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Abstract In transcranial static magnetic field stimulation (tSMS), a strong and small magnet placed over the head can modulate cortical functions below the magnet as well as those in the region remote from the magnet. We studied the neuromodulation induced by tSMS using transcranial magnetic stimulation (TMS) combined with simultaneous electroencephalography (EEG) to clarify the neurophysiological underpinnings of tSMS. tSMS or sham stimulation was applied over the left primary motor cortex (M1) for 20 min in 15 healthy subjects. Single pulse TMS was delivered over the left M1 before and after the intervention, while recording EEG. The amplitude around the P30 of the TMS-evoked potentials (TEPs) in the left primary sensorimotor area (SM1) significantly decreased after the real tSMS, and that around the N60 of the TEPs in the right SM1 significantly increased after the real tSMS. In addition, the alpha power of the TMS-induced oscillatory responses (IORs) in the left and right SM1 significantly decreased after the real tSMS. TMS-EEG is a powerful tool for studying local and global cortical reactivity to external stimuli at high temporal resolution. tSMS altered TEPs and IORs both at the stimulated cortex and at the contralateral cortex. These findings would be related to the neurophysiological mechanisms underlying the neuromodulation induced by tSMS.

Background: Grating orientation discrimination (GOD) is commonly used to assess somatosensory spatial processing. It allows discrimination between parallel and orthogonal orientations of tactile stimuli applied to the fingertip. Despite its widespread application, the underlying mechanisms of GOD, particularly the role of cortico-cortical interactions and local brain activity in this process, remain elusive. Therefore, we aimed to investigate how a specific cortico-cortical network and inhibitory circuits within the primary somatosensory cortex (S1) and secondary somatosensory cortex (S2) contribute to GOD. Methods: In total, 51 healthy young adults were included in our study. We recorded resting-state magnetoencephalography (MEG) and somatosensory-evoked magnetic field (SEF) in participants with open eyes. We converted the data into a source space based on individual structural magnetic resonance imaging. Next, we estimated S1- and S2-seed resting-state functional connectivity (rs-FC) at the alpha and beta bands through resting-state MEG using the amplitude envelope correlation method across the entire brain (i.e., S1/S2-seeds × 15,000 vertices × two frequencies). We assessed the inhibitory response in the S1 and S2 from SEFs using a paired-pulse paradigm. We automatically measured the GOD task in parallel and orthogonal orientations to the index finger, applying various groove widths with a custom-made device. Results: We observed a specific association between the GOD threshold (all P < 0.048) and the alpha rs-FC in the S1–superior parietal lobule and S1–adjacent to the parieto-occipital sulcus (i.e., lower rs-FC values corresponded to higher performance). In contrast, no association was observed between the local responses and the threshold. Discussion: The results of this study underpin the significance of specific cortico-cortical networks in recognizing variations in tactile stimuli.

Abstract Background The mechanical tactile stimulation, such as plastic pins and airflow-driven membrane, induces cortical activity. The cortical activity depends on the mechanical tactile stimulation pattern. Therefore, the stimulation pattern of mechanical tactile stimuli intervention may influence its effect on the somatosensory function. However, the effect of the mechanical tactile stimulation input pattern on the somatosensory function has not yet been investigated at the behavioral level. The present study aimed to clarify the effects of mechanical tactile stimuli intervention with different stimulation patterns on the ability to discriminate moving directions. Results Twenty healthy adults participated in the experiment. Three conditions were used for mechanical tactile stimuli intervention: (1) the whole stimulus surface was stimulated, (2) the stimulus moved within the stimulus surface, and (3) a no-stimulus condition. The effects of mechanical tactile stimuli intervention on tactile discrimination were evaluated using a simple reaction task and a choice reaction task to discriminate the movement direction. Reaction time, correct rate, and rate correct score were calculated to measure task performance. We examined the effects of mechanical tactile stimuli intervention on the ability to discriminate the moving direction for a certain period under three intervention conditions. The results showed that the mean reaction time during the simple reaction task did not differ significantly before and after the intervention under all intervention conditions. Similarly, we compared the data obtained before and after the intervention during the choice reaction task. Our results revealed that the mean reaction time and correct rate did not differ significantly under vertical and horizontal conditions. However, the rate correct score showed a significant improvement after the horizontal moving tactile stimulation intervention under both vertical and horizontal conditions. Conclusions Our results showed that the effect of mechanical tactile stimuli intervention on mechanical tactile stimulation moving direction discrimination function depended on the input pattern of mechanical tactile stimuli intervention. Our results suggest the potential therapeutic benefits of sustained tactile stimulation intervention. This study revealed that it is possible to change behavioral levels via mechanical tactile stimuli intervention as well as the potential of mechanical tactile stimuli intervention in the field of rehabilitation.

Transcranial alternating current stimulation (tACS) is a noninvasive method for brain stimulation that artificially modulates oscillatory brain activity in the cortical region directly beneath the electrodes by applying a weak alternating current. Beta (β) oscillatory activity in the supplementary motor area (SMA) is involved in motor planning and maintenance, whereas gamma (γ) oscillatory activity is involved in the updating of motor plans. However, the effect of applying tACS to the SMA on motor learning has not yet been investigated. This study assessed the effects of applying tACS to the SMA on motor learning. Forty-two right-handed healthy adults (age 20.6 ± 0.5 years, 24 men and 18 women) were included. Motor learning was assessed using a visuomotor tracking task with pinch tension of the right thumb and right forefinger. Each trial lasted 60 s, and the error rates were measured. Conductive rubber electrodes were attached to the SMA and the left shoulder for tACS. Stimulation was applied at an intensity of 1.0 mA and frequencies of 70 and 20 Hz in the γ-tACS and β-tACS treatment groups, respectively. The sham group was only administered a fade-in/out. The visuomotor tracking task was performed for 10 trials before tACS and 10 trials after tACS. Two trials were conducted on the following day to determine motor skill retention. The average deviation measured during 60 s was considered the error value. Pre-stimulation learning rate was calculated as the change in error rate. Post-stimulation learning rate and retention rate were calculated as the change in error rate after stimulation and on the day after stimulation, respectively. In both the stimulation groups, differences in pre-stimulation learning, post-stimulation learning, and retention rates were not significant. However, in the γ-tACS group, baseline performance and pre-stimulation learning rate were positively correlated with post-stimulation learning rate. Therefore, applying γ-tACS to the SMA can increase post-stimulation learning rate in participants exhibiting low baseline performance and high pre-stimulation learning rate. Our findings suggest that motor learning can be effectively enhanced by applying γ-tACS to the SMA based on an individual’s motor and learning abilities.

Abstract This study aimed to evaluate the effects of the participant’s attention target during repetitive passive movement (RPM) intervention on reciprocal inhibition (RI) and joint movement function. Twenty healthy adults participated in two experiments involving four attention conditions [control (forward attention with no RPM), forward attention (during RPM), monitor attention (monitor counting task during RPM), ankle joint attention (ankle movement counting task during RPM)] during 10-min RPM interventions on the ankle joint. Counting tasks were included to ensure the participant’s attention remained on the target during the intervention. In Experiment 1, RI was measured before, immediately after, and 5, 10, 15, 20, and 30 min after the RPM intervention. In Experiment 2, we evaluated ankle joint movement function at the same time points before and after RPM intervention. The maximum ankle dorsiflexion movement (from 30° plantar flexion to 10° dorsiflexion) was measured, reflecting RI. In Experiment 1, the RI function reciprocal Ia inhibition was enhanced for 10 min after RPM under all attention conditions (excluding the control condition. D1 inhibition was enhanced for 20 min after RPM in the forward and monitor attention conditions and 30 min after RPM in the ankle joint attention condition. In Experiment 2, the joint movement function decreased under the forward and monitor attention conditions but improved under the ankle joint attention condition. This study is the first to demonstrate that the participant’s attention target affected the intervention effect of the RI enhancement method, which has implications for improving the intervention effect of rehabilitation.

BackgroundAutonomous sensory meridian response (ASMR) is a sensory response such as tingling and pleasantness from audiovisual stimuli. ASMR videos come in a wide variety of types, and personal preferences are biased. There are many reports of the effects os ASMR on sleep onset, anxiety relief, and other relaxation effects. However, prior task-oriented studies have used ASMR videos provided by the experimenter. We hypothesized that ASMR movies of a personal preference would show significantly increased activity in the nucleus accumbens, frontal cortex, and insular cortex, which are brain areas associated with relaxation. Therefore, the purpose of this study was to elucidate the neuroscientific basis for the relaxation effects of ASMR videos that match someone’s personal preferences.MethodsThis study included 30 healthy individuals aged ≥18 years. ASMR enthusiasts were included as the target population due to the need to have a clear preference for ASMR videos. A control video (1 type) and ASMR videos (20 types) were used as the stimulus tasks. Among the ASMR videos, those with high and low evaluation scores were considered liked and dislikedASMR videos, respectively. Functional magnetic resonance imaging was performed while the participants viewed a block design with a resting task in between. The data were analyzed using Statistical Parametric Mapping 12 to identify the areas activated by control, disliked, and liked ASMR videos.ResultsEmotion-related areas (the amygdala, frontal cortex, and insular cortex) not activated by control and unliked ASMR videos were activated only by liked ASMR videos.ConclusionThe amygdala, frontal cortex, and insular cortex may be involved in the limbic dopamine circuits of the amygdala and middle frontal gyrus and the autonomic balance of the left and right insular cortices. This suggests the potential of positive mood and its use as a treatment for patients with anxiety and depression. These results suggest that the use of ASMR videos to match individual preferences may induce relaxation and have beneficial effects on depression and other disorders, and also support the introduction of ASMR videos in mental health care.

Abstract Background Transcranial static magnetic field stimulation (tSMS) using a small and strong neodymium (NdFeB) magnet can temporarily suppress brain functions below the magnet. It is a promising non-invasive brain stimulation modality because of its competitive advantages such as safety, simplicity, and low-cost. However, current tSMS is insufficient to effectively stimulate deep brain areas due to attenuation of the magnetic field with the distance from the magnet. The aim of this study was to develop a brand-new tSMS system for non-invasive deep brain stimulation. Methods We designed and fabricated a triple tSMS system with three cylindrical NdFeB magnets placed close to each other. We compared the strength of magnetic field produced by the triple tSMS system with that by the current tSMS. Furthermore, to confirm its function, we stimulated the primary motor area in 17 healthy subjects with the triple tSMS for 20 min and assessed the cortical excitability using the motor evoked potential (MEP) obtained by transcranial magnetic stimulation. Results Our triple tSMS system produced the magnetic field sufficient for neuromodulation up to 80 mm depth from the magnet surface, which was 30 mm deeper than the current tSMS system. In the stimulation experiment, the triple tSMS significantly reduced the MEP amplitude, demonstrating a successful inhibition of the M1 excitability in healthy subjects. Conclusion Our triple tSMS system has an ability to produce an effective magnetic field in deep areas and to modulate the brain functions. It can be used for non-invasive deep brain stimulation.

BackgroundAutonomous sensory meridian response (ASMR) is the sensation of tingling from audiovisual stimuli that leads to positive emotions. ASMR is used among young people to relax, induce sleep, reduce stress, and alleviate anxiety. However, even without experiencing tingling, ASMR is used by many young people to seek relaxation. Auditory stimulation in ASMR is thought to play the most important role among its triggers, and previous studies have used a mixture of auditory and visual stimulation and auditory stimulation. This is the first study to approach the differences between the effects of direct audiovisual and auditory stimulation from the perspective of brain function using functional magnetic resonance imaging (fMRI) and to clarify the effects of ASMR, which attracts many young people.MethodsThe subjects were 30 healthy subjects over 19 years old or older who had not experienced tingling. Brain function was imaged by fMRI while watching ASMR videos or listening to the sound files only. We administered a questionnaire based on a Likert scale to determine if the participants felt a “relaxed mood” and “tingling mood” during the task.ResultsSignificant activation was found in the visual cortex for audiovisual stimulation and in the visual and auditory cortex for auditory stimulation. In addition, activation of characteristic sites was observed. The specific sites of activation for audiovisual stimulation were the middle frontal gyrus and the left nucleus accumbens, while the specific sites of activation for auditory stimulation were the bilateral insular cortices. The questionnaire showed no significant differences in either “relaxed mood” or “tingling mood” in response to auditory and visual stimulation or auditory stimulation alone.ConclusionThe results of this study showed that there was a clear difference between auditory and audiovisual stimulation in terms of the areas of activation in the brain, but the questionnaire did not reveal any difference in the subjects’ mood. Audiovisual stimulation showed activation of the middle frontal gyrus and the nucleus accumbens, whereas auditory stimulation showed activation of the insular cortex. This difference in brain activation sites suggests a difference in mental health effects between auditory and audiovisual stimulation. However, future research on comparisons between those who experience tingling and those who do not, as well as investigations of physiological indices, and examination of the relationship with activated areas in the brain may show that ASMR is useful for mental health.

IntroductionIt is widely known that motor learning changes the excitability of the primary motor cortex. More recently, it has been shown that the primary somatosensory cortex (S1) also plays an important role in motor learning, but the details have not been fully examined. Therefore, we investigated how motor skill training affects somatosensory evoked potential (SEP) in 30 neurologically healthy subjects.MethodsSEP N20/P25_component and N20/P25 SEP paired-pulse depression (SEP-PPD) were assessed before and immediately after complex or simple visuomotor tasks.ResultsMotor learning was induced more efficiently by the complex visuomotor task than by the simple visuomotor task. Both the N20/P25 SEP amplitude and N20/P25 SEP-PPD increased significantly immediately after the complex visuomotor task, but not after the simple visuomotor task. Furthermore, the altered N20/P25 SEP amplitude was associated with an increase in motor learning efficiency.ConclusionThese results suggest that motor learning modulated primary somatosensory cortex excitability.

The purpose of this study was to examine whether anodal transcranial direct current stimulation (a-tDCS) over the posterior parietal cortex (PPC) could affect visuomotor performance and proprioception in the lower extremities. We evaluated visuomotor performance in 15 healthy volunteers using a visuomotor control task by plantar dorsiflexion of the ankle joint, and calculated the absolute difference between the target and measured angle. In addition, we evaluated proprioception using a joint position matching task. During the task, the subject reproduced the ankle joint plantar dorsiflexion angle presented by the examiner. We calculated the absolute difference between the presented and measured angles (absolute error) and the variation of measured angles (variable error). Simultaneously, a-tDCS (1.5 mA, 15 min) or sham stimulation was applied to the right PPC. We observed that the absolute error of the visuomotor control task and the variable error of the joint position matching task significantly decreased after a-tDCS. However, the absolute error of the joint position matching task was not affected. This study suggests that a-tDCS over the PPC improves visuomotor performance and reduces the variable error in the joint position matching task.

Abstract Long-term skills training is known to induce neuroplastic alterations, but it is still debated whether these changes are always modality-specific or can be supramodal components. To address this issue, we compared finger-targeted somatosensory-evoked and auditory-evoked potentials under both Go (response) and Nogo (response inhibition) conditions between 10 baseball players, who require fine hand/digit skills and response inhibition, to 12 matched track and field (T&F) athletes. Electroencephalograms were obtained at nine cortical electrode positions. Go potentials, Nogo potentials, and Go/Nogo reaction time (Go/Nogo RT) were measured during equiprobable somatosensory and auditory Go/Nogo paradigms. Nogo potentials were obtained by subtracting Go trial from Nogo trial responses. Somatosensory Go P100 latency and Go/Nogo RT were significantly shorter in the baseball group than the T&F group, while auditory Go N100 latency and Go/Nogo RT did not differ between groups. Additionally, somatosensory subtracted Nogo N2 latency was significantly shorter in the baseball group than the T&F group. Furthermore, there were significant positive correlations between somatosensory Go/Nogo RT and both Go P100 latency and subtracted Nogo N2 latency, but no significant correlations among auditory responses. We speculate that long-term skills training induce predominantly modality-specific neuroplastic changes that can improve both execution and response inhibition.

Background: Autonomous sensory meridian response (ASMR) is used by young people to induce relaxation and sleep and to reduce stress and anxiety; it comprises somatosensation caused by audiovisual stimuli (triggers) that lead to positive emotions. Auditory stimuli play the most important role among the triggers involved in ASMR and have been reported to be more triggering than visual stimuli. On the other hand, classical music is also known to have a relaxing effect. This is the first study to clarify the difference in brain activation associated with relaxation effects between ASMR and classical music by limiting ASMR to auditory stimulation alone.Methods: Thirty healthy subjects, all over 20 years of age, underwent fMRI while listening to ASMR and classical music. We compared the differences in brain activation associated with classical music and ASMR stimulation. After the experiment, the subjects were administered a questionnaire on somatosensation and moods. After the experiment, the participants were asked whether they experienced ASMR somatosensation or frisson. They were also asked to rate the intensity of two moods during stimulation: “comfortable mood,” and “tingling mood”.Result: The results of the questionnaire showed that none of the participants experienced any ASMR somatosensation or frisson. Further, there was no significant difference in the ratings given to comfort mood, but there was a significant difference in those given to tingling mood. In terms of brain function, classical music and ASMR showed significant activation in common areas, while ASMR showed activation in more areas, with the medial prefrontal cortex being the main area of activation during ASMR.Conclusion: Both classical music and the ASMR auditory stimulus produced a pleasant and relaxed state, and ASMR involved more complex brain functions than classical music, especially the activation of the medial prefrontal cortex. Although ASMR was limited to auditory stimulation, the effects were similar to those of listening to classical music, suggesting that ASMR stimulation can produce a pleasant state of relaxation even if it is limited to the auditory component, without the somatic sensation of tingling. ASMR stimulation is easy to use, and appropriate for wellness purposes and a wide range of people.

Techniques of non-invasive brain stimulation (NIBS) of the human primary motor cortex (M1) are widely used in basic and clinical research to induce neural plasticity. The induction of neural plasticity in the M1 may improve motor performance ability in healthy individuals and patients with motor deficit caused by brain disorders. However, several recent studies revealed that various NIBS techniques yield high interindividual variability in the response, and that the brain-derived neurotrophic factor (BDNF) genotype (i.e., Val/Val and Met carrier types) may be a factor contributing to this variability. Here, we conducted a systematic review of all published studies that investigated the effects of the BDNF genotype on various forms of NIBS techniques applied to the human M1. The motor-evoked potential (MEP) amplitudes elicited by single-pulse transcranial magnetic stimulation (TMS), which can evaluate M1 excitability, were investigated as the main outcome. A total of 1,827 articles were identified, of which 17 (facilitatory NIBS protocol, 27 data) and 10 (inhibitory NIBS protocol, 14 data) were included in this review. More than two-thirds of the data (70.4–78.6%) on both NIBS protocols did not show a significant genotype effect of NIBS on MEP changes. Conversely, most of the remaining data revealed that the Val/Val type is likely to yield a greater MEP response after NIBS than the Met carrier type in both NIBS protocols (21.4–25.9%). Finally, to aid future investigation, we discuss the potential effect of the BDNF genotype based on mechanisms and methodological issues.

This study aimed to determine how transcutaneous vagus nerve stimulation (tVNS) alters autonomic nervous activity by comparing the effects of different tVNS frequencies and current intensities. We also investigated the sex-dependent autonomic response to tVNS. Thirty-five healthy adult participants were stimulated using a tVNS stimulator at the left cymba conchae while sitting on a reclining chair; tVNS-induced waveform changes were then recorded for different stimulus frequencies (Experiment 1: 3.0 mA at 100 Hz, 25 Hz, 10 Hz, 1 Hz, and 0 Hz (no stimulation)) and current intensities (Experiment 2: 100 Hz at 3.0 mA, 1.0 mA, 0.2 mA (below sensory threshold), and 0 mA (no stimulation)) using an electrocardiogram. Pulse widths were set at 250 µs in both experiment 1 and 2. Changes in heart rate (HR), root-mean-square of the difference between two successive R waves (RMSSD), and the ratio between low-frequency (LF) (0.04–0.15 Hz) and high-frequency (HF) (0.15–0.40 Hz) bands (LF/HF) in spectral analysis, which indicates sympathetic and parasympathetic activity, respectively, in heart rate variability (HRV), were recorded for analysis. Although stimulation at all frequencies significantly reduced HR (p = 0.001), stimulation at 100 Hz had the most pronounced effect (p = 0.001) in Experiment 1 and was revealed to be required to deliver at 3.0 mA in Experiment 2 (p = 0.003). Additionally, participants with higher baseline sympathetic activity experienced higher parasympathetic response during stimulation, and sex differences may exist in the autonomic responses by the application of tVNS. Therefore, our findings suggest that optimal autonomic changes induced by tVNS to the left cymba conchae vary depending on stimulating parameters and sex.

Abstract Introduction Spontaneous oscillations in the somatosensory cortex, especially of the alpha (8 − 14 Hz) and gamma (60 − 80 Hz) frequencies, affect tactile perception; moreover, these oscillations can be selectively modulated by frequency‐matched transcranial alternating current stimulation (tACS) on the basis of ongoing oscillatory brain activity. To examine whether tACS can actually improve tactile perception via alpha and gamma modulation, we measured the effects of 10‐Hz and 70‐Hz tACS (α‐ and γ‐tACS) on the left somatosensory cortex on right‐finger tactile spatial orientation discrimination, and the associations between performance changes and individual alpha and gamma activities. Methods Fifteen neurologically healthy subjects were recruited into this study. Electroencephalography (EEG) was performed before the first day, to assess the normal alpha‐ and gamma‐activity levels. A grating orientation discrimination task was performed before and during 10‐Hz and 70‐Hz tACS. Results The 10‐Hz tACS protocol decreased the grating orientation discrimination threshold, primarily in subjects with low alpha event‐related synchronization (ERS). In contrast, the 70‐Hz tACS had no effect on the grating orientation discrimination threshold. Conclusions This study showed that 10‐Hz tACS can improve tactile orientation discrimination in subjects with low alpha activity. Alpha‐frequency tACS may help identify the contributions of these oscillations to other neurophysiological and pathological processes.

A decrease in cortical excitability tends to be easily followed by an increase induced by external stimuli via a mechanism aimed at restoring it; this phenomenon is called “homeostatic plasticity.” In recent years, although intervention methods aimed at promoting motor learning using this phenomenon have been studied, an optimal intervention method has not been established. In the present study, we examined whether subsequent motor learning can be promoted further by a repetitive passive movement, which reduces the excitability of the primary motor cortex (M1) before motor learning tasks. We also examined the relationship between motor learning and the brain-derived neurotrophic factor. Forty healthy subjects (Val/Val genotype, 17 subjects; Met carrier genotype, 23 subjects) participated. Subjects were divided into two groups of 20 individuals each. The first group was assigned to perform the motor learning task after an intervention consisting in the passive adduction–abduction movement of the right index finger at 5 Hz for 10 min (RPM condition), while the second group was assigned to perform the task without the passive movement (control condition). The motor learning task consisted in the visual tracking of the right index finger. The results showed that the corticospinal excitability was transiently reduced after the passive movement in the RPM condition, whereas it was increased to the level detected in the control condition after the motor learning task. Furthermore, the motor learning ability was decreased immediately after the passive movement; however, the motor performance finally improved to the level observed in the control condition. In individuals carrying the Val/Val genotype, higher motor learning was also found to be related to the more remarkable changes in corticospinal excitability caused by the RPM condition. This study revealed that the implementation of a passive movement before a motor learning tasks did not affect M1 excitatory changes and motor learning efficiency; in contrast, in subjects carrying the Val/Val polymorphism, the more significant excitatory changes in the M1 induced by the passive movement and motor learning task led to the improvement of motor learning efficiency. Our results also suggest that homeostatic plasticity occurring in the M1 is involved in this improvement.

Changes in α-band cortical oscillatory activity (8–13 Hz) affect perception; however, how these changes in the left posterior parietal cortex (PPC) and primary somatosensory cortex (S1), which play different roles in determining the two-point discrimination (TPD) threshold, affect TPD threshold remains unelucidated. Therefore, to determine TPD threshold, we aimed to investigate the function of the left PPC and S1 by applying α-band transcranial alternating current stimulation (α-tACS; 10 Hz). TPD threshold was examined at the pad of the right index finger, contralateral to the stimulation site, in 17 healthy adults using a custom-made, computer-controlled, two-point tactile stimulation device, with random application of either active or sham α-tACS over the left PPC (Experiment 1) and left S1 (Experiment 2). Then, 50% TPD threshold was obtained in the active and sham conditions via logistic regression analysis. Afterward, we compared the difference between the active and sham conditions at 50% TPD threshold in each region and found that α-tACS reduced TPD threshold when applied over the left PPC (P = 0.010); however, its effect was insignificant when applied over the left S1 (P = 0.74). Moreover, a comparison of the change in 50% TPD threshold among the regions revealed that α-tACS applied over the left PPC significantly reduced TPD threshold compared with that applied over the left S1 (P = 0.003). Although we did not reveal the actual changes in cortical activity induced by α-tACS, this is the first empirical evidence that α-tACS applied over the left PPC and left S1 exerts region-specific effects on determining TPD threshold assessed in the contralateral index finger pad by stimulation.

Balance disorders are a risk factor for falls in the elderly population. Balance control involving the complex interaction among nervous, muscular, and sensory systems should be maintained to keep an upright posture and prevent falls. Vestibular sensation is one of the main senses essential for postural control. Noisy galvanic vestibular stimulation (nGVS) is a noninvasive stimulation method for vestibular organs. Recently, it has received increasing attention for the treatment of balance disorders. However, the effect of balance disorders on stimulus effect during the implementation of nGVS remains unknown. Therefore, this study aimed to determine the effects of different floor surface and visual conditions on the stimulus effects of the nGVS intervention. In this study, two experiments were conducted with 24 participants (12 each for Experiments 1 and 2). In Experiment 1, nGVS (0.4 mA; 0.1–640 Hz) was performed in the open-eyes standing position on a solid surface (nGVS condition) and in the closed-eye standing position on a foam rubber (nGVS + foam rubber condition). In Experiment 2, sham stimulation was performed under the same conditions as in Experiment 1, except for nGVS. Center of pressure (COP) sway was measured in all participants with them standing with open eyes at Pre and Post-1 (immediately after the intervention) and Post-2 (10 min after the measurement of post-1). In Experiment 1, under the nGVS condition, COP sway was significantly reduced in Post-1 and Post-2 compared with Pre. However, no significant difference was observed among Pre, Post-1, and Post-2 under the nGVS + foam rubber condition. Furthermore, the intervention effect was significantly greater in the nGVS condition than in the nGVS + foam rubber condition. In contrast, in Experiment 2, the COP sway did not significantly differ among Pre, Post-1, and Post-2 under either condition. Based on the results of this study, nGVS was found to be effective with open-eyes standing on a solid surface.

Elderly and stroke patients often have low spatial two-point discrimination function. The intervention effect of repetitive mechanical tactile stimulation has been shown to improve the spatial two-point discrimination function. The methods of tactile input are classified as either Active Touch or Passive Touch. In Passive Touch, the tactile stimulus is passively applied on the skin without voluntary movement, whereas in Active Touch, it is applied with voluntary movement. Based on the method of tactile input, tactile stimulation activate different cerebral cortex areas. A previous study reported that the tactile stimulation with Active Touch activate posterior parietal cortex, activated during a spatial two-point discrimination task. Therefore, the present study aimed to investigate the effects of two mechanical tactile stimulation intervention methods on two-point discrimination: tactile stimulation with voluntary movement (Active Touch) and without voluntary movement (Passive Touch). We recruited 15 healthy volunteers aged 20–23 years and applied tactile stimuli on their right index finger for 10 min. The mechanical tactile stimulator comprised 24 tiny plastic pins driven by piezoelectric actuators. In the Active Touch intervention, the pin was rubbed by voluntary movement of the right index finger (abduction 0°–10°) after the appearance of 12 pins. The Passive Touch intervention stimulated the index finger with the 12 pins setting at the centre of index finger. Tactile thresholds were measured using a two-point discrimination measurement device. Two-point discrimination threshold showed significant reduction after Active Touch intervention compared with those pre-intervention (Pre). Two-point discrimination threshold were not significantly modulated after Passive Touch intervention; however, significant negative correlation was observed between the intervention effect on two-point discrimination threshold and the performance Pre. This study suggesting that the effects of repetitive mechanical tactile stimulation depend on the method of tactile input. An effective intervention for improving two-point discrimination threshold is the application of Active Touch condition for 10 min.

Abstract Background Balance disorders are a risk factor for falls in the elderly. Although noisy galvanic vestibular stimulation (nGVS) has been reported to improve balance in young people, randomised control trials targeting community-dwelling elderly people have not been conducted to date. We aimed to assess the influence of nGVS on COP sway in the open-eye standing posture among community-dwelling elderly people in a randomised controlled trial. Methods A randomised controlled trial of 32 community-dwelling elderly people randomly assigned to control (sham stimulation) and an nGVS groups. All participants underwent centre of pressure (COP) sway measurements while standing with open eyes at baseline and during stimulation. The control group underwent sham stimulation and the nGVS group underwent noise stimulation (0.4 mA; 0.1–640 Hz). Results In the nGVS group, sway path length, mediolateral mean velocity and anteroposterior mean velocity decreased during stimulation compared with baseline (P

The aim of this study was to compare scapular kinematics between men and women during shoulder flexion, scapular plane elevation, and shoulder abduction. Eleven healthy men and 11 healthy women participated in this study. As participants performed shoulder flexion, scapular plane elevation, and abduction at a consistent speed, an electromagnetic motion capture system was used to analyze scapular motion. The change in scapular orientation from its resting position was calculated at 30°, 60°, 90° and 120° of humeral elevation. The study found that scapular upward rotation and posterior tilt angles increased significantly with each successive humeral elevation angle, but less so in women than in men. Scapular internal or external rotation differed significantly according to the plane of elevation, that is the scapula was internally rotated during flexion, with no change during scapular plane elevation, and it was externally rotated during abduction. This variation was more marked in women. This study revealed gender differences in scapular kinematics during shoulder motion. During shoulder elevation, the scapulothoracic joint played a greater role in men than in women, whereas the glenohumeral joint played a greater role in women.

Abstract Background In the present study, CFLs harvested from cadavers were categorized according to the differences in the angle of the CFL with respect to the long axis of the fibula and their shape, and then three-dimensional reconstructions of the CFLs were used to simulate and examine the differences in the angles of the CFLs with respect to the long axis of the fibula and how they affect CFL function. Methods The study sample included 81 ft from 43 Japanese cadavers. CFLs were categorized according to their angle with respect to the long axis of the fibula and the number of fiber bundles. Five categories were subsequently established: CFL20° (angle of the CFL with respect to the long axis of the fibula from 20° to 29°); CFL30° (range 30–39°); CFL40° (range 40–49°); CFL50° (range 50–59°); and CFL2 (CLFs with two crossing fiber bundles). Three-dimensional reconstructions of a single specimen from each category were then created. These were used to simulate and calculate CFL strain during dorsiflexion (20°) and plantarflexion (30°) on the talocrural joint axis and inversion (20°) and eversion (20°) on the subtalar joint axis. Results In terms of proportions for each category, CFL20° was observed in 14 ft (17.3%), with CFL30° in 22 ft (27.2%), CFL40° in 29 ft (35.8%), CFL50° in 15 ft (18.5%), and CFL2 in one foot (1.2%). Specimens in the CFL20° and CFL30° groups contracted with plantarflexion and stretched with dorsiflexion. In comparison, specimens in the CFL40°, CFL50°, and CFL2 groups stretched with plantarflexion and contracted with dorsiflexion. Specimens in the CFL20° and CFL2 groups stretched with inversion and contracted with eversion. Conclusions CFL function changed according to the difference in the angles of the CFLs with respect to the long axis of the fibula.

Motor evoked potentials (MEPs) evoked by transcranial magnetic stimulation (TMS) a few milliseconds after this cortical activity following electrical stimulation (ES) result in an inhibition comparable to that by TMS alone; this is called short-latency afferent inhibition (SAI). Cortical activity is observed after mechanical tactile stimulation (MS) and is affected by the number of stimuli by ES. We determined the effects of somatosensory stimulus methods and multiple conditioning stimuli on SAI in 19 participants. In experiment 1, the interstimulus intervals between the conditioning stimulation and TMS were 25, 27 and 29 ms for ES and 28, 30 and 32 ms for MS. In experiment 2, we used 1, 2, 3 and 4 conditioning stimulations of ES and MS. The interstimulus interval between the ES or MS and TMS was 27 or 30 ms, respectively. In experiment 1, MEPs were significantly decreased in both the ES and MS conditions. In experiment 2, MEPs after ES were significantly decreased in all conditions. Conversely, MEPs after MS were significantly decreased after one stimulus and increased after four stimulations, indicating the SAI according to the number of stimuli. Therefore, the somatosensory stimulus methods and multiple conditioning stimuli affected the SAI.

Recent studies have reported that acute aerobic exercise modulates intracortical excitability in the primary motor cortex (M1). However, whether acute low-intensity aerobic exercise can also modulate M1 intracortical excitability, particularly intracortical excitatory circuits, remains unclear. In addition, no previous studies have investigated the effect of acute aerobic exercise on short-latency afferent inhibition (SAI). The aim of this study was to investigate whether acute low-intensity aerobic exercise modulates intracortical circuits in the M1 hand and leg areas. Intracortical excitability of M1 (Experiments 1, 2) and spinal excitability (Experiment 3) were measured before and after acute low-intensity aerobic exercise. In Experiment 3, skin temperature was also measured throughout the experiment. Transcranial magnetic stimulation was applied over the M1 non-exercised hand and exercised leg areas in Experiments 1, 2, respectively. Participants performed 30 min of low-intensity pedaling exercise or rested while sitting on the ergometer. Short- and long-interval intracortical inhibition (SICI and LICI), and SAI were measured to assess M1 inhibitory circuits. Intracortical facilitation (ICF) and short-interval intracortical facilitation (SICF) were measured to assess M1 excitatory circuits. We found that acute low-intensity aerobic exercise decreased SICI and SAI in the M1 hand and leg areas. After exercise, ICF in the M1 hand area was lower than in the control experiment, but was not significantly different to baseline. The single motor-evoked potential, resting motor threshold, LICI, SICF, and spinal excitability did not change following exercise. In conclusion, acute low-intensity pedaling modulates M1 intracortical circuits of both exercised and non-exercised areas, without affecting corticospinal and spinal excitability.

Repetitive passive movement (PM) affects corticospinal excitability; however, it is unknown whether a duty cycle which repeats movement and rest, or subjects’ conscious attention to movements, affects corticospinal excitability. We aimed to clarify the effect of the presence or absence of a duty cycle and subjects’ attention on corticospinal excitability. Three experiments were conducted. In Experiment 1, PM of the right index finger was performed for 10 min. Three conditions were used: (1) continuous PM (cPM) at a rate of 40°/s; (2) intermittent PM (iPM) with a duty cycle at 40°/s; and (3) iPM at 100°/s. In conditions 1 and 3, motor evoked potential (MEP) amplitude was significantly reduced. In Experiment 2, PM was performed for 30 min: condition 1 comprised cPM at a rate of 40°/s and Condition 2 comprised iPM at 40°/s. MEP amplitude significantly decreased in both conditions. In Experiment 3, PM was performed for 10 min: condition 1 comprised paying attention to the moving finger during iPM and Condition 2 was similar to Condition 1 but while counting images on a monitor without looking at the movement finger, and Condition 3 comprised counting images on a monitor without performing PM. MEP amplitude significantly increased only under Condition 1. Thus, afferent input from movements above a certain threshold may affect corticospinal excitability reduction. Furthermore, corticospinal excitability increases when paying attention to passive finger movement.

Transcranial direct current stimulation (tDCS) and peripheral nerve electrical stimulation (PES) can change corticospinal excitability. tDCS can be used to non-invasively modulate the cerebral cortex's excitability by applying weak current to an electrode attached to the head, and the effect varies with the electrode's polarity. Previous studies have reported the effect of combined tDCS and PES on corticospinal excitability; when compared to single stimulation, combined stimulation increases cortical excitability. In contrast, another study reported that the effect of tDCS is attenuated by PES; hence, there is no consensus opinion on the effect on combined stimulation. Therefore, this study aimed to clarify the effect of combined tDCS and PES on corticospinal excitability. In Experiment 1, the combined stimulation of anodal tDCS and PES (anodal tDCS + PES) was performed, and in Experiment 2, a combined stimulation with PES, after cathodal tDCS (PES after cathodal tDCS), was performed using a homeostatic metaplasticity theoretical model. In Experiment 1, anodal tDCS produced a significant increase from baseline in motor-evoked potential (MEP) amplitude 10 min after stimulation, but no significant changes in MEP amplitude were observed with PES or the anodal tDCS + PES condition. Experiment 2 showed a significant decrease in MEP amplitude immediately after cathodal tDCS, and a significant increase in MEP amplitude 15 min after PES, but no significant change in MEP amplitude was observed with sequential PES following cathodal tDCS. In conclusion, our data indicate that PES with anodal tDCS suppressed the effect of tDCS. Also, PES after cathodal tDCS did not induce homeostatic metaplasticity and increase corticospinal excitability.

Introduction: Excessive co-contraction interferes with smooth joint movement. One mechanism is the failure of reciprocal inhibition against antagonists during joint movement. Reciprocal inhibition has been investigated using joint torque as an index of intensity during co-contraction. However, contraction intensity as an index of co-contraction intensity has not been investigated. In this study, we aimed to evaluate the influence of changes in contraction intensity during co-contraction on reciprocal inhibition.Methods: We established eight stimulus conditions in 20 healthy adult males to investigate the influence of changes in contraction intensity during co-contraction on reciprocal inhibition. These stimulus conditions comprised a conditioning stimulus-test stimulation interval (C–T interval) of -2, 0, 1, 2, 3, 4, or 5 ms plus a test stimulus without a conditioning stimulus (single). Co-contraction of the tibialis anterior and soleus muscles at the same as contraction intensity was examined at rest and at 5, 15, and 30% maximal voluntary contraction (MVC).Results: At 5 and 15% MVC in the co-contraction task, the H-reflex amplitude was significantly decreased compared with single stimulation at a 2-ms C–T interval. At 30% MVC, there was no significant difference compared with single stimulation at a 2-ms C–T interval. At a 5-ms C–T interval, the H-reflex amplitude at 30% MVC was significantly reduced compared with that at rest.Discussion: The findings indicated that during co-contraction, reciprocal Ia inhibition worked at 5 and 15% MVC. Contrary inhibition of reciprocal Ia inhibition did not apparently work at 30% MVC, and presynaptic inhibition (D1 inhibition) might work.

Objective This study aimed to investigate the correlation between the face scale and heart rate (HR), exercise load and oxygen uptake (V̇O2) during cardiopulmonary exercise testing.MethodsThis was a prospective, observational study of face scale rating of perceived exertion (RPE) and HR, exercise load and V̇O2 during cardiopulmonary exercise testing. A total of 30 healthy college men and 21 healthy college women were included. Subjects performed a cardiopulmonary exercise test with ramps and an increment increase in workload of 20 W/min. We recorded the responses of subjects using a face scale for RPE, HR, exercise load and V̇O2 every minute during the cardiopulmonary exercise test.Results In men, there was a significant positive correlation between the face scale RPE and HR (ρ=0.856, p

Older adults who have survived cancer experience significantly more falls compared with healthy adults. Adult cancer survivors may also have a lower balance function than healthy adults. We examined muscle strength and balance function among 19 cancer survivors and 14 healthy subjects. The mean age of the cancer survivors was 51.5 ± 11.2 years; 6 men and 13 women. Cancer diagnoses included breast cancer, retroperitoneal sarcoma, acute leukemia, lung cancer, colorectal cancer, thyroid cancer, Ewing’s sarcoma, and tongue cancer. The mean age of healthy subjects was 47.4 ± 14 years; 3 men, 11 women. Muscle strength was assessed using hand grip and knee extensor strength tests. Balance function was evaluated using the Timed Up and Go (TUG) test, and body sway was tested using a force platform. No significant differences were found with respect to right and left grip strength or right and left knee extension strength between the 2 groups. A significantly higher TUG time was observed in cancer survivors than in healthy subjects ( P < .05). With eyes open, the area of the center of pressure was significantly larger in cancer survivors than in healthy subjects ( P < .05). Similarly, the length per area was significantly lower both with eyes open and closed for cancer survivors than for healthy subjects ( P < .05). TUG was significantly correlated with muscle strength in both groups ( P < .05). However, no body sway parameters were related to muscle strength in either group. Cancer survivors had lower balance function that might not have been related to muscle strength. Cancer survivors should be evaluated for balance function as there is a potential for impairment. The findings of this study will be relevant for planning the prevention of falls for cancer survivors.

The Met allele of the brain-derived neurotrophic factor (BDNF) gene confers reduced cortical BDNF expression and associated neurobehavioral changes. BDNF signaling influences the survival, development, and synaptic function of cortical networks. Here, we compared gamma-aminobutyric acid (GABA)ergic network activity in the human primary motor cortex (M1) between the Met (Val/Met and Met/Met) and non-Met (Val/Val) genotype groups. Short- and long-interval intracortical inhibition, short-latency afferent inhibition (SAI), and long-latency afferent inhibition were measured using transcranial magnetic stimulation (TMS) as indices of GABAergic activity. Furthermore, the considerable inter-individual variability in inhibitory network activity typically measured by TMS may be affected not only by GABA but also by other pathways, including glutamatergic and cholinergic activities; therefore, we used 3-T magnetic resonance spectroscopy (MRS) to measure the dynamics of glutamate plus glutamine (Glx) and choline concentrations in the left M1, left somatosensory cortex, and right cerebellum. All inhibitory TMS conditions produced significantly smaller motor-evoked potentials than single-pulses. SAI was significantly stronger in the Met group than in the Val/Val group. Only the M1 Glx concentration was significantly lower in the Met group, while the BDNF genotype did not affect choline concentration in any region. Further, a positive correlation was observed between SAI and Glx concentrations only in M1. Our findings provide evidence that the BDNF genotype regulates both the inhibitory and excitatory circuits in human M1. In addition, lower Glx concentration in the M1 of Met carriers may alter specific inhibitory network on M1, thereby influencing the cortical signal processing required for neurobehavioral functions.

The mass and structure of bone tissue adapt to the mechanical loads imparted by gravity and movement, and are controlled by the balance between bone formation and bone resorption. The primary adaptations of bone to disuse are demineralization and loss (thinning) of trabecular and cortical bone. Exercise training and electrical muscle stimulation (ES) induce adaptive changes in bone that improve bone strength and inhibit bone loss. ES has been generally applied to patients undergoing physical rehabilitation to maintain and/or recover muscle mass and force-generating capacity in disused muscles. ES-induced muscle contraction of disused muscle can also ameliorate deleterious post-disuse adaptation of bone. The mechanical effects of ES-induced muscle contraction are essential for the maintenance of bone mass and strength, which are achieved through the cooperative functions of osteocytes, osteoblasts, and osteoclasts. The effects of ES, however, are dependent on the stimulation paradigm, including the intensity, frequency, and number of stimuli and the duration of the intervention. This review summarizes the literature on the effects of ES-induced muscle contraction on disuse osteopenia.

Magnetoencephalography is primarily sensitive to current sources tangential to the skull. Therefore, currents generated in area 3b of the primary somatosensory cortex (S1) and area 4 of primary motor cortex (M1) located on the posterior and anterior banks of the central sulcus, respectively, are easily detected. The movement-related cortical magnetic fields (MRCFs) following voluntary movement and the somatosensory magnetic fields (SEFs) generated by peripheral mixed nerve stimulation (e.g., median nerve) have been widely used to investigate the physiology of normal somatosensory cortical processing. Here, we describe the MRCFs produced by two types of movement (experiment 1) and the SEFs elicited by motor point stimulation (experiment 2), passive movement (experiments 3 and 4), and mechanical stimulation (experiments 5, 6, and 7). In addition, we examined the modulation of these fields.

Recent research has shown that the human motor cortex can be modulated by the application of static magnetic fields through the scalp. Transcranial static magnetic field stimulation (tSMS) has since received significant attention as a new non-invasive brain stimulation (NIBS) technique alongside conventional methods, such as repetitive transcranial magnetic stimulation and transcranial direct current stimulation. The advantages of the strong neodymium, iron and boron (NdFeB) magnet used in tSMS over other NIBS methods include the ease of use, absence of uncomfortable sensations for subjects, a lack of necessity for high operational skills and expensive devices, and conclusive sham stimulation allowing for controlled experiments and randomized controlled clinical trials. Hence, tSMS may be a new potential NIBS tool to modulate cerebral excitability.

This study aimed to investigate the relationship between relative or absolute intensity and changes in range of motion and passive stiffness after static stretching. A total of 65 healthy young adults voluntarily participated in this study and performed static stretching of the plantar flexor-muscle for 120 s. Dorsiflexion range of motion and passive torque during passive dorsiflexion before and after stretching were assessed. We measured the passive torque at a given angle when the minimum angle was recorded before and after stretching. The angle during stretching was defined as the absolute intensity. Dorsiflexion range of motion before stretching was defined as 100%, and the ratio (%) of the angle during stretching was defined as the relative intensity. A significant correlation was found between absolute intensity and change in passive torque at a given angle (r = −0.342), but relative intensity and range of motion (r = 0.444) and passive torque at dorsiflexion range of motion (r = 0.259). A higher absolute intensity of stretching might be effective in changing the passive properties of the muscle-tendon unit. In contrast, a higher relative intensity might be effective in changing the range of motion, which could be contributed by stretch tolerance.

The supplementary motor area (SMA) may modulate spinal reciprocal inhibition (RI) because the descending input from the SMA is coupled to interneurons in the spinal cord via the reticulospinal tract. Our study aimed to verify whether the anodal transcranial direct current stimulation (anodal-tDCS) of the SMA enhances RI. Two tDCS conditions were used: the anodal stimulation (anodal-tDCS) and sham stimulation (sham-tDCS) conditions. To measure RI, there were two conditions: one with the test stimulus (alone) and the other with the conditioning-test stimulation intervals (CTIs), including 2 ms and 20 ms. RI was calculated at multiple time points: before the tDCS intervention (Pre); at 5 (Int 5) and 10 min; and immediately after (Post 0); and at 5, 10 (Post 10), 15, and 20 min after the intervention. In anodal-tDCS, the amplitude values of H-reflex were significantly reduced for a CTI of 2 ms at Int 5 to Post 0, and a CTI of 20 ms at Int 5 to Pot 10 compared with Pre. Stimulation of the SMA with anodal-tDCS for 15 min activated inhibitory interneurons in RIs by descending input from the reticulospinal tract via cortico–reticulospinal projections. The results showed that 15 min of anodal-tDCS in the SMA enhanced and sustained RI in healthy individuals.

Somatosensory inputs induced by repetitive passive movement (RPM) modulate primary motor cortex (M1) excitability; however, it is unclear whether RPM affects primary somatosensory cortex (S1) excitability. In this study, we investigated whether RPM affects somatosensory evoked potentials (SEPs) and resting state brain oscillation, including alpha and beta bands, depend on RPM frequency. Nineteen healthy subjects participated in this study, and SEPs elicited by peripheral nerve electrical stimulation were recorded from the C3’ area in order to assess S1 excitability (Exp. 1: n = 15). We focused on prominent SEP components such as N20, P25 and P45-reflecting S1 activities. In addition, resting electroencephalograms (EEGs) were recorded from C3’ area to assess the internal state of the brain network at rest (Exp. 2: n = 15). Passive abduction/adduction of the right index finger was applied for 10 min at frequencies of 0.5, 1.0, 3.0, and 5.0 Hz in Exp. 1, and 1.0, 3.0, and 5.0 Hz in Exp. 2. No changes in N20 or P25 components were observed following RPM. The 3.0 Hz-RPM decreased the P45 component for 20 min (p < 0.05), but otherwise did not affect the P45 component. There was no difference in the alpha and beta bands before and after any RPM; however, a negative correlation was observed between the rate of change of beta power and P45 component at 3.0 Hz-RPM. Our findings indicated that the P45 component changes depending on the RPM frequency, suggesting that somatosensory inputs induced by RPM influences S1 excitability. Additionally, beta power enhancement appears to contribute to the P45 component depression in 3.0 Hz-RPM.

Transcranial alternating current stimulation (tACS) can be used to modulate oscillatory brain activity. In this study, we investigated whether tACS applied over the primary motor cortex (M1) and cerebellar cortex region improved motor performance. We applied tACS (1.0 mA) to 20 healthy adults while they performed an isometric force task with some visuomotor control using their right index finger. Gamma (70 Hz) oscillations in the Experiment 1 or beta (20 Hz) oscillations in the Experiment 2 were applied for 30 s over the left M1, right cerebellar hemisphere or both regions (“M1-Cerebellum”), and errors performing the task were compared. Beta-oscillation tACS did not affect motor performance. With the gamma-oscillation tACS, a negative correlation was found between the difference of error in the M1-Cerebellum condition and the number of errors in the sham condition (P = 0.005, Pearson’s r = −0.597), indicating that motor performance improved with M1-Cerebellum tACS for subjects with low motor performance in the sham condition. Those who performed poorly in the sham condition made significantly fewer errors with M1-Cerebellum tACS (P = 0.004). Thus, for subjects with poorer motor performance, tACS with gamma oscillations applied over the M1 and contralateral cerebellar hemisphere improved their performance.

Transcranial static magnetic field stimulation (tSMS) is a novel and inexpensive, non-invasive brain stimulation (NIBS) technique. Here, we performed non-invasive modulation of intra-epidermal electrical stimulation-evoked potentials (IES-EPs) by applying tSMS or sham stimulation over the primary motor (M1) and somatosensory (S1) cortices in 18 healthy volunteers for 15 min. We recorded EPs after IES before, right after, and 10 min after tSMS. The IES-EP amplitude was significantly reduced immediately after tSMS over M1, whereas tSMS over S1 and sham stimulation did not affect the IES-EP amplitude. Thus, tSMS may affect cortical nociceptive processing. Although the results of intervention for experimental acute pain in healthy subjects cannot be directly translated into the clinical situation, tSMS may be a potentially useful NIBS method for managing chronic pain, in addition to standard of care treatments.

We investigated the effects of different patterns of mechanical tactile stimulation (MS) on corticospinal excitability by measuring the motor-evoked potential (MEP). This was a single-blind study that included nineteen healthy subjects. MS was applied for 20 min to the right index finger. MS intervention was defined as simple, lateral, rubbing, vertical, or random. Simple intervention stimulated the entire finger pad at the same time. Lateral intervention stimulated with moving between left and right on the finger pad. Rubbing intervention stimulated with moving the stimulus probe, fixed by protrusion pins. Vertical intervention stimulated with moving in the forward and backward directions on the finger pad. Random intervention stimulated to finger pad with either row protrudes. MEPs were measured in the first dorsal interosseous muscle to transcranial magnetic stimulation of the left motor cortex before, immediately after, and 5–20 min after intervention. Following simple intervention, MEP amplitudes were significantly smaller than preintervention, indicating depression of corticospinal excitability. Following lateral, rubbing, and vertical intervention, MEP amplitudes were significantly larger than preintervention, indicating facilitation of corticospinal excitability. The modulation of corticospinal excitability depends on MS patterns. These results contribute to knowledge regarding the use of MS as a neurorehabilitation tool to neurological disorder.

This study examined the effects of joint angle and passive movement direction on corticospinal excitability. The subjects were 14 healthy adults from whom consent could be obtained. We performed two experiments. In Experiment 1, we measured motor evoked potential (MEP) amplitude, F-wave and M-wave at 0° and 20° adduction during adduction or abduction movement, in the range of movement from 10° abduction to 30° adduction. In Experiment 2, MEPs were measured at static 0° and 20° adduction during passive adduction from 10° adduction to 30° adduction and static 20° adduction. MEP, F-waves and M-waves were recorded from the right first dorsal interosseous (FDI) muscle. Experiment 1 revealed significantly increased MEP amplitude at 0° during passive adduction compared to static 0° (p < 0.01). No other significant differences in MEP, M-wave and F-wave parameters were observed. In Experiment 2, MEP amplitude was significantly higher at 20° adduction during passive adduction compared with static 0° (p < 0.01). Based on these findings, it appears that fluctuations in MEP amplitude values during passive movement are not influenced by joint angle, but rather it is possible that it is due to intracortical afferent facilitation (AF) dependent on afferent input due to the start of movement and interstimulus interval (ISI) of transcranial magnetic stimulation (TMS).

Damage to the vestibular cerebellum results in dysfunctional standing posture control. Patients with cerebellum dysfunction have a larger sway in the center of gravity while standing compared with healthy subjects. Transcranial direct current stimulation (tDCS) is a noninvasive technique for selectively exciting or inhibiting specific neural structures with potential applications in functional assessment and treatment of neural disorders. However, the specific stimulation parameters for influencing postural control have not been assessed. In this study, we investigated the influence of tDCS when applied over the cerebellum on standing posture control. Sixteen healthy subjects received tDCS (20 min, 2 mA) over the scalp 2 cm below the inion. In experiment 1, all 16 subjects received tDCS under three stimulus conditions, Sham, Cathodal, and Anodal, in a random order with the second electrode placed on the forehead. In experiment 2, five subjects received cathodal stimulation only with the second electrode placed over the right buccinator muscle. Center of gravity sway was measured twice for 60 s before and after tDCS in a standing posture with eyes open and legs closed, and average total locus length, locus length per second, rectangular area, and enveloped area were calculated. In experiment 1, total locus length and locus length per second decreased significantly after cathodal stimulation but not after anodal or sham stimulation, while no tDCS condition influenced rectangular or enveloped areas. In experiment 2, cathodal tDCS again significantly reduced total locus length and locus length per second but not rectangular and enveloped areas. The effects of tDCS on postural control are polarity-dependent, likely reflecting the selective excitation or inhibition of cerebellar Purkinje cells. Cathodal tDCS to the cerebellum of healthy subjects can alter body sway (velocity).

Athletic training is known to induce neuroplastic alterations in specific somatosensory circuits, which are reflected by changes in somatosensory evoked potentials and event-related potentials. The aim of this study was to clarify whether specific athletic training also affects somatosensory Nogo potentials related to the inhibition of movements. The Nogo potentials were recorded at nine cortical electrode positions (Fz, Cz, Pz, F3, F4, C3, C4, P3 and P4) in 12 baseball players (baseball group) and in 12 athletes in sports, such as track and field events and swimming, that do not require response inhibition, such as batting for training or performance (sports group). The Nogo potentials and Go/Nogo reaction times (Go/Nogo RTs) were measured under a somatosensory Go/Nogo paradigm in which subjects were instructed to rapidly push a button in response to stimulus presentation. The Nogo potentials were obtained by subtracting the Go trial from the Nogo trial. The peak Nogo-N2 was significantly shorter in the baseball group than that in the sports group. In addition, the amplitude of Nogo-N2 in the frontal area was significantly larger in the baseball group than that in the sports group. There was a significant positive correlation between the latency of Nogo-N2 and Go/Nogo RT. Moreover, there were significant correlations between the Go/Nogo RT and both the amplitude of Nogo-N2 and Nogo-P3 (i.e., amplitude of the Nogo-potentials increases with shorter RT). Specific athletic training regimens may induce neuroplastic alterations in sensorimotor inhibitory processes.

Whole-body water immersion (WI) has been reported to change sensorimotor integration. However, primary motor cortical excitability is not affected by low-intensity afferent input. Here we explored the effects of whole-body WI and water flow stimulation (WF) on corticospinal excitability and intracortical circuits. Eight healthy subjects participated in this study. We measured the amplitude of motor-evoked potentials (MEPs) produced by single transcranial magnetic stimulation (TMS) pulses and examined conditioned MEP amplitudes by paired-pulse TMS. We evaluated short-interval intracortical inhibition (SICI) and intracortical facilitation (ICF) using the paired-TMS technique before and after 15-min intervention periods. Two interventions used were whole-body WI with water flow to the lower limbs (whole-body WF) and whole-body WI without water flow to the lower limbs (whole-body WI). The experimental sequence included a baseline TMS assessment (T0), intervention for 15 min, a second TMS assessment immediately after intervention (T1), a 10 min resting period, a third TMS assessment (T2), a 10 min resting period, a fourth TMS assessment (T3), a 10 min resting period, and the final TMS assessment (T4). SICI and ICF were evaluated using a conditioning stimulus of 90% active motor threshold and a test stimulus adjusted to produce MEPs of approximately 1-1.2 mV, and were tested at intrastimulus intervals of 3 and 10 ms, respectively. Whole-body WF significantly increased MEP amplitude by single-pulse TMS and led to a decrease in SICI in the contralateral motor cortex at T1, T2 and T3. Whole-body WF also induced increased corticospinal excitability and decreased SICI. In contrast, whole-body WI did not change corticospinal excitability or intracortical circuits.

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.

During submaximal isometric contraction, there are two different load types: production of a constant force against a rigid restraint (force task), and maintenance of position against a constant load (position task). Previous studies reported that the time to task failure during a fatigue task was twice as long in the force task compared with the position task. Sensory feedback processing may contribute to these differences. The purpose of the current study was to determine the influence of load types during static muscle contraction tasks on the gating effect, i.e., attenuation of somatosensory-evoked potentials (SEPs) and the cortical silent period (cSP). Ten healthy subjects contracted their right first dorsal interosseus muscle by abducting their index finger for 90 s, to produce a constant force against a rigid restraint that was 20% of the maximum voluntary contraction (force task), or to maintain a constant position with 10° abduction of the metacarpophalangeal joint against the same load (position task). Somatosensory evoked potentials (SEPs) were recorded from C3' by stimulating either the right ulnar or median nerve at the wrist while maintaining contraction. The cortical silent period (cSP) was also elicited by transcranial magnetic stimulation. Reduction of the amplitude of the P45 component of SEPs was significantly larger during the position task than during the force task and under control rest conditions when the ulnar nerve, but not the median nerve, was stimulated. The position task had a significantly shorter cSP duration than the force task. These results suggest the need for more proprioceptive information during the position task than the force task. The shorter duration of the cSP during the position task may be attributable to larger amplitude of heteronymous short latency reflexes. Sensorimotor modulations may differ with load type during constant finger force or position tasks.