This study is a single-arm, open-label, feasibility trial for the assessment of the clinical effects of a course of accelerated bilateral sequential theta burst stimulation (TBS) for late life depression (LLD). Over approximately 1 year, 30 outpatients at the Centre for Addiction and Mental Health (CAMH) meeting diagnostic criteria for LLD will be recruited and will receive 5 consecutive days (always Monday to Friday) of TBS repetitive transcranial magnetic stimulation (rTMS), administered 8 times daily at approximately 1 hour intervals, with continuous theta-burst stimulation (cTBS) applied to the right dorsolateral prefrontal cortex (DLPFC) followed by left DLPFC intermittent theta-burst stimulation (iTBS).

Patients will undergo a series of assessments as well as motor threshold testing to determine the appropriate site and strength of stimulation according to standard methods and then begin treatment.

Repetitive transcranial magnetic stimulation (rTMS) is an evidenced based treatment for medically refractory major depressive disorder (MDD). rTMS involves direct stimulation of cortical neurons using externally applied, powerful, focused magnetic field pulses. Dozens of studies and several meta-analyses over the last 15 years have shown that rTMS of the dorsolateral prefrontal cortex (DLPFC) produces statistically significant improvements in MDD, even when medications have failed. In the most recent generation of randomized controlled trials, rTMS consistently achieves response rates of 50-55% and remission rates of 30-35% in medically refractory MDD patients. rTMS has been shown to be effective and well tolerated for depression in younger and older adults. However, early rTMS studies with older adults were limited by suboptimal stimulation parameters, small sample sizes and insufficient treatment durations. The optimal parameters for rTMS are still in the process of being established, however the most widely-used rTMS protocols apply excitatory, 10 Hz stimulation to the left DLPFC; high frequency left (HFL) or inhibitory, 1 Hz stimulation to the right DLPFC; low frequency right (LFR), or both. Taken together with the reported findings of several other groups, results suggest that accelerated rTMS may be feasible, tolerable, and capable of achieving comparable and potentially better remission rates than longer 20 to 30 day courses. However, all of these studies were small, open-label case series, focused on younger adults.

Inclusion Criteria:

1. Are voluntary and competent to consent to treatment
2. are an outpatient
3. are ≥60 years old
4. have a Mini-International Neuropsychiatric Interview (MINI 6.0) confirmed diagnosis of major depressive disorder (MDD), with a current major depressive episode (MDE)
5. have failed to achieve a clinical response to an adequate dose of an antidepressant based on an Antidepressant Treatment History Form (ATHF) score of > 3 in the current episode or have failed to tolerate two separate trials of an antidepressant
6. have a score > 18 on the Montgomery-Asberg Depression Rating Scale (MADRS)
7. have had no increase or initiation of any antidepressant or antipsychotic medication in the 4 weeks prior to screening
8. Pass the TMS adult safety screening (TASS) questionnaire

Exclusion Criteria:

1. have a history of substance dependence or abuse within the last 3 months
2. have a concomitant major unstable medical illness as determined by one of the study physicians
3. have active suicidal intent
4. have a lifetime MINI diagnosis of bipolar I or II disorder, or primary psychotic disorder
5. have current psychotic symptoms
6. have a diagnosis of obsessive compulsive disorder, post-traumatic stress disorder (current or within the last year), anxiety disorder (generalized anxiety disorder, social anxiety disorder, panic disorder), or dysthymia, assessed by a study investigator to be primary. One of these comorbidities will not be exclusionary if they are not deemed to be primary.
7. have a diagnosis of any personality disorder as assessed by a study investigator to be primary and causing greater impairment than MDD
8. have presumed or probable dementia or clinical evidence of dementia as assessed by a Short Blessed Test score of greater than 10.
9. did not respond to a course of electroconvulsive therapy (ECT) in the current depressive episode
10. have received rTMS in the current episode, patients who have had rTMS in a previous episode would be eligible
11. have a history of a primary seizure disorder or a seizure associated with an intracranial lesion.
12. have an intracranial implant (e.g., aneurysm clips, shunts, stimulators, cochlear implants, or electrodes) or any other metal object within or near the head, excluding the mouth, that cannot be safely removed
13. have a implanted electronic device that is currently function such as a defibrillator
14. currently take more than lorazepam 2 mg daily (or equivalent) or any dose of an anticonvulsant
15. if participating in psychotherapy, must have been in stable treatment for at least 3 months prior to entry into the study, with no anticipation of change in the frequency of therapeutic sessions, or the therapeutic focus over the duration of the study
16. non-correctable clinically significant sensory impairment (i.e., cannot hear well enough to cooperate with interview).