Is there a neurological explanation for blind partisanship? According to this press release, scientists, using fMRI scans, have found that when "committed Democrats and Republicans" are faced with criticism of their favorite politician, they show no increase in activity of the parts of their brains associated with reasoning. (Incidentally, or not, the subjects of the study were all men.) That's not all that surprising, really, although I wonder whether this holds equally for all education groups, or whether it's possible to train oneself not to do this. At any rate, one could note that a good number of media types who worship at the altar of "non-partisanship" tend to turn off the rational bits in their brains fairly frequently
On a related note, economists Sendhil Mullainathan and Ebonya Washington recently put out a paper suggesting that voters have an irrational preference for the candidates they've just voted for. They found that twenty-year-olds who had voted in a particular election two years prior showed more polarization in their opinions about the elected candidates than did nineteen-year-olds who, incidentally, missed the chance to vote that year. (Assuming, of course, that there's no other reason why twenty-year-olds and nineteen-year-olds should have such different political views.)
Meanwhile, Senators who are elected in high-turnout presidential years are more polarizing figures among the public than those elected in off-years. That could partially explain why incumbents keep winning, and suggests that term limits, perhaps, could inject a bit more rationality into politics. Although if that's the goal, we're a fair ways off.