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Cerebellar brain inhibition (CBI) is an inhibitory output from the cerebellum to the primary motor cortex, which is decreased in early motor learning. Transcranial random noise stimulation (tRNS) is a noninvasive brain stimulation to induce brain plastic changes; however, the effects of cerebellar tRNS on CBI and motor learning have not been investigated yet to our knowledge. In this study, whether cerebellar tRNS decreases CBI and improves motor learning was examined, and pupil diameter was measured to examine physiological changes due to the effect of tRNS on motor learning. Thirty-four healthy subjects were assigned to either the cerebellar tRNS group or the Sham group. The subjects performed visuomotor tracking task with ten trials each in the early and late learning stages while receiving the stimulus intervention. CBI and motor evoked potentials were measured before the learning task, after the early learning stage, and after the late learning stage, and pupil diameter was measured during the task. There was no change in CBI in both groups. No group differences in motor learning rates were observed at any learning stages. Pupil diameter was smaller in the late learning stage than in the early learning stage in both groups. The cerebellar tRNS was suggested not to induce changes in CBI and improvement in motor learning, and it did not affect pupil diameter., Competing Interests: Declaration of Competing Interest The authors report no conflicts of interest., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

Although transcranial random noise stimulation (tRNS) to the primary motor cortex (M1) increases corticospinal excitability and improves motor function, the effects of tRNS timing have not been clarified when combined with motor training. The purpose of this study was to clarify the effects of different tRNS timing on corticospinal excitability and motor function. We applied tRNS to the left M1 using a frequency of 0.1-640 Hz for 10 min to 15 healthy subjects. Subjects performed visuomotor tracking tasks with right hand for 10 min and participated in the following four conditions based on the timing of tRNS: (1) "before" condition, tRNS was performed before motor training; (2) "during" condition, tRNS was performed during motor training; (3) "after" condition, tRNS was performed after motor training; and (4) sham condition, the control group. Motor evoked potential (MEP) amplitudes were recorded from the right first dorsal interosseous muscle using transcranial magnetic stimulation. MEP amplitudes were assessed by baseline followed by three sessions at 10 min intervals. The motor function was assessed before and after tRNS and motor training. The MEP amplitude increased after tRNS in the before and during conditions but not in the after condition. Motor function after motor training improved in all conditions, but there were no significant differences between these conditions. The present study revealed that the timing of tRNS affects corticospinal excitability but not motor learning., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Unimanual motor tasks change the corticospinal excitability of the trained and untrained side. However, whether the motor task type influences the modulation of the corticospinal excitability of the untrained side remains unclear. This study aimed to clarify the effects of motor tasks on the corticospinal excitability of the untrained side and the relationship between the excitability and motor function. In Experiment I, we measured the corticospinal excitability of the untrained side and motor function after 10 min of motor training in two conditions (gripping task and ball rotation task). The gripping task decreased the excitability. In contrast, excitability remained unchanged after the ball rotation task; further, the modulation of excitability and motor function showed a correlation. In Experiment II, we measured the corticospinal excitability of the untrained side and motor function after two sessions of the ball rotation task. The excitability increased, but motor function remained unchanged after the first session, whereas the excitability decreased to the level observed before training, and motor function improved after the second session. We suggest that the training condition modulates the corticospinal excitability of the untrained side and that this is related to the modulation of motor function., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Somatosensory stimulation modulates corticospinal excitability. Mechanical tactile stimulation (MS) activates cortical activity depending on tactile stimulation patterns. In this study, we examined whether the effects of mechanical tactile stimulation on corticospinal excitability and motor function depend on different pin protrusions patterns. This single-blind study included 18 healthy subjects. Two types of MS interventions were used: repetitive global stimulus (RGS) intervention was used to stimulate the finger by using 24 pins installed on a finger pad, and sequential stepwise displacement stimulus (SSDS) intervention was used to stimulate the finger by moving a row of 6 pins between the left and right sides on the finger pad. MS interventions were applied to the right index finger for 20 min (stim on/stim off, 1 s/5 s) at a frequency of 20 Hz. After RGS intervention, motor evoked potentials (MEPs) by transcranial magnetic stimulation were observed to be significantly smaller than pre-intervention MEPs; however, motor function using the grooved pegboard task remained unchanged. After SSDS intervention, MEPs were significantly larger and motor function significantly improved compared with pre-intervention values. Our results demonstrated that MS intervention can modulate corticospinal excitability and motor function and that the effects of MS intervention depend on MS intervention patterns.

Although transcranial random noise stimulation (tRNS) over the primary motor cortex (M1) region can be used to enhance cortical excitability, it remains unclear whether tRNS over the M1 region improves motor performance. The present study aims to clarify the effect of tRNS on both corticospinal excitability and motor performance. We applied tRNS at the frequency range of 0.1-640 Hz over the left M1 for 10 min to 16 healthy adults. All subjects were tested in the following two interventions: (1) tRNS condition and (2) sham condition. Motor evoked potential (MEP) amplitudes were recorded from the right first dorsal interosseous muscle by transcranial magnetic stimulation. The motor performance was evaluated using a visuomotor tracking task by isometric abduction motion of the right index finger. MEP amplitudes and motor performance were measured before intervention, immediately after and 10 min after the intervention. The two interventions (tRNS and sham) were randomly performed separated by a break of at least 1 week. In the tRNS condition, MEP amplitudes were significantly increased immediately and 10 min after the intervention, while the motor performance was significantly improved 10 min after the intervention. The present study revealed that tRNS over the M1 region is effective for cortical excitability as well as for motor performance., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Post-exercise cortical depression (PED) is induced by non-fatiguing finger movement. Because the type of exercise that causes PED remains unclear, we conducted two experiments to clarify which exercise factors induce PED. Fifteen healthy participants performed repetitive abduction movements of the right index finger at 2.0 Hz (simple rhythmic task) and 0.2 Hz (adjustment task) for 6 min each in experiment 1. Twelve healthy participants performed repetitive and isometric abduction contractions of the right index finger at 1.0 Hz with visuomotor tracking (visuomotor task) and without visuomotor tracking (simple isometric task) for 5 min each in experiment 2. Muscle contraction levels were 10% of the maximum voluntary contraction in all tasks. Motor evoked potentials (MEPs) evoked by transcranial magnetic stimulation were recorded from the right first dorsal interosseous muscle before and after the movement tasks. The simple rhythmic task transiently reduced MEP amplitudes when compared with baseline in experiment 1. In contrast, the visuomotor task increased MEP amplitudes in experiment 2. No MEP changes were observed following the adjustment task in experiment 1 and the simple isometric task in experiment 2. This study suggests that PED is induced by simple rhythmic movement., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Somatosensory inputs affect primary motor cortex (M1) excitability; however, the effect of movement-induced somatosensory inputs on M1 excitability is unknown. This study examined whether M1 excitability is modulated by somatosensory inputs with passive movement in 29 healthy subjects. Motor-evoked potentials (MEPs), elicited by transcranial magnetic stimulation (TMS) were recorded from the first dorsal interosseous (FDI) muscle (Experiment 1). M- and F-waves were measured from the FDI muscle (Experiment 2). Passive movements of the index finger were performed in the adduction direction. TMS pulses were preceded by starting passive movements with interstimulus intervals (ISIs) of 30, 60, 90, 120, 150, 180, and 210 ms. TMS or electrical stimulation was performed in the midrange of the metacarpophalangeal joint during passive movements. MEPs were significantly facilitated at 90, 120, and 150 ms (p < 0.05). No M- or F-wave changes were observed for any ISI. In addition, we investigated whether MEP changes were dependent on passive movement velocity and joint angle. Passive movement was performed at two movement velocities (Experiment 3) or joint angles (Experiment 4). MEP facilitation was observed depending on the movement velocities or joint angles. These experiments demonstrated that somatosensory inputs induced by passive movements facilitated M1 excitability depending on the ISIs, passive movement velocity, and joint angle., (Copyright © 2018 The Authors. Published by Elsevier Ltd.. All rights reserved.)

The present study aimed to investigate the effects of changes in motor-evoked potential (MEP) amplitude on short-latency afferent inhibition (SAI) and short-interval intracortical inhibition (SICI). MEPs in response to transcranial magnetic stimulation (TMS) of the left primary motor cortex were measured from the right first dorsal interosseous muscle of 10 healthy participants. SAI was evaluated by measuring MEPs in response to variable-intensity test TMS pulses delivered 22 ms following electrical stimulation of the right ulnar nerve (intensity fixed at the motor threshold). SICI was evaluated by pairing a constant conditioning TMS pulse [80% of resting motor threshold (RMT)] with a second variable-intensity TMS test pulse (interstimulus interval of 2 ms). The intensity of the test stimulus was set at 110, 115, 120, 125, or 130%RMT on a given trial. SAI was significantly reduced when evoked by a 125%RMT test TMS pulse compared with 110%RMT, and absent at 130%RMT. There was no significant difference in SICI at 110-130%RMT. Significant positive correlations were detected between the unconditioned and conditioned MEP amplitudes at both SAI and SICI. This study demonstrated that SAI and SICI are highly sensitive to the MEP amplitude and SAI decreases with increasing MEP amplitude, whereas SICI does not change. The different responses for SAI and SICI to the increasing MEP amplitude is interpreted as evidence that different inhibitory neural circuits may be involved in SAI and SICI.

This study aimed to clarify the influence of range of repetitive passive finger movement on corticospinal excitability. Thirteen healthy subjects participated in this study. Passive index finger adduction-abduction movements were performed from 15° abduction to 15° adduction, 15° abduction to 0°, 0° to 15° adduction, and 15° adduction to 30° adduction, each at 15°/s for 10min on separate days. Motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation and M- and F-waves were measured before and after each repetitive passive index finger movement protocol to evaluate changes in corticospinal excitability. MEP amplitude significantly decreased after all passive movements, while F-wave amplitude, F-wave persistence, and M-wave amplitude remained stable. These results suggest that cortical excitability decreases after repetitive passive movement. However, the range of repetitive passive movement does not markedly influence the magnitude of cortical depression., (Copyright © 2017 Elsevier B.V. All rights reserved.)

The authors aimed to calculate and compare cortical relay time (CRT) between intrinsic hand muscles and between homonymous muscles of dominant and nondominant hands. The participants comprised 22 healthy volunteers. The CRT for long-latency reflexes (LLRs) was calculated by subtracting the peak latency of somatosensory evoked potentials of component N20 and the onset latency of motor evoked potentials from the onset latency of LLRs. CRT was significantly shorter for the first dorsal interosseous muscle than for the abductor pollicis brevis muscle, regardless of hand dominance. CRT for the abductor pollicis brevis muscle was significantly shorter in the dominant hand than in the nondominant hand. Evaluation of CRT for intrinsic muscles might be beneficial in the understanding of individuated finger functions.

Introduction: This study aimed to clarify cortical circuit mechanisms contributing to corticomotor excitability during postexercise depression (PED) following repetitive nonfatiguing movement. We investigated changes in short-latency afferent inhibition (SAI) and short-interval intracortical inhibition (SICI) by paired-pulse transcranial magnetic stimulation (TMS) during PED., Methods: A total of 16 healthy subjects performed repetitive abduction movements of the right index finger at 2.0 Hz for 6 min at 10% maximum voluntary contraction. We measured SAI evoked by pairing ulnar nerve stimulation with TMS (interstimulus interval, 22 ms) before and during PED ( n  = 10, experiment 1). We also measured SICI evoked by paired TMS (interstimulus interval, 2 ms) at 80% resting motor threshold ( n  = 10, experiment 2), and at 80% active motor threshold ( n  = 8, experiment 3) before and during PED., Results: Single motor evoked potential amplitude significantly decreased 1-2 min after the movement task in all experiments, indicating reliable PED induction. In experiment 1, SAI significantly decreased (disinhibited) 1-2 min during PED, whereas in experiments 2 and 3, SICI showed no significant change during PED., Conclusion: This study suggests that cholinergic inhibitory circuit activity decreases during PED following repetitive nonfatiguing movement, whereas GABA A circuit activity remains stable.

The aim of this study was to investigate the effects of cathodal transcranial direct current stimulation (tDCS) applied over the primary somatosensory cortex (S1) on short-interval afferent inhibition (SAI). Thirteen healthy individuals participated in this study. Cathodal tDCS was applied for 15 min at 1 mA over the left S1. Motor-evoked potentials (MEPs) were measured from the right first dorsal interosseous muscle in response to transcranial magnetic stimulation (TMS) of the left motor cortex before tDCS (pre), immediately after tDCS (immediately), and 15 min after tDCS (post-15 min). SAI was evaluated by measuring MEPs in response to TMS pulses applied 40 ms after peripheral electrical stimulation of the index finger. For each measurement period (pre, immediately, and post-15 min), MEP amplitude was significantly smaller when TMS followed index finger stimulation (SAI condition) than when TMS was delivered alone (single TMS) (P<0.01), indicating expression of SAI. The MEP ratio (MEP of SAI/MEP of single TMS) at post-15 min was significantly larger than that of pre (P<0.05), indicating suppression of SAI. However, no significant difference was observed between pre and immediately, and immediately and post-15 min. These results suggest that cathodal tDCS applied over the S1 causes a decrease in S1 excitability following peripheral electrical stimulation and cathodal tDCS applied over the S1 decreased the inhibitory effects of SAI.

Previous studies examining the influence of afferent stimulation on corticospinal excitability have demonstrated that the intensity of afferent stimulation and the nature of the afferents targeted (cutaneous/proprioceptive) determine the effects. In this study, we assessed the effects of whole-hand water immersion (WI) and water flow stimulation (WF) on corticospinal excitability and intracortical circuits by measuring motor evoked potential (MEP) recruitment curves and conditioned MEP amplitudes. We further investigated whether whole-hand WF modulated movement-related cortical activity. Ten healthy subjects participated in three experiments, comprising the immersion of participants' right hands with (whole-hand WF) or without (whole-hand WI) water flow, and no immersion (control). We evaluated MEP recruitment curves produced by a single transcranial magnetic stimulation (TMS) pulse at increasing stimulus intensities, short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF) using the paired TMS technique before and after 15 min of intervention. Movement-related cortical potentials (MRCPs) were evaluated to examine primary motor cortex, supplementary motor area, and somatosensory cortex excitability upon movement before and after whole-hand WF. After whole-hand WF, the slope of the MEP recruitment curve significantly increased, whereas SICI decreased and ICF increased in the contralateral motor cortex. The amplitude of the Bereitschaftspotential, negative slope, and motor potential of MRCPs significantly increased after whole-hand WF. We demonstrated that whole-hand WF increased corticospinal excitability, decreased SICI, and increased ICF, although whole-hand WI did not change corticospinal excitability and intracortical circuits. Whole-hand WF modulated movement-related cortical activity, increasing motor cortex activation for the planning and execution of voluntary movements., (Copyright © 2015 the American Physiological Society.)

Horizontal intracortical projections for agonist and antagonist muscles exist in the primary motor cortex (M1), and reward may induce a reinforcement of transmission efficiency of intracortical circuits. We investigated reward-induced change in M1 excitability for agonist and antagonist muscles. Participants were 8 healthy volunteers. Probabilistic reward tasks comprised 3 conditions of 30 trials each: 30 trials contained 10% reward, 30 trials contained 50% reward, and 30 trials contained 90% reward. Each trial began with a cue (red fixation cross), followed by blue circle for 1 s. The subjects were instructed to perform wrist flexion and press a button with the dorsal aspect of middle finger phalanx as quickly as possible in response to disappearance of the blue circle without looking at their hand or the button. Two seconds after the button press, reward/non-reward stimulus was randomly presented for 2-s duration. The reward stimulus was a picture of Japanese 10-yen coin, and each subject received monetary reward at the end of experiment. Subjects were not informed of the reward probabilities. We delivered transcranial magnetic stimulation of the left M1 at the midpoint between center of gravities of agonist flexor carpi radialis (FCR) and antagonist extensor carpi radialis (ECR) muscles at 2 s after the red fixation cross and 1 s after the reward/non-reward stimuli. Relative motor evoked potential (MEP) amplitudes at 2 s after the red fixation cross were significantly higher for 10% reward probability than for 90% reward probability, whereas relative MEP amplitudes at 1 s after reward/non-reward stimuli were significantly higher for 90% reward probability than for 10% and 50% reward probabilities. These results implied that reward could affect the horizontal intracortical projections in M1 for agonist and antagonist muscles, and M1 excitability including the reward-related circuit before and after reward stimulus could be differently altered by reward probability.

We investigated whether anodal transcranial direct current stimulation (tDCS) applied to the motor cortex during non-exhaustive active or passive movements enhances corticomotor excitability after tDCS or whether it reduces post-exercise depression (PED) after non-exhaustive active or passive movements if PED was observed without tDCS. Nine healthy subjects participated in this study. Anodal tDCS with a current of 2 mA was applied to the left scalp over the primary motor area. All subjects underwent the following five interventions: tDCS delivered for 10 min during relaxation (tDCS condition) and repetitive voluntary and passive finger abduction-adduction movements, each performed without and with tDCS for 10 min (active condition, tDCS+active condition, passive condition, tDCS+passive condition). The active movements were performed at 10% maximum voluntary contraction. Motor evoked potentials (MEPs) were recorded from the right first dorsal interosseus muscle before the intervention (pre-intervention) and 2 and 10 min after the intervention (post-2 min and post-10 min, respectively). Under the tDCS condition, the MEP amplitudes at post-2 and -10 min were significantly increased compared with those before the intervention. Under the active, passive, and tDCS+active conditions, the MEP amplitudes at post-2 min were significantly decreased compared with those before the interventions. Under the tDCS+passive condition, the MEP amplitude remained unchanged. These results demonstrated that anodal tDCS did not reduce PED after active movements but after passive movements and that the anodal tDCS effects were highly dependent on the state of the subject during stimulation., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Objective: The aim of the present study was to investigate the effect of water immersion (WI) on short- and long-latency afferent inhibition (SAI and LAI), short-interval intracortical inhibition (SICI), and intracortical facilitation (ICF)., Methods: Motor evoked potentials (MEPs) were measured from the first dorsal interosseous (FDI) muscle of fifteen healthy males before, during, and after a 15-min WI at 30°C up to the axilla. Both SAI and LAI were evaluated by measuring MEPs in response to transcranial magnetic stimulation (TMS) of the left motor cortex following electrical stimulation of the right median nerve (fixed at about three times the sensory threshold) at interstimulus intervals (ISIs) of 20 ms to assess SAI and 200 ms to assess LAI. The paired-pulse TMS paradigm was used to measure SICI and ICF., Results: Both SAI and LAI were reduced during WI, while SICI and ICF were not significantly different before, during, and after WI., Conclusions: WI decreased SAI and LAI by modulating the processing of afferent inputs., Significance: Changes in somatosensory processing and sensorimotor integration may contribute to the therapeutic benefits of WI for chronic pain or movement disorders., (Copyright © 2013 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.)

Background: The cortical silent period (CSP) elicited by transcranial magnetic stimulation (TMS) is affected by changes in TMS intensity. Some studies have shown that CSP is shortened or prolonged by short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF), Those studies, however, used different TMS intensities to adjust the amplitude of the motor evoked potential (MEP). Therefore, it is unclear whether changes in CSP duration are induced by changes in TMS intensities or by SICI and ICF. The purpose of this study was to confirm the effects of muscle contractions and stimulus intensities on MEP amplitude and the duration of CSP induced by single-pulse TMS and to clarify the effects of SICI and ICF on CSP duration.MEP evoked by TMS was detected from the right first dorsal interosseous muscle in 15 healthy subjects. First, MEP and CSP were induced by single-pulse TMS with an intensity of 100% active motor threshold (AMT) at four muscle contraction levels [10%, 30%, 50%, and 70% electromyogram (EMG)]. Next, MEP and CSP were induced by seven TMS intensities (100%, 110%, 120%, 130%, 140%, 150%, and 160% AMT) during muscle contraction of 10% EMG. Finally, SICI and ICF were recorded at the four muscle contraction levels (0%, 10%, 30%, and 50% EMG)., Results: MEP amplitudes increased with increases in muscle contraction and stimulus intensity. However, CSP duration did not differ at different muscle contraction levels and was prolonged with increases in stimulus intensity. CSP was shortened with SICI compared with CSP induced by single-pulse TMS and with ICF at all muscle contraction levels, whereas CSP duration was not significantly changed with ICF., Conclusions: We confirmed that CSP duration is affected by TMS intensity but not by the muscle contraction level. This study demonstrated that CSP is shortened with SICI, but it is not altered with ICF. These results indicate that after SICI, CSP duration is affected by the activity of inhibitory intermediate neurons that are activated by the conditioning SICI stimulus.

Reciprocal inhibition of antagonist muscles is crucial for motor skill learning in humans. However, the changes in reciprocal inhibition function during the motor learning process are unknown. The aim of this study was to systematically observe the changes in reciprocal inhibition function. We investigated the optimal coil position for simultaneously eliciting motor evoked potentials (MEPs) of reciprocal muscles, and the reciprocal changes in input-output (IO) curves during motor skill training. From ten healthy volunteers, the IO curves of MEPs were measured for the midpoint between the center of gravity (CoG) of the extensor carpi radialis (ECR) and the flexor carpi radialis (FCR) muscles, for the CoG of ECR, and for the FCR muscles using transcranial magnetic stimulation (TMS). In addition, the IO curves of the ECR and the FCR muscles were measured before and after the motor skill training of rapid wrist extension. The IO curves measured at the midpoint between the CoGs of the ECR and the FCR muscles and the CoG of each muscle were homogenous. However, after training to perform rapid wrist extension, the IO curve of the agonist (ECR) muscle was increased, while the antagonist (FCR) muscle was decreased. The present findings validate the IO curves simultaneously measured for reciprocal muscles, and suggest that motor skill training could induce reciprocal change in corticospinal excitability., (Copyright © 2012 Elsevier B.V. All rights reserved.)

We examined the amplitude and latency of movement-related cerebral field (MRCF) waveforms, the generator and afferent feedback of movement-evoked field 1 (MEF1), and the relationship between motor field neuromagnetic activity and electromyographic activity during performance of two types of voluntary index extension. Eight healthy, right-handed male volunteers participated in this study. Experiments for each subject consisted of recording of MRCFs following two types of finger movement. One (Task 1) involved voluntary extension of the right index finger to about 40 degrees . In the second (Task 2), an elastic band was placed on the right index fingertip, producing a resistance of about 1.5 times the electromyographic activity associated with the voluntary movement yielding extension to approximately 40 degrees . Peak amplitude and the ECD moment of the motor field differed significantly between the two tasks. In Task 2, the electromechanical delay from EMG onset to movement onset (77.8+/-16.2) was longer than in Task 1 (44.4+/-10.4). However, the latency from EMG onset to MEF1 peak was 87.6+/-8.5 ms in Task 2, and did not differ significantly from that in Task 1 (88.6+/-8.5). The ECDs of MEF1 were located significantly medial to N20 m and lateral and posterior to the motor field. These findings suggest that the ECD of MEF1 is located in area 3b, but is slightly different from N20 m, and that this MEF1 component activation is due not to the onset of joint movement but to that of muscular contraction.