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The corticospinal tract (CST) is the preeminent voluntary motor pathway that controls human movements. Consequently, long-standing interest has focused on CST location and function in order to understand both loss and recovery of neurological function after incomplete cervical spinal cord injury, such as traumatic central cord syndrome. The hallmark clinical finding is paresis of the hands and upper-extremity function with retention of lower-extremity movements, which has been attributed to injury and the sparing of specific CST fibers. In contrast to historical concepts that proposed somatotopic (laminar) CST organization, the current narrative summarizes the accumulated evidence that 1) there is no somatotopic organization of the corticospinal tract within the spinal cord in humans and 2) the CST is critically important for hand function. The evidence includes data from 1) tract-tracing studies of the central nervous system and in vivo MRI studies of both humans and nonhuman primates, 2) selective ablative studies of the CST in primates, 3) evolutionary assessments of the CST in mammals, and 4) neuropathological examinations of patients after incomplete cervical spinal cord injury involving the CST and prominent arm and hand dysfunction. Acute traumatic central cord syndrome is characterized by prominent upper-extremity dysfunction, which has been falsely predicated on pinpoint injury to an assumed CST layer that specifically innervates the hand muscles. Given the evidence surveyed herein, the pathophysiological mechanism is most likely related to diffuse injury to the CST that plays a critically important role in hand function.

Purpose Cerebellar connectivity is thought to be abnormal in cervical dystonia (CD) and other dystonia subtypes, based on evidence from imaging studies and animal work. The authors investigated whether transcranial magnetic stimulation-induced cerebellar brain inhibition (CBI), a measure of cerebellar efficiency at inhibiting motor outflow, is abnormal in patients with CD and/or is associated with clinical features of CD. Because of methodological heterogeneity in CBI reporting, the authors deployed additional controls to reduce potential sources of variability in this study. Methods Cerebellar brain inhibition was applied in 20 CD patients and 14 healthy control subjects. Cerebellar brain inhibition consisted of a cerebellar conditioning stimulus delivered at four different interstimulus intervals (ISIs) before a test stimulus delivered to hand muscle representation in the motor cortex. The average ratio of conditioned to unconditioned motor evoked potential was computed for each ISI. Cervical dystonia clinical severity was measured using the Toronto Western Spasmodic Torticollis Rating Scale. Control experiments involved neuronavigated transcranial magnetic stimulation, neck postural control in patients, and careful screening for noncerebellar pathway inhibition via cervicomedullary evoked potentials. Results There was no difference between CBI measured in healthy control subjects and CD patients at any of the four ISIs; however, CBI efficiency was significantly correlated with worsening CD clinical severity at the 5 ms ISI. Conclusions Cerebellar brain inhibition is a variable measure in both healthy control subjects and CD patients; much of this variability may be attributed to experimental methodology. Yet, CD severity is significantly associated with reduced CBI at the 5 ms ISI, suggestive of cerebello-thalamo-cortical tract dysfunction in this disorder.

Our current understanding of synergistic muscle control is based on the analysis of muscle activities. Modules (synergies) in muscle coordination are extracted from electromyographic (EMG) signal envelopes. Each envelope indirectly reflects the neural drive received by a muscle; therefore, it carries information on the overall activity of the innervating motor neurons. However, it is not known whether the output of spinal motor neurons, whose number is orders of magnitude greater than the muscles they innervate, is organized in a low-dimensional fashion when performing complex tasks. Here, we hypothesized that motor neuron activities exhibit a synergistic organization in complex tasks and therefore that the common input to motor neurons results in a large dimensionality reduction in motor neuron outputs. To test this hypothesis, we factorized the output spike trains of motor neurons innervating 14 intrinsic and extrinsic hand muscles and analyzed the dimensionality of control when healthy individuals exerted isometric forces using seven grip types. We identified four motor neuron synergies, accounting for >70% of the variance of the activity of 54.1 ± 12.9 motor neurons, and we identified four functionally similar muscle synergies. However, motor neuron synergies better discriminated individual finger forces than muscle synergies and were more consistent with the expected role of muscles actuating each finger. Moreover, in a few cases, motor neurons innervating the same muscle were active in separate synergies. Our findings suggest a highly divergent net neural inputs to spinal motor neurons from spinal and supraspinal structures, contributing to the dimensionality reduction captured by muscle synergies. SIGNIFICANCE STATEMENT We addressed whether the output of spinal motor neurons innervating multiple hand muscles could be accounted for by a modular organization, i.e., synergies, previously described to account for the coordination of multiple muscles. We found that motor neuron synergies presented similar dimensionality (implying a >10-fold reduction in dimensionality) and structure as muscle synergies. Nonetheless, the synergistic behavior of subsets of motor neurons within a muscle was also observed. These results advance our understanding of how neuromuscular control arises from mapping descending inputs to muscle activation signals. We provide, for the first time, insights into the organization of neural inputs to spinal motor neurons which, to date, has been inferred through analysis of muscle synergies.

Background: Literature shows that intensive Functional Electrical Stimulation facilitates upper limb motor recovery after Stroke. Aim: To assess the effects of 4 weeks of FES therapy on right upper limb motor functions in patient with Chronic Stroke. Materials and Methods: The participant was thirty year old male Right Hemiparesis who had experienced Chronic Ischemic Stroke. FES therapy was given for forty five minutes per session, three sessions a week for complete four weeks. The pre and post intervention score were measured with Fugl Meyer Assessment, Voluntary Control Grading and MAS. Results: The Fugl Meyer Assessment score for right upper limb showed improvement with progression in stage of VCG for right upper limb and hand. Also improved MAS score was noted for right shoulder, elbow and hand muscles. Conclusion: The current study confirms that application of FES therapy improves upper limb motor functions in Chronic stage of Stroke after 4 weeks.

A dynamic splint is superior to traditional static splint, offering more benefits such as reduced spasticity, allowing comfortable stretch, repositioning fingers in extension positions, and increasing hand performance. This paper suggested the development of a dynamic splint based on a pulley rotation with a locking system as a home rehabilitation device to reduce hand spasticity in stroke patients. Moreover, this study consisted of two main activities: simulation using finite element analysis and clinical experimental trials. Eight stroke patients participated in 4 weeks of intervention using the proposed dynamic splint for a combined total of least 3 hours per day at home. Outcome measures included Fugl-Meyer Assessment (FMA) and Modified Modified Ashworth Scale (MMAS) at baseline, 2 weeks, and 4 weeks. After 4 weeks of wearing, participants were also asked to fill out a satisfaction questionnaire. The results showed that wearing this proposed dynamic splint over 4 weeks, the hand function of participants increased significantly(p < 0.05), and the spasticity of the hand muscles decreased significantly(p < 0.05). With an overall rating of 8 out of 10 points, stroke participants had a high level of satisfaction with this home-use dynamic splint. The findings indicated that stroke patients who used this proposed splint showed substantial changes in hand function and reduced hand spasticity.

This is a correlational research. The population of this research is all students participating in the badminton extracurricular at SMAN 06 Mukomuko 25 students. The sampling is done by using total sampling method which result in 25 male students. The data collection techniques are : 1) hand power is tested by one hand medicine ball put, 2) wrist flexibility is measured by using arc-ruler, 3) jumping smash hit skill is tested by using badminton court with grading boxes. The data is analysed by product moment correlation and dual correlation with α = 0.05 significance. The result of the data analysis are : 1) There is a significant relation between hand muscle power and students jumping smash hit skill in badminton extracurricular class at SMAN 06 Mukomuko, Bengkulu and the contribution is 39,19%, 2) There is significant relation between wrist flexibility and the students jumping smash hit skill and the contribution is 38,69%, 3) There is significant contribution of both muscle power and wrist flexibility to the students jumping smash hit skill as much as 55,65%.

Study Design Case report. Introduction A severe wrist fracture can cause permanent physical disabilities and deformities, leading to limit patients in their occupation and social environment. Purpose of the Study We aim at presenting a treatment protocol and the functional outcome of a patient with severe clinical state after a rare wrist fracture. Methods We provided physical therapy intervention associated with serious games for muscle strengthening. Results and Discussion There was an increase in strengthening and a decrease in Disability of the Arm, Shoulder and Hand score and Patient Rated Wrist Evaluation scores. The International Classification of Functioning scores have changed from severe to light or to absent in many of the domains. Conclusion The use of serious games combined with a conventional physical therapy intervention played a fundamental role in recovery and return to work activities, and there was also an important recovery of general health condition.

Purpose Targeted muscle reinnervation (TMR) has emerged as a treatment for, and prevention of, symptomatic neuromas and has been reported to be of benefit in the hand. Anatomical studies establishing landmarks for consistent identification of the motor entry points (MEPs) to the intrinsic muscles have not been performed. The purpose of this study was to provide details regarding the MEPs to the intrinsic muscles, determine which MEPs are identifiable dorsally, and develop recommended sensory to MEP nerve coaptations for prophylactic TMR at the time of ray amputation or for management of symptomatic neuromas. Methods Motor entry points to the intrinsic hand muscles were dissected in 5 fresh latex-injected cadavers. Number of MEPs, diameter, surface of entry, and distance from dorsal (Lister tubercle) and volar (hamate hook) landmarks were recorded for each target muscle. The digital sensory nerve diameters were measured for size comparison. Results Motor entry points were identified to all 19 intrinsic muscles through a volar approach and 12 through a dorsal approach. For all fingers, at least 2 MEPs were consistently identified dorsally at the base of each amputation site innervating expendable muscles. Motor entry points to the thenar muscles were only reliably identified through a volar approach. Two recommended nerve coaptations for each digit amputation were identified. All had a favorable sensory-to-MEP diameter ratio less than 2:1. Conclusions The intrinsic hand muscles have MEPs at consistent distances from bony landmarks both dorsally and volarly. Clinical relevance These results can be applied clinically to assist surgeons in identifying the locations of MEPs to the intrinsic muscles when performing TMR in the hand for both neuroma treatment and prevention.

Objective To explore the diagnostic accuracy of the split-hand index (SHI) for amyotrophic lateral sclerosis (ALS) and spinal muscular atrophy (SMA) using sonographic assessment of muscle thickness. Methods We performed a prospective sonographic assessment of hand muscle thickness in 59 controls, 87 patients with ALS, and 33 patients with SMA. We determined the diagnostic accuracy of SHI for differentiating patients with ALS and SMA from controls. Results Patients with ALS and SMA had significantly lower muscle thickness and SHI values compared with controls. SHI showed excellent diagnostic accuracy for differentiating ALS from controls, and good diagnostic accuracy for differentiating SMA from controls. Conclusions SHI determined by sonographic measurement of hand muscle thickness seems to be a promising tool for the diagnosis of ALS and may be added easily when performing neuromuscular ultrasound. Significance SHI determined by sonographic measurement of hand muscle thickness can differentiate between healthy subjects and patients with ALS and SMA.

It is believed that exposure to whole-body vibration (WBV) may increase seated occupant drowsiness and seated. The purpose of this paper is to investigate the strength of the hand grip among the young adults in Malaysia. Also, to examine the correlation between anthropometry factors such as hand length (HL), hand breadth (HB), wrist circumference (WC) and body mass index (BMI) with average full hand grip strength of young adults. 40 Malaysian young adults with equal females and males and the range age of 23 to 28 years old voluntarily basis participated in this study. Three experiments were conducted in sitting position according to American Standard Hand Therapist (ASHT) with 45º, 90o and 135o of hand flexion using dynamometer. The results show the significant different full hand grip strength between Malaysian young adult females and females, the difference full hand grip strength for different hand flexion angles in sitting position and difference correlations between anthropometry factors and full hand grip strength for both young adult males and females.

Bilateral voluntary contractions involve functional changes in both primary motor cortices. However how the unilateral voluntary contraction of hand muscles influences the contralateral corticomuscular synchronous oscillations mechanisms remains unclear. In the bimanual tasks, nine healthy subjects were instructed to generate force by abducting their left-hand index finger against a force sensor and simultaneously the right-hand precise pinch task with visual feedback. They were divided into four conditions according to the two contraction force levels of the left-hand muscles 5% and 50% maximal isometric voluntary contraction (MVC) and with/without visual feedback for the right hand. Corticomuscular synchronization of the right hand in the beta band was revealed when the subjects performed the bimanual exercise with 5% MVC of left-hand muscles, which is consistent with previous studies. As the contraction strength of the left-hand muscle increased to 50% MVC, the corticomuscular coherence (CMC) frequency of the right hand shifted to gamma band, and the CMC in beta band decreased significantly (P < 0.05) in the electroencephalography→electromyography direction. This phenomenon suggests that the corticomuscular synchronous oscillation will shift from beta band to higher frequencies (principally gamma) as the contraction force of the contralateral hand increases, which may be due to the changes in the subject's attention and more frequent synchronization of neuromuscular motor neurons oscillations. These findings will be helpful to explore the hand motion control and feedback mechanisms, and further provide a basis for the application of neuromuscular coupling in clinical rehabilitation evaluation.Video abstract: http://links.lww.com/WNR/A571.

Mechanical perturbations in one upper limb often elicit corrective responses in both the perturbed as well as its contralateral and unperturbed counterpart. These crossed corrective responses have been shown to be sensitive to the bimanual requirements of the perturbation, but crossed responses (CRs) in hand muscles are far less well studied. Here, we investigate corrective CRs in an intrinsic hand muscle, the first dorsal interosseous (1DI), to clockwise and anticlockwise mechanical perturbations to the contralateral index finger while participants performed a bimanual finger abduction task. We found that the CRs in the unperturbed 1DI were sensitive to the direction of the perturbation of the contralateral index finger. However, the size of the CRs was not sensitive to the amplitude of the contralateral perturbation nor its context within the bimanual task. The onset latency of the CRs was too fast to be purely transcortical ( NEW & NOTEWORTHY An intrinsic hand muscle shows a crossed response to a perturbation of the contralateral index finger. The crossed response is dependent on the direction of the contralateral perturbation but not on the amplitude or the bimanual requirements of the movement, suggesting a far less flexible control policy than those governing crossed responses in more proximal muscles. The crossed response is too fast to be purely mediated by transcortical pathways, suggesting subcortical contributions.

In this study, we address the issue of whether vibrotactile feedback can enhance the motor cortex excitability translated into the plastic changes in local cortical areas during motor imagery (MI) BCI-based training. For this purpose, we focused on two of the most notable neurophysiological effects of MI – the event-related-desynchronization (ERD) level and the increase in cortical excitability assessed with navigated transcranial magnetic stimulation (nTMS). For TMS navigation, we used individual high-resolution 3D brain MRIs. Ten BCI-naive and healthy adults participated in this study. The MI (rest or left/right hand imagery using Graz-BCI paradigm) tasks were performed separately in the presence and absence of feedback. To investigate how much the presence/absence of vibrotactile feedback in MI BCI-based training could contribute to the sensorimotor cortical activations, we compared the MEPs amplitude during MI after training with and without feedback. In addition, the ERD levels during MI BCI-based training were investigated. Our findings provide evidence that applying vibrotactile feedback during MI training leads to (i) an enhancement of the desynchronization level of mu-rhythm EEG patterns over the contralateral motor cortex area corresponding to the MI of the non-dominant hand; (ii) an increase in motor cortical excitability in hand muscle representation corresponding to a muscle engaged by the MI.

Hand movement is controlled by a large number of muscles acting on multiple joints in the hand and forearm. In a forearm amputee the control of a hand prosthesis is traditionally depending on electromyography from the remaining forearm muscles. Technical improvements have made it possible to safely and routinely implant electrodes inside the muscles and record high-quality signals from individual muscles. In this study, we present a database of intramuscular EMG signals recorded with fine-wire electrodes alongside recordings of hand forces in an isometric setup and with the addition of spike-sorted metadata. Six forearm muscles were recorded from twelve able-bodied subjects and nine forearm muscles from two subjects. The fully automated recording protocol, based on command cues, comprised a variety of hand movements, including some requiring slowly increasing/decreasing force. The recorded data can be used to develop and test algorithms for control of a prosthetic hand. Assessment of the signals was done in both quantitative and qualitative manners., Measurement(s)muscle electrophysiology trait • muscle contractionTechnology Type(s)micro electrode • strain gaugesFactor Type(s)age • muscleSample Characteristic - OrganismHomo sapiens Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.11310011

Introduction. Coexistent involvement of upper and lower motor neurons is a characteristic feature of amyotrophyc lateral syndrome (ALS) necessary for the diagnosis. Diagnosis of upper motor neuron involvement in ALS is based solely on clinical features, which may not be detected at the disease onset and in rare forms manifesting clinically as the local lower motor neuron syndrome (LLMNS). The main method of assessment of the functional state of the upper motor neuron in ALS is transcranial magnetic stimulation (TMS). It allows assessing the excitability of motor cortex, corticospinal path function, and mapping of cortical representation of the muscles. In patients with ALS changes of various indicators demonstrating hyperexcitability as well as degenerative lesions of the motor cortex and the corticospinal tracts are recorded on TMS. Objective: to discuss changes in the TMS in patients with LAS, pathophysiological mechanisms of their formation and possible diagnostic value. Results. In 22 patients with LLMNS, navigation TMS revealed disturbances of intracortical suppression on paired stimulation with recording period of silence, increase of motor threshold in dominant hemisphere, decrease of the weighted square and reorganization of cortical representations of the hand muscles. Conclusion. The data obtained allow to consider navigation TMS as a promising technology for identifying upper motor neuron involvement in patients with ALS., №2 (2018)

Most of the motor mapping procedures using navigated transcranial magnetic stimulation (nTMS) follow the conventional somatotopic organization of the primary motor cortex (M1) by assessing the representation of a particular target muscle, disregarding the possible coactivation of synergistic muscles. In turn, multiple reports describe a functional organization of the M1 with an overlapping among motor representations acting together to execute movements. In this context, the overlap degree among cortical representations of synergistic hand and forearm muscles remains an open question. This study aimed to evaluate the muscle coactivation and representation overlapping common to the grasping movement and its dependence on the stimulation parameters. The nTMS motor maps were obtained from one carpal muscle and two intrinsic hand muscles during rest. We quantified the overlapping motor maps in size (area and volume overlap degree) and topography (similarity and centroid’s Euclidean distance) parameters. We demonstrated that these muscle representations are highly overlapped and similar in shape. The overlap degrees involving the forearm muscle were significantly higher than only among the intrinsic hand muscles. Moreover, the stimulation intensity had a stronger effect on the size compared to the topography parameters. Our study contributes to a more detailed cortical motor representation towards a synergistic, functional arrangement of M1. Understanding the muscle group coactivation may provide more accurate motor maps when delineating the eloquent brain tissue during pre-surgical planning.

The spatial accuracy of transcranial magnetic stimulation (TMS) may be as small as a few millimeters. Despite such great potential, navigated TMS (nTMS) mapping is still underused for the assessment of motor plasticity, particularly in clinical settings. Here, we investigate the within‐limb somatotopy gradient as well as absolute and relative reliability of three hand muscle cortical representations (MCRs) using a comprehensive grid‐based sulcus‐informed nTMS motor mapping. We enrolled 22 young healthy male volunteers. Two nTMS mapping sessions were separated by 5–10 days. Motor evoked potentials were obtained from abductor pollicis brevis (APB), abductor digiti minimi, and extensor digitorum communis. In addition to individual MRI‐based analysis, we studied normalized MNI MCRs. For the reliability assessment, we calculated intraclass correlation and the smallest detectable change. Our results revealed a somatotopy gradient reflected by APB MCR having the most lateral location. Reliability analysis showed that the commonly used metrics of MCRs, such as areas, volumes, centers of gravity (COGs), and hotspots had a high relative and low absolute reliability for all three muscles. For within‐limb TMS somatotopy, the most common metrics such as the shifts between MCR COGs and hotspots had poor relative reliability. However, overlaps between different muscle MCRs were highly reliable. We, thus, provide novel evidence that inter‐muscle MCR interaction can be reliably traced using MCR overlaps while shifts between the COGs and hotspots of different MCRs are not suitable for this purpose. Our results have implications for the interpretation of nTMS motor mapping results in healthy subjects and patients with neurological conditions.

Acute exercise can modulate the excitability of the non-exercised upper-limb representation in the primary motor cortex (M1). Accumulating evidence demonstrates acute exercise affects measures of M1 intracortical excitability, with some studies also showing altered corticospinal excitability. However, the influence of distinct M1 interneuron populations on the modulation of intracortical and corticospinal excitability following acute exercise is currently unknown. We assessed the impact of an acute bout of leg cycling exercise on unique M1 interneuron excitability of a non-exercised intrinsic hand muscle using transcranial magnetic stimulation (TMS) in young adults. Specifically, posterior-to-anterior (PA) and anterior-to-posterior (AP) TMS current directions were used to measure the excitability of distinct populations of interneurons before and after an acute bout of exercise or rest. Motor evoked potentials (MEPs) and short-interval intracortical inhibition (SICI) were measured in the PA and AP current directions in M1 at two time points separated by 25 minutes of rest, as well as immediately and 30 minutes after a 25-minute bout of moderate-intensity cycling exercise. Thirty minutes after exercise, MEP amplitudes were significantly larger than other timepoints when measured with AP current, whereas MEP amplitudes derived from PA current did not show this effect. Similarly, SICI was significantly decreased immediately following acute exercise measured with AP but not PA current. Our findings suggest that the excitability of unique M1 interneurons are differentially modulated by acute exercise. These results indicate that M1 interneurons preferentially activated by AP current may play an important role in the exercise-induced modulation of intracortical and corticospinal excitability.

Dissociated muscle atrophy is an established clinical phenomenon of amyotrophic lateral sclerosis (ALS), heralded by the split-hand sign which is clinically characterised by preferential wasting of thenar group of intrinsic hand muscles (abductor pollicis brevis (APB) and first dorsal interosseous (FDI)), when compared with the hypothenar group.1–3 The specificity of the split-hand phenomenon in ALS was further established by the split-hand index, a neurophysiological biomarker utilising motor amplitudes.4 Additionally, dissociated patterns of muscle atrophy in ALS may also be characterised by the split-hand plus (preferential dysfunction of thenar muscles compared with flexor pollicis longus),4 split-elbow (preferential weakness of biceps brachii compared with triceps muscle)5 and split-leg signs (preferential dysfunction of ankle plantar flexor compared with the dorsiflexor muscles). …

Currently, myoelectric prostheses lack dexterity and ease of control, in part because of inadequate schemes to extract relevant muscle features that can approximate muscle activation patterns that enable individuated dexterous finger motion. This project seeks to apply a novel algorithm pipeline that extracts muscle activation patterns from one limb, as well as from forearm muscles of the opposite limb, to predict muscle activation data of opposite limb intrinsic hand muscles, with the long-range goal of informing dexterous prosthetic control.

Electromyography (EMG) based interfaces have been used in various robotics studies ranging from teleoperation and telemanipulation applications to the EMG based control of prosthetic, assistive, or robotic rehabilitation devices. But most of these studies have focused on the decoding of user’s motion or on the control of the robotic devices in the execution of simple tasks (e.g., grasping tasks). In this work, we present a learning scheme that employs High Density Electromyography (HD-EMG) sensors to decode a set of dexterous, in-hand manipulation motions (in the object space) based on the myoelectric activations of human forearm and hand muscles. To do that, the subjects were asked to perform roll, pitch, and yaw motions manipulating two different cubes. The first cube was designed to have a center of mass coinciding with the geometric center of the cube, while for the second cube the center of mass was shifted 14 mm to the right (off-centered design). Regarding the acquisition of the myoelectric data, custom HD-EMG electrode arrays were designed and fabricated. Using these arrays, a total of 89 EMG signals were extracted. The object motion decoding was formulated as a regression problem using the Random Forests (RF) technique and the muscle importances were studied using the inherent feature variables importance calculation procedure of the RF. The muscle importance results show that different subjects use different strategies to execute the same motions on same object when the weight is off-centered. Finally, the decoded motions were used to control a five fingered robotic hand in a proof-of-concept application.

Transcranial magnetic stimulation (TMS) of the precentral hand knob can evoke motor evoked potentials (MEP) in contralateral hand muscles. Biophysical modelling points to the dorsal premotor cortex (PMd) in the superficial crown-lip region as primary site of TMS-induced neuronal excitation. Here, we used a sulcus-aligned MRI-informed TMS mapping approach to determine the optimal site (hotspot) for evoking MEPs in the precentral hand knob. Individual precentral hotspot location varied along the rostro-caudal axis. Individuals with a more rostral location had longer MEP latencies. Spatiotemporal “hotspot rostrality” was associated with higher precentral myelin-related signals, stronger movement-related activation of PMd in the precentral crown, and higher temporal precision during paced finger tapping. Together, our multimodal mapping approach provides first-time evidence for behaviourally relevant, structural and functional phenotypic variation in the crown of human precentral motor hand knob. The results have important implications for physiological and interventional TMS studies targeting the precentral hand knob.

In this study, we investigated the electrophysiologic recovery of the abductor pollicis brevis (APB) muscle after contralateral seventh cervical (cC7) nerve transfer for the treatment of global brachial plexus avulsion (GBPA). We retrospectively analyzed the electromyography records of 95 patients with GBPA, comprising 81 men and 14 women, focusing on the motor unit potential (MUP) recovery of the APB. All patients underwent cC7-median nerve (MN) transfer. The cC7 nerve was transferred to the MN alone in 58 patients (One-Nerve Group), whereas 37 patients underwent cC7 transfer to the MN and another nerve (Two-Nerve Group). Fifty-three patients (MUP Group) exhibited MUP recovery of the APB, whereas 42 patients did not (No-MUP Group). The MUP Group comprised 32 patients from the One-Nerve Group and 21 patients from the Two-Nerve Group. The mean age of the MUP Group was significantly lower than that of the No-MUP Group. In summary, electrophysiologic recovery of the APB was common in patients with GBPA after cC7-MN transfer, indicating that it may be possible to restore the function of the intrinsic muscles of the hand after GBPA. The rehabilitation strategy for patients with GBPA, which overlooks the restoration of intrinsic hand muscle function, may require amendment.

Biosignals from skeletal muscle have been used to control human–machine interface. Signals from paretic muscles of humans with stroke are distorted and highly variable. Here, we examine the stability of surface electromyography (sEMG) features from paretic hand muscles to enable continuous, real-time multicommand control of a human–computer interface (HCI). Subjects with long standing cortical strokes (>6 months, $n$ = 12) and neurologically intact controls ( $n$ = 12) performed two wrist rotations (wrist extend and wrist flex) and two grips (power grip and fine grip) with the nondominant (controls) or paretic (stroke patients) hand. Data reduction analyses revealed a distinct pattern of coactivation across muscles for each gesture. These synergies were similar for control and stroke groups and stable across sessions. Results of offline experiments involving wrist rotation and hand grips confirmed that gestures performed in isolation or combination were recognized at greater than chance level in both groups ( $p$ $p$ < 0.01). Taken together, these results demonstrate that sEMG synergy features from paretic hand muscles can be used to drive continuous, real-time multicommand control of an HCI.

In anthropological sciences, muscle attachments are typically utilized for reconstructing the physical activities of past human populations. This approach relies on the concept that entheseal bone morphology is influenced by cumulative biomechanical stress. A fundamental criterion for assessing the stage of entheseal change involves the proportion of elevated bone area. However, it is not yet clear if bone elevation is associated with biomechanical forces exerted during physical activity, while the histology of the entheses of the human hand, the least-bodyweight-bearing anatomical area, is not fully investigated. Multiple previous studies on entheses have concluded that the concentration of calcified fibrocartilage reflects the level of applied forces. On this basis, if hand entheseal surface elevation was associated with the level of biomechanical stress, then a greater amount of calcified fibrocartilage would be expected in entheses' central and more projecting bone areas. More importantly, individual entheses with a greater proportion of elevated bone areas would present a higher total concentration of calcified fibrocartilage. To test these hypotheses, this pilot study conducted a histological quantitative analysis on two thumb entheses of four fully-documented body donors. Across individuals, all central entheseal regions presented greater calcified fibrocartilage, while the entheses showing additional bone elevation in their marginal areas comprised substantially higher total values. The observations of this small-scale pilot study support the concept that interindividual differences in entheseal bone morphology are related to varying levels of biomechanical loading. Furthermore, they encourage future research to compile larger sample sizes, for comparing individuals with distinct lifelong activities. Anat Rec, 302:1093-1103, 2019. © 2018 Wiley Periodicals, Inc.

Limb amputation injuries and their subsequent replantation is a time-critical exercise if function is to be restored. The exact time limit to functional replantation is still poorly defined in the literature owing to the multitude of factors that influence functional recovery. The relative metabolic activity of a tissue is lower under hypothermic conditions, and subsequently, moderate delays in restoring circulation can still achieve good functional outcomes if the amputated part is transported appropriately. Some surgeons have adopted the practice of, in cases where the delay to replantation is beyond 8–10 h, resecting skeletal muscle from the amputated part to avoid the sequelae of its ischaemic period. We report the case of a traumatic trans-carpal hand amputation in a 40-year-old male, with a second-level injury more distally at the metacarpal heads, who was replanted with a total ischaemic time of 19 h and 25 min. The decision was made to retain his intrinsic hand muscles in contradiction to common practice. At 2.5 years follow-up, he has regained a remarkable level of function of his hand including activation of his intrinsic hand muscles. His Semmes Weinstein testing has also shown good sensory recovery of his repaired nerves and he enjoys little, if any, disability as a result of his injury (despite a double-level injury on the dorsal ulna aspect of his forearm). This suggests, in cases of hand amputation with appropriate hypothermic transportation of the amputated part, ischaemia times up to 20 h may be compatible with restoration of intrinsic hand function. Level of Evidence: Level V, risk / prognostic study.

The aim of this study was to test the effects of kilohertz frequency alternating current (KHFAC) surface stimulation applied to the ulnar nerve on force and myoelectrical activity of the abductor digiti minimi (ADM) muscle. Eighteen healthy volunteers (age: 27.6 ± 7.9 years; 10 males, 8 females) were included in the study. Each subject participated in one session during which a biphasic 7 kHz rectangular pulse was delivered above the medial epicondyle of the humerus to induce ulnar nerve blocking. ADM electromyographic (EMG) activity and contraction force were measured before (Pre), immediately after, and following 5 and 10 min post stimulation (post 1, post 2). The results showed that EMG activity decreased immediately after stimulation compared to prestimulation, it returned to the level of prestimulation at 5 min (post 1), and decreased again at 10 min (post 2). Furthermore, analysis of compound adjusted z-score indicated significant decrease of force and myoelectrical activity immediately, and 10 min post stimulation. The findings, which demonstrate that KHFAC surface stimulation of the ulnar nerve may decrease the motor activity of intrinsic hand muscle, can help to develop future methods of neuromodulation to treat hand spasticity.

Digital sesamoids are found in the metapodial-phalangeal joints of most mammals and quadrupedal tetrapods, yet their functional significance is still unclear. During primate evolution, a slight decline in their frequency has been associated with brachiation in gibbons, followed by a quasi-complete absence in orangutans then a slight resurgence occurred in gorillas and chimpanzees. Simultaneously, forearm muscles showed a progressive division in hominoid evolution towards a more "individualistic" musculature yielding more mobility and independence to some fingers. In humans, sesamoids are consistently observed in thumbs and big toes and frequently in other hypermobile digits such as the index and little fingers. Using a simple mathematical equation, this paper attempted to quantify a presumed association between hypermobile fingers and sesamoid frequency and distribution in humans. To this, an anatomic definition of digital independence has been formulated which includes three variables; (1) number and (2) frequency of independent flexor/extensor forearm muscles destined to a single finger, (3) and number of free/absent webspace. Results of previous meta-analyses and means of big sample studies were used to evaluate the frequency of such muscles. The expected values obtained via this model were found to be very close to the observed (published) values of the ossified sesamoids in human hands, and that in terms of frequency and distribution. The findings in humans showed a quasi-linear association between the degree of mobility and sesamoid frequency. The more the number of independent muscles destined to a finger, the more its metacarpo-phalangeal joint is likely to bear sesamoids. Based on our results and on a new analysis of primates' forearm/hand muscles and sesamoid evolution, a new hypothesis is proposed to answer two questions; the evolution of digital sesamoid frequency in primates and its sesamoid distribution in human digits. It claims that the number/frequency of independent forearm/hand muscles, and particularly the independent extensors, is likely to be a major factor in sesamoid reversion in hominoids. The argument is based on the link between the metatarsal break induced by the digitigrade locomotion observed in quadrupedal mammals and tetrapods and the amount of extra-extension of the metacarpo-phalangeal joints conferred by the individualization of some forearm extensors. The same rationale yielded similar conclusions when applied to both the hand and foot. The manipulative function of the hand and the plantigrade locomotion of the foot required such extra-extension in specific digits and consequently, a higher frequency of digital sesamoids was associated with these two different functions. The new evolutionary analysis suggests evolutionary pathways for both, the sesamoids of the hands and feet, and speculates that muscle individualization would have induced a very slow re-acquisition of digital sesamoids when compared to their rapid decline after brachiation. It is the first hypothesis offering a plausible explication on the recent evolution of digital sesamoids; specifically, the progression of sesamoid frequency in African apes and its resurgence, prevalence and distribution in humans. Anat Rec, 301:1046-1060, 2018. © 2018 Wiley Periodicals, Inc.

The hand knob area is the cortical representation of motor hand function. The current study aimed to investigate the effects of eloquent area gliomas on the morphometry of the hand motor cortex and preoperative hand motor function. A retrospective study of 320 glioma patients was conducted. Seventy-eight patients with gliomas involving motor functional area were finally enrolled. Using axial T2-weight magnetic resonance images, the width and height of the hand knob were measured in both hemispheres, and differences were compared between the affected and unaffected hemispheres. Receiver operating characteristic (ROC) curve and logistic regression analysis were used to estimate the degree of correlation between distance measurements and motor impairment. The width and height of the hand knob in the affected and unaffected hemispheres were significantly different (p

Experimental muscle pain inhibits corticomotor excitability (CE) of upper limb muscles. It is unknown if this inhibition affects overlapping muscle representations within the primary motor cortex to the same degree. This study explored CE changes of the first dorsal interosseus (FDI) and extensor carpi radialis (ECR) muscles in response to muscle pain. Participants (n=13) attended two sessions (≥48 hours in-between). Hypertonic saline was injected in the ECR (session one) or the FDI (session two) muscle. CE, assessed by transcranial magnetic stimulation (TMS) motor-evoked potentials (MEPs), was recorded at baseline, during pain, and twenty minutes postinjection together with pain intensity ratings. Pain intensity ratings did not differ between the two pain sites (p=0.19). In response to FDI muscle pain, the MEPs of the FDI muscle were reduced at 2 and 4 min postinjection (p≤0.03), but not after ECR muscle pain. No significant MEP change was detected for the ECR muscle (p=0.62). No associations between MEPs and pain intensity were found (p>0.2). The present results indicate that the output from overlapping cortical representations of two muscles differentially adapts to acute muscle pain.

The dorsal and ventral premotor cortices (PMd and PMv, respectively) each take part in unique aspects for the planning and execution of hand movements. These premotor areas are components of complex anatomical networks that include the primary motor cortex (M1) of both hemispheres. One way that PMd and PMv could play distinct roles in hand movements is by modulating the outputs of M1 differently. However, patterns of effects from PMd and PMv on the outputs of M1 have not been compared systematically. Our goals were to study how PMd within the same (i.e., ipsilateral or iPMd) and in the opposite hemisphere (i.e., contralateral or cPMd) can shape M1 outputs and then compare these effects with those induced by PMv. We used paired-pulse protocols with intracortical microstimulation techniques in sedated female cebus monkeys while recording EMG signals from intrinsic hand and forearm muscles. A conditioning stimulus was delivered in iPMd or cPMd concurrently or before a test stimulus in M1. The patterns of modulatory effects from PMd were compared with those from PMv collected in the same animals. Striking differences were revealed. Conditioning stimulation in iPMd induced more frequent and powerful inhibitory effects on M1 outputs compared with iPMv. In the opposite hemisphere, cPMd conditioning induced more frequent and powerful facilitatory effects than cPMv. These contrasting patterns of modulatory effects could allow PMd and PMv to play distinct functions for the control of hand movements and predispose them to undertake different, perhaps somewhat opposite, roles in motor recovery after brain injury. SIGNIFICANCE STATEMENT The dorsal and ventral premotor cortices (PMd and PMv, respectively) are two specialized areas involved in the control of hand movements in primates. One way that PMd and PMv could participate in hand movements is by modulating or shaping the primary motor cortex (M1) outputs to hand muscles. Here, we studied the patterns of modulation from PMd within the same and in the opposite hemisphere on the outputs of M1 and compared them with those from PMv. We found that PMd and PMv have strikingly different effects on M1 outputs. These contrasting patterns of modulation provide a substrate that may allow PMd and PMv to carry distinct functions for the preparation and execution of hand movements and for recovery after brain injury.

Introduction This study seeks to elucidate the optimal scan time to detect fasciculations by using ultrasound in the diagnosis of amyotrophic lateral sclerosis (ALS). Methods The intervals between fasciculations were recorded from tongue, abdominal, and limb muscles in ALS patients, incorporating assessment of the cumulative probability of 2 fasciculations occurring. Results From prospective studies of 228 muscles from 19 ALS patients, fasciculations were detectable in 68% of patients. The longest interfasciculation interval recorded was 81.4 s in the hand muscle. The cumulative probability of 2 fasciculations occurring was calculated as ≥0.9 in all muscles during a period of 60 s. Discussion A definition of 2 or more fasciculations occurring during a scan time of 60 s reliably allowed detection of fasciculations in ALS. Muscle Nerve, 2017

Introduction. “Man-in-the-barrel syndrome” is a neurological phenotype with brachial diplegia, normal sensation, and preserved motor function of the lower limb. It has been described in various neuropathological conditions affecting the cerebral hemispheres, pons, upper spinal cord, and peripheral neurons. Severe hypotension leading to watershed infarctions leading to this phenotype has been reported. We describe the first case of “man-in-the-barrel syndrome” in a patient with a precipitous drop in blood pressure following oral antihypertensive medications. Case Presentation. A 75-year-old Sri Lankan male presented following a generalized tonic-clonic seizure to a tertiary care hospital. Upon recovery, he was noted to have severe brachia diplegia affecting shoulder movements with preserved hand muscle power and motor functions of the lower limb. The previous day, he was newly diagnosed with markedly elevated blood pressure without acute end organ involvement. Treatment with three antihypertensives had been initiated. Noncontrast CT of the brain revealed watershed infarctions affecting both cerebral hemispheres. Conclusion. It is generally unwise to lower blood pressure very rapidly, as ischemic damage can occur in vascular beds that are habituated to high levels of blood pressure in the brain. Ischemic damage caused by rapid lowering of blood pressure may rarely result in “man-in-the-barrel syndrome” leading to severe functional disability.

OBJECTIVE Neuromuscular electrical stimulation can help activate muscles of individuals with neurological disorders. However, conventional electrical stimulation targets distal branches of motor axons, and activates muscles non-physiologically. For example, stimulation at the muscle belly activates muscles in a highly synchronized manner. Accordingly, we investigated whether the muscle activation pattern was more asynchronized through transcutaneous stimulation near the cervical spinal cord (tsCSC). APPROACH A stimulation array was placed on the posterior side near the cervical spinal cord, to target the arm and hand muscles. Stimulation trains of 10 Hz and 30 Hz were delivered. Electromyogram signals were recorded to quantify the muscle activation patterns. Arm and finger joint kinematics were also recorded using a motion capture system. MAIN RESULTS After an initial synchronized activation prior to 35 ms after stimulation onset, we observed substantial asynchronized muscle activities with a long latency (>35 ms). The asynchronized activation is also more evident in distal muscles compared with the proximal muscles. In addition, the decreased synchronization level of muscle activities correlated with a reduced fluctuation of joint movement. The highly asynchronized muscle activities indicated an activation of the sensory axons and/or dorsal roots as well as a possible involvement of some spinal-supraspinal circuitry. SIGNIFICANCE Our tsCSC approach can improve the muscle activation pattern during electrical stimulation with a possible involvement of the spinal and supraspinal pathways, which can facilitate applications on rehabilitation/assistance of individuals with impaired motor function.

Fatiguing exercise causes a reduction in motor drive to the muscle. Group III/IV muscle afferent firing is thought to contribute to this process; however, the effect on corticospinal and intracortical networks is poorly understood. In two experiments, participants performed sustained maximal isometric finger abductions of the first dorsal interosseous (FDI) muscle, with postexercise blood flow occlusion (OCC) to maintain the firing of group III/IV afferents or without occlusion (control; CON). Before and after exercise, single- and paired-pulse transcranial magnetic stimulation (TMS) tested motor evoked potentials (MEPs), intracortical facilitation [ICF (12 ms)], and short-interval intracortical inhibition [SICI2 (2 ms), SICI3 (3 ms)]. Ulnar nerve stimulation elicited maximal M waves (MMAX). For experiment 1 ( n = 16 participants), TMS intensities were 70% and 120% of resting motor threshold (RMT) for the conditioning and MEP stimuli, respectively. For experiment 2 ( n = 16 participants), the MEP was maintained at 1 mV before and after exercise and the conditioning stimulus individualized. In experiment 1, MEP/MMAX was reduced after exercise (~48%, P = 0.007) but was not different between conditions. No changes occurred in ICF or SICI. In experiment 2, MEP/MMAX increased (~27%, P = 0.027) and less inhibition (SICI2: ~21%, P = 0.021) occurred after exercise for both conditions, whereas ICF decreased for CON only (~28%, P = 0.006). MEPs and SICI2 were modulated by fatiguing contractions but not by group III/IV afferent firing, whereas sustained afferent firing appeared to counteract postexercise reductions in ICF in FDI. The findings do not support the idea that actions of group III/IV afferents on motor cortical networks contribute to the reduction in voluntary activation observed in other studies. NEW & NOTEWORTHY This is the first study to investigate, in human hand muscles, the action of fatigue-related group III/IV muscle afferent firing on intracortical facilitation and inhibition. In fatigued and nonexercised hand muscles, intracortical inhibition is reduced after exercise but is not modulated differently by the firing of group III/IV afferents. However, facilitation is maintained for the fatigued muscle when group III/IV afferents fire, but these results are unlikely to explain the reduction in voluntary activation observed in other studies.

Objective: The aim of this study was to analyze finger strength and effects of muscle fatigue on the ability to shoot. Background: The finger and hand muscles of soldiers are subject to high loads. For example, the trigger pull of military pistols can amount up to 58 N (≈6 kg) and could cause muscle fatigue in the trigger finger. For soldiers, however, maintaining the ability to shoot is essential for self-defense and survival. Method: The marksmanship training of 30 German soldiers (15 female) ages 18 to 40 years was evaluated. Three consecutive exercises with a total of 60 rounds were fired from target ranges of 5 and 10 m, equally using a single-action and double-action trigger mode. Maximum voluntary isometric contraction of the index finger (MVCIF) was measured before and after each of the three firing exercises. Results: Shooting reduced MVCIF in female (88.2 ± 15.8 N to 67.3 ± 17.7 N, p < .001) and male soldiers (145.8 ± 21.7 N to 112.7 ± 26.6 N, p < .001). Of the 30 subjects, 23 were unable to shoot due to fatigue, including 15 of 15 female soldiers. The higher MVCIF was at rest, the less commonly (r = .73, p < .001) and the later (r = 0.82, p < .001) task failure occurred. Two intermissions of approximately 6 min did not suffice for a significant recovery. Conclusion: Excessive trigger pull weight causes muscle fatigue of the index finger and can ultimately lead to task failure during pistol marksmanship training. Short breaks are insufficient for the recovery of finger muscles. Application: This study presents a new perspective on ideal trigger pull weight, which should be carefully considered by manufacturers to allow repetitive firing and simultaneously ensure safe handling., publishedVersion

Neurons in the primate motor cortex, including identified pyramidal tract neurons projecting to the spinal cord, respond to the observation of others’ actions, yet this does not cause movement in the observer. Here, we investigated changes in spinal excitability during action observation by monitoring short latency electromyographic responses produced by single shocks delivered directly to the pyramidal tract. Responses in hand and digit muscles were recorded from two adult rhesus macaques while they performed, observed or withheld reach-to-grasp and hold actions. We found modest grasp-specific facilitation of hand muscle responses during hand shaping for grasp, which persisted when the grasp was predictable but obscured from the monkey’s vision. We also found evidence of a more general inhibition before observed movement onset, and the size of this inhibition effect was comparable to the inhibition after an explicit NoGo signal. These results confirm that the spinal circuitry controlling hand muscles is modulated during action observation, and this may be driven by internal representations of actions. The relatively modest changes in spinal excitability during observation suggest net corticospinal outflow exerts only minor, sub-threshold changes on hand motoneuron pools, thereby preventing any overflow of mirror activity into overt movement.

Wrist posture impacts the muscle lengths and moment arms of the extrinsic finger muscles that cross the wrist. As a result, the electromyographic (EMG) activity associated with digit movement at different wrist postures may also change. Therefore, we sought to quantify the posture-dependence of extrinsic finger muscle activity. Fine-wire bipolar electrodes were inserted in the extrinsic hand muscles of able-bodied subjects to record EMG activity during wrist and finger movements in various postures. EMG activity of all the recorded finger muscles were significantly different (p

The study aimed to examine the effect of a priming cathodal transcranial direct current stimulation (ctDCS) before subsequent anodal-tDCS (atDCS) was applied during low workload cycling exercise on the corticospinal responses in young healthy individuals. Eleven young subjects participated in two sessions receiving either priming ctDCS or sham stimulation, followed by atDCS while cycling (i.e. ctDCS-atDCS, sham-atDCS) at 1.2 times their body weight (84 ± 20 W) in a counterbalanced double-blind design. Corticospinal excitability was measured with motor evoked potentials (MEPs) elicited via transcranial magnetic stimulation with the intensity set to produce an MEP amplitude of 1 mV in a resting hand muscle at baseline (PRE), following priming tDCS (POST-PRIMING) and post atDCS combined with cycling exercise (POST-TEST). There was a significant interaction between time and intervention (P < 0.01) on MEPs. MEPs increased from PRE (1.0 ± 0.06 mV) to POST-TEST (1.3 ± 0.06 mV) during ctDCS-atDCS (P < 0.001) but did not change across time during sham-atDCS (1.0 ± 0.06 mV, P > 0.7). Furthermore, MEPs were higher in ctDCS-atDCS compared to sham-atDCS (P < 0.01) at both POST-PRIMING (ctDCS-atDCS: 1.1 ± 0.06, sham-atDCS: 1.0 ± 0.06) and POST-TEST (ctDCS-atDCS: 1.3 ± 0.06, sham-atDCS: 1.0 ± 0.06). These outcomes demonstrate that cathodal tDCS priming can enhance corticospinal excitability following anodal tDCS applied in combination with cycling exercise. The findings have implications for the application of tDCS in combination with cycling exercise in rehabilitation and sporting contexts.

Hand gesture and grip formations are produced by the muscle synergies arising between extrinsic and intrinsic hand muscles and many functional hand movements involve repositioning of the thumb relative to other digits. In this study we explored whether changes in thumb posture in able-body volunteers can be identified and classified from the modulation of forearm muscle surface-electromyography (sEMG) alone without reference to activity from the intrinsic musculature. In this proof-of-concept study, our goal was to determine if there is scope to develop prosthetic hand control systems that may incorporate myoelectric thumb-position control. Healthy volunteers performed a controlled-isometric grip task with their thumb held in four different opposing-postures. Grip force during task performance was maintained at 30% maximal-voluntary-force and sEMG signals from the forearm were recorded using 2D high-density sEMG (HD-sEMG arrays). Correlations between sEMG amplitude and root-mean squared estimates with variation in thumb-position were investigated using principal-component analysis and self-organizing feature maps. Results demonstrate that forearm muscle sEMG patterns possess classifiable parameters that correlate with variations in static thumb position (accuracy of 88.25 ± 0.5% anterior; 91.25 ± 2.5% posterior musculature of the forearm sites). Of importance, this suggests that in transradial amputees, despite the loss of access to the intrinsic muscles that control thumb action, an acceptable level of control over a thumb component within myoelectric devices may be achievable. Accordingly, further work exploring the potential to provide myoelectric control over the thumb within a prosthetic hand is warranted.

Summary Background Somatotopy is considered the hallmark of the primary motor cortex. While this is fundamentally true for the major body parts (head, upper and lower extremities), evidence supporting the existence of within-limb somatotopy is scarce. Method We report a young man presenting recurrent ischemic strokes with selective finger weakness in whom serial motor cortex mapping procedures were performed. Result Following the first stroke, which largely spared the motor cortex, motor mapping displayed overlap of the motor representations of the hand muscles. The second focal stroke, affecting the lateral part of the hand knob, resulted in selective loss of the first dorsal interosseous muscle motor evoked potentials while sparing those of the adductor digiti minimi muscle. This observation is in apparent contradiction with the first mapping results that suggested complete overlap of motor representations. Discussion Our mapping results provide evidence for the existence of very precise within-limb somatotopy and confirm the proposed homuncular order, whereby lateral fingers are represented laterally and medial fingers medially. The discrepancy between the initial and subsequent mapping results is discussed in light of functional organization of the primary motor cortex.

Motor-evoked potentials (MEPs), elicited by Transcranial Magnetic Stimulation (TMS) over the motor cortex, are reduced during the preparatory period in delayed response tasks. Here we examine how MEP suppression varies as a function of the anatomical organization of the motor cortex. MEPs were recorded from a left index muscle while participants prepared a hand or leg movement in Experiment 1, or prepared an eye or mouth movement in Experiment 2. In this manner, we assessed if the level of MEP suppression in a hand muscle varied as a function of the anatomical distance between the agonist for the forthcoming movement and the muscle targeted by TMS. MEPs suppression was attenuated when the cued effector was anatomically distant from the hand (e.g., leg or facial movement compared to finger movement). A similar effect was observed in Experiment 3 in which MEPs were recorded from a muscle in the leg and the forthcoming movement involved the upper limb or face. These results demonstrate an important constraint on preparatory inhibition: It is sufficiently broad to be manifest in a muscle that is not involved in the task, but is not global, showing a marked attenuation when the agonist muscle belongs to a different segment of the body.New & NoteworthyUsing TMS, we examine changes in corticospinal excitability as people prepare to move. Consistent with previous work, we observe a reduction in excitability during the preparatory period, an effect observed in both task relevant and task irrelevant muscles. However, this preparatory inhibition is anatomically constrained, attenuated in muscles belonging to a different body segment than the agonist of the forthcoming movement.

The H (Hoffman) reflex is a noninvasive technique used to evaluate the synaptic organization of the spinal cord, as well as the excitability of the reflex arc. In this procedure, percutaneous electrical stimuli are applied to the peripheral nerve to evoke reflex responses that can be measured by the electromyogram of the target muscle. Different factors can modulate the H-reflex amplitude. Nonetheless, few studies have investigated how contraction intensity influence the excitability of spinal cord circuits controlling upper limb muscle. Therefore, the present project is aimed at investigating the effect of contraction intensity on the excitability of spinal cord circuits of a hand muscle.

The role of the hand is crucial for the performance of activities of daily living, thereby ensuring a full and autonomous life. Its motion is controlled by a complex musculoskeletal system of approximately 38 muscles. Therefore, measuring and interpreting the muscle activation signals that drive hand motion is of great importance in many scientific domains, such as neuroscience, rehabilitation, physiotherapy, robotics, prosthetics, and biomechanics. Electromyography (EMG) can be used to carry out the neuromuscular characterization, but it is cumbersome because of the complexity of the musculoskeletal system of the forearm and hand. This paper reviews the main studies in which EMG has been applied to characterize the muscle activity of the forearm and hand during activities of daily living, with special attention to muscle synergies, which are thought to be used by the nervous system to simplify the control of the numerous muscles by actuating them in task-relevant subgroups. The state of the art of the current results are presented, which may help to guide and foster progress in many scientific domains. Furthermore, the most important challenges and open issues are identified in order to achieve a better understanding of human hand behavior, improve rehabilitation protocols, more intuitive control of prostheses, and more realistic biomechanical models.

[Purpose] Handgrip strength is a surrogate indicator for assessing disease-related and age-related skeletal muscle loss. Clinical utility as such a surrogate can be at least partially explained by the close relationship between handgrip strength and whole-body skeletal muscle mass. The handgrip strength is related to hand muscle size. Thus, the present study examined whether hand muscle thickness is associated with whole-body skeletal muscle mass. [Subjects and Methods] Thirty healthy male adults participated in this study. All subjects were right-hand dominant. Two muscle thicknesses (lumbrical and interosseous muscles) in the right hand were measured using ultrasonography. Whole-body and appendicular skeletal muscle masses were assessed using dual-energy X-ray absorptiometry. [Results] Although lumbrical muscle thickness was not correlated with whole-body skeletal muscle mass, there was a significant correlation with appendicular skeletal muscle mass. Furthermore, interosseous muscle thickness was significantly correlated with both whole-body and appendicular skeletal muscle masses. [Conclusion] The present findings suggest that two muscle thicknesses in the hand are related to whole-body and/or appendicular skeletal muscle mass in healthy adults. Therefore, we propose that despite being smaller than other limb muscles, hand muscle thickness may be useful as surrogate indicator for assessing disease-related and age-related skeletal muscle loss.

This study aimed to investigate whether a touch-screen tablet device can be used to avoid underestimation of cognitive function due to hand disability in patients with stroke. Thirty patients with stroke and hemiplegia were divided according to whether the paretic side corresponded to their dominant or non-dominant hand. They were given the cube-copying task twice, once via paper and once via tablet. The results between paper- and tablet-based tasks were more likely to be concordant in participants with a non-paretic dominant hand (z = 2.80, p = 0.005) when the stroke type, education years, and sex were included in the model. All participants with discordant test results had a paretic dominant hand and showed lower muscle power in the wrist and hand muscles. In conclusion, cognitive function in patients with a paretic dominant hand may be underestimated in the cube-copying task, because it requires handwriting ability. This could be prevented by using a touch-screen device.

Background. Secondary-progressive multiple sclerosis (SPMS) patients have structural cortical damage resulting in increased compensatory cortical activity during (submaximal) performance. However, functional effects of changed cortical output are difficult to measure. The interpolated-twitch technique allows for measurement of voluntary activation (VA) necessary for force production. This study aimed to determine VA, force, and muscle fatigue during brief and sustained contractions in SPMS patients. Because fatigue effects are not confined to the motor system, we additionally examined fatiguing effects on cognitive performance. Methods. Twenty-five SPMS and 25 sex-, age-, and education-matched participants performed brief (5 seconds) and sustained (2 minutes) maximal index finger abductions. To evaluate VA, double-pulse twitches were evoked before, during, and after contractions. Additionally, data were compared with data obtained in relapsing–remitting multiple sclerosis (RRMS) patients. Subjects also performed choice-reaction time tasks before and after the sustained contraction. Results. During brief contractions, VA (85% vs 94%, P = .004) and force (25 N vs 32 N, P = .011) were lower for SPMS patients than controls. During sustained contractions, VA ( P = .001) was also lower, resulting in greater force decline (73% vs 63%, P < .001) and reduced peripheral fatigue (19% vs 50%, P < .001). Comparisons with RRMS resulted in lower VA, greater force decline, and greater estimated central fatigue in SPMS. SPMS patients were slower ( P < .001) and made more errors ( P < .001) than controls, but neither group reduced their performance after the sustained contraction. Conclusion. SPMS patients had lower VA than RRMS patients and controls. The importance of voluntary activation for muscle force and fatigability warrants targeted rehabilitation strategies.

Objective. We present a non-invasive framework for investigating efferent commands to 14 extrinsic and intrinsic hand muscles. We extend previous studies (limited to a few muscles) on common synaptic input among pools of motor neurons in a large number of muscles. Approach. Seven subjects performed sinusoidal isometric contractions to complete seven types of grasps, with each finger and with three combinations of fingers in opposition with the thumb. High-density surface EMG (HD-sEMG) signals (384 channels in total) recorded from the 14 muscles were decomposed into the constituent motor unit action potentials. This provided a non-invasive framework for the investigation of motor neuron discharge patterns, muscle coordination and efferent commands of the hand muscles during grasping. Moreover, during grasping tasks, it was possible to identify common neural information among pools of motor neurons innervating the investigated muscles. For this purpose, principal component analysis (PCA) was applied to the smoothed discharge rates of the decoded motor units. Main results. We found that the first principal component (PC1) of the ensemble of decoded motor neuron spike trains explained a variance of (53.0 ± 10.9) % and was positively correlated with force (R = 0.67 ± 0.10 across all subjects and tasks). By grouping the pools of motor neurons from extrinsic or intrinsic muscles, the PC1 explained a proportion of variance of (57.1 ± 11.3) % and (56.9 ± 11.8) %, respectively, and was correlated with force with R = 0.63 ± 0.13 and 0.63 ± 0.13, respectively. Significance. These observations demonstrate a low dimensional control of motor neurons across multiple muscles that can be exploited for extracting control signals in neural interfacing. The proposed framework was designed for hand rehabilitation perspectives, such as post-stroke rehabilitation and hand-exoskeleton control.

A 72-year-old man presented to the emergency department with 5-year history of progressive bilateral distal arm weakness. There was bilateral atrophy of the thenar eminences (figure 1) and weakness of median-innervated hand muscles. There was sensory abnormality of the palm around the base of the first four digits. He also had non-pruritic shiny papules on the face and tongue, which were bilateral and worsening for the last 2 …

The field of Brain Machine Interfaces (BMI) has attracted an increased interest due to its multiple applications in the health and entertainment domains. A BMI enables a direct interface between the brain and machines and is capable of translating neuronal information into meaningful actions (e.g., Electromyography based control of a prosthetic hand). One of the biggest challenges in developing a surface Electromyography (sEMG) based interface is the selection of the right muscles for the execution of a desired task. In this work, we investigate optimal muscle selections for sEMG based decoding of dexterous in-hand manipulation motions. To do that, we use EMG signals derived from 14 muscle sites of interest (7 on the hand and 7 on the forearm) and an optical motion capture system that records the object motion. The regression problem is formulated using the Random Forests methodology that is based on decision trees. Regarding features selection, we use the following time-domain features: root mean square, waveform length and zero crossings. A 5-fold cross validation procedure is used for model assessment purposes and the importance values are calculated for each feature. This pilot study shows that the muscles of the hand contribute more than the muscles of the forearm to the execution of inhand manipulation tasks and that the myoelectric activations of the hand muscles provide better estimation accuracies for the decoding of manipulation motions. These outcomes suggest that the loss of the hand muscles in certain amputations limits the amputees’ ability to perform a dexterous, EMG based control of a prosthesis in manipulation tasks. The results discussed can also be used for improving the efficiency and intuitiveness of EMG based interfaces for healthy subjects.