, triads and tetrads, whose right hands were physically coupled together, followed a common moving target. Surprisingly, superior individuals followed the target accurately even when coupled to an inferior group, and the interaction benefits increased with the group size. A computational model shows that these benefits arose as each individual uses their respective interaction force to infer the collective’s target and enhance their movement planning, which permitted coordination in seconds independent of the collective’s size. By estimating the collective’s movement goal, its individuals make physical interact...
Previous research has demonstrated that barely visible (subliminal) goal-priming with motivationa... more Previous research has demonstrated that barely visible (subliminal) goal-priming with motivational reward can alter the state of the motor system and enhance motor output. Research shows that these affective-motivational effects result from associations between goal representations and positive affect without conscious awareness. Here, we tested whether motivational priming can increase motor output even if the priming is fully visible (supraliminal), and whether the priming effect occurs through increased cortical excitability. Groups of participants were primed with either barely visible or fully visible words related to effort and control sequences of random letters that were each followed by fully visible positively reinforcing words. The priming effect was measured behaviourally by handgrip force and reaction time to the grip cue after the priming was complete. Physiologically, the effects were measured by pupil dilation and motor-evoked potentials (MEPs) in response to transcr...
Excitability of both stretch reflex (SR) and motor evoked potential (MEP) elicited in the tibiali... more Excitability of both stretch reflex (SR) and motor evoked potential (MEP) elicited in the tibialis anterior (TA) muscle by transcranial magnetic stimulation were tested in standing humans. The results demonstrated significantly greater values for both SR and MEP in the TA while standing than while in the supine posture, although background electromyographic activity was silent in the two conditions. Taken together with previous reports that both pathways are facilitated in the TA at the early stance phase of human walking, our findings suggest that a common neural mechanism underlies both observations, one that might be functionally relevant for securing ankle joint stabilization during upright standing.
The human sensorimotor control has evolved in the Earth’s environment where all movement is influ... more The human sensorimotor control has evolved in the Earth’s environment where all movement is influenced by the gravitational force. Changes in this environmental force can severely impact the performance of arm movements which can be detrimental in completing certain tasks such as piloting or controlling complex vehicles. For this reason, subjects that are required to perform such tasks undergo extensive training procedures in order to minimize the chances of failure. We investigated whether local gravity simulation of altered gravitational conditions on the arm would lead to changes in kinematic parameters comparable to the full-body experience of microgravity and hypergravity onboard a parabolic flight. To see if this would be a feasible approach for on-ground training of arm reaching movements in altered gravity conditions we developed a robotic device that was able to apply forces at the wrist in order to simulate micro- or hypergravity conditions for the arm while subjects perfo...
The main aim of the study was to evaluate how the brain of a Paralympic athlete with severe disab... more The main aim of the study was to evaluate how the brain of a Paralympic athlete with severe disability due to cerebral palsy has reorganized after continuous training geared to enhance performance. Both corticospinal excitability of upper-limb muscles and electromyographic activity during swimming were investigated for a Paralympic gold medalist in swimming competitions. Transcranial magnetic stimulation (TMS) to the affected and intact hand motor cortical area revealed that the affected side finger muscle cortical representation area shifted towards the temporal side, and cortico-spinal excitability of the target muscle was prominently facilitated, i.e., the maximum motor evoked potential in the affected side, 6.11 ± 0.19 mV was greater than that in the intact side, 4.52 ± 0.39 mV (mean ± standard error). Electromyographic activities during swimming demonstrated well-coordinated patterns as compared with rather spastic activities observed in the affected side during walking on land. These results suggest that the ability of the brain to reorganize through intensive training in Paralympic athletes can teach interesting lessons to the field neurorehabilitation.
Like electroencephalographic (EEG) activity during reaction time tasks, EEG activity during tasks... more Like electroencephalographic (EEG) activity during reaction time tasks, EEG activity during tasks without overt responses may also consist of two components: stimulus-locked and-unlocked components. The extraction of such stimulus-unlocked components has been difficult owing to the unknown delays. Here, we propose a novel method to extract both of the two components from single-channel EEG epochs. In this method, we initially set random values for the delays and extract uncontaminated stimulus-locked and-unlocked components using the preset delays and a discrete Fourier transform. Then, we reconstruct the EEG by overlapping the extracted components with the preset delays, and calculate the residual errors between the reconstructed and original EEG. This procedure is repeated by updating the delays until the residual errors become adequately small. After verifying the performance of this method by two kinds of simulations with artificial and EEG data, we apply the method to EEG during NoGo trials of a Go/NoGo task, and obtain the stimulus-unlocked components, the magnitudes of which are comparable with those of the stimulus-locked components. By applying this method, it is possible to study internal and subjective brain activity, which occurs with variable delays.
We propose a generalized method to estimate waveforms common across trials from electroencephalog... more We propose a generalized method to estimate waveforms common across trials from electroencephalographic (EEG) data. From single/multi-channel EEGs, the proposed method estimates the number of waveforms common across trials, their delays in individual trials, and all of the waveforms. After verifying the performance of this method by a number of simulation tests with artificial EEGs, we apply it to EEGs during a Go/NoGo task. This method can be used in general situations where the number and the delays of EEG waveforms common across trials are unknown.
Direct evidence supporting the contribution of upper limb motion on the generation of locomotive ... more Direct evidence supporting the contribution of upper limb motion on the generation of locomotive motor output in humans is still limited. Here, we aimed to examine the effect of upper limb motion on locomotor-like muscle activities in the lower limb in persons with spinal cord injury (SCI). By imposing passive locomotion-like leg movements, all cervical incomplete ( n = 7) and thoracic complete SCI subjects ( n = 5) exhibited locomotor-like muscle activity in their paralyzed soleus muscles. Upper limb movements in thoracic complete SCI subjects did not affect the electromyographic (EMG) pattern of the muscle activities. This is quite natural since neural connections in the spinal cord between regions controlling upper and lower limbs were completely lost in these subjects. On the other hand, in cervical incomplete SCI subjects, in whom such neural connections were at least partially preserved, the locomotor-like muscle activity was significantly affected by passively imposed upper l...
We demonstrate that both detection of weak visual signals to the right eye and phase synchronizat... more We demonstrate that both detection of weak visual signals to the right eye and phase synchronization of electro-encephalogram (EEG) signals from widely separated areas of the human brain are increased by addition of weak visual noise to the left eye. We found a close relationship between the resulting noise-induced changes in behavioural performance and the similarly resulting changes in phase
Posters recently developed theta burst form of repetitive transcranial magnetic stimulation (TBS)... more Posters recently developed theta burst form of repetitive transcranial magnetic stimulation (TBS). Intermittent TBS (iTBS) and continuous (cTBS) were used to induce LTP-and LTD-like effects, respectively. Short form of cTBS (cTBS150) and iTBS (iTBS150) were used as the intervention. Results: The shorter protocols of cTBS150 and iTBS150 had no aftereffects when given alone. The potentiation effect induced by iTBS was completely erased by cTBS150 given 1 min after iTBS, whereas the depressive effect of cTBS was successfully abolished by iTBS150. The reversal was less effective when the intervention was given 10 min after induction of plasticity. Conclusions: We have shown for the first time that it is possible to reverse LTP/LTD-like effects in the conscious human brain with short bursts of stimulation that on their own have no apparent effect on cortical excitability. Moreover, the reversal of plasticity-like effect is time dependent. All these features are compatible with those of depotentiation and de-depression demonstrated in animal studies.
We demonstrate experimentally that enhanced detection of weak visual signals by addition of visua... more We demonstrate experimentally that enhanced detection of weak visual signals by addition of visual noise is accompanied by an increase in phase synchronization of EEG signals across widely-separated areas of the human brain. In our sensorimotor integration task, observers responded to a weak rectangular gray-level signal presented to their right eyes by pressing and releasing a button whenever they detected
The ability to suddenly stop a planned movement or a movement being performed and restart it afte... more The ability to suddenly stop a planned movement or a movement being performed and restart it after a short interval is an important mechanism that allows appropriate behavior in response to contextual or environmental changes. However, performing such stop-and-restart movements smoothly is difficult at times. We investigated performance (response time) of stop-and-restart movements using a go/stop/re-go task and found consistent stop-and-restart difficulties after short (,100 ms) stop-to-restart intervals (SRSI), and an increased probability of difficulties after longer (.200 ms) SRSIs, suggesting that two different mechanisms underlie stop-and-restart difficulties. Next, we investigated motor evoked potentials (MEPs) in a moving muscle induced by transcranial magnetic stimulation during a go/stop/re-go task. In re-go trials with a short SRSI (100 ms), the MEP amplitude continued to decrease after the re-go-signal onset, indicating that stopand-restart difficulties with short SRSIs might be associated with a neural mechanism in the human motor system, namely, stop-related suppression of corticomotor (CM) excitability. Finally, we recorded electroencephalogram (EEG) activity during a go/stop/re-go task and performed a single-trial-based EEG power and phase time-frequency analysis. Alpha-band EEG phase locking to re-go-signal, which was only observed in re-go trials with long SRSI (250 ms), weakened in the delayed rego response trials. These EEG phase dynamics indicate an association between stop-and-restart difficulties with long SRSIs and a neural mechanism in the human perception system, namely, decreased probability of EEG phase locking to visual stimuli. In contrast, smooth stop-and-restart human movement can be achieved in re-go trials with sufficient SRSI (150-200 ms), because release of stop-related suppression and simultaneous counter-activation of CM excitability may occur as a single task without second re-go-signal perception. These results suggest that skilled motor behavior is subject to various constraints in not only motor, but also perceptual (and attentional), systems.
Plantarflexors such as the soleus (SOL) and medial gastrocnemius (MG) play key roles in controlli... more Plantarflexors such as the soleus (SOL) and medial gastrocnemius (MG) play key roles in controlling bipedal stance; however, how the central nervous system controls the activation levels of these plantarflexors is not well understood. Here we investigated how the central nervous system controls the plantarflexors' activation level during quiet standing in a cosine tuning manner where the maximal activation is achieved in a preferred direction (PD). Further, we investigated how spinal cord injury affects these plantarflexors' activations. Thirteen healthy adults (AB) and thirteen individuals with chronic, incomplete spinal cord injury (iSCI) performed quiet standing trials. Their body kinematics, kinetics as well as electromyography signals from the MG and SOL were recorded. In the AB-group, we found that the plantarflexors followed the cosine tuning manner during quiet standing. That is, MG was most active when the ratio of plantarflexion torque to knee extension torque was ...
How can a human collective coordinate, for example to move a banquet table, when each person is i... more How can a human collective coordinate, for example to move a banquet table, when each person is influenced by the inertia of others who may be inferior at the task? We hypothesized that large groups cannot coordinate through touch alone, accruing to a zero-sum scenario where individuals inferior at the task hinder superior ones. We tested this hypothesis by examining how dyads, triads and tetrads, whose right hands were physically coupled together, followed a common moving target. Surprisingly, superior individuals followed the target accurately even when coupled to an inferior group, and the interaction benefits increased with the group size. A computational model shows that these benefits arose as each individual uses their respective interaction force to infer the collective’s target and enhance their movement planning, which permitted coordination in seconds independent of the collective’s size. By estimating the collective’s movement goal, its individuals make physical interact...
Previous research has demonstrated that barely visible (subliminal) goal-priming with motivationa... more Previous research has demonstrated that barely visible (subliminal) goal-priming with motivational reward can alter the state of the motor system and enhance motor output. Research shows that these affective-motivational effects result from associations between goal representations and positive affect without conscious awareness. Here, we tested whether motivational priming can increase motor output even if the priming is fully visible (supraliminal), and whether the priming effect occurs through increased cortical excitability. Groups of participants were primed with either barely visible or fully visible words related to effort and control sequences of random letters that were each followed by fully visible positively reinforcing words. The priming effect was measured behaviourally by handgrip force and reaction time to the grip cue after the priming was complete. Physiologically, the effects were measured by pupil dilation and motor-evoked potentials (MEPs) in response to transcr...
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Papers by Daichi Nozaki