Effects of focal brain damage on political behaviour across different political ideologies.

Intense political behaviour is associated with brain regions involved in emotional and cognitive processing. However, it remains unclear if this neuroanatomy is causal, compensatory or otherwise correlated. We employed lesion network mapping in a cross-sectional study of 124 male military veterans with penetrating head trauma. Approximately 40-45 years after the injury, participants reported current political behaviour and recollection of political behaviour pre-injury. Using a normative connectome database (n = 1000), we mapped the circuitry functionally connected to lesions associated with changes in intensity of political involvement, ideological polarity and party affiliation. No significant neuroanatomical circuit was associated with political ideology or party affiliation, but a distinct circuit was associated with intensity of political involvement. Political involvement was more intense after lesions connected to the left dorsolateral prefrontal cortex and posterior precuneus, in the full sample and in conservative-leaning participants. Political involvement was less intense after lesions connected to the amygdala and anterior temporal lobe, in the full sample and in liberal-leaning participants. These effects survived cross-validation in the full sample (P = 0.01) and in both conservative-leaning and liberal-leaning participants. These findings may inform cognitive mechanisms of political behaviour as well as clinical assessment after brain lesions.