Accelerated Bilateral Sequential Theta Burst Stimulation in Older Adults With Treatment-resistant Depression

Inclusion Criteria 1. Aged 50 years or older; 2. Mini International Neuropsychiatric Interview (MINI)-confirmed diagnosis of a non-psychotic major depressive disorder; 3. Currently in a major depressive episode with a score on HAMD-17 of 17 or more; 4. Insufficient response (i.e., failure to achieve remission) to at least two appropriate courses of antidepressant medications during the current depressive episode (i.e., meeting the criteria for TRD); 5. Participants taking or not taking any psychotropic medication/s. If the eligible participant is on any psychotropic medications, the participant should have taken the medication/s at a stable dose for at least 1 week before the start of study intervention treatment and be willing to remain on a stable dose throughout the study follow-up; 6. Passing the TMS safety screen; and 7. Those who have the capacity to provide consent and who voluntary consent to participate in the study. Exclusion Criteria 1. Those with MINI-confirmed active substance use disorder within the last 3 months; 2. Those with lifetime MINI-confirmed diagnosis of bipolar I disorder, delusional disorder, schizophrenia, schizoaffective disorder, or schizophreniform disorder; 3. Those with major unstable medical comorbidities (i.e., rapidly deteriorating medical/neurological conditions that poses a significant risk to a person's life); 4. Those with a diagnosis of dementia confirmed using the Global Clinical Dementia Rating (CDR) with a score greater than or equal to 1. 5. Those with significant neurological conditions, such as those with any disease process associated with increased intracranial pressure, space-occupying intracranial lesion, history of epilepsy/seizure except those induced by ECT, or febrile seizure of infancy or a single occurrence of seizure associated with a known drug, cerebral aneurysm, or major head trauma resulting to loss of consciousness more than 5 minutes; 6. Those with cardiac pacemaker or implanted mediation pump; 7. Those with intracranial implants/hardwares, including but not limited to aneurysm clips, shunts, stimulators, cochlear implants, electrodes, or any other metal material inside or near the head (excluding the mouth) that cannot be safely removed; 8. Those who are taking more than 2 mg of Lorazepam daily (or equivalent) or taking any dose of an anticonvulsant that may potentially hamper rTMS efficacy; 9. Those who are unable to express and understand using the English language; and 10. Individuals who are pregnant or who are likely pregnant.