There was a study I read longer ago than I wish wherein a group of college professors seeded college "mixers" with mental patients. If I recall correctly, the end result was that some mental illnesses could, to a degree, be considered symptomatically or behaviorally contagious. Extremely reckless and probably illegitimate study, but it did ring true to me on certain levels, and actually gave me some insights into the nature of propaganda, and modelled thinking. I've tried finding the study and completely struck out. Maybe I'm nuts and imagined it!