ATLANTA - Loyal Republicans listening to President Bush's State of the Union speech tonight are apt to embrace his words, and staunch Democrats likely will scoff at them. But facts will have little to do with how either side reaches their conclusions.
A study from Emory University, which for the first time examined the brains of political partisans, found that it's emotion - not reason - that drives the political thought process.
Committed partisans will reach emotionally biased decisions, hearing those things that reinforce their beliefs and rejecting information that contradicts them, the study found.
Emory researchers studied Democratic and Republican men in the three months leading up to the 2004 presidential election. Fifteen supporters of John Kerry and 15 for George Bush were confronted with "threatening" information about their candidate.
Kerry backers might be told, for instance, that the Democrat has flip-flopped on Social Security. A Bush voter would be shown statements in which he embraced former Enron chief Kenneth Lay.
Using sophisticated imaging equipment, researchers mapped the brains of the participants as they processed the information.
The study's lead author, Drew Westen, Emory's director of clinical psychology, said the results proved what he always suspected: "It's the emotions, stupid."
As the subjects puzzled over the information presented to them, the network of emotion circuits in the brain's orbital frontal cortex lit up. The area associated with logical reasoning saw no increase in activity.
Circuits involved in regulating emotion and resolving conflicts were especially busy as study participants presumably sought ways to rationalize or ignore information that could cast their candidate in a negative light.
Once participants reached a conclusion supporting their candidate, they would get a blast of activation in brain circuits typically involved in reward, similar to what addicts receive when they get a fix.
Mr. Westen said participants appear to "twirl the cognitive kaleidoscope" until they get the result they want.