Tracking politically motivated reasoning in the brain: the role of mentalizing, value-encoding, and error-detection networks

Susceptibility to misinformation and belief polarization often reflect people's tendency to incorporate information in a biased way. Despite the presence of competing theoretical models, the underlying neurocognitive mechanisms of motivated reasoning remain elusive as previous empirical work did not properly track the belief formation process. To address this problem, we employed a design that identifies motivated reasoning as directional deviations from a Bayesian benchmark of unbiased belief updating. We asked members of a pro-immigration or an anti-immigration group how much they endorse factual messages on foreign criminality, a polarizing political topic. Both groups exhibited a desirability bias by over-endorsing attitude-consistent messages and under-endorsing attitude-discrepant messages and an identity bias by over-endorsing messages from ingroup members and under-endorsing messages from outgroup members. In both groups, neural responses to the messages predicted subsequent expression of desirability and identity biases suggesting a common neural basis of motivated reasoning across ideologically opposing groups. Specifically, brain regions implicated in encoding value, error detection, and mentalizing tracked the degree of desirability bias. Less extensive activation in the mentalizing network tracked the degree of identity bias. These findings illustrate the distinct neurocognitive architecture of desirability and identity biases and inform existing cognitive models of politically motivated reasoning.