Fluid intelligence is supported by the multiple-demand system not the language system

A set of frontoparietal brain regions—the multiple-demand (MD) system1,2—has been linked to fluid intelligence in brain imaging3,4 and in studies of patients with brain damage5–7. For example, the amount of damage to frontal or parietal, but not temporal, cortices predicts fluid intelligence deficit 5 . However, frontal and parietal lobes are structurally 8 and functionally9,10 heterogeneous. They contain domain-general regions that respond...