Found this interesting article on Huffington Post about how brain scans can predict political affiliation. This does make sense; my experience is that after interacting with someone only for a brief period of time, I can accurately guess which way they lean. Not always, of course — and some turn out to be centrists or libertarians, who wouldn't necessarily fit into the left/right model. But it's an intriguing scientific approach to the madness.
Comparing the Democrat and Republican participants turned up differences in two brain regions: the right amygdala and the left posterior insula. Republicans showed more activity than Democrats in the right amygdala when making a risky decision. This brain region is important for processing fear, risk and reward.
Meanwhile, Democrats showed more activity in the left posterior insula, a portion of the brain responsible for processing emotions, particularly visceral emotional cues from the body. The particular region of the insula that showed the heightened activity has also been linked with "theory of mind," or the ability to understand what others might be thinking.
While their brain activity differed, the two groups' behaviors were identical, the study found.
Schreiber and his colleagues can't say whether the functional brain differences nudge people toward a particular ideology or not. The brain changes based on how it is used, so it is possible that acting in a partisan way prompts the differences.
The functional differences did mesh well with political beliefs, however. The researchers were able to predict a person's political party by looking at their brain function 82.9 percent of the time. In comparison, knowing the structure of these regions predicts party correctly 71 percent of the time, and knowing someone's parents' political affiliation can tell you theirs 69.5 percent of the time, the researchers wrote.