It's long been known that if you want someone to do something (especially if that "something" is contrary to what they're likely to do in the first place), give them an "expert" advice. But why is that?

Emory University Neuroscientist Greg Berns and colleagues have found the answer: a brain-scanning study of people making financial choices found that when given the so-called expert advice, the decision-making parts of their brains often shut down.

In the study, Berns' team hooked 24 college students to brain scanners as they contemplated swapping a guaranteed payment for a chance at a higher lottery payout. Sometimes the students made the decision on their own. At other times they received written advice from Charles Noussair, an Emory University economist who advises the U.S. Federal Reserve. Though the recommendations were delivered under his imprimatur, Noussair himself wouldn't necessarily follow it. The advice was extremely conservative, often urging students to accept tiny guaranteed payouts rather than playing a lottery with great odds and a high payout. But students tended to follow his advice regardless of the situation, especially when it was bad. When thinking for themselves, students showed activity in their anterior cingulate cortex and dorsolateral prefrontal cortex — brain regions associated with making decisions and calculating probabilities. When given advice from Noussair, activity in those regions flat lined.

http://blog.wired.com/wiredscience/2009/03/financebrain.html