Volume 21, Issue 8, 26 April 2011, Pages 677–680
Political Orientations Are Correlated with Brain Structure in Young Adults
- 1 University College London Institute of Cognitive Neuroscience, 17 Queen Square, London WC1N 3AR, UK
- 2 BBC Radio 4, Television Centre, Wood Lane, London W12 7RJ, UK
- 3 Wellcome Trust Centre for Neuroimaging, University College London, 12 Queen Square, London WC1N 3BG, UK
- Received 11 January 2011, Revised 10 February 2011, Accepted 4 March 2011, Available online 7 April 2011
- Published online: April 7, 2011
Summary
Substantial differences exist in the cognitive styles of liberals and conservatives on psychological measures [1]. Variability in political attitudes reflects genetic influences and their interaction with environmental factors [2 and 3]. Recent work has shown a correlation between liberalism and conflict-related activity measured by event-related potentials originating in the anterior cingulate cortex [4]. Here we show that this functional correlate of political attitudes has a counterpart in brain structure. In a large sample of young adults, we related self-reported political attitudes to gray matter volume using structural MRI. We found that greater liberalism was associated with increased gray matter volume in the anterior cingulate cortex, whereas greater conservatism was associated with increased volume of the right amygdala. These results were replicated in an independent sample of additional participants. Our findings extend previous observations that political attitudes reflect differences in self-regulatory conflict monitoring [4] and recognition of emotional faces [5] by showing that such attitudes are reflected in human brain structure. Although our data do not determine whether these regions play a causal role in the formation of political attitudes, they converge with previous work [4 and 6] to suggest a possible link between brain structure and psychological mechanisms that mediate political attitudes.
Highlights
► Political liberalism and conservatism were correlated with brain structure ► Liberalism was associated with the gray matter volume of anterior cingulate cortex ► Conservatism was associated with increased right amygdala size ► Results offer possible accounts for cognitive styles of liberals and conservatives
Results and Discussion
For many years, psychologists and sociologists asked what kind of psychological or environmental factors influence the political orientation of individuals [1]. Although political attitudes are commonly assumed to have solely environmental causes, recent studies have begun to identify biological influences on an individual's political orientation. For example, a twin study shows that a substantial amount of the variability in political ideology reflects genetic influences [2]. Moreover, such genetic influences interact with social environment. For example, political orientation in early adulthood is influenced by an interaction between a variant of a dopamine receptor gene linked with novelty seeking and an environmental factor of friendship [3]. Here we hypothesized that these interactions between genotype, environment, and political phenotype may be reflected in the structure of the brain.
Several pioneering studies have begun examining the relationship between brain activity and political attitudes [4 and 6], but none have characterized brain structure. Political attitudes are typically captured on a single-item measure in which participants self-report using a five-point scale ranging from “very liberal” to “very conservative.” Despite the simplicity of such a scale, it accurately predicts voting behaviors of individuals [7] and has been used successfully to determine genetic contributions to political orientation [3]. Psychological differences between conservatives and liberals determined in this way map onto self-regulatory processes associated with conflict monitoring. Moreover, the amplitude of event-related potentials reflecting neural activity associated with conflict monitoring in the anterior cingulate cortex (ACC) is greater for liberals compared to conservatives [4]. Thus, stronger liberalism is associated with increased sensitivity to cues for altering a habitual response pattern and with brain activity in anterior cingulate cortex. Here we explored this relationship further by examining whether political attitudes correlated not just with function but also with anatomical structure of these regions.
To test the hypothesis that political liberalism (versus conservatism) is associated with differences in gray matter volume in anterior cingulate cortex, we recorded structural magnetic resonance imaging (MRI) scans from 90 healthy young adults (61% female) who self-reported their political attitudes confidentially on a five-point scale from “very liberal” to “very conservative” [3 and 7]. We then used voxel-based morphometry (VBM) analyses [8] to investigate the relationship between these attitudes, expressed as a numeric score between one and five, and gray matter volume. We found that increased gray matter volume in the anterior cingulate cortex was significantly associated with liberalism (Figure 1A) (R = −2.71, T(88) = 2.633, p = 0.010 corrected; see Experimental Procedures for full details of analyses). We regressed out potential confounding variables of age and gender in our analysis (see Experimental Procedures). Therefore, our findings are not attributable to these factors.
- Figure 1.
Individual Differences in Political Attitudes and Brain Structure
(A) Regions of the anterior cingulate where gray matter volume showed a correlation with political attitudes (see Experimental Procedures for full details) are shown overlaid on a T1-weighted MRI anatomical image in the stereotactic space of the Montreal Neurologic Institute Template [29]. A statistical threshold of p < 0.05, corrected for multiple comparisons (see Experimental Procedures), is used for display purposes. The correlation (left) between political attitudes and gray matter volume (right) averaged across the region of interest (error bars represent 1 standard error of the mean, and the displayed correlation and p values refer to the statistical parametric map presented on the right) is shown.
(B) The right amygdala also showed a significant negative correlation between political attitudes and gray matter volume. Display conventions and warnings about overinterpreting the correlational plot (left) are identical to those for (A).
Apart from the anterior cingulate cortex, other brain structures may also show patterns of neural activity that reflect political attitudes. Conservatives respond to threatening situations with more aggression than do liberals [1] and are more sensitive to threatening facial expressions [5]. This heightened sensitivity to emotional faces suggests that individuals with conservative orientation might exhibit differences in brain structures associated with emotional processing such as the amygdala. Indeed, voting behavior is reflected in amygdala responses across cultures [6]. We therefore further investigated our structural MRI data to evaluate whether there was any relationship between gray matter volume of the amygdala and political attitudes. We found that increased gray matter volume in the right amygdala was significantly associated with conservatism (Figure 1B) (R = 0.23, T(88) = −2.22, p < 0.029 corrected). No significant correlation was found in the left amygdala (R = 0.15, T(88) = −1.43, p = 0.15 corrected; see Figure S1 available online for the individual gray matter volumes of the ACC and amygdala).