sufijazz writes "A story by Gregory Mone on the Popular Science website talks about trials to use deep brain stimulation to cure chronic depression. It's a deeper exploration of the 'brain pacemaker' discussed here on the site before, and a practical application of research discussed even earlier. Why the pulses affect mood is still unclear, but scientists believe that they may facilitate chemical communication between brain cells, possibly by forcing ions through nerve fibers called axons. In turn, this may trigger the release of mood-regulating chemicals like serotonin and norepinephrine. Similar trials are being conducted in other places. Exact numbers are hard to ascertain, but it's estimated that fewer than 50 patients in North America are walking around with wires in their brain."