Patients with major depression (N=20) will be recruited for the 8-week clinical trial of quetiapine XR 100 - 300 mg (flexible dosing). Patients who consent to participate will be referred for an initial fMRI scanning session prior to the initiation of quetiapine XR. Baseline fMRI will be obtained during the index assessment prior to initiating quetiapine XR therapy and then will be re-acquired at the final study visit at 8 weeks (the time of scheduled visits). Ten demographically matched healthy subjects will receive the same fMRI investigations on two occasions in order to provide a healthy baseline comparison to permit interpretation of the patient findings (e.g., whether initial and final fMRI measures in patients are abnormal and to control for any adaptation to the task that may normally occur).