Is political ideology correlated with brain structure? A preregistered replication.

We revisit the hypotheses that conservatism positively correlates with amygdala and negatively with anterior cingulate cortex (ACC) gray matter volume.Using diverse measures of ideology and a large and representative sample (Amsterdam Open MRI Collection [n = 928]), we replicate a small positive relationship between amygdala volume and conservatism. However, we fail to find consistent evidence in support of the ideology-ACC volume link. Using a split-sample strategy,we conducted exploratory whole-brain analyses on half the data, preregistered the findings, and then conducted subsequent confirmatory tests that additionally highlight weak, positive associations between the right fusiform gyri and conservatism. This is the largest preregistered replication study in the context of political neuroscience. By using Dutch as opposed to British or American data, we also extend the amygdala-conservatism link to a multiparty, multidimensional political context. We discuss the implications for future investigations of the neural substrates of ideology.