American Society for Peripheral Nerve

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Facial Muscle Electromyography Activity for Neuroprosthetic Device Control in Facial Reanimation: Dynamic Relation between Facial Surface EMG and Facial Displacements
Diego L. Guarin, Ph.D; Nate Jowett, MD
Harvard Medical School / Massachusetts Eye and Ear Infirmary, Boston, MA

Introduction: Hemi-facial palsy is a devastating clinical condition resulting from absence or insult to the facial nerve, with resultant impairment or absence of mimetic muscle control. We recently introduced a novel paradigm for neuroprosthetic device reanimation of symmetric facial expressions in hemi-facial palsy in a rat model. Herein, signals derived from healthy-side facial electromyography (EMG) activity are employed to elicit whisking and blink movements though functional electrical stimulation in near real-time. Clinical translation requires proper understanding of the dynamic relation between human facial muscle activation and facial displacements, in order to elicit symmetric contralateral facial expressions from sensed healthy-side muscle activity. Herein we introduce a novel methodology to characterize this relation.

Methods: Specific facial expressions (full effort smile, brow elevation, and lower lip depression) in five subjects were captured using high-speed videography, concurrent with surface EMG recordings from facial musculature. A novel machine learning algorithm was employed to identify facial landmarks, and specific facial displacements calculated as Euclidian distances between specific landmarks over time. The dynamic relation between facial displacements and EMG was estimated by a non-parametric linear model using half of the data-set, with the remainder used for model validation by percent variance accounted for (%VAF) between measured and predicted displacements.

Results: Estimated dynamic models accurately predicted facial displacements from EMG recordings. %VAF between measured and predicted displacements was larger than 80% in all cases.

Conclusions: Use of healthy side facial muscle EMG activity for control of a neuroprosthetic device for reanimation of symmetric expression in humans is feasible.

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