Individualism, conservatism, and radicalism as criteria for processing political beliefs: a parametric fMRI study.

Politics is a manifestation of the uniquely human ability to debate, decide, and reach consensus on decisions affecting large groups over long durations of time. Recent neuroimaging studies on politics have focused on the association between brain regions and specific political behaviors by adopting party or ideological affiliation as a criterion to classify either experimental stimuli or subjects. However, it is unlikely that complex political beliefs (i.e., "the government should protect freedom of speech") are evaluated only on a liberal-to-conservative criterion. Here we used multidimensional scaling and parametric functional magnetic resonance imaging to identify which criteria/dimensions people use to structure complex political beliefs and which brain regions are concurrently activated. We found that three independent dimensions explained the variability of a set of statements expressing political beliefs and that each dimension was reflected in a distinctive pattern of neural activation: individualism (medial prefrontal cortex and temporoparietal junction), conservatism (dorsolateral prefrontal cortex), and radicalism (ventral striatum and posterior cingulate). The structures we identified are also known to be important in self-other processing, social decision-making in ambivalent situations, and reward prediction. Our results extend current knowledge on the neural correlates of the structure of political beliefs, a fundamental aspect of the human ability to coalesce into social entities.