Computer-controlled electrical stimulation of facial muscles by facial neuromuscular electrical stimulation (fNMES): Hardware and software solutions.

BACKGROUND: Computer controlled electrical stimulation of facial muscles is a promising method to study facial feedback effects, though little guidance is available for new adopters. NEW METHOD: Facial Neuromuscular Electrical Stimulation (fNMES) offers a spatially and temporally precise means of manipulating facial muscles during experiments, and can be combined with EEG to study the neurological basis of facial feedback effects. Precise delivery of stimulation requires hardware and software solutions to integrate stimulators and a stimulus-presenting computer. We provide open-source hardware schematics and relevant computer code in order to achieve this integration, so as to facilitate the use of fNMES in the laboratory. RESULTS: Hardware schematics are provided for the building of a bespoke control module, which allows researchers to finely control stimulator output whilst participants complete computer tasks. In addition, we published code that new adopters of NMES can use within their experiments to control the module and send event triggers to another computer. These hard- and software solutions were successfully used to investigate the effects of facial muscle activation on felt and perceived emotion. We summarise these findings and discuss the integration of fNMES with EEG and peripheral physiological measures. COMPARISON WITH EXISTING METHODS: Our inexpensive hardware solution allows fNMES parameters to be computer controlled, and thus allows to stimulate facial muscles with high precision. This opens up new possibilities to investigate, for example, facial feedback effects. CONCLUSIONS: We provide tools and guidance to build a control module in order to precisely deliver electrical stimulation to facial muscles using a stimulus computer (while recording EEG or other peripheral physiology).

Zygomaticus activation through facial neuromuscular electrical stimulation (fNMES) induces happiness perception in ambiguous facial expressions and affects neural correlates of face processing.

The role of facial feedback in facial emotion recognition remains controversial, partly due to limitations of the existing methods to manipulate the activation of facial muscles, such as voluntary posing of facial expressions or holding a pen in the mouth. These procedures are indeed limited in their control over which muscles are (de)activated when and to what degree. To overcome these limitations and investigate in a more controlled way if facial emotion recognition is modulated by one's facial muscle activity, we used computer-controlled facial neuromuscular electrical stimulation (fNMES). In a pre-registered EEG experiment, ambiguous facial expressions were categorised as happy or sad by 47 participants. In half of the trials, weak smiling was induced through fNMES delivered to the bilateral Zygomaticus Major muscle for 500 ms. The likelihood of categorising ambiguous facial expressions as happy was significantly increased with fNMES, as shown with frequentist and Bayesian linear mixed models. Further, fNMES resulted in a reduction of P1, N170 and LPP amplitudes. These findings suggest that fNMES-induced facial feedback can bias facial emotion recognition and modulate the neural correlates of face processing. We conclude that fNMES has potential as a tool for studying the effects of facial feedback.

Facial feedback manipulation influences the automatic detection of unexpected emotional body expressions.

Unexpected or changing facial expressions are known to be able to engage more automatic processing than frequently occurring facial expressions, thereby inducing a neural differential wave response known as expression mismatch negativity (EMMN). Recent studies have shown that EMMN can be modulated by the observer's facial feedback (i.e., feedback from their own facial movements). A similar EMMN activity has been discovered for body expressions, but thus far only a few emotion types have been investigated. It is unknown whether the EMMNs evoked by body expressions can be influenced by facial feedback. To explore this question, we recorded EEG activity of 29 participants in the reverse oddball paradigm. Here two unexamined categories of body expressions were presented, happy and sad, placed in two paired stimulus sequences: in one the happy body was presented with a probability of 80% (standards) while the sad body was presented with a probability of 20% (deviants), and in the other the probabilities were reversed. The facial feedback was manipulated by different pen holding conditions (i.e., participants holding the pen with the teeth, lips, or nondominant hand). The nonparametric cluster permutation test revealed significant happy and sad body-related EMMN (bEMMN) activities. The happy-bEMMN were more negative than sad-bEMMN within the range of 100-150 ms. Additionally, the bEMMN amplitude of both emotions is modulated by the facial feedback conditions. These results expand the range of emotional types applicable to bEMMN and provide evidence for the validity of the facial feedback hypothesis across emotional carriers.

Inability to move one's face dampens facial expression perception.

Humans rely heavily on facial expressions for social communication to convey their thoughts and emotions and to understand them in others. One prominent but controversial view is that humans learn to recognize the significance of facial expressions by mimicking the expressions of others. This view predicts that an inability to make facial expressions (e.g., facial paralysis) would result in reduced perceptual sensitivity to others' facial expressions. To test this hypothesis, we developed a diverse battery of sensitive emotion recognition tasks to characterize expression perception in individuals with Moebius Syndrome (MBS), a congenital neurological disorder that causes facial palsy. Using computer-based detection tasks we systematically assessed expression perception thresholds for static and dynamic face and body expressions. We found that while MBS individuals were able to perform challenging perceptual control tasks and body expression tasks, they were less efficient at extracting emotion from facial expressions, compared to matched controls. Exploratory analyses of fMRI data from a small group of MBS participants suggested potentially reduced engagement of the amygdala in MBS participants during expression processing relative to matched controls. Collectively, these results suggest a role for facial mimicry and consequent facial feedback and motor experience in the perception of others' facial expressions.

Application of facial neuromuscular electrical stimulation (fNMES) in psychophysiological research: Practical recommendations based on a systematic review of the literature.

Facial neuromuscular electrical stimulation (fNMES), which allows for the non-invasive and physiologically sound activation of facial muscles, has great potential for investigating fundamental questions in psychology and neuroscience, such as the role of proprioceptive facial feedback in emotion induction and emotion recognition, and may serve for clinical applications, such as alleviating symptoms of depression. However, despite illustrious origins in the 19th-century work of Duchenne de Boulogne, the practical application of fNMES remains largely unknown to today's researchers in psychology. In addition, published studies vary dramatically in the stimulation parameters used, such as stimulation frequency, amplitude, duration, and electrode size, and in the way they reported them. Because fNMES parameters impact the comfort and safety of volunteers, as well as its physiological (and psychological) effects, it is of paramount importance to establish recommendations of good practice and to ensure studies can be better compared and integrated. Here, we provide an introduction to fNMES, systematically review the existing literature focusing on the stimulation parameters used, and offer recommendations on how to safely and reliably deliver fNMES and on how to report the fNMES parameters to allow better cross-study comparison. In addition, we provide a free webpage, to easily visualise fNMES parameters and verify their safety based on current density. As an example of a potential application, we focus on the use of fNMES for the investigation of the facial feedback hypothesis.

You look stressed: A pilot study on facial action unit activity in the context of psychosocial stress.

Quality and quantity of the human stress response are highly individual. Not only are there differences in terms of psychological and physiological stress reactivity, but also with regard to facial muscle stress reactivity. In a first correlative pilot study to decipher the signature of stress as it presents in the physiognomy of a stressed individual, we investigated how stress-induced muscle movement activity in the face is associated with stress marker activation during a standardized laboratory stress test. Female and male participants (N = 62) completed the Trier Social Stress Test and provided multiple measurements of salivary cortisol, subjective experience, heart rate, and high-frequency heart rate variability. In addition, participants were filmed during stress induction to derive the activation of 13 individual muscles or muscle groups, also termed action units (AU). Mean AU intensity and occurrence rates were measured using the opensource software OpenDBM. We found that facial AU activity correlated with different aspects of the psychosocial stress response. Higher stress-induced cortisol release was associated with more frequent upper eyelid raiser (AU05) and upper lip raiser (AU10) occurrences, while more lip corner pulling (AU12) went along with lower cortisol reactivity. More frequent eyelid tightener (AU07) occurrences were linked to higher subjective stress reactivity but decreased heart rate and HF-HRV reactivity. Last, women showed greater stress-induced smiling intensity and occurrence rates than men. We conclude that psychosocial stress reactivity is systematically linked to facial muscle activity, with distinct facial stress profiles emerging for different stress markers. From all the AUs studied, eyelid tightening (AU07) seems to provide the strongest potential for future attempts of diagnosing phases of acute stress via facial activity.

Facial feedback effect on the sense of body ownership during the rubber hand illusion.

The sense of body ownership, a feeling that one's body belongs to the self, is an essential aspect of self-consciousness. Studies have focused on emotions and bodily states that could influence multisensory integration for the sense of body ownership. Based on the Facial Feedback Hypothesis, the purpose of this study was to examine whether displaying specific facial expressions affects the rubber hand illusion. We hypothesized that the expression of a smiling face changes the emotional experience and facilitates the formation of a sense of body ownership. In the experiment, participants (n = 30) were asked to hold a wooden chopstick in their mouths to simulate smile, neutral, and disgusted facial expressions during the induction of the rubber hand illusion. The results did not support the hypothesis, showing that proprioceptive drift (an index of illusory experience) was enhanced when the subjects displayed a disgusted facial expression, while the subjective reports of the illusion were not affected. These results, together with the previous studies regarding the effect of positive emotions, suggest that bodily affective information, regardless of its valence, facilitates multisensory integration and could influence the conscious representation of the bodily self.

An Audience Facilitates Facial Feedback: A Social-Context Hypothesis Reconciling Original Study and Nonreplication.

Nonreplications of previously undisputed phenomena tend to leave a theoretical vacuum. This theoretical perspective seeks to fill the gap left by the failure to replicate unobtrusive facial feedback. In the emblematic original study, participants who held a pen between the teeth (i.e., requiring activity of the zygomaticus major muscle) rated cartoons more positively than participants who held the pen between the lips. We argue that the same social mechanisms (e.g., the presence of an audience) modulate facial feedback to emotion as are involved in the feed-forward shaping of facial actions by emotions. Differing social contexts could thus help explain the contrast between original findings and failures to obtain unobtrusive facial feedback. An exploratory analysis that included results only from (unobtrusive) facial-feedback studies without explicit reference to emotion in the facial manipulation provided preliminary support for this hypothesis. Studies with a social context (e.g., due to experimenter presence) showed a medium-sized aggregate facial-feedback effect, whereas studies without a social context (e.g., when facial actions were only filmed), revealed a small effect. Video awareness strengthened facial feedback considerably within an engaging social context, but seemed to reduce it without a social context. We provisionally conclude that a (pro-)social interpretation of facial actions facilitates feedback to (primarily positive) emotion, and suggest further research explicitly manipulating this context.

Influence of advisees' facial feedback on subsequent advice-giving by advisors: Evidence from the behavioral and neurophysiological approach.

Previous work has demonstrated the interpersonal implications of advisees' decisions (acceptance or rejection) on advisors' advice-giving behavior in subsequent exchanges. Here, using an ERP technique, we investigated how advisees' facial feedback (smiling, neutral, or frowning) accompanying their decisions (acceptance or rejection) influenced advisors' feedback evaluation from advisees and their advice-giving in subsequent exchanges. Behaviorally, regardless of whether the advice was accepted or rejected, advisors who received smiling-expression feedback would show higher willingness rates in subsequent advice-giving decisions, while advisors who received frowning-expression feedback would show lower willingness rates. On the neural level, in the feedback evaluation stage, the FRN and P3 responses were not sensitive to facial feedback. In contrast, frowning-expression feedback elicited a larger LPC amplitude than neutral- and smiling-expression feedback, regardless of whether the advice was accepted or rejected. In the advice decision stage, advisors who received neutral-expression feedback showed a larger N2 in making decisions than advisors who received frowning-expression feedback only after the advice was rejected. Additionally, Advisors who received smiling- and neutral-expression feedback showed a larger P3 in making decisions than advisors who received frowning-expression feedback only after the advice was accepted. In sum, the current findings extended previous research findings by showing that the effect of advisees' facial expressions on the advisors' advice-giving existed in multiple stages, including both the feedback evaluation stage and the advice decision stage.

Pilot study of facial and bodily feedback.

BACKGROUND: The modulation hypothesis of facial feedback has not adequately examined how combining facial expressions and bodily postures might influence our experience of emotional stimuli. This pilot study examined a new method for manipulating both face and body together, which is important in furthering our understanding of how face and body interact to influence emotional experiences in the real world. METHODS: Using a within-subjects design, 30 participants viewed positive film clips under four conditions: (1) positive face with positive body (PP), (2) positive face with neutral body (PN), (3) neutral face with positive body (NP) and (4) neutral face with neutral body (NN). Measures of positive and negative affect were taken before and after each clip, to assess the subjective emotional experience. RESULTS: Repeated-measures analysis of variance (ANOVA) was conducted to examine differences in the emotional experience under each condition. Post hoc pairwise comparisons demonstrated that positive affect in the PP condition was significantly higher than in the NP and NN conditions. There was no significant difference between the PP and NN conditions. CONCLUSION: Whilst the study findings are difficult to interpret, this pilot study generated a number of important methodological learnings that are relevant to future research of this kind.

I spy with my little eye: The detection of changes in emotional faces and the influence of facial feedback in Parkinson disease.

BACKGROUND AND PURPOSE: Parkinson disease (PD) is a progressive neurodegenerative disorder that affects the motor system but also involves deficits in emotional processing such as facial emotion recognition. In healthy participants, it has been shown that facial mimicry, the automatic imitation of perceived facial expressions, facilitates the interpretation of the emotional states of our counterpart. In PD patients, recent studies revealed reduced facial mimicry and consequently reduced facial feedback, suggesting that this reduction might contribute to the prominent emotion recognition deficits found in PD. METHODS: We investigated the influence of facial mimicry on facial emotion recognition. Twenty PD patients and 20 healthy controls (HCs) underwent a classical facial mimicry manipulation (holding a pen with the lips, teeth, or nondominant hand) while performing an emotional change detection task with faces. RESULTS: As expected, emotion recognition was significantly influenced by facial mimicry manipulation in HCs, further supporting the hypothesis of facial feedback and the related theory of embodied simulation. Importantly, patients with PD, generally and independent from the facial mimicry manipulation, were impaired in their ability to detected emotion changes. Our data further show that PD patients' facial emotional recognition abilities are completely unaffected by mimicry manipulation, suggesting that PD patients cannot profit from an artificial modulation of the already impaired facial feedback. CONCLUSIONS: These findings suggest that it is not the hypomimia and the absence of facial feedback per se, but a disruption of the facial feedback loop, that leads to the prominent emotion recognition deficit in PD patients.

Enhanced Empathic Pain by Facial Feedback.

The facial feedback hypothesis states that feedback from cutaneous and muscular afferents affects our emotion. Based on the facial feedback hypothesis, the purpose of this study was to determine whether enhancing negative emotion by activating a facial muscle (corrugator supercilii) increases the intensity of cognitive and emotional components of empathic pain. We also assessed whether the muscle contraction changed the pupil size, which would indicate a higher level of arousal. Forty-eight individuals completed 40 muscular contraction and relaxation trials while looking at images of five male and five female patients with neutral and painful facial expressions, respectively. Participants were asked to rate (1) how much pain the patient was in, and (2) how unpleasant their own feelings were. We also examined their facial muscle activities and changes in pupil size. No significant differences in pain or unpleasantness ratings were detected for the neutral face between the two conditions; however, the pain and unpleasantness ratings for the painful face were considerably higher in the contraction than relaxation condition. The pupils were considerably larger in the contraction than relaxation condition for both the painful and neutral faces. Our findings indicate that, by strengthening the corrugator supercilii, facial feedback can affect both the cognitive evaluative and affective sharing aspects of empathic pain.

Is There a Difference in Facial Emotion Recognition after Stroke with vs. without Central Facial Paresis?

The Facial Feedback Hypothesis (FFH) states that facial emotion recognition is based on the imitation of facial emotional expressions and the processing of physiological feedback. In the light of limited and contradictory evidence, this hypothesis is still being debated. Therefore, in the present study, emotion recognition was tested in patients with central facial paresis after stroke. Performance in facial vs. auditory emotion recognition was assessed in patients with vs. without facial paresis. The accuracy of objective facial emotion recognition was significantly lower in patients with vs. without facial paresis and also in comparison to healthy controls. Moreover, for patients with facial paresis, the accuracy measure for facial emotion recognition was significantly worse than that for auditory emotion recognition. Finally, in patients with facial paresis, the subjective judgements of their own facial emotion recognition abilities differed strongly from their objective performances. This pattern of results demonstrates a specific deficit in facial emotion recognition in central facial paresis and thus provides support for the FFH and points out certain effects of stroke.

Treatment of Depression with Botulinum Toxin.

Injection of botulinum toxin (BoNT) into the glabellar region of the face is a novel therapeutic approach in the treatment of depression. This treatment method has several advantages, including few side effects and a long-lasting, depot-like effect. Here we review the clinical and experimental evidence for the antidepressant effect of BoNT injections as well as the theoretical background and possible mechanisms of action. Moreover, we provide practical instructions for the safe and effective application of BoNT in the treatment of depression. Finally, we describe the current status of the clinical development of BoNT as an antidepressant and give an outlook on its potential future role in the management of mental disorders.

Facial Emotion Recognition in Patients with Post-Paralytic Facial Synkinesis-A Present Competence.

Facial palsy is a movement disorder with impacts on verbal and nonverbal communication. The aim of this study is to investigate the effects of post-paralytic facial synkinesis on facial emotion recognition. In a prospective cross-sectional study, we compared facial emotion recognition between n = 30 patients with post-paralytic facial synkinesis (mean disease time: 1581 ± 1237 days) and n = 30 healthy controls matched in sex, age, and education level. Facial emotion recognition was measured by the Myfacetraining Program. As an intra-individual control condition, auditory emotion recognition was assessed via Montreal Affective Voices. Moreover, self-assessed emotion recognition was studied with questionnaires. In facial as well as auditory emotion recognition, on average, there was no significant difference between patients and healthy controls. The outcomes of the measurements as well as the self-reports were comparable between patients and healthy controls. In contrast to previous studies in patients with peripheral and central facial palsy, these results indicate unimpaired ability for facial emotion recognition. Only in single patients with pronounced facial asymmetry and severe facial synkinesis was an impaired facial and auditory emotion recognition detected. Further studies should compare emotion recognition in patients with pronounced facial asymmetry in acute and chronic peripheral paralysis and central and peripheral facial palsy.

Facial Imitation Improves Emotion Recognition in Adults with Different Levels of Sub-Clinical Autistic Traits.

We used computer-based automatic expression analysis to investigate the impact of imitation on facial emotion recognition with a baseline-intervention-retest design. The participants: 55 young adults with varying degrees of autistic traits, completed an emotion recognition task with images of faces displaying one of six basic emotional expressions. This task was then repeated with instructions to imitate the expressions. During the experiment, a camera captured the participants' faces for an automatic evaluation of their imitation performance. The instruction to imitate enhanced imitation performance as well as emotion recognition. Of relevance, emotion recognition improvements in the imitation block were larger in people with higher levels of autistic traits, whereas imitation enhancements were independent of autistic traits. The finding that an imitation instruction improves emotion recognition, and that imitation is a positive within-participant predictor of recognition accuracy in the imitation block supports the idea of a link between motor expression and perception in the processing of emotions, which might be mediated by the mirror neuron system. However, because there was no evidence that people with higher autistic traits differ in their imitative behavior per se, their disproportional emotion recognition benefits could have arisen from indirect effects of imitation instructions.

The Use of Botulinum Toxin for Treatment of Depression.

A series of clinical studies have shown that botulinum toxin can treat major depression. Subjects suffering from unipolar depression may experience a quick, strong, and sustained improvement in the symptoms of depression after a single glabellar treatment with botulinum toxin.Preliminary data suggest that botulinum toxin therapy may also be effective in the treatment of other mental disorders characterized by an excess of negative emotions, such as borderline personality disorder.The mood-lifting effect of botulinum toxin therapy is probably mediated by the interruption of a proprioceptive feedback loop from the facial musculature to the emotional brain.

[Myofascial facial massage as a possible method of correction of psychoemotional states]. / Miofastsial'nyi massazh litsa kak vozmozhnyi metod korrektsii psikhoemotsional'nykh sostoyanii.

The work highlights the current problems of the relationship between the tonic activity of facial muscles and psychoemotional states. The frequency and severity of psychoemotional conditions and indicators of tonic activity of the facial muscles in 67 healthy women were studied. The currently known methods for the correction of psycho-emotional states based on the feedback mechanism are analyzed. The effectiveness of use of myofascial face massage as an instrument for the correction of psychological status was assessed. The influence of various massage techniques aimed at relaxing facial muscles on the psychoemotional state in the long term has been proved. The most effective tools for correcting muscle tone for the correction of psychoemotional states are proposed.

Mimicking and sharing emotions: a re-examination of the link between facial mimicry and emotional contagion.

Facial mimicry has long been considered a main mechanism underlying emotional contagion (i.e. the transfer of emotions between people). A closer look at the empirical evidence, however, reveals that although these two phenomena often co-occur, the changes in emotional expressions may not necessarily be causally linked to the changes in subjective emotional experience. Here, we directly investigate this link, by testing a model in which facial activity served as a mediator between the observed emotional displays and subsequently felt emotions (i.e. emotional contagion). Participants watched videos of different senders displaying happiness, anger, or sadness, while their facial activity was recorded. After each video, participants rated their own emotions and assessed the senders' likeability and competence. Participants both mimicked and reported feeling the emotions displayed by the senders. Moreover, their facial activity partially explained the association between the senders' emotional displays and self-reported emotions, thereby supporting the notion that facial mimicry may be involved in emotional contagion.