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Perceptual learning generally improves with training intensity, but the number of training trials sufficient for transient and long-term improvement in tactile grating orientation task (GOT) discrimination has not been systematically studied. To define reliable trial numbers for tactile discrimination learning, we compared tactile orientation discrimination performance of the right-finger following 200 and 400 training trials. Fifty-one neurologically healthy subjects were recruited. Tactile spatial acuity for orientation (parallel or orthogonal to the long axis of the finger) across different grating frequencies was assessed before, immediately after, 30 min after, and 24 h after sessions consisting of 200 training trials (50/block × 4 blocks), 400 training trials (50/block × 8 blocks), or no training (sham control). Both the 200- and 400-trial training conditions reduced the grating orientation discrimination threshold at 24 h after training. In contrast, the control condition had no effect on the grating orientation discrimination threshold. There was a negative correlation between the baseline grating orientation discrimination threshold and training-induced change in threshold (improvement) following both 200 and 400 trials. Fewer GOT trials (200) substantially prolong tactile discrimination learning, presumably by promoting the consolidation of the underlying neuroplastic mechanisms. In this widely used perceptual learning paradigm, 200 and 400 training trials appear effective for inducing short-term and long-term perceptual memory.

Background Patients with chronic pain exhibit hypervigilance (heightened responsiveness to stimuli) to innocuous auditory stimuli as well as noxious stimuli. "Generalized hypervigilance" suggests that individuals who show heightened responsiveness to one sensory system also show hypervigilance to other modalities. However, research exploring the existence of generalized hypervigilance in healthy subjects is limited. Methods We investigated whether hypervigilance to pain is associated with auditory stimuli in healthy subjects using the pain vigilance and awareness questionnaire (PVAQ) and auditory change-related cortical responses (ACRs). ACRs are thought to reflect a change detection system, based on preceding sensory memory. We recorded ACRs under conditions that varied in terms of the accumulation of sensory memory as follows: short-ACR, with short preceding continuous stimuli and long-ACR, with long preceding continuous stimuli. In addition, the attention to pain (PVAQ-AP) and attention to changes in pain (PVAQ-ACP) subscales were evaluated. Results Amplitudes of long-ACR showed significant positive correlations with PVAQ-ACP, whereas those of short-ACR did not show any significant correlations. Conclusions Generalized hypervigilance may be observed even in healthy subjects. ACR may be a useful index to evaluate the hypervigilance state in the human brain.

Background: This study aimed to determine the relationship between exercise performance and spinal function based on clenching strength. Hypothesis: Low-intensity clenching contributes to joint movement, whereas high-intensity clenching contributes to joint fixation. Study Design: Randomized crossover trial. Level of Evidence: Level 3. Methods: Two experiments were conducted using 2 groups of 20 healthy adults. The 4 clenching conditions in experiment 1 were 0%, 12.5%, 25%, and 50% of the maximum voluntary contraction (MVC) of the masseter muscle. Experiment 2 consisted of 3 conditions: no-bite condition, moderate effort, and maximum effort (max condition). In experiment 1, spinal function and ankle dorsiflexion tasks were measured for each clenching condition, and the ankle dorsiflexion task was measured in experiment 2. Regarding spinal function, we measured spinal reciprocal inhibition (RI) and excitability of spinal anterior horn cells. For the ankle dorsiflexion task, ankle dorsiflexion MVC was performed for 3 seconds under each clenching condition. The items analyzed were reaction time, peak ankle dorsiflexion torque, and soleus (Sol)/tibialis anterior (TA) electromyography (EMG) ratio. Results: The results of experiment 1 illustrated that RI was significantly attenuated or eliminated with increasing clenching strength (>25% MVC). Spinal anterior horn cell excitability increased significantly with increasing clenching strength. The peak torque was significantly higher at 50% MVC than that at 0% MVC. In experiment 2, the peak torque was significantly higher under moderate and max conditions than no-bite condition, and the Sol/TA EMG ratio was significantly higher under max condition than that under moderate condition. Conclusion/Clinical Relevance: The results illustrated that during high-strength clenching (≥50% MVC), antagonist muscles are activated simultaneously to increase muscle strength. High-strength clenching improved kinetic performance (joint fixation), whereas low-strength clenching (

Noisy galvanic vestibular stimulation (nGVS) involves the application of a weak, noisy, electrical current to the vestibular end organs and their afferent nerves, through electrodes placed bilaterally over the mastoid process. Center of pressure (COP) sway was shown to decrease during nGVS under conditions of static standing posture. However, whether nGVS can improve balance functions other than the static standing posture remains unclear. This study aimed to elucidate the effects of nGVS on COP sway during one-legged standing. We randomly assigned 36 participants to either a control group (sham stimulation), a 0.2 mA group (nGVS at 0.2 mA), or a 0.4 mA group (nGVS at 0.4 mA). All participants were measured for COP sway standing on one leg, with open eyes, both before and during stimulation. In the 0.2 mA group, the sway path length, mediolateral mean velocity, and anteroposterior mean velocity decreased during stimulation compared with before stimulation. Conversely, no significant differences in COP sway were detected for either the control group or the 0.4 mA group. The stimulation effects for all COP sway parameters were significantly higher in the 0.2 mA group than in either the control group or the 0.4 mA group. The results of this study suggested that nGVS not only decreases COP sway during static standing postures but can also reduce COP sway during one-legged standing.

Transcranial alternating current stimulation (tACS) is a non-invasive method of brain stimulation that modulates oscillatory neural activity in the cortical area under the electrodes. Gamma (γ)-tACS applied over the primary motor cortex (M1) and cerebellar hemisphere is known to improve motor performance; however, it is not yet known whether it affects motor learning. Thus, here we investigated whether γ-tACS applied over the M1 and cerebellar hemisphere affects motor learning. This study involved 30 healthy subjects (14 females, 16 males) performing a visuomotor control task (eight trials) during an administration of either γ-tACS or a sham stimulation (15 subjects per condition) over their right M1 and left cerebellar hemisphere. Each subject performed five trials after 24 h. The motor learning efficiency, motor learning retention and re-motor learning efficiency in each condition were compared. The motor learning retention in the γ-tACS condition was significantly higher than that in the sham condition (p = 0.031). Thus, subjects who were administered γ-tACS maintained their motor performance the next day better than sham-stimulated subjects. There was no significant difference between the conditions in the motor learning efficiency and those in the re-motor learning efficiency. Our results demonstrate that γ-tACS administered over the M1 and cerebellar hemisphere during a motor learning task can enhance motor learning retention.

Repetitive passive movement (RPM) is a rehabilitation technique that increases spinal reciprocal inhibition (RI) as movement speed increases. However, characterization of the RPM number, frequency and range relative to the afferent impulses of muscle spindles and RI modulation has not been performed. In this study, we attempted to clarify these factors and evaluate their relationship to RI. We used 20 healthy adults for our first experiment (Experiment 1) and 16 healthy adults for our second experiment (Experiment 2). In Experiment 1, the RPM task was performed in the 80°-120° range for the ankle joint for 618 times at 80°/s (80°/s_618 times), 309 times at 160°/s (160°/s_309 times) and 618 times at 160°/s (160°/s_618 times). In Experiment 2, the RPM task focused on two ranges for the ankle joint (80°-100° and 100°-120°) and was performed at 160°/s with a movement time of 10 min. To measure RI, electrical stimulation was used to evoke a conditioning stimulus in the common peroneal nerve and the test stimulus in the tibial nerve. Conditions included the test stimulus only and conditioning stimulation-test stimulation intervals (CTI) of 2 and 20 ms. RI was measured before (Pre); immediately after; and 5, 10, 15 and 20 min after the task. Our findings suggest that the faster the movement speed of the RPM and the wider the movement range, the greater the increase in Ia firing. This may have enhanced RI by activating the inhibitory interneurons of RI.

Past eccentric contraction (ECC)-induced muscle injury reduces the severity of symptoms of subsequent muscle injury; this phenomenon is known as a repeated bout effect (RBE). It has been reported that increases in the duration of the interval between the first and second bouts are linked to weakening of the RBE. However, the histology following the attenuation of the RBE remains unclear. We examined the sustained effects of the second bout with regard to myofiber permeability and muscle force. Sixty-four male rats were randomly assigned to eight groups that varied in the number of exercise sessions and the duration of the interval between the first and second bouts: the non-ECC (Control); the single-injury (Post 1st bout); groups that were allowed to recover for 1, 2, and 4 weeks after a single injury (Pre 2nd bout_1w, Pre 2nd bout_2w, and Pre 2nd bout_4w); and groups that were subjected to second injuries 1, 2, and 4 weeks after the first (Post 2nd bout_1w, Post 2nd bout_2w, and Post 2nd bout_4w). The tibialis anterior was electrically stimulated in each ECC group. Twenty-four hours before muscle sampling, Evans blue dye (EBD) (a marker of myofiber damage) was administered. The maximal isometric contraction tension was measured immediately before sampling. The number of EBD-positive (+) fibers was determined via histological analysis. An RBE was revealed by functional examination at the 1- and 2-week and histological examination at the 1-, 2-, and 4-week time points (P < 0.05). In terms of myofiber permeability, prolongation of the interval before the second bout weakened this effect (P < 0.05). Experiments with 1-, 2-, and 4-week intervals indicated that prolongation of the interval before the second bout weakened the RBE with regard to myofiber permeability.

Injuries are inevitable for athletes, and when injuries end up causing chronic pain, they usually force athletes to withdraw from training. Chronic pain is known to be caused by plastic changes in the brain; thus, the purpose of this study was to assess the somatosensory evoked potential (SEP) and the paired-pulse inhibition (PPI) in athletes suffering from chronic pain as compared to pain-free athletes. Twenty track and field (T&F) athletes, that were also undergraduate students, were recruited for this study. These athletes (12 men; 8 women) were divided into two groups of 10 based on their self-reporting of actively experiencing chronic pain (defined as pain that persisted for more than 3 months) or not. Both SEP and PPI in the primary somatosensory cortex (SI) were elicited by constant current square-wave pulses (of 0.2 ms duration) that were delivered to the right median nerve by an electrical stimulator through a surface bar electrode with a cathode proximal. Paired-pulse stimulation was set at interstimulus intervals of 30 and 100 ms. Subjects were randomly presented with 1,500 single- and paired-pulse stimuli at 2 Hz. Our measurements demonstrated a trend toward a lower N20 and P25 amplitude as well as a disinhibition of the PPI_30 ms in the athletes suffering from chronic pain. These findings suggest that chronic pain may modulate excitatory and inhibitory function of the SI in athletes as well as in patients suffering from complex regional pain syndrome or fibromyalgia.

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.

Repetitive passive movement (RPM) activates afferent Ia fibers. The input of afferent Ia fibers from antagonist muscle may modulate the extent of spinal reciprocal inhibition (RI). However, effects of RPM on RI remain unknown. We aimed to clarify these effects in 20 healthy adults. Four RPM tasks (40°/s, 80°/s, 120°/s, and 160°/s), with the range of ankle joint movement set to 40°, ranging from 10° in dorsiflexion to 30° in plantar flexion, were performed for 10 min. For measuring RI, a deep peroneal nerve as a conditioning stimulus, tibial nerve as a test stimulus, and three condition-test stimulus intervals (CTIs; single, 2 ms, and 20 ms) were used. The stimulation frequency was 0.3 Hz for 36 times (3 stimulation conditions × 12 sets). RI was measured before, immediately after, and 5, 10, 15, and 20 min (Pre, Post 5, 10, 15, and 20, respectively) after the task. The extent of reciprocal Ia inhibition (CTI 2 ms) significantly increased in Post 5 and 10 at RPM speed of ≥ 120°/s. The extent of D1 inhibition (CTI 20 ms) significantly increased in Post 5 and 10 at RPM speed of ≥ 80°/s, and continued to increase until Post 15 at RPM speed of 160°/s. The extent of RI was the highest at RPM speed of 160°/s for both Ia and D1. Therefore, high RPM may increase the extent of reciprocal Ia inhibition and D1 inhibition, suggesting that rapid movements affect RI by increasing the firing frequency from the muscle spindle to afferent Ia fibers.

Cancer survivors experience late and long-term effects of treatment; also, the disease itself might be responsible for persisting functional impairments. The purpose of this study was to investigate muscle strength, balance function using the Mini-Balance Evaluation Systems Test and Timed Up and Go test with single and cognitive dual tasks and body sway in breast cancer survivors and healthy women and non-breast cancer survivors and healthy participants.Twenty-six cancer survivors and 19 healthy participants were assessed for grip and knee extension strength with the Mini-Balance Evaluation Systems Test, Timed Up and Go, and body sway test performance.Breast cancer survivors had significantly lower hand grip strength (p .05) and Mini-Balance Evaluation Systems Test scores than healthy women (p .05). Additionally, in breast cancer survivors, hand grip strength had a significant relationship with Mini-Balance Evaluation Systems Test and Timed Up and Go scores (p .05) but had no relationship with the total center of pressure length. Hand grip strength and Mini-Balance Evaluation Systems Test scores were not significantly different in non-breast cancer survivors and healthy participants. In non-breast cancer survivors, knee extension strength had a significant relationship with the Timed Up and Go scores (p .05).The relationship between muscle strength and balance function may be characterized by the different diagnoses in cancer survivors. The current findings showed the changes in balance function and muscle strength among cancer survivors.

Transcranial alternating current stimulation (tACS) has been shown to modulate neural connectivity in the cortical area under experimental electrodes. Although gamma tACS over the M1 region and the cerebellar hemisphere has been shown to improve motor performance, the optimal stimulation method has not been clarified. In this study, we aimed to clarify whether the effect of gamma tACS over M1 and the cerebellar hemisphere depends on current intensity. Twenty healthy adults performed a visuomotor control task using their right index finger for 30 s during tACS (70 Hz) over the left M1 and the right cerebellar hemisphere. Each subject participated in 10 trials, separated by intervals of 3 min. Three stimulation conditions were applied: (1) pseudo-stimulation (sham condition), (2) tACS with a current intensity of 1.0 mA and (3) tACS with a current intensity of 2.0 mA. Our results indicated that regardless of the current intensity, participants with the lower motor performance had better motor performance under both tACS conditions. Such a correlation was not observed under the sham condition. Collectively, our findings demonstrated that the effect of gamma tACS over M1 and the cerebellar hemisphere does not depend on current intensity, and that motor performance slightly improved in both tACS conditions for participants with lower motor performance.

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.

Electrical stimulation (ES)-induced muscle contraction has multiple effects; however, mechano-responsiveness of bone tissue declines with age. Here, we investigated whether daily low-frequency ES-induced muscle contraction treatment reduces muscle and bone loss and ameliorates bone fragility in early-stage disuse musculoskeletal atrophy in aged rats. Twenty-seven-month-old male rats were assigned to age-matched groups comprising the control (CON), sciatic nerve denervation (DN), or DN with direct low-frequency ES (DN+ES) groups. The structural and mechanical properties of the trabecular and cortical bone of the tibiae, and the morphological and functional properties of the tibialis anterior (TA) muscles were assessed one week after DN. ES-induced muscle contraction force mitigated denervation-induced muscle and trabecular bone loss and deterioration of the mechanical properties of the tibia mid-diaphysis, such as the stiffness, but not the maximal load, in aged rats. The TA muscle in the DN+ES group showed significant improvement in the myofiber cross-sectional area and muscle force relative to the DN group. These results suggest that low-frequency ES-induced muscle contraction treatment retards trabecular bone and muscle loss in aged rats in early-stage disuse musculoskeletal atrophy, and has beneficial effects on the functional properties of denervated skeletal muscle.

Sleep has long been shown as important for memory processing and retention, and has recently been implicated in motor memory consolidation. However, it is not known whether sports skills, including basketball shooting skills, are also affected by sleep in young, healthy individuals. Therefore, we investigated whether sleep before and after basketball shooting skill training affected the acquisition and retention of shooting skills. This study included 19 healthy male subjects who participated in a basketball shooting skill training session (100 shots) and a retention test performed 2 days later (30 shots). The learning and retention indices were calculated using performance scores that evaluated each subject’s shooting skills. A wearable activity tracker was used to measure sleep parameters for 4 consecutive days, 2 days before and 2 days after training. We discovered the relationship between sleep duration before and after training and retention of shooting skills (sleep duration before training; p = 0.044, r = 0.467, sleep duration after training; p = 0.006, r = 0.606). The retention index for the subgroup with long sleep duration before and after training was significantly higher than that for the subgroup with short sleep duration before and after training, respectively (p = 0.021 for both). There was no significant relationship between learning index and each sleep parameter. Our results demonstrated that sleep duration before and after training was related to retention of shooting skills following basketball shooting skills training.

AIM Intensive rehabilitation effectively improves physical functions in patients with acute stroke, but the frequency of intervention and its cost-effectiveness are poorly studied. This study aimed to examine the effect of early high-frequency rehabilitation intervention on inpatient outcomes and medical expenses of patients with stroke. METHODS The study retrospectively included 1759 patients with acute stroke admitted to the Kobe City Medical Center General Hospital between 2013 and 2016. Patients with a transient ischemic attack, subarachnoid hemorrhage, and those who underwent urgent surgery were excluded. Patients were divided into two groups according to the frequency of rehabilitation intervention: the high-frequency intervention group (>2 times/day, n = 1105) and normal-frequency intervention group (

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.

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., 10‐Hz tACS can improve tactile orientation discrimination in subjects with low alpha activity. Conversely, 70‐Hz tACS had no effect on tactile orientation discrimination.

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.

A recent study based on near-infrared spectrometry (NIRS) showed that a single session of moderate-intensity exercise increases the cortical oxyhemoglobin (O2Hb) level. However, changes in the laterality of O2Hb throughout such exercises remain unknown. In the present study, we evaluated changes in the laterality of O2Hb in the prefrontal cortex (PFC) and premotor area (PMA) during moderate-intensity cycling for 20 min. Twelve healthy volunteers performed the exercise at 50% of the maximal oxygen consumption after a 3-min rest period. O2Hb levels in the right (R-) and left (L-) PFC and PMA were measured using multichannel NIRS and averaged every 5 min during the exercise period, and the laterality index (LI) for each 5-min period was calculated. LI for PFC showed significant changes in each period (first, second, third, and fourth periods: −0.40 ± 0.21, −0.03 ± 0.12, 0.14 ± 0.15, and 0.16 ± 0.10, respectively; p < 0.05), whereas that for PMA showed no significant changes (−0.07 ± 0.09, 0.23 ± 0.08, 0.17 ± 0.12, and 0.19 ± 0.09, respectively; p = 0.12). These findings suggest that the laterality of cortical oxygenation in PFC of healthy, young individuals changes during moderate-intensity exercise for 20 min, thus providing an insight into the mechanisms underlying exercise-induced improvements in brain function.

Introduction: The Borg scale rating of perceived exertion is a reliable indicator and widely used to monitor and guide exercise intensity. We aimed to evaluate the relationships between the Borg scale score and oxygenated hemoglobin (O2Hb) and deoxygenated hemoglobin (HHb) concentrations in the leg muscle as measured by near-infrared spectroscopy (NIRS) during cardiopulmonary exercise testing (CPET) in healthy adult men. We also investigated the relationships between the Borg scale score and the work rate (WR), heart rate (HR), oxygen uptake (VO2), and minute ventilation (VE). Methods: Participants comprised 12 healthy men. Cardiopulmonary and NIRS parameters were assessed during each minute of CPET and at the end of the test. Results: The Borg scale score was significantly correlated with cardiopulmonary parameters including WR, HR, VO2, and VE during CPET (Rs = 0.87–0.95; p < 0.05). Furthermore, the Borg scale score was significantly correlated with NIRS parameters including O2Hb and HHb levels during CPET (Rs = −0.48 and 0.45, respectively; p < 0.05). Discussion: The Borg scale score is significantly correlated with cardiopulmonary parameters (WR, HR, VO2, and VE), as well as with leg-muscle oxygenation parameters as assessed by NIRS, during CPET in healthy adults. The correlation coefficients obtained from NIRS parameters were lower than those of cardiopulmonary parameters. Conclusions: The Borg scale score might better reflect cardiopulmonary responses than muscle deoxygenation during exercise. These results can aid in the planning of rehabilitation programs for healthy adults.

BACKGROUND The aim of this study was to investigate the differences between the Face Pain and Borg Scales for rating of perceived exertion (RPE) during cardiopulmonary exercise testing (CPET) in healthy adults, and their relationships with work rate (watts), heart rate (HR), oxygen uptake (VO 2 ), and minute ventilation (VE). METHODS In this prospective observational study, two experiments were conducted. In Experiment 1, 77 healthy adults were randomly assigned to either the group using the Face Pain Scale (19 men, 18 women) or using the Borg Scale (21 men, 19 women) for the RPE during CPET. In Experiment 2, 40 healthy adults (20 men, 20 women) used both the Face Pain and Borg Scales for the RPE during CPET. In both experiments, CPET was performed on ramp protocols with incremental increases in the work rate by 20 watts/minute. Their responses in terms of watts, HR, VO 2 , VE, and RPE (assessed using the Face Pain Scale or Borg Scale) were recorded each minute. RESULTS There were significant relationships between the two scales and all physiological variables during CPET in 74 out of the 77 participants in Experiment 1 and in all subjects in Experiment 2 (P

A previous study reported that cancer survivors exhibit decreased postural stability compared to age-matched controls. Another study showed that cancer survivors have a lower quality of life (QOL) compared to healthy subjects, and there was a significant relationship between muscle strength and QOL in cancer survivors. We aimed to investigate differences in the associations between balance function and QOL in cancer survivors and healthy subjects. Forty-one cancer survivors and 33 healthy subjects were included. Balance function was evaluated using the timed up and go test, and body sway was tested using a force platform. QOL was assessed using the medical outcome study 36-item short-form health survey. Cancer survivors exhibited significantly higher timed up and go and lower QOL than that of healthy subjects (P

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.

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&ndash, reticulospinal projections. The results showed that 15 min of anodal-tDCS in the SMA enhanced and sustained RI in healthy individuals.

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. 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-intervention. 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.

Measurement of oxyhemoglobin (O2Hb) changes in the cerebral cortex using near-infrared spectroscopy (NIRS) shows that its levels increase during moderate-intensity exercise and persists after exercise. However, the effects of exercise duration on O2Hb persistence in the premotor cortex (PMC) are unknown. We aimed to determine the effects of exercise duration on the persistence of O2Hb changes after moderate-intensity cycling as exercise. Healthy young volunteers were recruited to participate in this study. After a 3-min rest period, the exercise was initiated at a workload corresponding to 50% VO2peak. The exercise continued for 10 min and 20 min, followed by 15 min of rest. The O2Hb levels in the right (R-PMC) and left premotor cortices (L-PMC) were measured using an NIRS system. The O2Hb values during the 15-min post-exercise rest period in the R-PMC were 0.010 ± 0.011 mM·cm after the 10-min exercise and 0.035 ± 0.010 mM·cm after the 20-min exercise, without significant differences (p = 0.104). The O2Hb value in the L-PMC during post-exercise rest (0.055 ± 0.010 mM·cm) after the 20-min exercise was significantly higher than that after the 10-min exercise (0.023 ± 0.007 mM·cm; p = 0.014). Thus, the effects of exercise duration on O2Hb persistence have laterality in the PMC.

Selective afferent activation can be used to improve somatosensory function, possibly by altering cortical inhibitory circuit activity. Peripheral electrical stimulation (PES) is widely used to induce selective afferent activation, and its effect may depend on PES intensity. Therefore, we investigated the effects of high- and low-intensity PES applied to the right index finger on tactile discrimination performance and cortical somatosensory-evoked potential paired-pulse depression (SEP-PPD) in 25 neurologically healthy subjects. In Experiment 1, a grating orientation task (GOT) was performed before and immediately after local high- and low-intensity PES (both delivered as 1-s, 20-Hz trains of 0.2-ms electrical pulses at 5-s intervals). In Experiment 2, PPD of SEP components N20/P25_SEP-PPD, N20_SEP-PPD and P25_SEP-PPD, respectively, were assessed before and immediately after high- and low-intensity PES. Improved GOT discrimination performance after high-intensity PES (reduced discrimination threshold) was associated with lower baseline performance (higher baseline discrimination threshold). Subjects were classified into low and high (baseline) GOT performance groups. Improved GOT discrimination performance in the low GOT performance group was significantly associated with a greater N20_SEP-PPD decrease (weaker PPD). Subjects were also classified into GOT improvement and GOT decrement groups. High-intensity PES decreased N20_SEP-PPD in the GOT improvement group but increased N20_SEP-PPD in the GOT decrement group. Furthermore, a greater decrease in GOT discrimination threshold was significantly associated with a greater N20_SEP-PPD decrease in the GOT improvement group. These results suggest that high-intensity PES can improve somatosensory perception in subjects with low baseline function by modulating cortical inhibitory circuits in primary somatosensory cortex.

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.

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

Paired-pulse depression (PPD) has been widely used to investigate the functional profiles of somatosensory cortical inhibition. However, PPD induced by somatosensory stimulation is variable, and the reasons for between- and within-subject PPD variability remains unclear. Therefore, the purpose of this study was to clarify the factors influencing PPD variability induced by somatosensory stimulation. The study participants were 19 healthy volunteers. First, we investigated the relationship between the PPD ratio of each component (N20m, P35m, and P60m) of the somatosensory magnetic field, and the alpha, beta, and gamma band changes in power [event-related desynchronization (ERD) and event-related synchronization (ERS)] induced by median nerve stimulation. Second, because brain-derived neurotrophic factor (BDNF) gene polymorphisms reportedly influence the PPD ratio, we assessed whether BDNF genotype influences PPD ratio variability. Finally, we evaluated the test–retest reliability of PPD and the alpha, beta, and gamma ERD/ERS induced by somatosensory stimulation. Significant positive correlations were observed between the P60m_PPD ratio and beta power change, and the P60m_PPD ratio was significantly smaller for the beta ERD group than for the beta ERS group. P35m_PPD was found to be robust and highly reproducible; however, P60m_PPD reproducibility was poor. In addition, the ICC values for alpha, beta, and gamma ERD/ERS were 0.680, 0.760, and 0.552 respectively. These results suggest that the variability of PPD for the P60m deflection may be influenced by the ERD/ERS magnitude, which is induced by median nerve stimulation. Electronic supplementary material The online version of this article (10.1007/s10548-018-0648-5) contains supplementary material, which is available to authorized users.

The purpose of this study was to investigate the preventive effect of streptomycin (Str) administration on changes in membrane permeability and the histomorphological characteristics of damaged muscle fibers following eccentric contraction (ECC ). Eighteen 7-week-old male Fischer 344 rats were randomly assigned to three groups: control (Cont), ECC, and ECC with Str (ECC + Str). The tibialis anterior (TA) muscles in both ECC groups were stimulated electrically and exhibited ECC. Evans blue dye (EBD), a marker of muscle fiber damage associated with increased membrane permeability, was injected 24 hr before TA muscle sampling. The number of EBD-positive fibers, muscle fiber cross-sectional area (CSA), and roundness were determined via histomorphological analysis. The ECC intervention resulted in an increased fraction of EBD-positive fibers, a larger CSA, and decreased roundness. The fraction of EBD-positive fibers was 79% lower in the ECC + Str group than in the ECC group. However, there was no difference in the CSA and roundness of the EBD-positive fibers between the two ECC groups. These results suggest that Str administration can reduce the number of myofibers that increase membrane permeability following ECC, but does not ameliorate the extent of fiber swelling in extant EBD-positive fibers. Anat Rec, 301:1096-1102, 2018. © 2018 Wiley Periodicals, Inc.

Background The vestibular system is involved in the control of standing balance. Galvanic vestibular stimulation (GVS) is a noninvasive technique that can stimulate the vestibular system. In recent years, noisy GVS (nGVS) using noise current stimulation has been attempted, but it has not been clarified whether it affects postural sway in open-eye standing. Objective The purpose of this study was to clarify the influence of nGVS on the center of pressure (COP) sway measurement in open-eye standing postural control and identify the responders of nGVS. Methods nGVS (0.1–640 Hz) was delivered at 0.4 and 1.0 mA over the bipolar mastoid. COP sway root mean square area, sway path length, medio-lateral (ML) mean velocity, and antero-posterior (AP) mean velocity before and during nGVS in an open-eye standing posture was measured. Results nGVS at 0.4 and 1.0 mA significantly reduced sway path length, mean velocity. The stimulation effect of nGVS was also large in subjects with a long sway path. For subjects with high COP sway of Baseline, nGVS was effective even with stimulation for a short duration (5 s). Conclusions These findings suggest that nGVS improves postural sway in an open-eye standing posture among young subjects.

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.

The enthesis transmits a physiological load from soft to hard tissue via fibrocartilage. The histological alterations induced by this physiological loading remain unclear. This study was performed to examine the histomorphological alterations in the collagen fiber bundle alignment and depth of collagen interdigitation between the calcified fibrocartilage and the bone. We examined the Achilles enthesis of rats with sciatic denervation to explore the mechanical effects of structural changes in the enthesis. The parallelism of the collagen fiber bundles was significantly reduced 8 weeks after denervation. However, the depth of collagen interdigitation significantly increased at 2 and 4 weeks after denervation and then significantly decreased 8 weeks after denervation. In conclusion, a lack of muscle loading induced structural alterations in the distal calcified fibrocartilage. These findings suggest that while structural changes in the enthesis are necessary for the development of physiological loading, structural deformities are required in the long term. Anat Rec, 300:2166-2174, 2017. © 2017 Wiley Periodicals, Inc.

[Purpose] Chondrocytes in articular cartilage are aligned as columns from the joint surface. Notably, loss of chondrocyte and abnormalities of differentiation factors give rise to osteoarthritis (OA). However, the relationship between chondrocyte alignment and OA progression remains unclear. This study was performed to investigate temporal alterations in surgically-induced OA rats. [Subjects and Methods] Thirteen-week-old Wistar rats (n=30) underwent destabilized medial meniscus surgery in their right knee and sham surgery in their left knee. Specimens (n=5) were collected at 0, 1, 2, 4 and 8 weeks after surgery. Histological analysis with Osteoarthritis Research Society International (OARSI) scores, cell density ratios, cell alignments and correlation between OARSI scores and cell density/alignment was performed. [Results] OARSI scores were significantly higher at 1, 2, 4 and 8 weeks in the DMM group than in the control. Cell density ratios were decreased significantly in the DMM group at 2, 4 and 8 weeks compared with the control. Chondrocyte alignment was decreased significantly in the DMM group at 4 and 8 weeks. There were negative correlations between OA severity and cell density / cell alignment. [Conclusion] The results suggest a relationship between chondrocyte alignment and cartilage homeostasis, which plays an important role in OA progression.

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.

Although it is known that motor learning changes the corticospinal tract excitability, the time course of bilateral corticospinal tract excitability in the motor-learning process has not been clarified. The study aimed to investigate the time course of bilateral corticospinal tract excitability during the motor-learning process. Sixteen subjects performed 10 trials of the visuomotor tracking task by using their right index finger for one minute. The movement intensity of the visuomotor tracking task ranged from 5%-17% of the maximum index finger abduction force and the movement frequency was 0.5 Hz. To assess bilateral corticospinal excitability, we stimulated the bilateral primary motor cortex with transcranial magnetic stimulation between each trial and measured motor-evoked potential (MEP) from the bilateral first dorsal interosseous (FDI) muscle. Motor performance improved rapidly to the sixth trial (P0.05), and motor performance did not change from the seventh to the tenth trial. The MEP amplitude of the right FDI increased significantly from the fifth to the ninth trial relative to that before the task (P0.05). Conversely, the MEP amplitude of the left FDI did not change during the motor-learning process. This study revealed that primary motor cortex excitability on the contralateral side to the exercising muscle increased in the late motor learning stage and that primary motor cortex excitability on the ipsilateral side to the exercising muscle did not change in the motor-learning process.

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.

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.

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.

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.

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.

Transcranial alternating current stimulation (tACS) can regulate the frequency of neuronal activity in the cerebral cortex. Beta (β) activity in the supplementary motor area (SMA) is involved in motor planning and maintenance while gamma (γ) activity is involved in updating motor plans. We investigated the effect of tACS in the β- and γ-bands (β-tACS and γ- tACS) applied to the SMA on bimanual movement performance. This study included 32 right-handed healthy participants performing a Purdue Pegboard Test (PPT) during the administration of either β-tACS (20 Hz), γ-tACS (80 Hz), or sham stimulation over the SMA. Each participant performed nine PPT trials during each stimulation condition. The linear approximation of the number of parts and their differences for the 9 trials performed by each participant was calculated. A significant positive correlation was found between the difference from linear approximation for the β-tACS condition and the intercept of the linear approximation (p = 0.007, Pearson's r = 0.464), and significant negative correlation was found for the γ-tACS condition (p = 0.012, Pearson's r = -0.438). In the low-performance subgroup, the mean values of the difference from linear approximation under the γ-tACS condition was significantly larger than that under the β-tACS condition (p = 0.048). These results were opposite for the high-performance subgroup (p = 0.002) and sham group (p = 0.014). We demonstrated that the effect of tACS over the SMA depended on the stimulus frequency and the participant's motor performance and may modulate the maintenance and updating of motor plans.

Noisy galvanic vestibular stimulation (nGVS) enhances the vestibular system. The center of pressure (COP) sway has been shown to decrease during nGVS, but the after-effect of nGVS remains unclear. The aim of this study is to elucidate the after-effect of nGVS on COP sway. We randomly assigned 26 participants to either control (sham stimulation) or nGVS groups. All participants were measured for COP sway while standing with open eyes at baseline, during stimulation, and after stimulation. In the nGVS group, sway path length, mediolateral mean velocity, and anteroposterior mean velocity decreased both during stimulation and after stimulation compared with baseline. Conversely, no significant difference in COP sway was detected in the control group. There was a correlation between the stimulation effect and the after-effect in the nGVS group, indicating that nGVS is effective for people with high baseline COP sway.

Acute aerobic exercise beneficially affects brain function. The effect of acute aerobic exercise on the inhibitory mechanism of the primary somatosensory cortex (S1) and somatosensory function remains unclear. We investigated whether acute aerobic exercise modulates S1 inhibitory function and somatosensory function. In Experiment 1, we measured somatosensory evoked potentials (SEP) and paired-pulse inhibition (PPI) in 15 healthy right-handed participants. The right median nerve underwent electrical stimulation (ES). Interstimulus intervals were 5 ms, 30 ms, and 100 ms. In Experiment 2, we assessed the somatosensory function by using a somatosensory temporal discrimination task. Single or paired ES was applied to the distal phalanx of the right index finger. Both the experiments involved three sessions: 20 min of moderate-intensity exercise, 30 min of low-intensity exercise, and 30 min of seated rest. Before and after each session, PPI and somatosensory temporal discrimination task performance were measured. The N20 latency was significantly shortened immediately after moderate exercise. The SEP amplitude was not modulated in any session. The PPI at 30 ms (PPI_30ms) significantly decreased 20 min after moderate exercise, whereas the PPI at 5 ms (PPI_5ms) and PPI at 100 ms (PPI_100ms) did not change. The 50% and 75% thresholds and reaction time did not improve in any session. We found negative relationships between the change in PPI_5ms and the change in the 75% threshold under low-intensity exercise condition. Thus, acute aerobic exercise modulated S1 inhibitory function depending on exercise intensity. The exercise-induced change in PPI was associated with the change in temporal discrimination.

Two-point discrimination (TPD) has been widely used as a parameter for the examination of higher-order perceptual functions in the field of rehabilitation. Previous research has shown that the threshold of TPD increases with aging or pathological conditions such as stroke or chronic pain. It has also been reported that the threshold can be decreased by continuous tactile or electrical stimulation. The cognitive process in the cortex has been shown to be involved in the determination of the TPD threshold. However, the reliability of TPD has been questioned, because differences in the firing rate of the responding receptors and afferent fibers occur, depending on how the measuring instrument is applied. To investigate the influence of the stimulus condition on the TPD threshold, we utilized a computer-controlled two-point tactile stimulator and measured the TPD threshold by alternating stimulus speed and stimulus penetration depths. We found that a stimulus speed of 5.0 mm/s or 10.0 mm/s and a stimulus penetration depth of 1.0 mm were the optimum condition for measurement, at which the TPD threshold becomes lowest. We also found that no influence is exerted on the threshold by repeated measurement under the stimulus conditions utilized in this experiment. Our findings suggest that TPD measurement should be performed under certain stimulus conditions, as identified in this present study, to obtain reliable results that reflect the highest ability of the subject for spatial discrimination.

The American College of Sports Medicine and American Heart Association recommends resistance training involving 60-70% of 1-repetition maximum (1RM) for 8-12 repetitions on 2 or 3 nonconsecutive days per week for the elderly. The Borg 6-20 scale, Borg category ratio (CR-10) scale, and OMNI scale are used to determine the rating of perceived exertion (RPE) for resistance training. Areas covered: RPE scales for resistance training performed by elderly individuals are described. The RPE has been related to resistance training intensity, and the RPE scale was used to determine the resistance training intensity of elderly or ill individuals. Expert commentary: RPE scales can determine the resistance training intensity of elderly individuals and may be used at home or in nursing homes, if they do not have specific resistance training machines. RPE is simple and useful, and may improve skeletal muscle strength or other health-related issues.

The spinal reciprocal inhibition during co-contraction remains unclear. Reports on the reciprocal Ia and D1 inhibitions in the co-contraction are lacking, and a point about the muscle activity amount during co-contraction is unclear. This study aimed to clarify the influence of changes in the ratio of soleus (Sol) and tibialis anterior (TA) muscle activities in co-contraction on reciprocal Ia and D1 inhibitions. Twenty healthy adults were subjected to four stimulatory conditions: a conditioning stimulus–test stimulation interval (CTI) of − 2, 2, or 20 ms or a test stimulus without a conditioning stimulus (single). Co-contraction [change in (Sol)/(TA) activity] was examined at task A, 0%/0% maximal voluntary contraction (MVC); task B, 5%/5% MVC; task C, 15%/15% MVC; task D, 5%/15% MVC; and task E, 15%/5% MVC. At 2-ms CTI, the H-reflex amplitude value was significantly lower in tasks A, B, C, and D than in the single condition. Among the tasks, the H-reflex amplitude values were lower for A, B, C, and D than for E. At 20-ms CTI, the H-reflex amplitude was significantly lower in tasks A, B, C, D, and E. Among the tasks, the H-reflex amplitude was significantly lower from task A and B to task E. The change in the muscle activity ratio during co-contraction could modulate reciprocal Ia inhibition depending on the Sol/TA muscle activity ratio. D1 inhibition at rest did not differ significantly when the Sol/TA ratio was equal or when TA muscle activity was high. During co-contraction with high Sol muscle activity, D1 inhibition decreased from rest.