Functional electrical stimulation for facial pacing: Effects of waveforms on movement intensity and ratings of discomfort

Application of facial Neuromuscular Electrical Stimulation (fNMES) in psychophysiological research – practical recommendations based on a systematic review of the literature

“…However, few studies have investigated this issue with facial muscles. Ilves et al (2020) investigated four waveforms (square wave, square wavelet, sine wave, and sinusoidal wavelet) on the frontalis muscle in terms of subjective comfort and magnitude of forehead movement. The authors report that all waves performed equally well and did not significantly differ in terms of reported comfortother facial regions may differ due to anatomical differences, such as the amount of subcutaneous fat.…”

“…The latter output is the current densitybe aware that if this exceeds 2 mA rms/cm 2 extra attention should be paid not to cause damage to the skin. Be aware that the app assumes a mono-or biphasic square waveformit does not work for other waveforms, like the square wavelet and sinusoidal wavelet used by Ilves et al (2020).…”

“…it was only described as "symmetrical" (e.g. Sapphire, which according to its user manual uses a square wave); 6) in case of polyphasic waveforms (Rantanen et al 2018;Ilves et al, 2020), we provided the frequency of the pulse train, and not of the pulses inside of polyphasic "packages"; 7) if several amplitudes were used, we noted the largest one; 8) separate entries were created if a study included several experiments with different parameters. Once completed, Table 1 was loaded into R, where we computed duty cycle, Irms/cm 2 based on the formulas provided below (section Formulas), unless relevant parameters were missing, which unfortunately was the case for the large majorities (27 of the 34) of studies.…”

“…Another 15 studies had various goals, e.g. they investigated the effects of variations in fNMES parameters on physiology and subjective reports (Ilves et al, 2020;Rantanen et al, 2018), and were thus classified as "Other". Various stimulation sites were targeted, including the frontalis, orbicularis oculi, orbicularis oris, zygomaticus major, depressor anguli oris, and masseter muscles.…”

“…Five studies have investigated the use of fNMES to recover muscular function after Ball's palsy, or other forms of facial paresis (Cui et al, 2021;Makela et al, 2020). The goal of some studies was to further explore the physiological and subjective effects of varying fNMES parameters, such as the waveform (Ilves et al, 2020;Rantanen et al, 2018). Surprisingly, only three studies have used fNMES to modulate mood and/or emotion (Goto et al, 2018;Kapadia et al, 2019;Zariffa et al, 2014), and thus investigate aspects of the facial feedback hypothesis, despite the great potential that this technique has to help investigate aspects central to psychological mechanisms and theories, such as embodied cognition and sensorimotor simulation (Halberstadt et al, 2009;Niedenthal, 2007;Wood et al, 2016).…”