Here's an interesting essay from Michael Shermer, whom I adore:
http://www.sciam.com/print_version.cfm? ... 414B7F0162
What is particularly intriguing is the discovery that the portion of the brain involved in confirmation bias is completely unrelated to the reasoning portion of our brain:
During the run-up to the 2004 presidential election, while undergoing an fMRI bran scan, 30 men--half self-described as "strong" Republicans and half as "strong" Democrats--were tasked with assessing statements by both George W. Bush and John Kerry in which the candidates clearly contradicted themselves. Not surprisingly, in their assessments Republican subjects were as critical of Kerry as Democratic subjects were of Bush, yet both let their own candidate off the hook.
The neuroimaging results, however, revealed that the part of the brain most associated with reasoning--the dorsolateral prefrontal cortex--was quiescent. Most active were the orbital frontal cortex, which is involved in the processing of emotions; the anterior cingulate, which is associated with conflict resolution; the posterior cingulate, which is concerned with making judgments about moral accountability; and--once subjects had arrived at a conclusion that made them emotionally comfortable--the ventral striatum, which is related to reward and pleasure.
"We did not see any increased activation of the parts of the brain normally engaged during reasoning," Westen is quoted as saying in an Emory University press release. "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." Interestingly, neural circuits engaged in rewarding selective behaviors were activated. "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," Westen said.
Boy, that explains a lot about internet debates!! ;)