This protocol describes a single-site, double-blind, randomized, sham-controlled pilot trial evaluating bilateral functional electrical stimulation (FES) of facial muscles as a treatment for major depressive disorder (MDD). Sixty participants will complete 20 on-site stimulation sessions over four weeks, plus online study visits including screening, baseline, and four follow-up assessments. The trial aims to assess efficacy, safety, and tolerability and to measure effects on depressive symptoms, anxiety, quality of life, and sleep. Adherence and adverse events will be tracked. Results are intended to guide a larger multisite randomized controlled trial and to refine FES parameters.
MDD is a leading cause of global disability. Conventional first-line treatments such as antidepressants are limited by side effects, treatment delays, and partial response: many patients experience adverse effects and some discontinue treatment. Neurostimulation options (electroconvulsive therapy, repetitive transcranial magnetic stimulation, and home-based transcranial direct current stimulation) offer alternatives but are constrained by variable efficacy, invasiveness, and logistical barriers. These limitations motivate the investigation of alternative neurostimulation modalities with distinct mechanisms and practical advantages.
FES delivers low-energy electrical impulses to activate neuromuscular units and produce muscle contractions. When applied to muscles of facial expression, FES may engage the facial feedback mechanism: afferent proprioceptive and interoceptive signals from facial musculature influence emotional processing. The literature summarized in the protocol highlights pathways to limbic structures, particularly the amygdala, via trigeminal, glossopharyngeal, and vagus-related inputs. Activation of specific facial muscles associated with smiling—the zygomaticus major and the orbicularis oculi—may differentially influence emotional experience; a Duchenne smile (zygomaticus plus orbicularis oculi) is linked more consistently to positive affect than a non-Duchenne (zygomaticus alone).
Pilot and open-label investigations provide preliminary support for mood effects of facial muscle stimulation. A 2014 pilot in healthy volunteers compared single-session FES targeting Duchenne smile muscles with controls and reported changes in affect-related items on the PANAS-X. An open-label trial in patients with MDD found clinically meaningful reductions in depression rating scales after 10 FES sessions. Studies of facial neuromuscular electrical stimulation (fNMES) also show that stronger stimulation of smile-related muscles produces more positive emotional reports compared with stimulation of muscles associated with negative expressions. The protocol cites these studies to justify a randomized, sham-controlled design to more rigorously evaluate repetitive FES in MDD.
The protocol specifies a single-site, double-blind, randomized, sham-controlled pilot RCT. Sixty participants will be enrolled. Participants and blinded study personnel will be involved to preserve allocation concealment and blinding. The trial will provide 20 stimulation sessions over four weeks as the active regimen. The protocol emphasizes this pilot as preparatory work to inform a future multisite definitive trial and to refine stimulation parameters.
Eligible participants will complete 20 on-site intervention visits distributed over four weeks (five visits per week) and an additional six online visits covering screening, baseline, and four post-stimulation follow-ups. The active intervention consists of bilateral facial FES targeting muscles involved in the Duchenne smile; the control arm will receive a sham stimulation designed to maintain blinding. Specific technical parameters of stimulation and sham implementation are described in the full protocol text.
Primary trial objectives are to evaluate the efficacy, safety, and tolerability of bilateral facial FES in MDD. The study will assess changes in depressive symptom severity and will also measure associated anxiety, quality of life, and sleep. Tolerability will be assessed via protocol adherence and dropout rates, while safety will be evaluated through monitoring and reporting of adverse events throughout the trial.
Adverse events will be monitored continuously during the trial period to evaluate safety. Participant dropout rates and adherence to the 20-session schedule will be recorded to assess tolerability and feasibility of the intervention protocol. The protocol notes standard trial procedures for safety reporting and participant monitoring.
The authors intend that findings from this pilot RCT will inform the design of a larger multisite randomized controlled trial and support refinement of FES treatment parameters for MDD. The pilot is positioned to provide feasibility data, preliminary efficacy signals, and safety/tolerability information necessary to plan a definitive efficacy trial.
The trial is registered on ClinicalTrials.gov (NCT07629050; date registered 2026-06-08). Funding is provided by the Canadian Institutes of Health Research (CIHR; Grant No. 471191). Competing interests disclosed include that two authors are inventors on U.S. Patent No. 9,259,576 related to FES for mood alteration; other authors report fellowships or no competing interests. This article is a study protocol and contains no study data. If further methodological details or full stimulation parameter tables are required, the reader should consult the complete protocol as published.