Increased EMG-EMG coherence in the theta and alpha bands during bimanual force modulation

Bimanual coordination and neuromuscular synchronization in Parkinson's disease and healthy adults

Parkinson's disease (PD) is a progressive neurodegenerative disorder that significantly impairs motor function, affecting over 1.5 million people in the U.S. PD is characterized by deficits in movement speed, force timing, and force modulation, particularly during coordinated upper limb actions. These impairments contribute to reduced functional independence and a diminished quality of life in individuals with PD. This study investigated the impact of PD on bimanual coordination, focusing on temporal accuracy, force production, and neuromuscular synchronization. The goal was to compare these parameters across individuals with PD, healthy older adults (HOA), and healthy young adults (HYA) during a stable force coordination task. Thirteen individuals with PD (median age [min-max] = 73 [60-83] years; 6 males), 13 HOAs median age [min-max] = 74 [60-84] years; 7 males), and 15 HYAs (median age [min-max] = 21 [18-23] years; 7 males) performed a 1:1 in-phase (0°) bimanual coordination task, requiring participants to rhythmically produce isometric forces with their left and right index fingers. Muscle activity from the First Dorsal Interosseus (FDI) muscles were recorded using electromyography (EMG). Each participant completed 21, 30-second trials. Temporal accuracy and stability were assessed using frequency ratio, absolute error (AE), and variability (VE) of relative phase. Force production was evaluated in terms of force harmonicity, force asymmetry, and peak force. Neuromuscular synchronization was analyzed using force-force and EMG-EMG coherence across different frequency bands. All groups achieved the target frequency ratio of 1.0, with no significant differences in AE or VE, suggesting comparable temporal accuracy and stability across groups. However, the PD group demonstrated significantly lower harmonicity, indicating less smooth force production, and greater force asymmetry compared to HOA and HYA groups. Reduced force-force coherence, especially in the 1-4 Hz and 4-8 Hz frequency bands, further highlighted challenges in bilateral force synchronization for the PD group. EMG-EMG coherence analysis revealed that the HYA group exhibited higher muscle activation synchronization, particularly in the alpha band, compared to the PD group. These findings suggest that while basic temporal coordination remains intact in PD, the disease impairs the smoothness and symmetry of force production, likely due to disrupted neural synchronization. The observed correlations between higher force coherence, greater harmonicity, and lower force asymmetry underscore the critical role of neural drive coherence in achieving smooth and symmetrical force production. However, it is important to consider the impact of medication state, since all participants were tested around their "ON" medication state. Understanding these impairments can inform the development of targeted interventions and rehabilitation strategies aimed at improving motor function and quality of life in individuals with PD.

A novel muscle network approach for objective assessment and profiling of bulbar involvement in ALS

Introduction

As a hallmark feature of amyotrophic lateral sclerosis (ALS), bulbar involvement significantly impacts psychosocial, emotional, and physical health. A validated objective marker is however lacking to characterize and phenotype bulbar involvement, positing a major barrier to early detection, progress monitoring, and tailored care. This study aimed to bridge this gap by constructing a multiplex functional mandibular muscle network to provide a novel objective measurement tool of bulbar involvement.

Methods

A noninvasive electrophysiological technique-surface electromyography-was combined with graph network analysis to extract 48 features measuring the regulatory mechanisms, connectivity, integration, segregation, assortativity, and lateralization of the functional muscle network during a speech task. These features were clustered into 10 interpretable latent factors. To evaluate the utility of the muscle network as a bulbar measurement tool, a heterogenous ALS cohort, consisting of eight individuals with overt clinical bulbar symptoms and seven without, along with 10 neurologically healthy controls, was employed to train and validate statistical and machine learning algorithms to assess the disease effects on the network features and the relation of the network performance to the current clinical diagnostic standard and behavioral patterns of bulbar involvement.

Results

Significant disease effects were found on most network features. The most robust effects were manifested by reduced and more variable myoelectric activities, and reduced functional connectivity and integration of the muscle network. The 10 latent factors (1) demonstrated acceptably high efficacy for detecting bulbar neuromuscular changes across all clinically confirmed symptomatic cases and clinically silent prodromal cases (area under the curve = 0.89-0.91; F1 score = 0.85-0.87; precision = 0.84-0.86; recall = 0.87-0.88); and (2) selectively correlated with clinically meaningful behavioral patterns (conditional R 2 = 0.45-0.81).

Conclusion

The functional muscle network shows promise for an objective quantifiable measurement tool to improve early detection and profiling of bulbar involvement across the prodromal and symptomatic stages. This tool has various strengths, including the use of a clinically readily available noninvasive instrument, fully automated data processing and analytics, and generation of interpretable objective outcome measures (i.e., latent factors), together rendering it highly scalable in routine clinical practice for assessing and monitoring of bulbar involvement.

Human Cervical Epidural Spinal Electrogram Topographically Maps Distinct Volitional Movements

Little is known about the electrophysiologic activity of the intact human spinal cord during volitional movement. We analyzed epidural spinal recordings from a total of five human subjects of both sexes during a variety of upper extremity movements and found that these spinal epidural electrograms contain spectral information distinguishing periods of movement, rest, and sensation. Cervical epidural electrograms also contained spectral changes time-locked with movement. We found that these changes were primarily associated with increased power in the theta (4-8 Hz) band and feature increased theta phase to gamma amplitude coupling, and this increase in theta power can be used to topographically map distinct upper extremity movements onto the cervical spinal cord in accordance with established myotome maps of the upper extremity. Our findings have implications for the development of neurostimulation protocols and devices focused on motor rehabilitation for the upper extremity, and the approach presented here may facilitate spatiotemporal mapping of naturalistic movements.

The effect of inherent and incidental constraints on bimanual force control in simulated Martian gravity

The ability to coordinate actions between the limbs is important for many operationally relevant tasks associated with space exploration. A future milestone in space exploration is sending humans to Mars. Therefore, an experiment was designed to examine the influence of inherent and incidental constraints on the stability characteristics associated with the bimanual control of force in simulated Martian gravity. A head-up tilt (HUT)/head-down tilt (HDT) paradigm was used to simulate gravity on Mars (22.3° HUT). Right limb dominant participants (N = 11) were required to rhythmically coordinate patterns of isometric forces in 1:1 in-phase and 1:2 multifrequency patterns by exerting force with their right and left limbs. Lissajous displays were provided to guide task performance. Participants performed 14 twenty-second practice trials at 90° HUT (Earth). Following a 30-min rest period, participants performed 2 test trials for each coordination pattern in both Earth and Mars conditions. Performance during the test trials were compared. Results indicated very effective temporal performance of the goal coordination tasks in both gravity conditions. However, results indicated differences associated with the production of force between Earth and Mars. In general, participants produced less force in simulated Martian gravity than in the Earth condition. In addition, force production was more harmonic in Martian gravity than Earth gravity for both limbs, indicating that less force distortions (adjustments, hesitations, and/or perturbations) occurred in the Mars condition than in the Earth condition. The force coherence analysis indicated significantly higher coherence in the 1:1 task than in the 1:2 task for all force frequency bands, with the highest level of coherence in the 1-4 Hz frequency band for both gravity conditions. High coherence in the 1-4 Hz frequency band is associated with a common neural drive that activates the two arms simultaneously and is consistent with the requirements of the two tasks. The results also support the notion that neural crosstalk stabilizes the performance of the 1:1 in-phase task. In addition, significantly higher coherence in the 8-12 Hz frequency bands were observed for the Earth condition than the Mars condition. Force coherence in the 8-12 Hz bands is associated with the processing of sensorimotor information, suggesting that participants were better at integrating visual, proprioceptive, and/or tactile feedback in Earth than for the Mars condition. Overall, the results indicate less neural interference in Martian gravity; however, participants appear to be more effective at using the Lissajous displays to guide performance under Earth's gravity.

A multimodal approach to automated hierarchical assessment of bulbar involvement in amyotrophic lateral sclerosis

Introduction

As a hallmark feature of amyotrophic lateral sclerosis (ALS), bulbar involvement leads to progressive declines of speech and swallowing functions, significantly impacting social, emotional, and physical health, and quality of life. Standard clinical tools for bulbar assessment focus primarily on clinical symptoms and functional outcomes. However, ALS is known to have a long, clinically silent prodromal stage characterized by complex subclinical changes at various levels of the bulbar motor system. These changes accumulate over time and eventually culminate in clinical symptoms and functional declines. Detection of these subclinical changes is critical, both for mechanistic understanding of bulbar neuromuscular pathology and for optimal clinical management of bulbar dysfunction in ALS. To this end, we developed a novel multimodal measurement tool based on two clinically readily available, noninvasive instruments-facial surface electromyography (sEMG) and acoustic techniques-to hierarchically assess seven constructs of bulbar/speech motor control at the neuromuscular and acoustic levels. These constructs, including prosody, pause, functional connectivity, amplitude, rhythm, complexity, and regularity, are both mechanically and clinically relevant to bulbar involvement.

Methods

Using a custom-developed, fully automated data analytic algorithm, a variety of features were extracted from the sEMG and acoustic recordings of a speech task performed by 13 individuals with ALS and 10 neurologically healthy controls. These features were then factorized into 10 composite outcome measures using confirmatory factor analysis. Statistical and machine learning techniques were applied to these composite outcome measures to evaluate their reliability (internal consistency), validity (concurrent and construct), and efficacy for early detection and progress monitoring of bulbar involvement in ALS.

Results

The composite outcome measures were demonstrated to (1) be internally consistent and structurally valid in measuring the targeted constructs; (2) hold concurrent validity with the existing clinical and functional criteria for bulbar assessment; and (3) outperform the outcome measures obtained from each constituent modality in differentiating individuals with ALS from healthy controls. Moreover, the composite outcome measures combined demonstrated high efficacy for detecting subclinical changes in the targeted constructs, both during the prodromal stage and during the transition from prodromal to symptomatic stages.

Discussion

The findings provided compelling initial evidence for the utility of the multimodal measurement tool for improving early detection and progress monitoring of bulbar involvement in ALS, which have important implications in facilitating timely access to and delivery of optimal clinical care of bulbar dysfunction.