facial Neuromuscular Electrical Stimulation (fNMES) - review and recommendations

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.