Democrats and Republicans alike are adept at making decisions without letting the facts get in the way, a new study shows.

And they get quite a rush from ignoring information that's contrary to their point of view.

Researchers asked staunch party members from both sides to evaluate information that threatened their preferred candidate prior to the 2004 Presidential election. The subjects' brains were monitored while they pondered.

The results were announced today.

"We did not see any increased activation of the parts of the brain normally engaged during reasoning," said Drew Westen, director of clinical psychology at Emory University. "What we saw instead was a network of emotion circuits lighting up, including circuits hypothesized to be involved in regulating emotion, and circuits known to be involved in resolving conflicts."

Bias on both sides

The test subjects on both sides of the political aisle reached totally biased conclusions by ignoring information that could not rationally be discounted, Westen and his colleagues say.

Then, with their minds made up, brain activity ceased in the areas that deal with negative emotions such as disgust. But activity spiked in the circuits involved in reward, a response similar to what addicts experience when they get a fix, Westen explained.

The study points to a total lack of reason in political decision-making.

"None of the circuits involved in conscious reasoning were particularly engaged," Westen said. "Essentially, it appears as if partisans twirl the cognitive kaleidoscope until they get the conclusions they want, and then they get massively reinforced for it, with the elimination of negative emotional states and activation of positive ones."

Notably absent were any increases in activation of the dorsolateral prefrontal cortex, the part of the brain most associated with reasoning.

The tests involved pairs of statements by the candidates, President George W. Bush and Senator John Kerry, that clearly contradicted each other. The test subjects were asked to consider and rate the discrepancy. Then they were presented with another statement that might explain away the contradiction. The scenario was repeated several times for each candidate.

The brain imaging revealed a consistent pattern. Both Republicans and Democrats consistently denied obvious contradictions for their own candidate but detected contradictions in the opposing candidate.

"The result is that partisan beliefs are calcified, and the person can learn very little from new data," Westen said.

Vote for Tom Hanks

Other relatively neutral candidates were introduced into the mix, such as the actor Tom Hanks. Importantly, both the Democrats and Republicans reacted to the contradictions of these characters in the same manner.

The findings could prove useful beyond the campaign trail.

"Everyone from executives and judges to scientists and politicians may reason to emotionally biased judgments when they have a vested interest in how to interpret 'the facts,'" Westen said.

The researchers will present the findings Saturday at the Annual Conference of the Society for Personality and Social Psychology.