Specifically, the report shows that political conservatives have larger amygdalas, which mediate emotional reactions such as fear and aggression.
This report got picked up all over the mainstream press, as with this article in The Atlantic headlined Are Liberals and Conservatives Hard-Wired to Disagree? and another article over on Raw Story titled Brain structure differs in liberals, conservatives: study, which says "Liberals have more gray matter in a part of the brain associated with understanding complexity, while the conservative brain is bigger in the section related to processing fear, said the study on Thursday in Current Biology."
From a purely sociological standpoint, this may have some element of truth, at least in the sense that repeated sociological studies have shown conservatives to be motivated by fears of collapsing social order, loss of social hierarchy, and social disorder.
But qualifying conservatives as fearful and liberals as optimistic is really kind of silly, seems to me. Liberals, in my experience, are just as likely to be driven by irrational fears, and to make decisions based on poor evaluation of those fears, as conservatives are.
Take, for example, the nearly universal fear among those on the political left of nuclear power. Despite the fact that nuclear power is by far the safest form of large-scale electrical generation yet invented (coal power kills more human beings every year, primarily from air pollution but also from coal mining accidents, than nuclear power has killed in the entire history of its use combined--including Chernobyl), liberals are nearly universal in their stark raving terror of all things "nuclear."
Liberals like to mock conservatives as ignorant, uninformed, and anti-intellectual, but the reality is that across the United States, anti-intellectualism is extraordinarily popular; its cause is championed by people of all political stripes. It manifests differently, sure; conservatives tend to oppose pure science, particularly biological and geological science (but even physics is not immune; there are some highly vocal nutjobs on the right who claim that Einstein's theory of relativity is a sinful attempt to undermine public morality by embracing moral relativism), though quixotically they tend to embrace technology.
Liberals, on the other hand, claim to champion science, at least when they can be arsed to learn enough to be able to separate it from pseudoscience; but they reject technology, in forms ranging from vaccination to food processing. Liberals are particularly frightened of life sciences; their terror of genetically modified food is second only to their terror of nuclear power as a common source of fear.
I've been chewing on this for a while, and as I often do, I've made a chart.
The things that will actually kill you tend, by and large, not to be the things you're afraid of. Conservatives fear terrorism, which is stunningly unlikely to kill you; the number of Americans who lose their lives to terrorists every year is roughly on par with the number killed by sharks and bears, and is dwarfed by the number of people killed by falling off stepladders. On the other hand, as small as this number is, it's still mountains bigger than the number of Americans killed by nuclear power every year, which tends to hover year after year at somewhere around zero.
How ironic, then, that the billions spent fighting these fears and the work done on both sides to advocate for these fears, and it's actually driving to the office or not getting away from the TV to exercise that will do you in.