MRI scan Each subject will undergo a 3D sagittally orientated T1 weighted structural MR scan on the 1.5 Tesla MRI scanner at the Alfred or Toronto Western Hospital (128 slices). Analysis of scalp to cortex distance in prefrontal cortex and at the site of stimulation will be conducted using previously published methods [41] by a post doctoral research fellow with considerable experience in structural neuroimaging analysis using the ANALYSE software package. During scanning, the site of motor cortex and the stimulation site will be marked on the scalp with 2 vitamin E capsules. This will also allow the post hoc analysis of our actual site of stimulation in comparison to cortical landmarks of the DLPFC.