Would you kill somebody if you were told to by your boss or an authority figure? "Of course not. Are you nuts?" is probably the most common answer to this question. However, this can not be backed up with psychological research carried out in the sixties and seventies.
After Nazi-Germany had collapsed and the world started to realize the unbelievable things that had happened, a lot of sociological and psychological experiments were carried out to understand if, how, and when ordinary people lose their humanity.
PsyBlog published a nice article about the psychology of money.
Obviously money is a great way to trade stuff and services. Imagine how difficult it'll get if you're trying to trade food by offering your experiences as a web designer or politician. But there's more going on with money than just its practical use and the article lists some interesting psychological effects.
WIRED features an interesting interview with psychologist Philip Zimbardo who conducted the famous Stanford Prison Experiment. He links his research to actual events like Abu Ghraib or jewish wardens in nazi concentration camps.
Read "How Good People Turn Evil, From Stanford to Abu Ghraib" over at WIRED.
I once attended a course "Funktionsstörungen/Dysfunctions" at Aachen University, that dealt with disorders of several functions of the brain and insights that can be concluded therefrom. A recent TED talk by Vilayanur Ramachandran picked-up that topic and is definitely worth watching.