Intolerance of uncertainty modulates brain-to-brain synchrony during politically polarized perception

Political partisans see the world through an ideologically biased lens. What drives political polarization? Although it has been posited that polarization arises because of an inability to tolerate uncertainty and a need to hold predictable beliefs about the world, evidence for this hypothesis remains elusive. We examined the relationship between uncertainty tolerance and political polarization using a combination of brain-to-brain synchrony and intersubject representational similarity analysis, which measured committed liberals’ and conservatives’ (n = 44) subjective interpretation of naturalistic political video material. Shared ideology between participants increased neural synchrony throughout the brain during a polarizing political debate filled with provocative language but not during a neutrally worded news clip on polarized topics or a nonpolitical documentary. During the political debate, neural synchrony in mentalizing and valuation networks was modulated by one’s aversion to uncertainty: Uncertainty-intolerant individuals experienced greater brain-to-brain synchrony with politically like-minded peers and lower synchrony with political opponents—an effect observed for liberals and conservatives alike. Moreover, the greater the neural synchrony between committed partisans, the more likely that two individuals formed similar, polarized attitudes about the debate. These results suggest that uncertainty attitudes gate the shared neural processing of political narratives, thereby fueling polarized attitude formation about hot-button issues.

Countries around the world are experiencing the strain of growing political polarization (1–5). Opposing partisans come to see the world through different eyes. Where one sees the freedom to choose, another sees murder; where one sees the right to protest, another sees violent conduct (6–8). Such a polarized perception of reality hampers bipartisan cooperation and can even undermine the basic principles of democracy (8, 9).How does polarization arise? One popular theory posits that a need to have certain, structured, and stable beliefs about the world drives people toward political extremes (10–13). Rather than seeing the world in nuanced shades of gray, cognitively rigid individuals perceive information in black and white, painting the world in categorical and predictable terms (14)—a view that dovetails with the immutable taxonomy of political ideologues (15–19). The rigid mind is characterized by a trait-like tendency to find unpredictable and uncertain events aversive and threatening (14, 20, 21) and has long been theorized to play an outsized role in shaping polarized perceptions (22–26). Although recent work suggests that uncertainty can impact the evaluation of political candidates (27) and policy positions (28, 29) and is a major factor contributing to political conservatism (30, 31), the link between uncertainty and political polarization remains unclear. Here, we examine whether individual differences in intolerance of uncertainty (IUS) (20, 21) shape how naturalistic political information is processed in the brain at the time of perception. We test the hypothesis that uncertainty-intolerant individuals interpret polarizing political information through an ideologically biased, subjective “lens” that produces clear-cut judgments of the issue at hand (20, 32). We further examine whether the neural fingerprint of these uncertainty-driven polarized perceptions—that is, increased brain-to-brain synchrony between like-minded partisans—predicts the formation of polarized attitudes.We combine two techniques to measure polarized perceptions of political information. First, intersubject correlation [ISC (33)] provides a direct measure of the similarity in subjective interpretations of naturalistic social stimuli (e.g., video narratives) among participants (34, 35). This technique capitalizes on the neural processes triggered by incoming auditory and visual information. If two individuals exhibit similar neural profiles when processing the same incoming information (e.g., synchronized blood oxygen level-dependent [BOLD] responses in functional MRI [fMRI]), they likely have a shared perception and understanding of that information (36–40). Given that ISC offers an established metric to gauge whether individuals are processing information in a similar way, we can use it to test whether two individuals who share the same political ideology also have similar subjective perceptions of political information, which circumvents issues with demand characteristics and explicit self-report (41). Second, to make neural synchrony analyses sensitive to more subtle differences along the ideological continuum than simple left–right groupings and to test for interactive effects between ideology and intolerance to uncertainty, we combine ISC with intersubject representational similarity analysis [IS-RSA (42–44)]. This versatile approach enables us to leverage continuous individual differences and test whether uncertainty attitudes exacerbate the processing of political information in the brain to fuel polarized political attitude formation.Using a combination of targeted online and field recruiting (n = 360), we invited 22 liberals and 22 conservatives to participate in a study on political cognition (Fig. 1A). While undergoing fMRI, participants viewed three types of videos: a neutrally worded news segment on a politically charged topic (abortion; taken from Public Broadcasting Service [PBS] News), an inflammatory debate segment (police brutality and immigration; taken from the 2016 Cable News Network [CNN] Vice-Presidential debate), and a nonpolitical nature video (taken from British Broadcasting Corporation [BBC] Earth; Fig. 1B). Neural data analysis consisted of time locking the fMRI BOLD signal to the onset of the videos and computing voxel-wise time course correlations between each possible pairing of subjects across the entire participant pool, resulting in a “neural synchrony” measurement that indexes shared subjective interpretations of dynamic, naturalistic stimuli (35, 45, 46). We first analyzed behavioral responses to the videos to test whether ideology, IUS, or both predicted similarities in attitude formation about the presented political videos. Next, we analyzed variation in neural synchrony across participant dyads using IS-RSA (Fig. 1D) to test three interrelated hypotheses: 1) shared ideology between subjects will predict brain-to-brain synchrony during the perception of political stimuli, 2) IUS will modulate this neural synchrony in committed partisans, and 3) increasing neural synchrony will predict the subsequent expression of shared polarized attitudes about the political stimuli.Open in a separate windowFig. 1.(A) Participants underwent fMRI and behavioral testing as part of a larger study on political cognition. (B) Participants viewed three videos in a fixed order while undergoing fMRI. (C) Participants were clearly divided on political ideology. (D) Analytical approach. We tested for variation in neural synchrony as a function of ideology and IUS. The statistical map slice is taken from Fig. 2C.