Facial muscle activation patterns in healthy male humans: A multi-channel surface EMG study

Artificial Intelligence-Based Facial Palsy Evaluation: A Survey

Facial palsy evaluation (FPE) aims to assess facial palsy severity of patients, which plays a vital role in facial functional treatment and rehabilitation. The traditional manners of FPE are based on subjective judgment by clinicians, which may ultimately depend on individual experience. Compared with subjective and manual evaluation, objective and automated evaluation using artificial intelligence (AI) has shown great promise in improving traditional manners and recently received significant attention. The motivation of this survey paper is mainly to provide a systemic review that would guide researchers in conducting their future research work and thus make automatic FPE applicable in real-life situations. In this survey, we comprehensively review the state-of-the-art development of AI-based FPE. First, we summarize the general pipeline of FPE systems with the related background introduction. Following this pipeline, we introduce the existing public databases and give the widely used objective evaluation metrics of FPE. In addition, the preprocessing methods in FPE are described. Then, we provide an overview of selected key publications from 2008 and summarize the state-of-the-art methods of FPE that are designed based on AI techniques. Finally, we extensively discuss the current research challenges faced by FPE and provide insights about potential future directions for advancing state-of-the-art research in this field.

Nerve entry points in the mimic musculature of the horse head

Facial expressions are important in pain recognition in horses, but current observation-based pain scales remain subjective. A promising technique to quantitatively measure subtle changes in expression patterns, including changes invisible to the human eye, is surface electromyography (sEMG). To achieve high-quality and reliable sEMG signals, unilateral placement of bipolar electrodes is required in relation to the motor endplates (MEP). We aimed to localize the nerve entry points (NEPs; where the nerve branch first pierced the muscle belly) and the direction of the terminal nerve endings to estimate MEP locations of the innervating nerves in five equine facial muscles involved in pain expression. Three cadaveric Dutch Warmblood horse heads were dissected to identify the NEPs in the musculi caninus, levator anguli oculi medialis, nasolabialis, masseter and zygomaticus. These points were marked with pins and measured in relation to a reference line between two anatomical landmarks near the origin and insertion of the respective muscle. Relative distances were calculated from the most caudally situated landmark. NEPs were located at 33%-38% (caninus), 69%-86% (levator anguli oculi medialis) and 0%-18% (zygomaticus) from the caudal landmark. The nasolabialis showed two innervations zones. Its NEPs were located at 47%-72% (dorsal muscle branch) and 52%-91% (ventral branch). All terminal nerve endings were found to run in rostral direction. The masseter showed numerous NEPs diffusely spread within the muscle belly. Therefore, calculation of relative positions was not performed. These results could form the basis for feasibility studies and standardization of bipolar electrode positioning in vivo to measure facial muscle activity patterns in horses.

Correlation of 3D Morphometric Changes, Kinematics, and Muscle Activity During Smile

OBJECTIVE

Knowing the morphological, kinematic, and electrophysiological parameters of the smile in healthy individuals may contribute to evaluating, planning, and monitoring the smile reanimation. This study aimed to determine the correlation between 3D morphometric changes, movement kinematics, and muscle activity in the facial soft tissue of healthy individuals.

METHOD

In this cohort study, 20 volunteers were selected from healthy individuals with no facial disorders. During smiling, three-dimensional face scanning, facial motion capture, and surface electromyography (sEMG) were performed. The average displacement, velocity, and acceleration during facial movements were measured. The mean change in 3D surface morphometry and activation of the zygomaticus major were determined.

RESULTS

The volunteers, comprising 10 males and 10 females, had a mean age of 24 ± 10 years; for female, mean age was 23 ± 5 years and for men 26 ± 13 years. Significant correlations were found between kinematic and morphometric data (r = 0.51, p < 0.001), sEMG and morphometric (r = 0.50, p < 0.001) data, and sEMG and kinematic data (r = 0.49, p < 0.002). The maximum acceleration occurred during approximately 65% of the muscle activation time and 64% of the peak muscle activation value. Additionally, the maximum velocity was reached at around 73% of the muscle activation time and 67% of the peak muscle activation value. Furthermore, the maximum displacement values were observed at approximately 88% of the muscle activation time and 76% of the peak muscle activation value.

CONCLUSION

The findings may provide insights into the smile's functional parameters, contribute to understanding facial muscle-related disorders, and aid in improving the diagnosis and treatment of the smile.

LEVEL OF EVIDENCE

NA Laryngoscope, 134:3112-3119, 2024.

Is Surface Electromyography (sEMG) a Useful Tool in Identifying Muscle Tension Dysphonia? An Integrative Review of the Current Evidence

OBJECTIVE

This integrative review aims to determine the quality level of evidence on using surface electromyography (sEMG) as a diagnostic tool in identifying muscle tension dysphonia.

METHOD

Two independent reviewers used one search engine and five databases to identify sEMG studies published between January 1980 and December 2020, using a set of specified search terms related to muscle tension dysphonia. The selected articles were systematically evaluated by two independent raters using a modified critical appraisal of diagnostic evidence (m-CADE) form.

RESULTS

Nine articles that satisfied the inclusion criteria were selected from among 576 studies for evaluation. These nine studies showed varied methodological approaches in sEMG measurements, including electrode configuration and position, tasks used in sEMG data collection, outcome measure, and normalization procedures. Five studies showed relatively high m-CADE scores, which were indicative of "suggestive validity and compelling importance". Two studies were rated as "suggestive validity and importance", while two remaining studies were rated as "less suggestive or equivocal validity and importance".

CONCLUSIONS

The review found a moderate level of evidence that sEMG can be a potentially useful tool with diagnostic value in identifying muscle tension dysphonia. However, evidence is not yet available to determine the diagnostic accuracy of sEMG for muscle tension dysphonia. More studies are needed, and it is recommended that future studies involving sEMG and reference measurements should be undertaken using a blinding procedure in order to control any subjective biases. Details of the population that the sEMG has been tested on should be outlined clearly so that spectrum bias could be eliminated or minimized in the application process. Furthermore, it is suggested that a reliable and valid protocol in collecting sEMG data during speech should be developed to minimize the variability of sEMG measures in assessing muscle activities during speech.

Smile analysis in dentistry and orthodontics - a review

The desire for an attractive smile is a major reason people seek orthodontic and other forms of cosmetic dental treatment. An understanding of the features of a smile is important for dental diagnosis and treatment planning. The common methods of smile analysis rely on the visual analysis of smile aesthetics using posed photographs, and videos and gathering information about smiles through patient questionnaires and diaries. Recent emerging trends utilise artificial intelligence and automated systems capable of detecting and analysing smiles using motion capture, computer vision, computer graphics, infrared and thermal imaging, electromyography, and optical sensors. This review aims to provide an up-to-date summary of emerging trends in smile analysis in dentistry and orthodontics. Understanding the advantages and limitations of emerging tools for smile analysis will enable clinicians to provide tailored and up-to-date treatment plans.

Facial Surface Electromyography: A Novel Approach to Facial Nerve Functional Evaluation after Vestibular Schwannoma Surgery

BACKGROUND

Vestibular schwannoma (VS) surgery may cause facial nerve damage. However, a comprehensive evaluation of post-operative facial outcomes may be difficult to achieve. Surface electromyography (sEMG) is a promising non-invasive evaluation tool. However, its use in the follow-up after VS surgery has not been reported yet. The main objective was to develop and validate a new sEMG application specifically for the post-VS surgery setting. Secondary goals were to provide a systematic description of facial muscle activity after VS surgery and assess the association between sEMG parameters and Sunnybrook scale scores.

METHODS

Thirty-three patients with facial palsy following VS surgery were included. The clinical outcomes (Sunnybrook symmetry, movement, and synkinesis scores) and sEMG parameters (signal amplitude normalized by the maximal voluntary contraction (NEMG) and sEMG synkinesis score (ESS, number of synkinesis per movement sequence)) were evaluated at the end of the follow-up.

RESULTS

In all tested muscles, NEMG variance was significantly higher on the affected side than the contralateral (variance ratio test, p < 0.00001 for each muscle). In total, 30 out of 33 patients (90.9%) showed an ESS ≥ 1 (median: 2.5, IQR: 1.5-3.0). On the affected side, NEMG values positively correlated with both dynamic and overall Sunnybrook scores (Spearman's model, p < 0.05 for each muscle, except orbicularis oculi). ESS significantly correlated with the Sunnybrook synkinesis score (Spearman's rho: 0.8268, p < 0.0001).

CONCLUSIONS

We described and preliminarily validated a novel multiparametric sEMG approach based on both signal amplitude and synkinesis evaluation specifically for oto-neurosurgery. Large-scale studies are mandatory to further characterize the semiological and prognostic value of facial sEMG.

Wireless facial biosensing system for monitoring facial palsy with flexible microneedle electrode arrays

Facial palsy (FP) profoundly influences interpersonal communication and emotional expression, necessitating precise diagnostic and monitoring tools for optimal care. However, current electromyography (EMG) systems are limited by their bulky nature, complex setups, and dependence on skilled technicians. Here we report an innovative biosensing approach that utilizes a PEDOT:PSS-modified flexible microneedle electrode array (P-FMNEA) to overcome the limitations of existing EMG devices. Supple system-level mechanics ensure excellent conformality to the facial curvilinear regions, enabling the detection of targeted muscular ensemble movements for facial paralysis assessment. Moreover, our apparatus adeptly captures each electrical impulse in response to real-time direct nerve stimulation during neurosurgical procedures. The wireless conveyance of EMG signals to medical facilities via a server augments access to patient follow-up evaluation data, fostering prompt treatment suggestions and enabling the access of multiple facial EMG datasets during typical 6-month follow-ups. Furthermore, the device's soft mechanics alleviate issues of spatial intricacy, diminish pain, and minimize soft tissue hematomas associated with traditional needle electrode positioning. This groundbreaking biosensing strategy has the potential to transform FP management by providing an efficient, user-friendly, and less invasive alternative to the prevailing EMG devices. This pioneering technology enables more informed decision-making in FP-management and therapeutic intervention.

Encoding of multi-modal emotional information via personalized skin-integrated wireless facial interface

Human affects such as emotions, moods, feelings are increasingly being considered as key parameter to enhance the interaction of human with diverse machines and systems. However, their intrinsically abstract and ambiguous nature make it challenging to accurately extract and exploit the emotional information. Here, we develop a multi-modal human emotion recognition system which can efficiently utilize comprehensive emotional information by combining verbal and non-verbal expression data. This system is composed of personalized skin-integrated facial interface (PSiFI) system that is self-powered, facile, stretchable, transparent, featuring a first bidirectional triboelectric strain and vibration sensor enabling us to sense and combine the verbal and non-verbal expression data for the first time. It is fully integrated with a data processing circuit for wireless data transfer allowing real-time emotion recognition to be performed. With the help of machine learning, various human emotion recognition tasks are done accurately in real time even while wearing mask and demonstrated digital concierge application in VR environment.

Facial surface electromyography: A systematic review on the state of the art and current perspectives

PURPOSE

Peripheral facial nerve palsy is a severely disabling condition. In current clinical practice, the commonest tools to assess facial palsy are grading scales, digital face image analyses or facial muscle electrophysiology. However, these techniques suffer from subjectivity or invasiveness and cannot be applied as part of a routine clinical assessment. Therefore, novel non-invasive office-based tools are needed. Surface electromyography (sEMG) may potentially fulfill the requirements of objectivity, low examiner-dependence, and minimal invasiveness. The aim of this systematic review is to define the state of the art on the use of sEMG for facial nerve functional assessment.

MATERIALS AND METHODS

Pubmed, Scopus and Web of Science databases were systematically searched. The study protocol was registered on PROSPERO in January 2023. The review was conducted according to the PRISMA guidelines.

RESULTS

After the application of inclusion-exclusion criteria, 15 manuscripts with adequate relevance to this topic were included in the review.

CONCLUSIONS

Facial sEMG represents a potentially useful tool to implement objective quantification of facial nerve function in clinical practice. Given the heterogeneity of methods and analysis in the available studies, sEMG results are hardly comparable. The introduction of methodological guidelines, followed by large prospective studies on well-defined subsets of patients with facial nerve impairment, is advocated.

High-resolution surface electromyographic activities of facial muscles during the six basic emotional expressions in healthy adults: a prospective observational study

High-resolution facial surface electromyography (HR-sEMG) is suited to discriminate between different facial movements. Whether HR-sEMG also allows a discrimination among the six basic emotions of facial expression is unclear. 36 healthy participants (53% female, 18-67 years) were included for four sessions. Electromyograms were recorded from both sides of the face using a muscle-position oriented electrode application (Fridlund scheme) and by a landmark-oriented, muscle unrelated symmetrical electrode arrangement (Kuramoto scheme) simultaneously on the face. In each session, participants expressed the six basic emotions in response to standardized facial images expressing the corresponding emotions. This was repeated once on the same day. Both sessions were repeated two weeks later to assess repetition effects. HR-sEMG characteristics showed systematic regional distribution patterns of emotional muscle activation for both schemes with very low interindividual variability. Statistical discrimination between the different HR-sEMG patterns was good for both schemes for most but not all basic emotions (ranging from p > 0.05 to mostly p < 0.001) when using HR-sEMG of the entire face. When using information only from the lower face, the Kuramoto scheme allowed a more reliable discrimination of all six emotions (all p < 0.001). A landmark-oriented HR-sEMG recording allows specific discrimination of facial muscle activity patterns during basic emotional expressions.

Behavioral and neural underpinnings of empathic characteristics in a Humanitude-care expert

Background

Humanitude approaches have shown positive effects in elderly care. However, the behavioral and neural underpinnings of empathic characteristics in Humanitude-care experts remain unknown.

Methods

We investigated the empathic characteristics of a Humanitude-care expert (YG) and those of age-, sex-, and race-matched controls (n = 13). In a behavioral study, we measured subjective valence and arousal ratings and facial electromyography (EMG) of the corrugator supercilii and zygomatic major muscles while participants passively observed dynamic facial expressions associated with anger and happiness and their randomized mosaic patterns. In a functional magnetic resonance imaging (MRI) study, we measured brain activity while participants passively observed the same dynamic facial expressions and mosaics. In a structural MRI study, we acquired structural MRI data and analyzed gray matter volume.

Results

Our behavioral data showed that YG experienced higher subjective arousal and showed stronger facial EMG activity congruent with stimulus facial expressions compared with controls. The functional MRI data demonstrated that YG showed stronger activity in the ventral premotor cortex (PMv; covering the precentral gyrus and inferior frontal gyrus) and posterior middle temporal gyrus in the right hemisphere in response to dynamic facial expressions versus dynamic mosaics compared with controls. The structural MRI data revealed higher regional gray matter volume in the right PMv in YG than in controls.

Conclusion

These results suggest that Humanitude-care experts have behavioral and neural characteristics associated with empathic social interactions.

Test-retest reliability of high-resolution surface electromyographic activities of facial muscles during facial expressions in healthy adults: A prospective observational study

Objectives

Surface electromyography (sEMG) is a standard method for psycho-physiological research to evaluate emotional expressions or in a clinical setting to analyze facial muscle function. High-resolution sEMG shows the best results to discriminate between different facial expressions. Nevertheless, the test-retest reliability of high-resolution facial sEMG is not analyzed in detail yet, as good reliability is a necessary prerequisite for its repeated clinical application.

Methods

Thirty-six healthy adult participants (53% female, 18–67 years) were included. Electromyograms were recorded from both sides of the face using an arrangement of electrodes oriented by the underlying topography of the facial muscles (Fridlund scheme) and simultaneously by a geometric and symmetrical arrangement on the face (Kuramoto scheme). In one session, participants performed three trials of a standard set of different facial expression tasks. On one day, two sessions were performed. The two sessions were repeated two weeks later. Intraclass correlation coefficient (ICC) and coefficient of variation statistics were used to analyze the intra-session, intra-day, and between-day reliability.

Results

Fridlund scheme, mean ICCs per electrode position: Intra-session: excellent (0.935–0.994), intra-day: moderate to good (0.674–0.881), between-day: poor to moderate (0.095–0.730). Mean ICC’s per facial expression: Intra-session: excellent (0.933–0.991), intra-day: good to moderate (0.674–0.903), between-day: poor to moderate (0.385–0.679). Kuramoto scheme, mean ICC’s per electrode position: Intra-session: excellent (0.957–0.970), intra-day: good (0.751–0.908), between-day: moderate (0.643–0.742). Mean ICC’s per facial expression: Intra-session: excellent (0.927–0.991), intra-day: good to excellent (0.762–0.973), between-day: poor to good (0.235–0.868). The intra-session reliability of both schemes were equal. Compared to the Fridlund scheme, the ICCs for intra-day and between-day reliability were always better for the Kuramoto scheme.

Conclusion

For repeated facial sEMG measurements of facial expressions, we recommend the Kuramoto scheme.

Crosstalk in Facial EMG and Its Reduction Using ICA

There is ample evidence that electromyography (EMG) signals from the corrugator supercilii and zygomatic major muscles can provide valuable information for the assessment of subjective emotional experiences. Although previous research suggested that facial EMG data could be affected by crosstalk from adjacent facial muscles, it remains unproven whether such crosstalk occurs and, if so, how it can be reduced. To investigate this, we instructed participants (n = 29) to perform the facial actions of frowning, smiling, chewing, and speaking, in isolation and combination. During these actions, we measured facial EMG signals from the corrugator supercilii, zygomatic major, masseter, and suprahyoid muscles. We performed an independent component analysis (ICA) of the EMG data and removed crosstalk components. Speaking and chewing induced EMG activity in the masseter and suprahyoid muscles, as well as the zygomatic major muscle. The ICA-reconstructed EMG signals reduced the effects of speaking and chewing on zygomatic major activity, compared with the original signals. These data suggest that: (1) mouth actions could induce crosstalk in zygomatic major EMG signals, and (2) ICA can reduce the effects of such crosstalk.

The Feasibility of An Automatical Facial Evaluation System Providing Objective and Reliable Results for Facial Palsy

Facial palsy would lead to a series of physical and mental problems, as facial function plays an important role in various aspects of daily life. However, the current strategies for evaluating facial function relied heavily on raters and the results varied from the experience of raters. Thus, an objective and accurate facial evaluation system is always claimed. In this study, a customized automatical facial evaluation system (AFES) was proposed, which might have the potential to be employed as an adjunctive and efficient assessing method in clinic. In order to investigate the feasibility of AFES, ninety-two participants with facial palsy were recruited and received scale-based subjective manual evaluation (including mHBGS and mSFGS) and objective automatical evaluation of AFES (including aHBGS, aSFGS and indicators of facial regional features) at enrollment and after two weeks. The correlations between the results of the two methods were analyzed and the participants were stratified according to the severity of facial function for further analyses. Strong positive correlations between manual and automatical HBGS and SFGS were observed and higher correlations were reported in the participants with normal-mild and moderate facial palsy. Significant improvements in clinical scales and indicator of eye synkinesis were found in forty-two participants in two weeks. Furthermore, some of the indicators were correlated with scale scores (I4, I7) and one of them presented a significant change between the baseline evaluation and follow-up evaluation (I7). According to the results, AFES could be considered as a viable method to perform objective and reliable evaluation for patients with facial palsy and provide clarified results for prognosis.

High-resolution surface electromyographic activities of facial muscles during mimic movements in healthy adults: A prospective observational study

Objectives

Surface electromyography (sEMG) is a standard tool in clinical routine and clinical or psychosocial experiments also including speech research and orthodontics to measure the activity of selected facial muscles to objectify facial movements during specific facial exercises or experiments with emotional expressions. Such muscle-specific approaches neglect that facial muscles act more as an interconnected network than as single facial muscles for specific movements. What is missing is an optimal sEMG setting allowing a synchronous measurement of the activity of all facial muscles as a whole.

Methods

A total of 36 healthy adult participants (53% women, 18-67 years) were included. Electromyograms were recorded from both sides of the face using an arrangement of electrodes oriented by the underlying topography of the facial muscles (Fridlund scheme) and simultaneously by a geometric and symmetrical arrangement on the face (Kuramoto scheme). The participants performed a standard set of different facial movement tasks. Linear mixed-effects models and adjustment for multiple comparisons were used to evaluate differences between the facial movement tasks, separately for both applied schemes. Data analysis utilized sEMG amplitudes and also their maximum-normalized values to account for amplitude differences between the different facial movements.

Results

Surface electromyography activation characteristics showed systematic regional distribution patterns of facial muscle activation for both schemes with very low interindividual variability. The statistical significance to discriminate between the different sEMG patterns was good for both schemes (significant comparisons for sEMG amplitudes: 87.3%, both schemes, normalized values: 90.9%, Fridlund scheme, 94.5% Kuramoto scheme), but the Kuramoto scheme performed considerably superior.

Conclusion

Facial movement tasks evoke specific patterns in the complex network of facial muscles rather than activating single muscles. A geometric and symmetrical sEMG recording from the entire face seems to allow more specific detection of facial muscle activity patterns during facial movement tasks. Such sEMG patterns should be explored in more clinical and psychological experiments in the future.

Subjective-Physiological Coherence during Food Consumption in Older Adults

BACKGROUND

Subjective-physiological emotional coherence is thought to be associated with enhanced well-being, and a relationship between subjective-physiological emotional coherence and superior nutritional status has been suggested in older populations. However, no study has examined subjective-physiological emotional coherence among older adults while tasting food. Accordingly, the present study compared subjective-physiological emotional coherence during food consumption among older and younger adults.

METHODS

Participants consumed bite-sized gel-type foods with different flavors and provided their subjective ratings of the foods while their physiological responses (facial electromyography (EMG) of the corrugator supercilia, masseter, and suprahyoid, and other autonomic nervous system signals) were simultaneously measured.

RESULTS

Our primary findings were that (1) the ratings of liking, wanting, and valence were negatively correlated with corrugator EMG activity in older and young adult participants; (2) the positive association between masseter EMG activity and ratings of wanting/valence was weaker in the older than in the young adult group; and (3) arousal ratings were negatively correlated with corrugator EMG activity in the older group only.

CONCLUSIONS

These results demonstrate commonalities and differences in subjective-physiological emotional coherence during food intake between older and young adults.

Exploration of Emotion Dynamics Sensing Using Trapezius EMG and Fingertip Temperature

Exploration of the physiological signals associated with subjective emotional dynamics has practical significance. Previous studies have reported that the dynamics of subjective emotional valence and arousal can be assessed using facial electromyography (EMG) and electrodermal activity (EDA), respectively. However, it remains unknown whether other methods can assess emotion dynamics. To investigate this, EMG of the trapezius muscle and fingertip temperature were tested. These measures, as well as facial EMG of the corrugator supercilii and zygomatic major muscles, EDA (skin conductance level) of the palm, and continuous ratings of subjective emotional valence and arousal, were recorded while participants (n = 30) viewed emotional film clips. Intra-individual subjective-physiological associations were assessed using correlation analysis and linear and polynomial regression models. Valence ratings were linearly associated with corrugator and zygomatic EMG; however, trapezius EMG was not related, linearly or curvilinearly. Arousal ratings were linearly associated with EDA and fingertip temperature but were not linearly or curvilinearly related with trapezius EMG. These data suggest that fingertip temperature can be used to assess the dynamics of subjective emotional arousal.

Robot touch with speech boosts positive emotions

A gentle touch is an essential part of human interaction that produces a positive care effect. Previously, robotics studies have shown that robots can reproduce a gentle touch that elicits similar, positive emotional responses in humans. However, whether the positive emotional effects of a robot's touch combined with speech can be enhanced using a multimodal approach remains unclear. This study supports the hypothesis that a multimodal interaction combining gentle touch and speech by a robot enhances positive emotional responses. Here, we conducted an experiment using a robotic arm to perform a gentle touch combined with speech and compared three conditions: touch alone, speech alone, and touch with speech. We assessed participants' subjective ratings of valence, arousal, and human likeliness using subjective emotional responses. Furthermore, we recorded facial electromyography (EMG) from the corrugator supercilii and zygomaticus major muscles and measured skin conductance levels (SCLs) as physiological emotional responses. Our results show that touch combined with speech elicited higher subjective valence and arousal ratings, stronger zygomaticus major EMG and SCL activities than touch alone. The results suggest that the positive emotional effects of robotic touch can be boosted by combining elements of speech.

Similarities and disparities between visual analysis and high-resolution electromyography of facial expressions

Computer vision (CV) is widely used in the investigation of facial expressions. Applications range from psychological evaluation to neurology, to name just two examples. CV for identifying facial expressions may suffer from several shortcomings: CV provides indirect information about muscle activation, it is insensitive to activations that do not involve visible deformations, such as jaw clenching. Moreover, it relies on high-resolution and unobstructed visuals. High density surface electromyography (sEMG) recordings with soft electrode array is an alternative approach which provides direct information about muscle activation, even from freely behaving humans. In this investigation, we compare CV and sEMG analysis of facial muscle activation. We used independent component analysis (ICA) and multiple linear regression (MLR) to quantify the similarity and disparity between the two approaches for posed muscle activations. The comparison reveals similarity in event detection, but discrepancies and inconsistencies in source identification. Specifically, the correspondence between sEMG and action unit (AU)-based analyses, the most widely used basis of CV muscle activation prediction, appears to vary between participants and sessions. We also show a comparison between AU and sEMG data of spontaneous smiles, highlighting the differences between the two approaches. The data presented in this paper suggests that the use of AU-based analysis should consider its limited ability to reliably compare between different sessions and individuals and highlight the advantages of high-resolution sEMG for facial expression analysis.

Learning from EMG: semi-automated grading of facial nerve function

The current grading of facial nerve function is based on subjective impression with the established assessment scale of House and Brackmann (HB). Especially for research a more objective method is needed to lower the interobserver variability to a minimum. We developed a semi-automated grading system based on (facial) surface EMG-data measuring the facial nerve function of 28 patients with vestibular schwannoma surgery. The sEMG was recorded preoperatively, postoperatively and after 3–12 months. In addition, the HB grade was determined. After manual selection and preprocessing, the data were subjected to machine learning classificators (Logistic regression, SVM and KNN). Lateralization indices were calculated and multivariant machine learning analysis was performed according to three scenarios [differentiation of normal (1) and slight (2) vs. impaired facial nerve function and classification of HB 1-3 (3)]. The calculated AUC for each scenario showed overall good differentiation capability with a median AUC of 0.72 for scenario 1, 0.91 for scenario 2 and multiclass AUC of 0.74 for scenario 3. This study approach using sEMG and machine learning shows feasibility regarding facial nerve grading in perioperative VS-surgery setting. sEMG may be a viable alternative to House Brackmann regarding objective evaluation of facial function especially for research purposes.

Lie to my face: An electromyography approach to the study of deceptive behavior

BACKGROUND

Deception is present in all walks of life, from social interactions to matters of homeland security. Nevertheless, reliable indicators of deceptive behavior in real-life scenarios remain elusive.

METHODS

By integrating electrophysiological and communicative approaches, we demonstrate a new and objective detection approach to identify participant-specific indicators of deceptive behavior in an interactive scenario of a two-person deception task. We recorded participants' facial muscle activity using novel dry screen-printed electrode arrays and applied machine-learning algorithms to identify lies based on brief facial responses.

RESULTS

With an average accuracy of 73%, we identified two groups of participants: Those who revealed their lies by activating their cheek muscles and those who activated their eyebrows. We found that the participants lied more often with time, with some switching their telltale muscle groups. Moreover, while the automated classifier, reported here, outperformed untrained human detectors, their performance was correlated, suggesting reliance on shared features.

CONCLUSIONS

Our findings demonstrate the feasibility of using wearable electrode arrays in detecting human lies in a social setting and set the stage for future research on individual differences in deception expression.

Brow and Masticatory Muscle Activity Senses Subjective Hedonic Experiences during Food Consumption

Sensing subjective hedonic or emotional experiences during eating using physiological activity is practically and theoretically important. A recent psychophysiological study has reported that facial electromyography (EMG) measured from the corrugator supercilii muscles was negatively associated with hedonic ratings, including liking, wanting, and valence, during the consumption of solid foods. However, the study protocol prevented participants from natural mastication (crushing of food between the teeth) during physiological data acquisition, which could hide associations between hedonic experiences and masticatory muscle activity during natural eating. We investigated this issue by assessing participants’ subjective ratings (liking, wanting, valence, and arousal) and recording physiological measures, including EMG of the corrugator supercilii, zygomatic major, masseter, and suprahyoid muscles while they consumed gel-type solid foods (water-based gellan gum jellies) of diverse flavors. Ratings of liking, wanting, and valence were negatively correlated with corrugator supercilii EMG and positively correlated with masseter and suprahyoid EMG. These findings imply that subjective hedonic experiences during food consumption can be sensed using EMG signals from the brow and masticatory muscles.

Atlas of voluntary facial muscle activation: Visualization of surface electromyographic activities of facial muscles during mimic exercises

Complex facial muscle movements are essential for many motoric and emotional functions. Facial muscles are unique in the musculoskeletal system as they are interwoven, so that the contraction of one muscle influences the contractility characteristic of other mimic muscles. The facial muscles act more as a whole than as single facial muscle movements. The standard for clinical and psychosocial experiments to detect these complex interactions is surface electromyography (sEMG). What is missing, is an atlas showing which facial muscles are activated during specific tasks. Based on high-resolution sEMG data of 10 facial muscles of both sides of the face simultaneously recorded during 29 different facial muscle tasks, an atlas visualizing voluntary facial muscle activation was developed. For each task, the mean normalized EMG amplitudes of the examined facial muscles were visualized by colors. The colors were spread between the lowest and highest EMG activity. Gray shades represent no to very low EMG activities, light and dark brown shades represent low to medium EMG activities and red shades represent high to very high EMG activities relatively with respect to each task. The present atlas should become a helpful tool to design sEMG experiments not only for clinical trials and psychological experiments, but also for speech therapy and orofacial rehabilitation studies.

Multimodal Data Fusion of Electromyography and Acoustic Signals for Thai Syllable Recognition

Speech disorders such as dysarthria are common and frequent after suffering a stroke. Speech rehabilitation performed by a speech-language pathologist is needed to improve and recover. However, in Thailand, there is a shortage of speech-language pathologists. In this paper, we present a syllable recognition system, which can be deployable in a speech rehabilitation system to provide support to the limited speech-language pathologists available. The proposed system is based on a multimodal fusion of acoustic signal and surface electromyography (sEMG) collected from facial muscles. Multimodal data fusion is studied to improve signal collection under noisy situations while reducing the number of electrodes needed. The signals are simultaneously collected while articulating 12 Thai syllables designed for rehabilitation exercises. Several features are extracted from sEMG signals and five channels are studied. The best combination of features and channels is chosen to be fused with the mel-frequency cepstral coefficients extracted from the acoustic signal. The feature vector from each signal source is projected by spectral regression extreme learning machine and concatenated. Data from seven healthy subjects were collected for evaluation purposes. Results show that the multimodal fusion outperforms the use of a single signal source achieving up to [Formula: see text] of accuracy. In other words, an accuracy improvement up to [Formula: see text] can be achieved when using the proposed multimodal fusion. Moreover, its low standard deviations in classification accuracy compared to those from the unimodal fusion indicate the improvement in the robustness of the syllable recognition.

Emotional valence sensing using a wearable facial EMG device

Emotion sensing using physiological signals in real-life situations can be practically valuable. Previous studies have developed wearable devices that record autonomic nervous system activity, which reflects emotional arousal. However, no study determined whether emotional valence can be assessed using wearable devices. To this end, we developed a wearable device to record facial electromyography (EMG) from the corrugator supercilii (CS) and zygomatic major (ZM) muscles. To validate the device, in Experiment 1, we used a traditional wired device and our wearable device, to record participants’ facial EMG while they were viewing emotional films. Participants viewed the films again and continuously rated their recalled subjective valence during the first viewing. The facial EMG signals recorded using both wired and wearable devices showed that CS and ZM activities were, respectively, negatively and positively correlated with continuous valence ratings. In Experiment 2, we used the wearable device to record participants’ facial EMG while they were playing Wii Bowling games and assessed their cued-recall continuous valence ratings. CS and ZM activities were correlated negatively and positively, respectively, with continuous valence ratings. These data suggest the possibility that facial EMG signals recorded by a wearable device can be used to assess subjective emotional valence in future naturalistic studies.

Comparison of Facial Muscle Activation Patterns Between Healthy and Bell's Palsy Subjects Using High-Density Surface Electromyography

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.

Facial EMG Activity Is Associated with Hedonic Experiences but not Nutritional Values While Viewing Food Images

The physiological correlates of hedonic/emotional experiences to visual food stimuli are of theoretical and practical interest. Previous psychophysiological studies have shown that facial electromyography (EMG) signals were related to subjective hedonic ratings in response to food images. However, because other data showed positive correlations between hedonic ratings and objective nutritional values of food, whether the facial EMG reactions to food images could reflect the hedonic evaluation or nutritional assessment of food remains unknown. To address this issue, we measured subjective hedonic ratings (liking, wanting, valence, and arousal) and physiological signals (facial EMG of the corrugator supercilii, zygomatic major, masseter, and suprahyoid muscles, skin potential responses, and heart rates) while participants observed food images that had objective nutritional information (caloric, carbohydrate, fat, and protein contents). The results revealed that zygomatic major EMG activity was positively correlated with ratings of liking, wanting, and valence, but not with any objective nutritional value. These data indicate that facial EMG signals in response to food images reflect subjective hedonic experiences, but not objective nutritional values, associated with the food item.

Quantitative analysis of movements in facial nerve palsy with surface electromyography and kinematic analysis

Facial nerve paralysis (FNP) has a significant effect on a person's quality of life. In individuals with FNP undergoing facial rehabilitation, methods to analyze the loss of function are useful in diagnosis, treatment and follow up. To propose a protocol with kinematic analysis coupled with sEMG to evaluate the outcomes of FNP, quantifying the excursion degrees of the facial muscles and symmetry of voluntary movements. 10 patients (Group A) were followed by diagnosis until the end of the rehabilitation program. Kinematic analysis of 20 healthy adults (group B) was performed as a starting point to have a normality range and to test intra-subject and inter- intra rater reliability. An optoelectronic system and sEMG wireless electrodes were used. In Group A, a significant improvement in the movement of frontalis muscle (P = 0.0118) after 4-week treatment from the beginning (T0) 9.8 ± 4.5 mm to the end of rehabilitation (T1) 16.3 ± 5.8 mm and orbicularis oris (P = 0.0143) from T0 14.8 ± 5.5 mm to T1 20.3 ± 3.3 mm and, a reduction of % of maximum voluntary contractions (MVC) at T1 for frontalis and orbicularis compared to T0. This protocol provides meaningful data in a simple, reliable and objective way for the functional assessment of patients with PNF.

Physiological correlates of subjective emotional valence and arousal dynamics while viewing films

An exploration of the physiological correlates of subjective emotional states has theoretical and practical significance. Previous studies have reported that subjective valence and arousal correspond to facial electromyography (EMG) and electrodermal activity (EDA), respectively, across stimuli. However, the reported results were inconsistent, no study investigated subjective-physiological concordance across time, and measures of arousal remain controversial. To investigate these issues, while healthy adults (n = 20) viewed emotional films, we assessed overall and continuous ratings of valence and arousal and recorded EMG from the corrugator supercilii and zygomatic major, EDA from the palms and forehead, and nose-tip temperature. The corrugator and zygomatic EMG were negatively and positively associated with valence ratings, respectively, across stimuli and time. EDA (both sites) and nose-tip temperature were positively and negatively associated with arousal ratings, respectively, across stimuli and time. It is concluded that subjective emotional valence and arousal dynamics have specific physiological correlates.

Facial Electromyography Mapping in Healthy and Bell's Palsy Subjects: A High-Density Surface EMG Study

Bell's palsy impairs the symmetry of facial appearance and movement. Detailed examination of facial muscle activities should be important for the diagnosis and treatment of the Bell's palsy. In this study, facial muscle activities in normal and Bell's palsy conditions were measured using a high-density (HD) electromyography (EMG) technique. The EMG signals during active tasks (four different facial expressions) and resting task were collected with a HD array of EMG electrodes from forehead and cheek muscles. To visualize facial EMG activities, the EMG maps were reconstructed from the HD-EMG recordings. The two-dimension (2D) correlation coefficients between right and left sides of facial EMG maps were calculated to evaluate the symmetry of facial muscle activities during these tasks. Our experimental results showed that the 2D correlation coefficients during active tasks were different significantly (P<0.01) between the healthy group(n=4) and Bell's palsy group(n=3). These results demonstrated that the synchronism of facial muscle activities during active tasks in healthy subjects is greater than that in the Bell's palsy subjects. This pilot study suggested that HD-EMG would be a potential technique to assess abnormal asymmetric activities of facial muscles for Bell's palsy.

Facial nerve electrodiagnostics for patients with facial palsy: a clinical practice guideline

PURPOSE

Facial nerve electrodiagnostics is a well-established and important tool for decision making in patients with facial nerve diseases. Nevertheless, many otorhinolaryngologist-head and neck surgeons do not routinely use facial nerve electrodiagnostics. This may be due to a current lack of agreement on methodology, interpretation, validity, and clinical application. Electrophysiological analyses of the facial nerve and the mimic muscles can assist in diagnosis, assess the lesion severity, and aid in decision making. With acute facial palsy, it is a valuable tool for predicting recovery.

METHODS

This paper presents a guideline prepared by members of the International Head and Neck Scientific Group and of the Multidisciplinary Salivary Gland Society for use in cases of peripheral facial nerve disorders based on a systematic literature search.

RESULTS

Required equipment, practical implementation, and interpretation of the results of facial nerve electrodiagnostics are presented.

CONCLUSION

The aim of this guideline is to inform all involved parties (i.e. otorhinolaryngologist-head and neck surgeons and other medical specialists, therapeutic professionals and the affected persons) and to provide practical recommendations for the diagnostic use of facial nerve electrodiagnostics.

Facial Muscle Activity Patterns in Clarinet Players: A Key to Understanding Facial Muscle Physiology and Dysfunction in Musicians

OBJECTIVES

Facial muscle activity is crucial to controlling musical performance in wind instrument playing. Facial muscle dysfunctions are common in wind instrument players, dramatically affecting their professional musical activity and potentially leading to disabling symptoms.The aim of this pilot study on a cohort of healthy clarinetists was to use surface electromyography to identify the facial muscle activity patterns involved in stabilizing the mouthpiece, controlling emission and articulation during musical tasks in physiological conditions, also comparing muscle activity between less and more experienced clarinetists (students vs postgraduates/professionals).

METHODS

Surface electromyographic measures of the sternocleidomastoid, masseter, mentalis, mylohyoid and buccinator muscles were obtained from eight healthy clarinet players (four students and four postgraduates/professionals) performing two standardized musical tasks.

RESULTS

Overall, mean IEMG activity was significantly lower for the sternocleidomastoid than for the other muscles (P = .000), and for the mouthpiece-stabilizing muscles (masseter and mentalis) than for those directly involved in controlling emission and articulation (buccinator and mylohyoid muscles) (P = .000).Regardless of the musical task, the mean IEMG values were significantly higher in the students for the masseter (P = .0007), buccinator (P = .0001) and mylohyoid (0.000), while they were significantly higher in the postgraduates/professionals for the mentalis (P = .000). No significant differences emerged between the two groups for the sternocleidomastoid (P = .207).

CONCLUSIONS

These preliminary data reflect a significantly higher overall facial muscle activity in the less-experienced group, potentially resulting in an overload, whereas the more expert players had more optimized muscle activity patterns.

Facial EMG Correlates of Subjective Hedonic Responses During Food Consumption

An exploration of physiological correlates of subjective hedonic responses while eating food has practical and theoretical significance. Previous psychophysiological studies have suggested that some physiological measures, including facial electromyography (EMG), may correspond to hedonic responses while viewing food images or drinking liquids. However, whether consuming solid food could produce such subjective–physiological concordance remains untested. To investigate this issue, we assessed participants’ subjective ratings of liking, wanting, valence, and arousal while they consumed gel-type food stimuli of various flavors and textures. We additionally measured their physiological signals, including facial EMG from the corrugator supercilii. The results showed that liking, wanting, and valence ratings were negatively correlated with corrugator supercilii EMG activity. Only the liking rating maintained a negative association with corrugator supercilii activity when the other ratings were partialed out. These data suggest that the subjective hedonic experience, specifically the liking state, during food consumption can be objectively assessed using facial EMG signals and may be influenced by such somatic signals.

Automatic Facial Paralysis Assessment via Computational Image Analysis

Facial paralysis (FP) is a loss of facial movement due to nerve damage. Most existing diagnosis systems of FP are subjective, e.g., the House-Brackmann (HB) grading system, which highly depends on the skilled clinicians and lacks an automatic quantitative assessment. In this paper, we propose an efficient yet objective facial paralysis assessment approach via automatic computational image analysis. First, the facial blood flow of FP patients is measured by the technique of laser speckle contrast imaging to generate both RGB color images and blood flow images. Second, with an improved segmentation approach, the patient's face is divided into concerned regions to extract facial blood flow distribution characteristics. Finally, three HB score classifiers are employed to quantify the severity of FP patients. The proposed method has been validated on 80 FP patients, and quantitative results demonstrate that our method, achieving an accuracy of 97.14%, outperforms the state-of-the-art systems. Experimental evaluations also show that the proposed approach could yield objective and quantitative FP diagnosis results, which agree with those obtained by an experienced clinician.

Study on the Validity of Surface Electromyography as Assessment Tools for Facial Nerve Palsy

Objectives

The purpose of this study was to find out validity of Surface Electromyography(sEMG) compared with Nerve Conduction Study and clinical assessment scale as assessment factors for facial palsy.

Methods

We investigated 50 cases of patients with peripheral facial palsy who had records of sEMG and NCS to check. Then we analyzed the correlation between sEMG and NCS that carried out around 1 week after onset. And we analyzed the correlation between sEMG and clinical assessment scales that were measured three times around 1 week, 3–4 weeks and 5–6 weeks after onset. Clinical assessment scales used in this study were House-brackmann grade, Yanagihara unweighted grading scale and Sunnybrook facial grading system. We used Pearson’s correlation for statistical analysis.

Results

sEMG and NCS, measured at similar times, were statistically correlated. Especially, the correlation with the forehead region was high. And sEMG and clinical assessment scale, measured at same time, were statistically correlated, especially after 5 weeks from onset.

Conclusion

According to this study, sEMG is expected to be useful to assessment facial palsy.

Association between muscle activity and overjet in class II malocclusion with surface electromyography

OBJECTIVES

The aim of the study was to assess the association and correlation between the overjet and muscle activity (the masseter and temporalis muscles) in patient with Class II malocclusion in different genders using surface electromyography (sEMG).

MATERIALS AND METHODS

The overjet (measured clinically) and electromyographical activity (rest, chew, post chew rest, clench and post clench rest) of the masseter and temporalis muscle of class II malocclusion patient were assessed in 18 patients (3 males and 15 females) from the School of Dental Science, Hospital University Sains Malaysia.

RESULTS

The results were compared by simple linear regression test to evaluate the association between overjet and muscle activity in different genders. Class II malocclusion patients with increased overjet group showed significant association with masseter muscle activity on chewing stage (P = 0.005, F = 6.081 and adj-R2 = 0.473). Left temporalis muscle in class II malocclusion showed a significant linear association (P = 0.014, F = 0.812 and adj-R2= -0.034) with gender during clench.

CONCLUSION

In conclusion, class II malocclusion patient with increased overjet can affect masticatory muscle function and as well as clench force may differ in gender.

A Wearable High-Resolution Facial Electromyography for Long Term Recordings in Freely Behaving Humans

Human facial expressions are a complex capacity, carrying important psychological and neurological information. Facial expressions typically involve the co-activation of several muscles; they vary between individuals, between voluntary versus spontaneous expressions, and depend strongly on personal interpretation. Accordingly, while high-resolution recording of muscle activation in a non-laboratory setting offers exciting opportunities, it remains a major challenge. This paper describes a wearable and non-invasive method for objective mapping of facial muscle activation and demonstrates its application in a natural setting. We focus on muscle activation associated with "enjoyment", "social" and "masked" smiles; three categories with distinct social meanings. We use an innovative, dry, soft electrode array designed specifically for facial surface electromyography recording, a customized independent component analysis algorithm, and a short training procedure to achieve the desired mapping. First, identification of the orbicularis oculi and the levator labii superioris was demonstrated from voluntary expressions. Second, the zygomaticus major was identified from voluntary and spontaneous Duchenne and non-Duchenne smiles. Finally, using a wireless device in an unmodified work environment revealed expressions of diverse emotions in face-to-face interaction. Our high-resolution and crosstalk-free mapping, along with excellent user-convenience, opens new opportunities in gaming, virtual-reality, bio-feedback and objective psychological and neurological assessment.

Simulation of facial expressions using person-specific sEMG signals controlling a biomechanical face model

PURPOSE

Functional inoperability in advanced oral cancer is difficult to assess preoperatively. To assess functions of lips and tongue, biomechanical models are required. Apart from adjusting generic models to individual anatomy, muscle activation patterns (MAPs) driving patient-specific functional movements are necessary to predict remaining functional outcome. We aim to evaluate how volunteer-specific MAPs derived from surface electromyographic (sEMG) signals control a biomechanical face model.

METHODS

Muscle activity of seven facial muscles in six volunteers was measured bilaterally with sEMG. A triple camera set-up recorded 3D lip movement. The generic face model in ArtiSynth was adapted to our needs. We controlled the model using the volunteer-specific MAPs. Three activation strategies were tested: activating all muscles [Formula: see text], selecting the three muscles showing highest muscle activity bilaterally [Formula: see text]-this was calculated by taking the mean of left and right muscles and then selecting the three with highest variance-and activating the muscles considered most relevant per instruction [Formula: see text], bilaterally. The model's lip movement was compared to the actual lip movement performed by the volunteers, using 3D correlation coefficients [Formula: see text].

RESULTS

The correlation coefficient between simulations and measurements with [Formula: see text] resulted in a median [Formula: see text] of 0.77. [Formula: see text] had a median [Formula: see text] of 0.78, whereas with [Formula: see text] the median [Formula: see text] decreased to 0.45.

CONCLUSION

We demonstrated that MAPs derived from noninvasive sEMG measurements can control movement of the lips in a generic finite element face model with a median [Formula: see text] of 0.78. Ultimately, this is important to show the patient-specific residual movement using the patient's own MAPs. When the required treatment tools and personalisation techniques for geometry and anatomy become available, this may enable surgeons to test the functional results of wedge excisions for lip cancer in a virtual environment and to weigh surgery versus organ-sparing radiotherapy or photodynamic therapy.

Measuring facial expression of emotion

Research into emotions has increased in recent decades, especially on the subject of recognition of emotions. However, studies of the facial expressions of emotion were compromised by technical problems with visible video analysis and electromyography in experimental settings. These have only recently been overcome. There have been new developments in the field of automated computerized facial recognition; allowing real-time identification of facial expression in social environments. This review addresses three approaches to measuring facial expression of emotion and describes their specific contributions to understanding emotion in the healthy population and in persons with mental illness. Despite recent progress, studies on human emotions have been hindered by the lack of consensus on an emotion theory suited to examining the dynamic aspects of emotion and its expression. Studying expression of emotion in patients with mental health conditions for diagnostic and therapeutic purposes will profit from theoretical and methodological progress.

Predicting 3D lip movement using facial sEMG: a first step towards estimating functional and aesthetic outcome of oral cancer surgery

In oral cancer, loss of function due to surgery can be unacceptable, designating the tumour as functionally inoperable. Other curative treatments can then be considered. Currently, predictions of these functional consequences are subjective and unreliable. We want to create patient-specific models to improve and objectify these predictions. A first step was taken by controlling a 3D lip model with volunteer-specific sEMG activities. We focus on the lips first, because they are essential for speech, oral food transport, and facial mimicry. Besides, they are more accessible to measurements than intraoral organs. 3D lip movement and corresponding sEMG activities are measured in five healthy volunteers, who performed 19 instructions repeatedly, to create a quantitative lip model by establishing the relationship between sEMG activities of eight facial muscles bilaterally on the input side and the corresponding 3D lip displacements on the output side. The relationship between 3D lip movement and sEMG activities was accommodated in a state-space model. A good relationship between sEMG activities and 3D lip movement was established with an average root mean square error of 2.43 mm for the first-order system and 2.46 mm for the second-order system. This information can be incorporated into biomechanical models to further personalise functional outcome assessment after treatment.

Surface electromyography analysis of blepharoptosis correction by transconjunctival incisions

Upper eyelid movement depends on the antagonistic actions of orbicularis oculi muscle and levator aponeurosis. Blepharoptosis is an abnormal drooping of upper eyelid margin with the eye in primary position of gaze. Transconjunctival incisions for upper eyelid ptosis correction have been a well-developed technique. Conventional prognosis however depends on clinical observations and lacks of quantitatively analysis for the eyelid muscle controlling. This study examines the possibility of using the assessments of temporal correlation in surface electromyography (SEMG) as a quantitative description for the change of muscle controlling after operation. Eyelid SEMG was measured from patients with blepharoptosis preoperatively and postoperatively, as well as, for comparative study, from young and aged normal subjects. The data were analyzed using the detrended fluctuation analysis method. The results show that the temporal correlation of the SEMG signals can be characterized by two indices associated with the correlation properties in short and long time scales demarcated at 3ms, corresponding to the time scale of neural response. Aging causes degradation of the correlation properties at both time scales, and patient group likely possess more serious correlation degradation in long-time regime which was improved moderately by the ptosis corrections. We propose that the temporal correlation in SEMG signals may be regarded as an indicator for evaluating the performance of eyelid muscle controlling in postoperative recovery.

Comparison of the classically conditioned withdrawal reflex in cerebellar patients and healthy control subjects during stance: 2. Biomechanical characteristics

This study addresses cerebellar involvement in classically conditioned nociceptive lower limb withdrawal reflexes in standing humans. A preceding study compared electromyographic activities in leg muscles of eight patients with cerebellar disease (CBL) and eight age-matched controls (CTRL). The present study extends and completes that investigation by recording biomechanical signals from a strain-gauge-equipped platform during paired auditory conditioning stimuli (CS) and unconditioned stimuli (US) trials and during US-alone trials. The withdrawal reflex performance-lifting the stimulated limb (decreasing the vertical force from that leg, i.e. 'unloading') and transferring body weight to the supporting limb (increasing the vertical force from that leg, i.e. 'loading')-was quantified by the corresponding forces exerted onto the platform. The force changes were not simultaneous but occurred as a sequence of multiple force peaks at different times depending on the specific limb task (loading or unloading). Motor learning, expressed by the occurrence of conditioned responses (CR), is characterized by this sequence beginning already within the CSUS window. Loading and unloading were delayed and prolonged in CBL, resulting in incomplete rebalancing during the analysis period. Trajectory loops of the center of vertical pressure-derived from vertical forces-were also incomplete in CBL within the recording period. However, exposing CBL to a CS resulted in motor improvement reflected by shortening the time of rebalancing and by optimizing the trajectory loop. In summary, associative responses in CBL are not absent although they are less frequent and of smaller amplitude than in CTRL.

The facial motor system

Facial movements support a variety of functions in human behavior. They participate in automatic somatic and visceral motor programs, they are essential in producing communicative displays of affective states and they are also subject to voluntary control. The multiplicity of functions of facial muscles, compared to limb muscles, is reflected in the heterogeneity of their anatomical and histological characteristics that goes well beyond the conventional classification in single facial muscles. Such parcellation in different functional muscular units is maintained throughout the central representation of facial movements from the brainstem up to the neocortex. Facial movements peculiarly lack a conventional proprioceptive feedback system, which is only in part vicariated by cutaneous or auditory afferents. Facial motor activity is the main marker of endogenous affective states and of the affective valence of external stimuli. At the cortical level, a complex network of specialized motor areas supports voluntary facial movements and, differently from upper limb movements, in such network there does not seem to be a prime actor in the primary motor cortex.