We propose a similar study with Quetiapine XR, focusing on thinking processes, mood and anxiety. Patients with depression who are SSRI treatment resistant will be treated with Quetiapine. Cognition will be evaluated in the UBC Mood Disorders Clinic two times: first before Quetiapine addition, then after 8 weeks. Depression symptoms and other measurements will be done at the 9 time points: before Quetiapine, and each week after treatment has begun.