Inclusion Criteria:
Patients will be included if they:
1. Meet the DSM-5 criteria for unipolar MDD with a current MDE without psychotic features, with ≤ 2 failed treatment trials (non-treatment-resistant depression), validated by MINI done by a trained research assistant.
2. Have no change in the medication regimen or other forms of treatments (e.g., psychotherapy) for at least 4 weeks (28 days) prior to beginning the study, and have no plan to change them during the 20-session treatment period (14 days), and the 4-week post-treatment observation period. This will be established through self-report, in combination with the ATHF filled out by the participant.
3. Have an MDD diagnosis as confirmed by the MADRS score of ≥7.
4. Age group between 18 and 70 years of age
Exclusion Criteria:
Patients will be excluded if they:
1. History of epilepsy or seizures.
2. Damage or dysfunction of facial nerves.
3. Metallic orthopedic implants in the mouth (e.g., plates or screws).
4. Current fibromyalgia or currently receiving or have received rTMS within the last 28 days before the screening.
5. History of treatment-resistant depression (TRD) with history of ECT, Magnetic Seizure Therapy, Intravenous Ketamine use in the past or failure of \>2 antidepressant treatments of adequate duration and dose during the current episode.
6. Past or current symptoms of mania, hypomania, mixed episodes, psychotic disorders, obsessive-compulsive disorder, post-traumatic stress disorder, active substance abuse or dependence (excluding nicotine and caffeine), neurodegenerative disease, or dementia. This will be confirmed on the MINI (77) administered by a trained research assistant.
7. Current suicidal intent or plan as demonstrated by a score of ≥4 on MADRS item 10.
8. Unable to understand instructions in English.
9. Unable to produce "Duchenne marker" expression with FES, secondary to any type of neurological condition or previous botulinum toxin treatments of facial muscles.
