The neurocognitive architecture of fluid ability in children and adolescents

Abstract Fluid ability is the capacity to solve novel problems in the absence of task-specific knowledge, and is highly predictive of outcomes like educational attainment and psychopathology. Here, we modelled the neurocognitive architecture of fluid ability in two cohorts: CALM (N=551, aged 5-17) and NKI-RS (N=335, aged 6-17). We used multivariate Structural Equation Modelling to test a preregistered ‘watershed model’ of fluid ability. We found that the watershed model fit the data well for both samples: White matter contributed to working memory and processing speed, which, in turn, contributed to fluid ability (R2(CALM)=51.2%, R2(NKI-RS)=78.3%). The relationship between cognitive abilities and white matter differed with age and showed a dip in strength around ages 7-12 years. Speculatively, this age-effect may reflect a reorganization of the neurocognitive architecture around pre- and early puberty. Overall, these findings highlight that fluid ability is part of a complex hierarchical system of partially independent effects.