We explore differences in brain function in liberals and conservatives by matching publicly-available voter records to 82 subjects who performed a risk-taking task during functional imaging. Although the risk-taking behavior of Democrats (liberals) and Republicans (conservatives) did not differ, their brain activity did. Democrats showed significantly greater activity in the left insula, while Republicans showed significantly greater activity in the right amygdala. In fact, a two parameter model of partisanship based on amygdala and insula activations yields a better fitting model of partisanship than a well-established model based on parental socialization of party identification long thought to be one of the core findings of political science. These results suggest that liberals and conservatives engage different cognitive processes when they think about risk, and they support recent evidence that conservatives show greater sensitivity to threatening stimuli.That's from "Red Brain, Blue Brain: Evaluative Processes Differ in Democrats and Republicans," by Darren Schreiber, Greg Fonzo, Alan N. Simmons, Christopher T. Dawes, Taru Flagan, James H. Fowler, and Martin P. Paulus. Just to be clear, the finding is that Democrats tend to use the insula, which is used in the monitoring of one's internal feelings, when assessing risk, while Republicans tend to use the amygdala, which is the brain's threat response center, for the same task.
Chris Mooney explains the causality involved:
Current research suggests not only that having a particular brain influences your political views, but also that having a particular political view influences and changes your brain. The causal arrow seems likely to run in both directions—which would make sense in light of what we know about the plasticity of the brain. Simply by living our lives, we change our brains. Our political affiliations, and the lifestyles that go along with them, probably condition many such changes.