Transcranial alternating current stimulation does not modulate corticospinal activity in humans

Transcranial alternating current stimulation (TACS) is commonly used to synchronise the output of a cortical area to other parts of the nervous system, but evidence for this based on brain recordings in humans is challenging. The brain transmits beta oscillations (~21Hz) to tonically contracted limb muscles linearly and through the fastest corticospinal pathways. Therefore, muscle activity may be used as a proxy measure for the level of beta entrainment in the corticospinal tract due to TACS over motor cortex. Here, we assessed if TACS is able to modulate the neural inputs to muscles, which would provide an indirect evidence for TACS-driven neural entrainment. In the first part of this study, we ran a series of simulations of motor neuron (MN) pools receiving inputs from corticospinal neurons with different levels of beta entrainment. Results indicated that MNs should be highly sensitive to changes in corticospinal beta activity. Then, we ran experiments on healthy human subjects (N=10) in which TACS (at 1mA) was delivered over the motor cortex at 21Hz (beta stimulation), or at 7Hz or 40Hz (control conditions) while the abductor digiti minimi (ADM) or the tibialis anterior muscle (TA) were tonically contracted. Muscle activity was measured using high-density electromyography, which allowed us to decompose the spiking activity of pools of motor units innervating the studied muscles. By analysing motor unit pool activity, we observed that none of the tested TACS conditions could consistently alter the spectral characteristics of the common neural inputs received by the muscles. These results suggest that 1mA-TACS over motor cortex given at frequencies in the beta band does not affect corticospinal beta entrainment.

The Effect of Facial Self-Resemblance on Emotional Mimicry

Social resemblance, like group membership or similar attitudes, increases the mimicry of the observed emotional facial display. In this study, we investigate whether facial self-resemblance (manipulated by computer morphing) modulates emotional mimicry in a similar manner. Participants watched dynamic expressions of faces that either did or did not resemble their own, while their facial muscle activity was measured using EMG. Additionally, after each presentation, respondents completed social evaluations of the faces they saw. The results show that self-resemblance evokes convergent facial reactions. More specifically, participants mimicked the happiness and, to a lesser extent, the anger of self-resembling faces. In turn, the happiness of non-resembling faces was less likely mimicked than in the case of self-resembling faces, while anger evoked a more divergent, smile-like response. Finally, we found that social evaluations were in general increased by happiness displays, but not influenced by resemblance. Overall, the study demonstrates an interesting and novel phenomenon, particularly that mimicry can be modified by relatively subtle cues of physical resemblance.

Whole Body Muscle Activity During Weightlifting Exercise Evaluated By Positron Emission Tomography

Background: This study investigated the whole-body skeletal muscle activity pattern of hang power clean (HPC), a major weight training exercise, using positron emission tomography (PET). Methods: Twelve college weightlifting athletes performed three sets of HPC 20 times with a barbell set to 40 kg both before and after an intravenous injection of 37 MBq 18F-fluorodeoxyglucose (FDG). PET-computed tomography images were obtained 50 min after FDG injection. Regions of interest were defined within 71 muscles. The standardized uptake value was calculated to examine the FDG uptake of muscle tissue per unit volume, and FDG accumulation was compared to the control group. The Mann–Whitney U-test was used to evaluate the differences in the mean SUV between groups. The difference between SUVs of the right and left muscles was evaluated by a paired t-test. A P-value <0.05 was considered statistically significant.Results: FDG accumulation within the vastus lateralis, vastus intermedius, and vastus medialis was higher than that of the rectus femoris. FDG accumulation within the triceps surae muscle was significantly higher only in the soleus. In the trunk and hip muscles, FDG accumulation of only the erector spinae was significantly increased. In all skeletal muscles, there was no difference between SUVs of the right and left muscles.Conclusions: The monoarticular muscles in the lower limbs were active in HPC. In contrast, deep muscles in the trunk and hip were not active during HPC. HPC is not suitable for core training and needs to be supplemented with other training.

Functional Reaction of the Cardiovascular System to Irritation of Vestibular Receptors in Students Engaged in Different Types of Martial Arts

Regular dosed physical activity in all cases has a tonic and healing effect on a person. Feasible muscle activity helps to improve the function of the heart, lungs, blood vessels and the nervous system. In martial arts, the reactivity of the vestibular apparatus is of great importance, providing the flow of information about the current position of the body in space, the success of movement in it and maintaining the stability of the posture due to the effective redistribution of muscle tone. Purpose of the work: to find out the dependence of the reaction of the cardiovascular system to the arising vestibular irritation in different types of martial arts. Martial arts classes help to increase the degree of vestibular stability. The statokinetic stability is very pronounced and increases in the course of hand-to-hand combat, which has a lot of moments with different severity of angular accelerations. The peculiarities of motor activity in any kind of martial arts inevitably affect the peculiarities of the reaction to the test with a change in the position of the head.

The Epidemiology of Bruxism in Relation to Psychological Factors

The aim of the present study was to establish the prevalence of sleep/awake bruxism among young students in Transylvania and to correlate the presence of this muscle activity with behavioral variations. This analytical, observational, cohort, cross-sectional, and prospective study involved 308 volunteers aged between 19 and 30 years of different nationalities, all students of the “Iuliu Hațieganu” University of Medicine and Pharmacy in Cluj-Napoca, Romania. Subjects were asked to complete an anonymous questionnaire which was structured in five sections. The results obtained from the questionnaires were analyzed separately for sleep bruxism and for awake bruxism. We did not find any statistically significant correlation between awake bruxism or sleep bruxism and age (p = 0.30 and p = 0.37, respectively), sex (p = 0.44 and p = 0.48, respectively), or nationality (p = 0.55 and p = 0.67, respectively). Only a high degree of stress and frustration (p = 0.035 and p = 0.020) was observed in European subjects except for the Romanians and the French, likely related to the difficulties of adapting to the language and lifestyle in Romania. Female sex was statistically significantly associated with an increased level of stress (p = 0.004), duty-related depression (p = 0.006), and duty-related anxiety (p = 0.003). Stress and anxiety can be favorable factors in the appearance of both types of bruxism; however, depression is associated only with awake bruxism.

Effect of the position of the interphalangeal joint on movements of the trapeziometacarpal joint during thumb opposition

The Kapandji test is a simple method to score thumb opposition; however, the position of the interphalangeal joint of the thumb during this test has not been described. We aimed to quantitatively examine the effect of the thumb interphalangeal joint position on movements of the trapeziometacarpal joint during thumb opposition using the Kapandji test. The Kapandji test was carried out in 20 healthy participants during thumb interphalangeal joint extension and flexion. Movements of the joints and the activity of thenar muscles were recorded using motion capture and electromyography, respectively. We found that interphalangeal joint extension increased the trapeziometacarpal joint movement and thenar muscle activity compared with interphalangeal joint flexion, which contributed to thumb opposition at Kapandji Positions 0–6. These findings suggest the position of the thumb interphalangeal joint affects the trapeziometacarpal joint during thumb opposition, and assessment of thumb opposition using the Kapandji test is best done with the thumb interphalangeal joint in extension.