Abstract
Facial muscle activities are essential for the appearance and communication of human beings. Therefore, exploring the activation patterns of facial muscles can help understand facial neuromuscular disorders such as Bell’s palsy. Given the irregular shape of the facial muscles as well as their different locations, it should be difficult to detect the activities of whole facial muscles with a few electrodes. In this study, a high-density surface electromyogram (HD sEMG) system with 90 electrodes was used to record EMG signals of facial muscles in both healthy and Bell’s palsy subjects when they did different facial movements. The electrodes were arranged in rectangular arrays covering the forehead and cheek regions of the face. The muscle activation patterns were shown on maps, which were constructed from the Root Mean Square (RMS) values of all the 90-channel EMG recordings. The experimental results showed that the activation patterns of facial muscles were distinct during doing different facial movements and the activated muscle regions could be clearly observed. Moreover, two features of the activation patterns, 2D correlation coefficient (corr2) and Centre of Gravity (CG) were extracted to quantify the spatial symmetry and the location of activated muscle regions respectively. Furthermore, the deviation of activated muscle regions on the paralyzed side of a face compared to the healthy side was quantified by calculating the distance between two sides of CGs. The results revealed that corr2 of the activated facial muscle region (classified into forehead region and cheek region) in Bell’s palsy subjects was significantly (p < 0.05) lower than that in healthy subjects, while CG distance of activated facial region in Bell’s palsy subjects was significantly (p < 0.05) higher than that in healthy subjects. The correlation between corr2 of these regions and Bell’s palsy [assessed by the Facial Nerve Grading Scale (FNGS) 2.0] was also significant (p < 0.05) in Bell’s palsy subjects. The spatial information on activated muscle regions may be useful in the diagnosis and treatment of Bell’s palsy in the future.
Highlights
The face is an important part of the appearance of the human body
The EMG maps showed that patterns of muscle activation during tasks were nearly symmetrical in healthy subjects
The results showed that the significance of the correlation between corr2 and Facial Nerve Grading Scale (FNGS) scores was related to the type of facial movement
Summary
The face is an important part of the appearance of the human body. the superficial geometric changes in the face are produced by the facial muscle (Cattaneo and Pavesi, 2014). As soon as the facial nerve exits the stylomastoid foramen, it splits into five terminal branches, namely the temporal, zygomatic, buccal, marginal (or mandibular), and cervical branches (Cattaneo and Pavesi, 2014). These branches anatomize with each other within the parotid gland and form a variably intricate plexus (Captier et al, 2005). It was reported that there exist considerable differences in the facial muscles of various individuals (D’Andrea and Barbaix, 2006) This complex and diverse anatomical structure of the facial neuromuscular system enables the face to perform a vast range of facial movements. It can provide a basis for understanding abnormalities in the facial neuromuscular system including Bell’s palsy
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