# Bilateral muscle activation in postparalytic facial synkinesis: a cross-sectional high-resolution surface electromyography study

## TL;DR

This study uses high-resolution surface electromyography to show that facial synkinesis involves complex, involuntary muscle activation on both sides of the face.

## Contribution

The study reveals that facial synkinesis involves widespread, involuntary muscle activation beyond the expected movement region.

## Key findings

- Facial movements in FS involve nearly all measured facial muscles with complex activation patterns.
- Patients with FS show higher muscle activity on the synkinetic and contralateral sides compared to healthy controls.
- Involuntary activation occurs in muscles not primarily involved in the intended movement.

## Abstract

Facial synkinesis (FS) is a facial muscle coordination disorder following facial paralysis. We hypothesized that FS involves the entire network of facial muscles on both sides of the face. Bilateral facial high-resolution surface electromyography (HR-sEMG), using a total of 58 electrodes, was performed during 11 standardized facial movements in 36 healthy adult participants (53% female, 18–67 years) and 36 patients with FS (81% female, 24–70 years). Differences between the synkinetic and contralateral sides of patients and healthy controls were evaluated using linear mixed-effects models. Each movement task elicited a complex activation pattern involving nearly all measured facial muscles. In healthy controls, HR-sEMG activity was highest in the muscles primarily responsible for generating the intended voluntary movement. Notably, in patients with FS, muscles not normally expected to be strongly involved in a given movement showed markedly higher activity on the synkinetic side, and often also on the contralateral side, compared with healthy controls. Thus, facial movements in FS evoke a complex pattern of activity that only partially serves the intended movement and is further characterized by involuntary activation in muscles outside the primary movement region and on the contralateral side.

The online version contains supplementary material available at 10.1038/s41598-026-36015-1.