We did not see (as a result of brain scans of partisan loyalists) any increased activation of the parts of the brain normally engaged during reasoning. 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. None of the circuits involved in conscious reasoning were particularly engaged. 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. ... The result is that partisan beliefs are calcified, and the person can learn very little from new data.
-- Drew Westen, Director of Clinical Psychology at Emory University, regarding a study using fMRI, NBC News, 24 January 2006