Application of facial Neuromuscular Electrical Stimulation (fNMES) in psychophysiological research – systematic review and practical recommendations

Abstract

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, as well as for clinical applications, such as alleviating depression symptoms. However, despite illustrious origins in 19th century work of Duchenne de Boulogne, the practical application of fNMES remains largely unknown to researchers in psychology and human physiology. In addition, published studies vary dramatically in use and reporting of parameters, such as stimulation frequency, amplitude, duration, and electrode size. 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. Here, we provide an introduction to fNMES, a systematic review of the existing literature focusing on stimulation parameters used, and we offer recommendations on how to safely and reliably deliver fNMES. In addition, we provide a free webpage, allowing to easily verify and compare the safety of fNMES parameters 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.

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

“…Our behavioural findings have positive implications for facial feedback interventions that utilise posing as a method to reduce or manage distress (Ansfield, 2007) and address symptoms of depression (Finzi & Rosenthal, 2014Fromage, 2018). Over-the-counter electrical stimulation devices, commonly used for pain management in the face, body, and craniofacial disorders (Efthimiou et al, 2022), may be harnessed to assist individuals with conditions that impede facial feedback, such as Bell's Palsy (Alakram & Puckree, 2010), Moebius syndrome (Stefani et al, 2019), and Parkinson's disease (Argaud et al, 2018). Furthermore, this technique holds promise for future research that can investigate the time course of facial feedback effects, specifically examining whether stimulus-congruent facial feedback occurs only after early visual processing has been completed (Halberstadt et al, 2009;Niedenthal, 2007).…”

“…Whether the state of activation/relaxation of facial muscles can affect the visual perception and recognition of emotional faces remains debated (Hess & Fischer, 2014;Wood, Rychlowska, et al, 2016). Advancing on that debate might require using methods that allow modulating facial feedback with great precision, and for that purpose, we have recently proposed to use computer-controlled fNMES (Efthimiou et al, 2022). Promising results of fNMES' ability to modulate participants' felt emotions and mood have been reported by a handful of studies (Zariffa et al, 2014;Kapadia et al, 2019;Warren, 2021).…”

“…Stimulation intensity was below 2 RMS mA/cm² following safety guidelines (see Efthimiou et al, 2022). EEG data were sampled at 512 Hz using an eego sports amplifier (ANT Neuro), and a 64-electrodes waveguard capelectrodes AFz and CPz served as ground and reference, respectively.…”

“…Facial neuromuscular electrical stimulation (fNMES) generates controlled facial muscle activations, and may thus help to overcome the limitations of the techniques used to manipulate facial feedback so far (Efthimiou et al, 2022). Indeed, fNMES allows researchers to selectively target specific muscleswhile controlling for the time of onset, duration, and intensity of their activationto generate movements associated with emotional facial expressions.…”