I found a great CBS News article about how political thinking is based on emotion and not logic:
When 30 self-described partisans were presented with contradictory quotes about the candidates (President Bush supporting, then denouncing Ken Lay; Sen. John Kerry supporting, then denouncing a Social Security overhaul), it was the portions of the brain that process emotion, not rational thinking, that became active. "The thinking caps went off and the feeling caps went on," is how Westen put it to me.
Normally, Westen says, a brain faced with contradictory information will fire up the zones where reason or rational thought happens. The 30 partisans in this study were presented with contradictory quotes from Bush and Kerry, but also from Hank Aaron, Tom Hanks and the writer William Styron. They processed the information about the non-politicians with the reasoning centers of the brain. It was politics that short-circuited them. ("This is your brain; this is your brain on politics.")
I blogged about the same study before, but I think the above quote does a better job of explaining it.
Some of the commenters to my recent posts have been using the emotional parts of their brains instead of the logical parts. But that's OK, I used to be like that also until I transcended partisan politics and become a utilitarian empiricist (at least that's a tag that some have given me).