This study aims to: (1) assess the feasibility and tolerability of two active dTMS coils - H4 and H7 - in older adults with depression; and (2) clinical response measured by change from baseline on the Hamilton Depression Rating Scale- 24 item; changes in cognitive function through neuropsychological assessment; and changes in regional electrophysiological activity and functional connectivity indexed by EEG. Through a parallel design, participants will complete a four-week course of five dTMS sessions per week, for a total of 20 stimulation sessions. Participants will be randomly assigned to either coil (H4 or H7) and will complete questionnaires examining side effects, mental health symptoms, and cognition. Participant EEG data will be measured and collected at baseline and at the end of each week. Collectively, the study will address the absolute and differential feasibility and tolerability of the two active coils to provide preliminary data for a future randomized controlled trial comparing one or both of these novel interventions to the established H1-coil and a sham stimulation (placebo) control.

Transcranial magnetic stimulation (TMS) is a non-invasive therapeutic technique used to stimulate regions of the brain using magnetic pulses. Repeated TMS delivers sequences of pulses for multiple days in a row and is an approved treatment for several psychiatric conditions. Deep TMS (dTMS) is a new technique that uses modified magnetic Hesed coils (H-coils) to stimulate deeper regions of the brain and has been FDA- and Health Canada-approved for major depressive disorder (MDD), obsessive-compulsive disorder, smoking cessation, and anxious-depression in adults. For older adults (60+), traditional rTMS has also shown efficacy for MDD (60+) and one RCT has found benefit for the H1 dTMS coil, but no trials have examined the H4 and H7 coils in this population. This innovative pilot study will explore dTMS feasibility and tolerability (i.e., side effects, impacts on mental health and cognition) of these two dTMS coils (H4, targeting insula and H7, targeting anterior cingulate cortex) in older adults with depression. The pilot will provide critical preliminary data for a future trial comparing these novel interventions to the H1-coil and a sham stimulation control. There is sparse literature examining the effects of dTMS on cognition, as measured by neuropsychological testing, and brain activity, as measured by electroencephalogram (EEG), while comparing different dTMS H-coils. Therefore, a second feature of the design includes assessing both domains over the course of treatment. The results will lay the foundation for a future randomized controlled trial examining the efficacy and mechanisms of one or both of these novel forms of neurostimulation for MDD in older adults.

Inclusion Criteria:

A) 60 - 85 years old

B) Able to provide informed consent to participate in the study

C) MDD diagnosis, single or recurrent episode, assessed using Evaluation of the Diagnostic Assessment Research Tool (DART) Screener for DSM-5 Mood Disorder Module

D) Total score of at least 20 on the 24-item Hamilton Depression Rating Scale (HDRS-24) at screening visit

E) Treatment resistance to antidepressant pharmacotherapy during the current episode as indexed by Antidepressant Treatment History Form - Short Form (ATHF - SF). Specifically, participants will be required to have failed at least one or to have had an inadequate trial (including intolerance) to at least two antidepressants in the current episode

F) Participants will be required to be on stable dosages of other psychotropic medications for at least 4 weeks prior to screening

Exclusion Criteria:

A) Primary diagnosis of bipolar I or II disorder; psychotic disorder; obsessive-compulsive, post-traumatic stress, anxiety, or personality disorder; participants with anxiety or personality disorders will be eligible if is not their primary diagnosis

B) Active suicidal behavior

C) Substance dependence/abuse in the past 3 months before entering the study (this will be screened via self-report and verified by urine screening test)

D) Possible dementia diagnosis based on a Mini Mental Status Exam (MMSE) score of <24 and clinical presentation of dementia

E) Unsuccessful ECT treatment on the current episode

F) Traditional contraindications to rTMS: Intracranial or metal implants in the head or nearby regions, excluding the mouth, that cannot be safely removed; History of epilepsy or seizures; Active unstable medical condition (recent laboratory and neuroimaging alterations); Pacemaker and/or implantable cardioverter-defibrillators; current use of bupropion >300 mg/day as it is associated with risk of seizures, treatment with equivalent benzodiazepine dose to lorazepam >2 mg/day

G) People with severe literacy, visual, or hearing issues that affect their ability to engage in the interviews

H) People with recurring migraines or headaches (weekly or more).

I) Individuals residing beyond the borders of the Greater Hamilton Area and its neighbouring vicinities.

We will implement a sex equity approach by aiming at a 50/50% rate of male and female but allowing an imbalance of maximum 60/40% from either side.

This is an open label trial. Only study staff processing and analyzing the data will be fully blinded.