3D Assessment of Facial Musculature Activation Patterns Using Muscle Synergy Analysis in Post-Stroke Rehabilitation

Project Abstract

This study investigates 3D facial musculature activation patterns in post-stroke rehabilitation using muscle synergy analysis to elucidate coordinated control strategies and recovery trajectories. We integrated high-resolution 3D motion capture with electromyographic (EMG) recordings from key perioral, zygomatic, frontalis, orbicularis oculi, and platysma muscles in a cohort of 40 stroke survivors at subacute and chronic stages, alongside 20 age-matched healthy controls. A standardized protocol captured facial expressions relevant to swallowing, speech articulation, and emotional expression under both voluntary and reflexive tasks. Preprocessing included signal normalization, noise reduction, and 3D surface reconstruction to map muscular activity onto a anatomically informed facial mesh, enabling spatially resolved activation patterns across facial regions. Muscle synergy analysis was conducted on concatenated EMG data using nonnegative matrix factorization to extract low-dimensional motor modules and their time-varying activation coefficients. The study examined the number and structure of synergies, inter-synergy similarity with controls, and the evolution of synergy recruitment during rehabilitation over a 6-month follow-up. We hypothesized that post-stroke individuals would display reduced synergy dimensionality and altered module composition, reflecting disrupted neural coordination, and that targeted therapies would promote a return toward normative synergy patterns. To complement EMG-derived synergies, 3D kinematic features such as peak displacements, velocity profiles, and synergistic joint-angle couplings were correlated with synergy activations to validate mechanical plausibility and to identify compensatory strategies. Clinical outcome measures, including the Fugl-Meyer Assessment for the upper extremity with added facial motor scales, Commissariat Swallowing Scale, and the Facial Clinimetrics Index, were collected to associate motor recovery with changes in synergy structure. Advanced statistical models, including mixed-effects regression and latent class analysis, assessed the relationship between baseline synergy configuration, rehabilitation intensity, and functional gains. Our results demonstrate that stroke survivors exhibit a reduced set of facial motor synergies with altered weighting of lip, cheek, and eyebrow modules, accompanied by compensatory recruitment in the contralesional hemisphere and perioral region. Over the course of rehabilitation, participants showed progressive normalization of synergy patterns, characterized by more modular activation and improved synchrony with 3D kinematic trajectories. Some individuals displayed persistent atypical synergies linked to speech articulation deficits and emotional expressivity, suggesting the necessity for individualized therapy targeting specific modules. These findings underscore the value of incorporating 3D facial kinematics and muscle synergy analysis into clinical assessment to capture latent recovery processes not evident through conventional scales. The study provides a framework for objective biomarkers of facial motor recovery, enabling the design of precision rehabilitation protocols that selectively train disrupted muscle synergies to optimize functional communication, swallowing safety, and social interaction post-stroke. Potential translational applications include real-time biofeedback systems, targeted neuromuscular electrical stimulation paradigms, and monitoring tools for prognostic stratification in neurorehabilitation programs.

Project Overview

What This Project Is About

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A plain-language overview of the topic and what the project investigates.

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The Problem It Addresses

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What problem or gap this project tackles and why it matters to the field or society.

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Objectives of the Project

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1. Identify how facial muscles activate during common tasks after stroke.
2. Use 3D imaging to map facial muscle activity patterns.
3. Apply muscle synergy analysis to simplify complex muscle data.
4. Explore relationships between activation patterns and functional recovery.
5. Provide visual and practical insights for therapy planning.

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What You Will Do Step by Step

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1. Learn basics of facial anatomy and post-stroke changes.
2. Collect safe facial movement data from participants using 3D imaging tools.
3. Process data to extract muscle activity signals (briefly explained).
4. Apply muscle synergy analysis to identify underlying activation patterns.
5. Interpret results and relate them to everyday facial movements.
6. Present findings with simple visuals for non-specialists.

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Expected Outcome

Expect a clearer picture of how facial muscles work together after stroke, with a simple framework to guide therapy and monitoring of progress.