Intensity dependency of peripheral nerve stimulation in spinal LTP induced by paired associative corticospinal-motoneuronal stimulation (PCMS)

Paired associative corticospinal-motoneuronal stimulation (PCMS) induces plasticity at synapses between corticospinal tracts (CSTs) and spinal motoneurons (SMs). We investigated the effects of peripheral nerve electrical stimulation (PNS) intensity on PCMS-induced plasticity. PCMS consisted of 180 paired stimuli of transcranial magnetic stimulation (TMS) over the left primary motor cortex with PNS on the right ulnar nerve at the wrist. We compared effects induced by different PNS intensities: supramaximal, twice and three times sensory threshold intensities. For evaluating efficacy of the synapse between CSTs and SMs, single-pulse TMS was delivered at cervicomedullary junction level, and cervicomedullary motor-evoked potentials (CMEPs) were recorded from the right first-dorsal interosseous muscle before and after PCMS. PCMS with the supramaximal PNS intensity increased CMEP amplitude. The facilitatory effect of PCMS with the supramaximal PNS was larger than those of PCMS with weaker PNS intensities. Sham TMS with the supramaximal PNS showed no CMEP changes after the intervention. PNS intensity of PCMS influences the magnitude of synaptic plasticity induction between the CSTs and SMs at the spinal level, and the supramaximal intensity is the best for induction of long-term potentiation-like effects. The PNS intensity may influence the number of activated SMs by axonal backpropagating pulses with PNS which must overlap with descending volleys induced by TMS.

Effects of Ischemic Compression on Trigger Points in the First Dorsal Interosseous Muscle in Patients with Thumb Carpometacarpal Osteoarthritis

Background: Thumb carpometacarpal osteoarthritis (CMC OA) is a common disorder that interferes with the ability to perform the activities of daily life. The purpose of this study was to investigate the immediate effects of ischemic compression on myofascial trigger points (MTrPs) in the first dorsal interosseous (FDI) muscle in patients with the diagnosis of thumb CMC OA. Methods: In a quasi-experimental clinical trial, thirty-one patients, 87% female (age: 82 ± 9.4 years), with thumb CMC OA, were consecutively assigned to either an experimental treatment that included the ischemic compression of the FDI MTrP or a sham treatment of the FDI MTrP for one session. The main outcome considered in the study was the pressure pain threshold (PPT). Measurements were taken pre- and post-treatment and at a 1-week follow-up period. Results: The PPT over the right (affected) FDI muscle showed statistically significant differences between groups at 1-week follow up (F = 3.518; p = 0.04) in favor of the experimental group. Conclusions: The ischemic compression of FDI-MTrPs is an appropriate part of a multimodal treatment to decrease local pain sensitivity in patients with CMC OA.

A Study on the Effect of Mental Practice Using Motor Evoked Potential-Based Neurofeedback

This study aimed to investigate whether the effect of mental practice (motor imagery training) can be enhanced by providing neurofeedback based on transcranial magnetic stimulation (TMS)-induced motor evoked potentials (MEP). Twenty-four healthy, right-handed subjects were enrolled in this study. The subjects were randomly allocated into two groups: a group that was given correct TMS feedback (Real-FB group) and a group that was given randomized false TMS feedback (Sham-FB group). The subjects imagined pushing the switch with just timing, when the target circle overlapped a cross at the center of the computer monitor. In the Real-FB group, feedback was provided to the subjects based on the MEP amplitude measured in the trial immediately preceding motor imagery. In contrast, the subjects of the Sham-FB group were provided with a feedback value that was independent of the MEP amplitude. TMS was applied when the target, moving from right to left, overlapped the cross at the center of the screen, and the MEP amplitude was measured. The MEP was recorded in the right first dorsal interosseous muscle. We evaluated the pre-mental practice and post-mental practice motor performance in both groups. As a result, a significant difference was observed in the percentage change of error values between the Real-FB group and the Sham-FB group. Furthermore, the MEP was significantly different between the groups in the 4th and 5th sets. Therefore, it was suggested that TMS-induced MEP-based neurofeedback might enhance the effect of mental practice.

Coexistence of peripheral potentiation and corticospinal inhibition following a conditioning contraction in human first dorsal interosseous muscle

We demonstrate that postactivation potentiation in human skeletal muscle is accompanied by central inhibition at the corticospinal level. However, the magnitude of central inhibition does not differ between peripherally evoked or voluntary conditioning contractions. Therefore, it is possible this central inhibition is related to muscle sensory feedback.

Do gaze behaviours during action observation predict interpersonal motor resonance?

Interpersonal motor resonance (IMR) is a common putative index of the mirror neuron system (MNS), a network containing specialised cells that fire during both action execution and observation. Visual content inputs to the MNS, however, it is unclear whether visual behaviours mediate the putative MNS response. We aimed to examine gaze effects on IMR during action observation. Neurotypical adults (N = 99; 60 female) underwent transcranial magnetic stimulation, electromyography, and eye-tracking during the observation of videos of actors performing grasping actions. IMR was measured as a percentage change in motor evoked potentials (MEPs) of the first dorsal interosseous muscle during action observation relative to baseline. MEP facilitation was observed during action observation, indicating IMR (65.43%, SE = 11.26%, P < 0.001). Fixations occurring in biologically relevant areas (face/hand/arm) yielded significantly stronger IMR (81.03%, SE = 14.15%) than non-biological areas (63.92%, SE = 14.60, P = 0.012). This effect, however, was only evident in the first of four experimental blocks. Our results suggest that gaze fixation can modulate IMR, but this may be affected by the salience and novelty of the observed action. These findings have important methodological implications for future studies in both clinical and healthy populations.