Quote the Raven? Always! A brain morphometric analysis of the intelligence hierarchy

Here we test the hypothesis that if the Raven Progressive Matrices Test (RAPM) is the best available single measure of the general factor of intelligence (g), then their brain correlates must show a greater overlap with g than that observed for other intelligence measures. For that purpose, gray matter correlates were analyzed at different levels of the intelligence hierarchy checking for consistencies and discrepancies among measurements and constructs. A group of 104 young adults completed a battery of nine intelligence tests measuring fluid-abstract (Gf), crystallized-verbal (Gc), and spatial (Gv) intelligence. They also undertook MRI scanning. Psychometric scores were computed for a higher-order factor representing general intelligence (g), first-order group factors representing Gf, Gc, and Gv, and, finally, the nine specific measures. Optimized voxel-based morphometry (VBM) and cortical surface-based morphometry (SBM, cortical thickness and cortical surface area) assessments were obtained and related to the scores. Overlaps among resulting brain maps were systematically inspected, controlling for sex, age, and handedness. VBM findings identified an overlap in a right middle frontal gyrus cluster, whereas cortical surface area results showed a key overlap in the right dorsolateral prefrontal cortex, for the RAPM, Gf, and g. These results were seen as consistent with the main hypothesis and, therefore, support the RAPM as the best single estimate of g.