The posterior medial prefrontal cortex (pMFC) region of the brain contributes to confirmation bias in humans, finds a study published this week in Nature Neuroscience. Specifically, the pMFC is less sensitive to the strength of others’ opinions that do not confirm one’s own belief.
Humans tend to discount information that undermines past choices and judgments. This confirmation bias has a significant impact on everything from politics to science and education, but little is known about the mechanisms underlying this characteristic of belief formation. Andreas Kappes, Tali Sharot, and colleagues hypothesized that this process might occur in the pMFC, which tracks decision-making information and signals when a decision should be changed.
Forty-two adults, split into pairs, were asked to individually judge whether the listing price of real-estate properties was more or less than a displayed price. Participants then wagered 1 - 60 cents, depending on how confident they were. Next, each participant was placed in an MRI scanner, shown the properties again and reminded of their initial judgments and wagers. They then saw their partner’s judgments and wagers for the same properties and were asked to submit a final wager, indicating how confident they were about their initial assessment.
The authors found that, when the partner’s judgment confirmed a participant’s initial assessment, participants increased their final wagers to larger amounts, and the participants’ final wagers correlated with their partners’ wagers. The authors also determined that pMFC activity mediated the effect that the partner’s wager had on the participant’s final wager, but only when participants agreed.
This suggests that the pMFC’s sensitivity to the strength of others’ opinions only occurs in the face of agreement, and is reduced during disagreement, which could contribute to confirmation bias.
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