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

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, 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.

Smiling and frowning induced by facial neuromuscular electrical stimulation (fNMES) modulate felt emotion and physiology

“…Stimulation was administered using a 70 Hz train of biphasic square pulses with a width of 100 µs and a pulse delay of 14 ms. We used disposable Ag/AgCI electrodes measuring 16 × 19 mm (Ambu BlueSensor BRS, surface area = 3.04 cm 2 ). The maximum stimulation intensity used was 35 mA, which corresponds to 0.96 Root Mean Square (RMS) mA/cm² and is well below the advised safety threshold of RMS 2 mA/cm 2 and follows the safety guidelines outlined in EN 60601-2-10:2000 (see Efthimiou, Hernandez, et al, 2023).…”

“…Facial neuromuscular electrical stimulation (fNMES) consists of delivering electrical currents to facial muscles using surface electrodes, allowing researchers to activate specific facial muscles non-invasively and with high temporal precision. fNMES has already shown promise as a treatment for depression (Demchenko et al, 2023;Kapadia et al, 2019), and we have recently emphasised its potential for testing aspects of the FFH (Efthimiou, Hernandez, et al, 2023). For a recent review of the literature on human surface fNMES, and recommendations on how to implement it in the psychology laboratory and combine it with EEG (see, Baker et al, 2023;Efthimiou, Baker, et al, 2023;Efthimiou, Hernandez, et al, 2023).…”

“…fNMES has already shown promise as a treatment for depression (Demchenko et al, 2023;Kapadia et al, 2019), and we have recently emphasised its potential for testing aspects of the FFH (Efthimiou, Hernandez, et al, 2023). For a recent review of the literature on human surface fNMES, and recommendations on how to implement it in the psychology laboratory and combine it with EEG (see, Baker et al, 2023;Efthimiou, Baker, et al, 2023;Efthimiou, Hernandez, et al, 2023).…”