Precision Pinch Research Articles

Effect of extension of the ulnar fingers on force control and muscle activity of the hand during a precision pinch.

Some individuals extend the three ulnar fingers when performing a precision pinch. The aim of the present study was to investigate the mechanisms and effect of the extension of the ulnar fingers during a pinch. When performing a pulp pinch task with the ulnar fingers in two positions (extension and flexion), 27 participants maintained 5% of their maximum force. The mean pinch force, force variability and time taken to reach the targeted force (reaching time) were calculated. Muscle activity was simultaneously measured, using surface electromyography, for nine muscles: the flexor pollicis brevis; abductor pollicis brevis; flexor pollicis longus; first lumbrical; first dorsal interosseous; flexor digitorum superficialis of the index finger; extensor indicis; and extensor digitorum of the index and ring fingers. No significant differences in the mean pinch force or force variability were found. However, the reaching time was significantly shorter (approximately 20% reduction) in the extension position and the activities in the flexor pollicis brevis, first lumbrical, extensor indicis and extensor digitorum of the ring finger were significantly higher. These findings suggest that extending the ulnar fingers during pinching enhances the activity of key muscles involved in the movement and allows for more rapid force exertion.

Clinical Outcomes of Lunocapitate Arthrodesis: A Retrograde Single-Screw Approach.

A single-site retrospective study was designed to evaluate the clinical outcomes of single-screw lunocapitate arthrodesis (LCA) using a retrograde approach for the treatment of scapholunate advanced collapse (SLAC) wrist. We retrospectively identified 31 patients (33 cases) between September 2010 and December 2019 with SLAC wrist changes who were treated with single-screw LCA. Objective outcomes included time to fusion, union rate, range of motion, and grip and pinch strength recovery. Subjective outcomes included Disabilities of the Arm, Shoulder, and Hand (DASH) scores. We report on 33 cases (7 female), mean age 58.4 years (range: 41-85), with SLAC wrist who underwent LCA. Our cohort reported a 94% union rate and a 90-day mean time to fusion. Final active wrist range of motion was 38° dorsiflexion, 35° volarflexion, 17° radial deviation, 17° ulnar deviation, 82° pronation, and 83° supination (mean: 450.8 days). Final grip and pinch strengths recovered was 75% gross grip, 84% lateral pinch, and 75% precision pinch (mean: 379.0 days) compared with the contralateral side. The mean postoperative DASH score was 27 (mean: 1203.9 days). Two nonunions were observed. Two hardware complications occurred: one symptomatic screw and one screw fatigue fracture. We found retrograde single-screw LCA to be an effective salvage procedure for SLAC wrist. LCA is a less-taxing procedure, requires shorter operating time, and produces range of motion and grip and pinch strength recovery comparable to those of 4-corner arthrodesis. Furthermore, the viability of single-screw fixation may reduce hardware-related operative costs without compromising union rates.

Single-Portal Antegrade Endoscopic Trigger Finger Release: Cadaveric and Clinical Outcomes.

This study aimed to examine the relationship between anatomical surface landmarks in fresh frozen cadavers as related to in vivo endoscopic trigger finger release (ETFR) and present clinical outcomes after a single-portal antegrade ETFR technique. Endoscopic trigger finger release was performed on 40 cadaveric digits. Each digit was dissected and the following measurements were recorded: distance from palmar digital crease and A1 pulley, length of the A1 pulley, percentage of A1 pulley released, and injury to vulnerable anatomy. A retrospective chart review was performed on 48 patients (62 digits) treated with ETFR. Outcome measures included grip and pinch strength, range of motion, Disability of Arm, Shoulder, and Hand (DASH) questionnaires, and Visual Analog Scale (VAS) pain scores. Release of the A1 pulley was achieved in 33 of the 40 cadaveric digits (83%) with an A2 pulley laceration rate of 25%. No flexor tendon or neurovascular injuries occurred. Gross grasp, lateral pinch, 3-jaw chuck, and precision pinch strength had 85%, 90%, 82%, and 90% recovery, respectively. At the final follow-up, average metacarpophalangeal joint, proximal interphalangeal joint, and distal interphalangeal joint range of motion were within the normal limits. Mean VAS scores decreased from 5.7 preoperatively to 1.0 postoperatively and mean DASH score at the final follow-up was 4.8. With the use of anatomical surface landmarks, ETFR may be performed in an efficient and reproducible manner. Patients treated with ETFR had low complication rates, good functional recovery, and improved pain at short-term follow-up. Further study of long-term outcomes and cost-effectiveness of ETFR is warranted.

Influence of emotion on precision grip force control: A comparison of pleasant and neutral emotion.

The present study aimed to investigate the impact of emotion on force steadiness of isometric precision pinch grip that is not direction-specific. Thirty-two healthy volunteer subjects participated in the present study. Subjects were divided into two experimental groups: pleasant image group and neutral image group. The isometric precision pinch grip task was performed for three times. Specifically, the first task was performed before pleasant or neutral picture viewing, the second task was performed immediately after picture viewing, further the third task was performed 30 seconds after the second task. During the isometric precision pinch grip task, participants were asked to exert pinch grip force at 10% of maximal voluntary contraction with visual feedback. The coefficient of variation of force production and normalized root mean square value of electromyography activity were calculated. After pleasant picture viewing, coefficient of variation of pinch force production and normalized root mean square value of electromyography was decreased. While, in the neutral image condition, theses variables were not altered. More important, compared to the neutral image condition, pleasant emotion led to lower coefficient of variation of pinch grip force production. These findings indicate that pleasant emotion improves force control of isometric precision pinch grip. Therefore, in clinical settings, the emotional state of patients may affect the effectiveness of rehabilitation and should be taken into consideration.

A Biomimetic Soft‐Rigid Hybrid Finger with Autonomous Lateral Stiffness Enhancement

The application of soft robotics improves the compliance of robotic fingers, which, however, usually loses sufficient stiffness. Here, a biomimetic soft‐rigid hybrid (BSH) finger that can achieve both inherent compliance and autonomous lateral stiffness enhancement is proposed. Driven by pneumatic artificial muscles, the proposed two‐joined BSH finger can produce two flexion degrees of freedom (DOFs) and one lateral DOF motion. Imitating the human finger anatomy, the BSH finger is designed with elliptical bony ridges and eccentrically arranged ligaments. By leveraging the contact interference of the ridges and tensioning of the ligaments, the lateral stiffness of the BSH finger can be autonomously enhanced through finger flexion. During its natural stage, the lateral stiffness is relatively low to ensure mobility and compliance, while in its flexion stage, its lateral stiffness can increase to resist lateral deflection and high payload. To further investigate the advantages of the design, four BSH fingers are assembled into a robotic hand prototype with three grasping types including enveloping grasp, precise pinch, and power grasp. Experimental results demonstrate that the robotic hand prototype is capable of grasping various objects with a wide range of diameters, lengths, thicknesses, and weights, which will verify the effectiveness of the design methodology.

Morphological Variations of Lumbrical Muscles of Hand in Sri Lankan Cadavers

Introduction: Lumbricals are the small, worm-like, intrinsic muscles responsible for performing the precision pinch movements of the hand. These are quite unique in their position owing to movable proximal and distal tendon attachments. Purpose of the study: The aim of the study was to identify anomalies of lumbrical muscle present in the Sri Lankan people. Materials and Methods: A sample of 39 formalin preserved cadaveric human hands were subjected to the gross morphological study. Results: It was encountered that 59% of the lumbricals were normal in proximal and distal attachments whereas the rest of the lumbicals (41%) indicated the morphological variations. Among the hands, unipennate third lumbrical was seen in 7.7% (Left-15.7%: Right 0%) and unipennate fourth lumbrical was seen in 5.1% (Left-10.5%: Right 0%). The bipennate second lumbrical was seen in 5.1% (Left 5.3%: Right 5.1%). The 10.3% of split insertion was encountered in third lumbricals (Left 10.5%: Right 10%) as well as in fourth lumbricals (Left 5.3%: Right 15%). The third lumbrical insertion on the medial side of the middle finger was seen in 2.5% (Left 5.3%: Right 0%). Conclusion: The left hand is having more lumbrical variations than the right hand of the subjected human cadavers. The most common variation site is the insertion site. The variants are numerous in third and fourth lumbricals. The most common type of variation is the split insertion. KEY WORDS: Lumbrical, Bipennate, Unipennate, Variations, Sri Lanka.

Arthroplasty of the Proximal Interphalangeal Joint With the TACTYS Prosthesis: Clinical and Radiographic Results With a Mean Follow-up of 5 Years.

Degenerative arthritis of the proximal interphalangeal (PIP) joint of the long fingers is a common disorder affecting mainly a female middle-aged population. Conservative treatment is often effective, but in some cases, pain can persist which can lead to invalidating function. Besides denervation and arthrodesis, arthroplasty is a valuable alternative treatment. The goal of this retrospective study was to determine the clinical and radiological outcomes of the TACTYS prosthesis with a mean follow-up of more than 5 years. Between October 2005 and August 2019 10 joints in 9 patients, one patient had two prostheses in two separate fingers (4 males and 6 women) were treated for painful degenerative arthritis of the long fingers with a TACTYS prosthesis (Stryker Inc, Kalamazoo, Michigan). Power grip and pinch force were tested preoperatively and postoperatively, and the functional outcome survey is performed using the Quick Disabilities of the Arm, Shoulder, and Hand (QuickDASH), recall QuickDASH, and Patient-Rated Wrist Evaluation standardized questionnaires scored of 100 and the Visual Analog Scale (VAS) from 0 to 10. Mean follow-up was 65.70 months (range: 23-106). Mean age was 71.5 years (range: 64-83). QuickDASH score evolved from 68.43 to 41.92, range of motion from 37.5° to 45.1°, VAS from 6.65 to 1/10. Power grip and precision pinch evolved from 16.44 to 20.80 kg and 1.97 to 2.85 kg, respectively. TACTYS arthroplasty can be proposed for people who have been treated long enough with unsuccessful conservative treatment. Infection rate is still the highest complication, which can evolve in invalidating arthrodesis. It should be proposed exceptionally if the PIP joint arthritis causes invalidating functional pain.

Effects of different motor imagery strategy on precision pinch force control and excitability of spinal neural function

Effects of different motor imagery strategy on precision pinch force control and excitability of spinal neural function

Reducing Anthropomorphic Hand Degrees of Actuation with Grasp-Function-Dependent and Joint-Element-Sparse Hand Synergies

In this paper, a set of grasp-function-dependent and joint-element-sparse hand synergies was proposed. First, hand synergies were extracted from five basic categories of movements by principal component analysis (PCA). Then, varimax rotation was applied on these synergies, so each sparse synergy only represented a limited number of joints. Next, according to the contribution to these sparse synergies, finger joints were clustered into different joint modules. Finally, integrating the joint modules in different categories of hand movements, the minimum number of actuators and joint synergic modules for anthropomorphic hands were determined. The results showed that using 5 groups of joint modules and 7–9 actuators we can achieve the best performance of grasp function and motion flexibility. Furthermore, through the reasonable design of adaptive and hyperextension functional joint modules, anthropomorphic hands can better meet the requirements of different tasks like power grasping and precision pinching. Comparing with traditional finger-based actuation strategy, the joint coupling scheme achieved better anthropomorphic performance and larger workspace. These above findings will benefit the development of mechanical structure design and control method of anthropomorphic hands.

Effects of vibrotactile-enhanced music-based intervention on sensorimotor control capacity in the hand of an aging brain: a pilot feasibility randomized crossover trial

BackgroundMusic-based interventions (MBI), using music as a therapeutic medium, has been utilized as a promising strategy for motor relearning and shaping. However, currently, MBI with active performance training is restricted to being extensively applied for patients with various levels of defects in fine motor skills and cognitive functions. Therefore, the integration of vibrotactile stimulation with MBI has been adopted as a motor training strategy intended to enhance motor learning through use of vibration stimuli. The current study was designed to investigate differences in the sensorimotor performance of older adults’ hands under baseline, a single session of active MBI, and vibrotactile-enriched MBI conditions.MethodsThirty healthy older adults were recruited and randomized to receive either the single session of 30-min of vibrotactile-enriched MBI or 30-min of active MBI at the beginning of the experiment. After a one-week washout period, they switched their treatment programs and then were assessed to study the training effects of both approaches through measuring precision pinch performance, hand function, and sensory status.ResultsThe results of the Pinch-Holding-Up Activity test revealed a statistically significant difference in the FRpeak parameter (F = 14.37, p < 0.001, η2p = 0.507) under the vibrotactile-enriched MBI condition compared to the baseline and active MBI conditions. In addition, significant beneficial effects were found on the results of the barognosis (F = 19.126, p < 0.001, η2p = 0. 577) and roughness differentiation subtests (F = 15.036, p < 0.001, η2p = 0.518) in the Manual Tactile Test for the participants in the vibrotactile-enriched MBI group. In addition, the participants under both the active MBI and vibrotactile-enriched MBI conditions exhibited better performance in the three subtests of the Purdue Pegboard Test as compared to under the baseline condition (p < 0.016).ConclusionsThe findings indicated that vibrotactile-enriched MBI potentially improves the precision pinch performance of hands in healthy older adults. In addition, the add-on effect of vibrotactile stimulation to the MBI condition provides beneficial effects on the sensory functions of the upper extremities.Trial registrationNCT04802564.Date of registration: 15/03/2021.The first posted date: 17/03/2021.

Development and Testing of a Virtual Reality Mirror Therapy System for the Sensorimotor Performance of Upper Extremity: A Pilot Randomized Controlled Trial

Mirror therapy (MT) has been proposed as an essential component of upper limb neurorehabilitation, using mirror illusion of the unaffected hand movement and superimposing it on the affected hand to improve neuroplasticity for improving motor recovery in stroke patients. In this paper, we developed a virtual reality mirror therapy (VRMT) system, and examined the performance of the proposed VRMT system. The VRMT system consists of a motion-tracking device, a VR goggle, and a VRMT software. Young, healthy participants, and stroke patients with mild-to-severe hemiparesis were recruited in this study, to validate the effectiveness of the proposed VRMT system. Experimental results based on the pinch-holding-up activity (PHUA) test revealed a significant effect on the precision pinch performance of young-healthy participants receiving VRMT, whereas traditional MT could not improve the precision pinch performance in young-healthy participants (Wilcoxon signed-rank test, Z = -2.693, p = 0.007). For patients having suffered a stroke and being treated with VRMT, significant beneficial effects examined by mixed effect model were found on the total score of FMA (p = 0.033) and hand part of FMA (p = 0.008). The findings in this study indicate that the VRMT system has a potentially positive effects on the sensorimotor performance of hands in healthy participants. In addition, add-on effect of VR to MT provides beneficial effects on motor function of the upper extremity in chronic stroke patients.

Scaphometacarpal arthrodesis with autologous structural bone graft as a salvage procedure after failed trapeziectomy – Surgical technique and initial results

Painful instability due to proximal migration of the first metacarpal remains a challenging problem in patients who have undergone multiple surgeries for trapeziometacarpal osteoarthritis. The objective of this study was to investigate whether scaphometacarpal (SMC) arthrodesis with a structural bone graft is an acceptable and definitive salvage procedure for the multioperated patient. Three patients underwent SMC arthrodesis using a structural iliac crest bone graft. All patients had symptomatic instability of the thumb base and had undergone three to four surgeries prior to the arthrodesis. All patients were satisfied with the outcomes. Mean opposition decreased from 8 to 7 and mean retropulsion remained at 1. Mean grip strength increased from 3.5 to 10.5kg and mean precision pinch strength increased from 1.5 to 2.5kg. Fusion was confirmed in all patients. SMC arthrodesis with a structural bone graft is an acceptable procedure that largely preserves thumb opposition and restores stability with increased grip and pinch strength. Although far from ideal, it can be considered as a definitive salvage procedure in patients who have already had multiple surgeries to the trapeziometacarpal joint.

Pushing the Rehabilitation Boundaries: Hand Motor Impairment Can Be Reduced in Chronic Stroke

Background. Stroke is one of the most common causes of physical disability worldwide. The majority of survivors experience impairment of movement, often with lasting deficits affecting hand dexterity. To date, conventional rehabilitation primarily focuses on training compensatory maneuvers emphasizing goal completion rather than targeting reduction of motor impairment. Objective. We aim to determine whether finger dexterity impairment can be reduced in chronic stroke when training on a task focused on moving fingers against abnormal synergies without allowing for compensatory maneuvers. Methods. We recruited 18 chronic stroke patients with significant hand motor impairment. First, participants underwent baseline assessments of hand function, impairment, and finger individuation. Then, participants trained for 5 consecutive days, 3 to 4 h/d, on a multifinger piano-chord-like task that cannot be performed by compensatory actions of other body parts (e.g., arm). Participants had to learn to simultaneously coordinate and synchronize multiple fingers to break unwanted flexor synergies. To test generalization, we assessed performance in trained and nontrained chords and clinical measures in both the paretic and the nonparetic hands. To evaluate retention, we repeated the assessments 1 day, 1 week, and 6 months post-training. Results. Our results showed that finger impairment assessed by the individuation task was reduced after training. The reduction of impairment was accompanied by improvements in clinical hand function, including precision pinch. Notably, the effects were maintained for 6 months following training. Conclusion. Our findings provide preliminary evidence that chronic stroke patient can reduce hand impairment when training against abnormal flexor synergies, a change that was associated with meaningful clinical benefits.

Reach to Grasp Planning for a Synergy-Controlled Robotic Hand based on Pesudo-Distance Formulation

In the past several years, grasp analysis of multi-fingered robotic hands has been actively studied through the use of posture synergies. In these grasping planning algorithms, a formulated optimization is usually performed in the hand’s low-dimensional representation together with the hand’s position and orientation. The optimization terminates at a stable grasp, often after repeated trials with different initial guesses. Furthermore, there is no guarantee that the generated grasp leads to a smooth reach-to-grasp trajectory since the grasping planning process mostly concerns hand poses with the fingers proximal to the object. A unified theoretical framework of a gradient-based iterative algorithm is hence proposed in this paper to plan a reach-to-grasp task, predicting the grasp quality and adjusting the hand’s posture synergies, position and orientation during the approaching phase to achieve a stable grasp. The grasp quality measurement is adopted from a highly efficient pseudo-distance formulation. Stable power grasp and precision pinch can be consistently and intentionally planned with different contact conditions specified in the formulation, which means that an intention for planning a power grasp would not generate a pinch result. Several numerical simulation case studies are presented to demonstrate the effectiveness of the proposed algorithm.

BLT Gripper: An Adaptive Gripper With Active Transition Capability Between Precise Pinch and Compliant Grasp

Achieving both the precise pinching and compliant grasping capabilities is a challenging goal for most robotic hands and grippers. Moreover, an active transition between the pinching pose and the grasping pose is difficult for limited degrees-of-freedom (DOF) hands or grippers. Even when using high DOF robotic hands, it requires a substantial amount of control effort and information from tactile sensors. In this letter, a 3-finger, 5-DOF adaptive gripper with active transition capability is presented. Each finger is composed of a minimum number of components using one rigid link, one belt, one fingertip frame and one motor for flexion motion. This simple and unique finger structure enables precise parallel pinching and highly compliant stable grasping with evenly distributed pressure. The other two motors are used for fingertip angle adjustment and change of the finger orientation respectively. Thorough kinematic and force analysis with detailed descriptions of the mechanical design clearly shows controllable transition property and stable grasping performance. The experiments including the grasping force and pressure measurement verify the performance of the proposed gripper and prove the practical usefulness for real-world applications.

Construction of Multiplex Muscle Network for Precision Pinch Force Control.

Muscle synergy is a fundamental mechanism of motor control. Despite a number of studies focusing on muscle synergy during power grip and pinch at high-level force, relatively less is known about the functional interactions between muscles within low-level force production during precision pinch. Traditional analytical tools such as nonnegative matrix factorization or principal component analysis have limitations in processing nonlinear dynamic electromyographic signals and have confined sensitivity particularly for the low-level force production. In this study, we developed a novel method - multiplex muscle networks, to investigate the dynamical coordination of muscle activities at low-level force production during precision pinch. The multiplex muscle network was constructed based on multiplex limited penetrable horizontal visibility graph (MLPHVG). Seven forearm and hand muscles, including brachioradialis (BR), flexor carpi ulnaris (FCU), flexor carpi radialis (FCR), flexor digitorum superficialis (FDS), extensor digitorum communis (EDC), abductor pollicis brevis (APB) and first dorsal interosseous (FDI), were examined using surface electromyography (sEMG). Eight healthy subjects were instructed to perform a visuomotor force tracking task by producing higher (10% MVC) and lower (1% MVC) precision pinch. Interlayer mutual information I, average edge overlap ω weighted clustering coefficient CW, weighted characteristic path length LW were selected as network metrics. We assessed the undirected weighted network generated from multiplex muscle network after taking the I between paired muscle network layers as edge. There are significant differences between higher and lower force level with higher I, ω, CW and lower LW at higher force level. Advanced efficiency of information processing in the regional and global perspective indicated dynamical alterations when human faces the higher force tracking task. It suggested that ω may be an important characteristic to classify different force control states with the average classification accuracy of 82.21%. These findings reveal related alterations of functional interactions between muscles involved in precision pinch. The novel method for constructing multiplex muscle network may provide insights into muscle synergies during precision pinch force control.

The Development of a Two-finger Dexterous Bionic Hand with Three Grasping Patterns-NWAFU Hand

Bionic inspiration from human thumb and index finger was the drive to design a high-performance two-finger dexterous hand. The size of each phalanx and the motion range of each joint in the human thumb and index finger were summarized, and the features of three grasping patterns were described in detail. Subsequently, a two-finger dexterous bionic hand with 6 Degrees of Freedom (DoFs) was developed. Both the mechanical thumb and index finger were made up of three rigid phalanx links and three mechanical rotation joints. Some grasp-release tests validated that the bionic hand can perform three grasping patterns: power grasp, precision pinch and lateral pinch. The grasping success rates were high under the following cases: (1) when power grasping was used to grasp a ring with external diameter 20 mm – 140 mm, a cylinder with mass < 500 g, or objects with cylinder, sphere or ellipsoid shape; (2) when the precision pinch was used to grasp thin or small objects; (3) when the lateral pinch was used to grasp low length-to-width ratio of objects. The work provided a method for developing two-finger bionic hand with three grasping patterns, and further revealed the linkage between the difference in finger structure and size and the hand manipulation dexterity.

Classification and Treatment of Ulnar Nerve Subluxation Following Endoscopic Cubital Tunnel Release

PurposeEndoscopic cubital tunnel release (ECuTR) is an effective procedure to alleviate cubital tunnel syndrome. To improve patient outcomes and lessen concerns regarding ulnar nerve subluxation (UNS) after ECuTR, the current study proposes an intraoperative UNS classification system and subsequent treatment protocol. We present a preliminary report of patients treated under these guidelines.MethodsWe retrospectively reviewed 87 patients (100 ECuTRs). Nerve mobility was classified during surgery, in which grade 1 = no movement or partial subluxation; deep retrocondylar groove and/or no generalized hypermobility (no further intervention); grade 2 = partial subluxation; shallow retrocondylar groove and/or inherent generalized hypermobility (required medial epicondylectomy); and grade 3 = complete anterior dislocation (required medial epicondylectomy or anterior transposition). Clinical outcomes at final follow-up (mean ± SD, 34 ± 20.3 weeks; range, 5–89 weeks) were collected and included Disabilities of the Arm, Shoulder, and Hand questionnaires, visual analog scale pain score, grip and pinch strength, 2-point discrimination, and range of motion.ResultsWe report 37 patients (42 cases), grade 1 (n = 30), grade 2 (n = 1), and grade 3 (n = 11). Gross grip strength, lateral, 3-jaw chuck, and precision pinch strength recovered 87%, 90%, 105%, and 87%, respectively. Wrist and elbow range of motion returned to normal limits, 2-point discrimination improved to normal scores at final follow-up, Disabilities of the Arm, Shoulder, and Hand scores were reduced from 59.8 before to 29.9 after surgery, and visual analog scale pain score improved from 7.2 before to 2.5 after surgery (P < .001).ConclusionsTo our knowledge, this is the first study to classify UNS after ECuTR and describe a guideline for ensuing treatment. Our preliminary report of patients shows satisfactory outcomes, which suggests that our intraoperative UNS classification system has promise in preventing adverse complications of ulnar nerve hypermobility after ECuTR.Type of study/level of evidenceTherapeutic IV.

Parkinson's Disease Exhibits Amplified Intermuscular Coherence During Dynamic Voluntary Action.

Parkinson's disease (PD) is typically diagnosed and evaluated on the basis of overt motor dysfunction, however, subtle changes in the frequency spectrum of neural drive to muscles have been reported as well. During dynamic actions, coactive muscles of healthy adults often share a common source of 6–15 Hz (alpha-band) neural drive, creating synchronous alpha-band activity in their EMG signals. Individuals with PD commonly exhibit kinetic action tremor at similar frequencies, but the potential relationship between the intermuscular alpha-band neural drive seen in healthy adults and the action tremor associated with PD is not well-understood. A close relationship is most tenable during voluntary dynamic tasks where alpha-band neural drive is strongest in healthy adults, and where neural circuits affected by PD are most engaged. In this study, we characterized the frequency spectrum of EMG synchronization (intermuscular coherence) in 16 participants with PD and 15 age-matched controls during two dynamic motor tasks: (1) rotation of a dial between the thumb and index finger, and (2) dynamic scaling of isometric precision pinch force. These tasks produce different profiles of coherence between the first dorsal interosseous and abductor pollicis brevis muscles. We sought to determine if alpha-band intermuscular coherence would be amplified in participants with PD relative to controls, if such differences would be task-specific, and if they would correlate with symptom severity. We found that relative to controls, the PD group displayed amplified, but similarly task-dependent, coherence in the alpha-band. The magnitude of coherence during the rotation task correlated with overall symptom severity as per the UPDRS rating scale. Finally, we explored the potential for our coherence measures, with no additional information, to discriminate individuals with PD from controls. The area under the Receiver Operating Characteristic curve (AUC) indicated a clear separation between groups (AUC = 0.96), even though participants with PD were on their typical medication and displayed only mild-moderate symptoms. We conclude that a task-dependent, intermuscular neural drive within the alpha-band is amplified in PD. Its quantification via intermuscular coherence analysis may provide a useful tool for detecting the presence of PD, or assessing its progression.

Gamma frequency band shift of contralateral corticomuscular synchronous oscillations with force strength for hand movement tasks.

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.