What do we know about mood disorders?

Editor's note: Dr. Charles Raison, CNNhealth's mental health expert, is an associate professor of psychiatry at the University of Arizona in Tucson.
(CNN) -- Judging by the 5 a.m. call I got yesterday from a national news network, and from the barrage of in-print, online and televised discussion I saw as the day wore on, it is clear that the revelation that Rep. Jesse Jackson Jr. is being treated at a "residential treatment facility" for a mood disorder has raised far more questions than it has answered.