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The relationship between contraction strength of the flexor-pronator muscles (FPMs) and elbow valgus braking function has not been clarified.The purpose of this study was to investigate changes in medial elbow joint space when there is a difference in contraction strength of FPMs under elbow valgus stress.Subjects were 20 healthy male university students, and the elbow joint on the nondominant hand side was used for measurements. The body position for limb measurement was sitting in a chair, with the shoulder abducted 60° and in 90° of external rotation, with 90° of elbow flexion. At first, maximum voluntary contraction (MVC) of the FPMs by grip motion was measured using a hand grip dynamometer under 60-N valgus stress. Contraction strengths of 10% MVC, 30% MVC, and 50% MVC were used. Ultrasonographic images of the medial elbow joint space (JS) were taken in the starting limb position. Using the Telos device system, load was then gradually increased by +10 N/s, and at the time of 60-N valgus stress, an image of the JS was taken. Furthermore, the subject adjusted to the set contraction strength (for about 5 sec) with 60-N valgus stress applied, and an image of the JS was taken while maintaining the set contraction strength. Each MVC condition (10% MVC, 30% MVC, and 50% MVC) was performed randomly. Three ultrasonographic images were taken within 10 seconds, and the average value of the three images was adopted as the JS.Compared with the JS under 60-N valgus stress, the JS was significantly reduced under 60-N valgus stress + 50% MVC. No significant difference was observed between the starting limb position and 60-N valgus stress + 50% MVC.FPMs may require muscle activity ≥50% MVC to brake 60-N elbow valgus stress.

The aim of this study was to clarify the effects of transcutaneous vagus nerve stimulation (tVNS) to the left cymba concha on the pain perception using nociceptive withdrawal reflex (NWR), which is known to be associated with chronic pain, and to investigate whether tVNS-induced suppression of the NWR and parasympathetic activation is correlated. We applied either 3.0 mA, 100 Hz tVNS for 120 s in the left cymba concha (tVNS condition) or the left earlobe (Sham condition) for twenty healthy adults. NWR threshold was measured before (Baseline), immediately after (Post 0), 10 min (Post 10) and 30 min after (Post 30) stimulation. The NWR threshold was obtained from biceps femoris muscle by applying electrical stimulation to the sural nerve. During tVNS, electrocardiograph was recorded, and changes in autonomic nervous activity were analyzed. We found that the NWR thresholds at Post 10 and Post 30 increased compared to baseline in the tVNS group (10 min after: p = 0.048 30 min after: p = 0.037). In addition, increased parasympathetic activity by tVNS correlated with a greater increase in NWR threshold at Post 10 and Post 30 (Post 10: p = 0.01; Post 30: p = 0.005). The present results demonstrate the pain-suppressing effect of tVNS as assessed with NWR threshold and suggest that the degree of parasympathetic activation during tVNS may predict the effect of tVNS after its application.

The aim of this study was to compare anterior knee laxity (AKL), genu recurvatum (GR), and muscle stiffness between reconstructed and contralateral sides in females who underwent anterior cruciate ligament (ACL) reconstruction during early follicular and ovulatory phases. AKL was measured as an anterior displacement of the tibia using a KS measure. GR was measured as the range of motion of knee hyperextension using a hyperextension apparatus. Muscle stiffness was measured for semitendinosus (ST) and biceps femoris long head (BF) using a MyotonPRO. The study investigated eighteen knees in nine females (Age, 20.4 ± 1.5 years; BMI, 21.5 ± 1.5) with normal menstrual cycles at least 1 year after reconstruction using hamstring autograft. E2 (Estradiol) concentration did not differ between the two phases, but AKL on the reconstructed side was lower during the ovulatory phase (8.3 [5.9–9.3] mm) than during the early follicular phase (9.4 [7.3–9.7] mm) (p = 0.044, r = 0.756), whereas there was no significant difference between the two phases on the contralateral side. AKL side-to-side difference, GR, and muscle stiffness (ST and BF) on both sides did not differ in either phase. These results indicate that AKL may behave differently on the reconstructed and contralateral sides during the menstrual cycle.

This study investigated the relationship between changes in foot characteristics and sex differences during the menstrual cycle in healthy male and female university students. We examined 10 female subjects and 14 male subjects. The menstrual cycle was divided into the three phases: the early follicular phase, ovulatory phase, and luteal phase via basal body temperature, an ovulation kit, and salivary estradiol and progesterone concentration measurements. Foot characteristics required for the calculation of the arch height index (AHI) were measured using a three-dimensional foot scanner under conditions of 10% and 50% weight-bearing loads. Arch height at 50% of foot length and truncated foot length were measured, and AHI was calculated by dividing arch height by truncated foot length. Arch height flexibility (AHF) was defined as the change in arch height from 10% weight-bearing load to 50% weight-bearing load. AHI was significantly lower in females than in males in the early follicular and ovulatory phases but did not differ significantly between males and females in each phase. AHF did not differ significantly between males and females in each phase. AHI and AHF showed no periodic fluctuation, suggesting that sex differences in AHF may be absent.

BackgroundThe purpose of this study was to clarify elbow valgus stability of the transverse bundle (TB). We hypothesized that the transverse bundle is involved in elbow valgus stability.MethodsTwelve elbows of six Japanese Thiel-embalmed cadavers were evaluated. The skin, subcutaneous tissue and origin of forearm flexors were removed from about 5 cm proximal to the elbow to about 5 cm distal to the elbow, and the ulnar collateral ligament was dissected (intact state). The cut state was defined as the state when the TB was cut in the middle. The joint space of the humeroulnar joint (JS) was measured in the intact state and then in the cut state. With the elbow flexed to 30°, elbow valgus stress was gradually increased to 30, 60 N using the Telos Stress Device, and the JS was measured by ultrasonography under each load condition. Paired t-testing was performed to compare the JS between the intact and cut states under each load.ResultsNo significant difference in JS was identified between the intact and cut state at start limb position. The JS was significantly higher in the cut state than in the intact state at both 30 N and 60 N.ConclusionThe findings from this study suggested that the TB may be involved in elbow valgus stability.

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.

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.

The purpose of this study was to classify the twisted structure of the fetal Achilles tendon. The study was conducted using 30 legs from 15 Japanese fetuses (mean weight, 1764.6 ± 616.9 g; mean crown–rump length, 283.5 ± 38.7 mm; 16 males, 14 females). According to attachment to the deep layer of the calcaneal tuberosity, cases showing only soleus attachment were classified as least twist (Type I), cases showing both lateral head of the gastrocnemius and soleus were classified as moderate twist (Type II), and cases with only lateral head of the gastrocnemius were classified as extreme twist (Type III). Viewing the Achilles tendon from cranially shows a structure twisted counterclockwise on the right side and clockwise on the left. The Achilles tendon was Type I in 4 legs (13%), Type II in 23 legs (77%), and Type III in 3 legs (10%). The twisted structure of the Achilles tendon can be classified as early as the second trimester and is similar to that seen in adults.

Background: The purpose of this study was to clarify the morphological characteristics of the infrapatellar fat pad (IFP) in Japanese cadavers and to elucidate the relationship between morphological characteristics of the IFP and degeneration of the patellofemoral joint. Methods: This investigation examined 41 legs from 25 Japanese cadavers. Morphological measurement was performed by one examiner, and the proximal IFP, IFP body length, width, and IFP volume were measured. The morphological characteristics of IFP proximal were used to categorize three types of IFP: Type I, IFP proximal located on medial and lateral sides of the patella; Type II, IFP proximal only located medially; and Type III, absence of IFP proximal medially and laterally. Articular surfaces were graded as macroscopically intact or mildly altered (Grade I), moderately altered (if fissuring or fibrillation was observed; Grade II), or severely altered (if eburnation was present; Grade III). Results: Type I was identified in 36.6%, Type II in 48.8%, and Type III in 14.6%. IFP medial proximal was seen in 85%, IFP lateral proximal in 36.6%, and loop type was 2.4%. Grade II was significantly more frequent than Grades I or III in Type II, and Grade III was significantly more frequent than Grades I or II in Type III. In addition, IFP volume was significantly larger in Type I than in Types II or III. Conclusion: Causal relationships remain unclear, but the deformation of patellofemoral joint may be related to decreased IFP volume (atrophy).

Background: This study aimed to clarify trunk muscle activity during jump header shooting and examine the immediate effects of trunk stabilization exercises on trunk muscle activity. Methods: Nineteen male college students who had played soccer in junior high and high school clubs and youth sports teams for over 5 years were assigned to either the trunk stabilization exercise group (n = 10) or the control group (n = 9). Muscle activity during jump header shooting was measured before and after intervention. The intervention in the trunk stabilization exercise group was trunk muscle training, whereas that in the control group was sitting. The phases of jump header shooting and the effects of the interventions were compared. Results: The internal oblique activity during the push-off phase and early floating phase was significantly greater than that during the late floating phase. The muscle activity of the internal oblique increased from the push-off phase, prior to the increase in muscle activity of the rectus abdominis and external oblique, whereas the muscle activity of all abdominal muscles increased immediately after take-off. The trunk stabilization exercise intervention decreased the muscle activity of the erector spinae during jump header shooting. Conclusions: These results provide useful coaching-related insights for jump header shooting.

The different cortical activity evoked by a mechanical tactile stimulus depends on tactile stimulus patterns, which demonstrates that simple stimuli (i.e., global synchronous stimulation the stimulus area) activate the primary somatosensory cortex alone, whereas complex stimuli (i.e., stimulation while moving in the stimulus area) activate not only the primary somatosensory cortex but also the primary motor area. Here, we investigated whether the effects of a repetitive mechanical tactile stimulation (MS) on somatosensory evoked magnetic fields (SEFs) and cortical oscillations depend on MS patterns. This single-blinded study included 15 healthy participants. Two types interventions of MS lasting 20 min were used: a repetitive global tactile stimulation (RGS) was used to stimulate the finger by using 24 pins installed on a finger pad, whereas a sequential stepwise displacement tactile stimulation (SSDS) was used to stimulate the finger by moving a row of six pins between the left and right sides on the finger pad. Each parameter was measured pre- and post-intervention. The P50m amplitude of the SEF was increased by RGS and decreased by SSDS. The modulation of P50m was correlated with its amplitude before RGS and with the modulation of beta band oscillation at the resting state after SSDS. This study showed that the effects of a 20-min MS on SEFs and cortical oscillations depend on mechanical tactile stimulus patterns. Moreover, our results offer potential for the modulation of tactile functions and selection of stimulation patterns according to cortical states.

Background: The purpose of this study was to clarify variations in the tibialis posterior tendon (TPT) attachment site using a large sample and to quantify the contribution of each attachment site by examining the surface area of the attachment region.Methods: We examined 100 feet from 50 Japanese cadavers. The TPT of attachment to the the navicular bone (NB), medial cuneiform bone [1], and lateral cuneiform bone (LCB) was set as the main attachment site (Type I). Type II was defined as one extra attachment site in addition to those of Type I, meaning attachment to a total of four sites. Classification up to Type VII was seen according to the number of additional attachment sites. Furthermore, surface area was measured using a 3-dimensional scanner to make the foot sample three-dimensional. Surface area was then calculated using 3-dimensional software.Results: Attachment to the NB, MCB, and LCB was present in all specimens. Attachment to the intermediate cuneiform bone was seen in 25 feet (25%), and to the cuboid bone in 66%. Among 1st–5th metatarsal bones, 4th metatarsal bone was the most attached, at 95%. The TPT attachment to the NB, MCB, and LCB were comprising 75.1% of total attachment surface area. The ratio of the NB, MCB and LCB in each type was about 90% in Types II and III, and 70–80% in Types IV–VII.Conclusion: Attachment of the TPT to the NB, MCB, and LCB may thus contribute to stability of the foot arch.

This study aimed to inspect anatomical variations in the insertion of the peroneus longus tendon (PLT) using a large sample of cadavers. In total, 104 legs from 52 Japanese cadavers were used. The PLT was identified behind the lateral malleolus and carefully followed up to its insertion in the foot. All insertion slips of the PLT were located and documented. Mainly, the PLT was inserted to the base of the first metatarsal (1MT) in all 104 ft. Attachment to the medial cuneiform was present in 20.2%, and the first dorsal interossei was present in 36.5%. The anterior frenular ligament was observed in 31.7%, and attachment to the flexor digiti minimi brevis and opponens digiti minimi was present in 31.7%. The posterior frenular ligament was observed in 5.8%. An additional band was observed in 3.9%, and the adductor hallucis consisting of a caput obliquum was present in 3.9%. No statistically significant differences in the PLT were observed between genders or laterality (right vs. left). These findings suggest that the main function of the PLT is resisting the varus force on the 1MT; however, as the PLT has various attachment sites, it may also be involved in the stabilizing action of the longitudinal and transverse arches. Therefore, these variations and functions appear to be associated with a difficult diagnosis at the first clinical evaluation.

Interoceptive inputs are ascending information from the internal body. Cortical activities have been shown to be elicited by interoceptive inputs from the heartbeat at approximately 200–600 ms after the R wave, and sensory processing is modulated by the heartbeat within the time window. However, the influence of interoceptive inputs and their timing on corticospinal excitability has not yet been fully elucidated. Moreover, in previous studies, individual differences in interoceptive accuracy—objective accuracy in detecting internal bodily sensations assessed by heartbeat perception tasks—can be considered as an important factor influencing cortical activities by the heartbeat. We therefore investigated the modulation of corticospinal excitability by the heartbeat and its timing by recording motor-evoked potentials elicited by transcranial magnetic stimulation of the primary motor cortex at various timings from the R wave. We also investigated the relationship between this modulation and individual interoceptive accuracy. We found a significant positive correlation between the modulation of corticospinal excitability at 200 ms after the R wave and interoceptive accuracy. Conversely, we found a significant negative correlation between the modulation of corticospinal excitability at 400 ms after the R wave and interoceptive accuracy. These results indicated that the corticospinal excitability was modulated at 200–400 ms after the R wave (systolic phase) and that the timing of excitatory or inhibitory states in the corticospinal pathway differed with interoceptive accuracy. Although the neural mechanism remains unclear, these findings may aid in determining new factors influencing corticospinal excitability.

The psychological characteristic of having difficulty expressing emotions, known as alexithymia, is associated with hypervigilance to pain and is considered one of the risk factors for chronic pain. The correlation between alexithymia and hypervigilance to pain can be observed even in healthy individuals. However, the factors influencing this correlation remain unknown. We explored the dopamine system, which is known to be involved in emotion and pain. The dopamine-degrading enzyme catechol-O-methyltransferase (COMT) has a genetic polymorphism known to influence dopamine metabolism in the prefrontal cortex. COMT polymorphism reportedly affects various aspects of pain and increases pain sensitivity in Met allele carriers. Therefore, we investigated whether the correlation between alexithymia and hypervigilance to pain is influenced by COMT polymorphism in healthy individuals. The results revealed a significant positive correlation between the “difficulty describing feelings” of the 20-item Toronto Alexithymia Scale and the “attention to changes in pain” of the pain vigilance and awareness questionnaire in COMT Met carriers but not in Val/Val individuals. This finding suggests that the correlation between alexithymia and hypervigilance to pain is influenced by COMT polymorphism.

Background: The purpose of this study was not only to examine the attachment site but also to quantify the effect of the tibialis posterior tendon (TPT) on each attachment site by examining the surface area of the attachment region. Methods: We examined 100 feet from 50 Japanese cadavers. The TPT attachment to the navicular bone (NB), medial cuneiform bone (MCB), and lateral cuneiform bone (LCB) were set as the main attachment sites (Type I). The attachment seen in Type I with the addition of one additional site of attachment was defined as Type II. Furthermore, surface area was measured using a three-dimensional scanner. Results: Attachment to the NB, MCB, and LCB was present in all specimens. The TPT attachment to the NB, MCB, and LCB comprised 75.1% of total attachment surface area. The ratio of the NB, MCB, and LCB in each type was about 90% in Types II and III, and 70–80% in Types IV–VII. Conclusion: The quantitative results demonstrated the NB, MCB, and LCB to be the main sites of TPT attachment, although individual differences in attachment sites exist, further developing the findings of previous studies.

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.

Background For the anterior talofibular ligament (ATFL), a three-fiber bundle has recently been suggested to be weaker than a single or double fiber bundle in terms of ankle plantarflexion and inversion braking function. However, the studies leading to those results all used elderly specimens. Whether the difference in fiber bundles is a congenital or an acquired morphology is important when considering methods to prevent ATFL damage. The purpose of this study was to classify the number of fiber bundles in the ATFL of fetuses. Methods This study was conducted using 30 legs from 15 Japanese fetuses (mean weight, 1764.6 ± 616.9 g; mean crown-rump length, 283.5 ± 38.7 mm; 8 males, 7 females). The ATFL was then classified by the number of fiber bundles: Type I, one fiber bundle; Type II, two fiber bundles; and Type III, three fiber bundles. Results Ligament type was Type I in 5 legs (16.7%), Type II in 21 legs (70%), and Type III in 4 legs (13.3%). Conclusions The present results suggest that the three fiber bundles of the structure of the ATFL may be an innate structure.

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.

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.

Background The aim of this study was to clarify the differences in morphological features between the long plantar ligament (LPL) and the short plantar ligament (SPL). Methods This investigation examined 50 legs from 25 Japanese cadavers. The LPL and SPL of each leg were classified into one of three types based on the shape and number of fiber bundles. Then, fiber bundle length, fiber bundle width, and fiber bundle thickness were measured. Results The LPL was rectangular in shape (Type I) in 12%, hourglass shape (Type II) in 62%, and triangular in shape (Type III) in 26%. The SPL was a single fiber bundle (Type I-a) in 26%, a surface fiber bundle and a deep fiber bundle (Type I-b) in 60%, and a surface fiber bundle (medial and lateral) and a deep fiber bundle (Type II) in 14%. Regarding the morphological characteristics, there were no significant differences among the types in the LPL, but there were differences between types and between surface and deep fiber bundles in the SPL. Conclusions For the LPL, the hourglass shape is the most common type. However, there appeared to be no functional difference due to the difference in the shape of the LPL, since there were no significant differences among the types in the LPL. For the SPL, there were types of single, double and triple fiber bundles; there may be functional differences based on the number of fiber bundles and between superficial and deep fibers.

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.

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.

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.

Transcranial electrical stimulation (tES) can be used to modulate inhibitory circuits in primary somatosensory cortex, resulting in improved somatosensory function. However, efficacy may depend on the specific stimulus modality and patterns. For instance, transcranial alternating current stimulation (tACS), transcranial random noise stimulation (tRNS), and transcranial pulsed current stimulation (tPCS) were found to stably and effectively modulate neuronal excitability, while anodal transcranial direct current stimulation (tDCS) appeared less effective overall but with substantial response heterogeneity among subjects. Therefore, we compared the effects of tES applied to primary somatosensory cortex on somatosensory evoked potential paired-pulse depression (SEP-PPD) and tactile discrimination performance in 17 neurologically healthy subjects. In Experiment 1, somatosensory evoked potential N20/P25_SEP-PPD, N20_SEP-PPD, and P25_SEP-PPD responses were assessed before and immediately after anodal tDCS, tACS (stimulation frequency, 140 Hz), tRNS (stimulation frequency, 0.1–640 Hz), anodal tPCS (pulse width, 50 ms; inter-pulse interval, 5 ms), and sham stimulation applied to primary somatosensory cortex. In Experiment 2, a grating orientation task (GOT) was performed before and immediately after the same anodal tDCS, tRNS, anodal tPCS, and sham stimulation regimens. Anodal tDCS and anodal tPCS decreased N20_SEP-PPD, and tRNS increased the first N20 SEP amplitude. Furthermore, tRNS and anodal tPCS decreased GOT discrimination threshold (improved performance). These results suggest that tRNS and anodal tPCS can improve sensory perception by modulating neuronal activity in primary somatosensory cortex.

Transcranial alternating current stimulation (tACS) modulates neural connectivity in the cortical area under the electrodes. Although gamma tACS over the M1 and the cerebellar hemisphere has been shown to improve motor performance, the details of this effect remain unclear. This study aimed to clarify whether the effect of gamma tACS over the M1 and the cerebellar hemisphere is a phase-specific. We applied tACS at 70 Hz over the left M1 and the right cerebellar hemisphere to 20 healthy adults while they performed a visuomotor control task using their right index finger for 30 s. Three stimulation conditions were applied: (1) pseudo-stimulation (sham condition), (2) 180° phase difference in the two cortical target areas (anti-phase condition) and (3) 0° phase difference (in-phase condition). The anti-phase condition decreased task error compared to the sham condition (P = 0.021), but did not differ from the in-phase condition. Our study demonstrated that the effect of gamma tACS over the M1 and the cerebellar hemisphere has phase specificity. This result suggests that intercortical functional synchronization is involved in the improvement of motor performance during gamma tACS over the M1 and the cerebellar hemisphere.