Impact of Facial Palsy and Reanimation Surgery on Emotion Recognition: A Magnetoencephalography Study of Early Face Processing: The M170 Component

<b>Introduction:</b> Facial palsy (FP) can impair nonverbal communication, and patients often report difficulty recognizing emotional expressions in others. <b>Objective:</b> To compare early cortical processing of emotional facial expressions in healthy controls, FP patients, and patients who had undergone facial reanimation surgery using magnetoencephalography (MEG) and analyzing the M170 component, a face-sensitive neuromagnetic response. <b>Methods:</b> Neuromagnetic responses were recorded with a whole-head 306-sensors MEG system. We studied M170 responses to <i>angry, happy, sad,</i> and <i>neutral</i> faces in 10 healthy controls, 5 untreated FP patients, 11 patients with hypoglossal-facial nerve transfer (HFNT), and 4 patients with temporalis muscle transfer. <b>Results:</b> Untreated FP patients had delayed M170 latencies (174.8 ± 14.5 ms) and increased amplitudes (430.2 ± 214.2 fT) compared with controls (162.8 ± 8.6 ms and 306.0 ± 185.0 fT). HFNT patients demonstrated reduced latencies (167.7 ± 12.5 ms) and amplitudes (285.5 ± 125.2 fT) relative to FP patients, approximating control values. No significant hemispheric effects or emotion-specific modulation were observed. <b>Conclusion:</b> These findings suggest that facial reanimation via HFNT may promote partial normalization of cortical processing of facial emotions, reflecting adaptive neuroplasticity. This study supports the facial feedback hypothesis, whereby the ability to express facial emotions contributes to effective emotion recognition.