I am reading an article in this month's SciAm mind about treating depression with deep-brain stimulation. Researchers found that an area known as Area 25 is overactive in patients with severe depression. From what I understand, this area is sort of a "traffic controller" for neural paths between the frontal cortex and the limbic system. They did some neuroimaging experiments and found that when a depression attack occurred, frontal cortex activity plummeted and Area 25 activity increased. As the depressive episode subsided, frontal activity revived and Area 25 activity settled down. Anyway, what they did to treat these patients was implant electrodes into Area 25, and then used an implanted "pacemaker" to send current to them. What I am not clear about is how the electrical stimulation inhibits rather than excites the firing in this area.