We hypothesized that individual differences in intelligence (Spearman's g) are supported by multiple brain regions, and in particular that fluid (gF) and crystallized (gC) components of intelligence are related to brain function and structure with a distinct profile of association across brain regions. In 225 healthy young adults scanned with structural and functional magnetic resonance imaging sequences, regions of interest (ROIs) were defined on the basis of a correlation between g and either brain structure or brain function. In these ROIs, gC was more strongly related to structure (cortical thickness) than function, whereas gF was more strongly related to function (blood oxygenation level-dependent signal during reasoning) than structure. We further validated this finding by generating a neurometric prediction model of intelligence quotient (IQ) that explained 50% of variance in IQ in an independent sample. The data compel a nuanced view of the neurobiology of intelligence, providing the most persuasive evidence to date for theories emphasizing multiple distributed brain regions differing in function.As background:
gC, sometimes described as verbal ability, is more dependent on accumulated knowledge in long-term storage, including semantic memory. gF refers to reasoning ability, and is known to depend on working memory. Although gC and gF are typically correlated and can be considered subfactors of g (Jensen), they are conceptually and empirically separable. For instance, gC continues to increase over the lifespan, but gF peaks in early adulthood and then declines . Furthermore, at the neural level, lesion studies demonstrated that patients with anterior temporal damages perform poorly on tests of semantic knowledge, whereas prefrontal patients typically show profound deficits in solving diverse reasoning tasks.