Grant: Operating Grant

Major Depressive Disorder is one of the most prevalent mental illnesses in North America, affecting approximately 4% of Canadians annually. Though a number of effective treatments are available, as many as 15% of those diagnosed with a depressive disorder die by suicide, 30-40% fail to respond to treatment and approximately 60% experience a relapse. These statistics emphasize the need to optimize treatment response and understand the brain mechanisms responsible for major depressive disorder in an effort to improve treatment outcome. Disrupted brain inhibition has been thought to be linked to the symptoms of major depressive disorder and its treatment. Inhibition refers to brain processes in which nerve cells selectively decrease the activity of other nerve cells in the brain. Transcranial magnetic stimulation is a safe and non-invasive way of measuring inhibition in the brain. In this study we hope to establish a definitive link between decreased inhibition in treatment-resistant depression and the likely reversal of this deficit with the two treatments that are preferentially used in patients with depression who do not respond to antidepressant medications, electroconvulsive therapy and repetitive transcranial magnetic stimulation. We expect that the results of this study will explain some of the brain mechanisms that may be altered in patients who do not respond to medications and may help guide its future treatment. The availability of additional treatment options is vital to enhancing our patients' quality of life and provides hope for those who would otherwise suffer from persistent illness.