Both invasive and non-invasive focal brain stimulation techniques have been proposed for treatment of psychiatric disorders with initially encouraging results. These techniques use different pulsed stimulation protocols to modify brain function. However, full clinical exploitation of these techniques is greatly limited by our poor understanding of their therapeutic mechanisms. Even though the stimulation is focally targeted to a particular brain region, the lasting effects of stimulation spread to the entire brain, as can be observed with functional MRI (fMRI). These diffuse brain network effects are key to understanding how brain stimulation can be used to treat different brain disorders. I therefore propose to study the neural bases of these network effects in a physiologically-accessible species, so that invasive measurements of neuronal activity can be linked to fMRI measurements. In particular, I will be investigating the relative contributions of excitatory and inhibitory cells to the lasting effects of stimulation, and building a model based on my findings which accurately predicts the fMRI results. Ultimately this research will lead to improved strategies for treatment with brain stimulation crossing diagnostic boundaries.