Causal reasoning is domain-specific in the human brain
Causal reasoning enables humans to explain the past, predict the future, and intervene on the present. Despite extensive interest in causal inference by philosophers, cognitive scientists, and developmental psychologists, few studies have investigated causal reasoning in the human brain. Here we use fMRI to ask whether a unified brain system exists that implements causal inference across content domains, or whether instead distinct brain systems are engaged in causal reasoning about social agents and physical objects. Across three pre-registered experiments, we find that causal reasoning about social and physical phenomena engage distinct cortical regions. The fronto-parietal Physics Network (PN), previously implicated in physical reasoning, and the temporo-parietal junction (TPJ), previously implicated in social reasoning, both showed stronger responses to causal than non-causal conditions, but only within their respective domains. Selective responses emerged in both a reading comprehension task (Experiment 1) and a sentence matching task (Experiment 2), and for preventative as well as generative causal reasoning (Experiment 3). No region selectively engaged causal reasoning or showed common patterns of response across voxels for causality in both physical and social domains in whole-brain analyses. Thus, despite its central role in human cognition, causal reasoning is implemented in separate domain-specific regions rather than a single unified brain region.