Neurocognitive reorganization between crystallized intelligence, fluid intelligence and white matter microstructure in two age-heterogeneous developmental cohorts

Abstract

Despite the reliability of intelligence measures in predicting important life outcomes such as educational achievement and mortality, the exact configuration and neural correlates of cognitive abilities remain poorly understood, especially in childhood and adolescence. Therefore, we sought to elucidate the factorial structure and neural substrates of child and adolescent intelligence using two cross-sectional, developmental samples (CALM: N = 551 (N = 165 imaging), age range: 5-18 years, NKI-Rockland: N = 337 (N = 65 imaging), age range: 6-18 years). In a preregistered analysis, we used structural equation modelling (SEM) to examine the neurocognitive architecture of individual differences in childhood and adolescent cognitive ability. In both samples, we found that cognitive ability in lower and typical-ability cohorts is best understood as two separable constructs, crystallized and fluid intelligence, which became more distinct across development, in line with the age differentiation hypothesis. Further analyses revealed that white matter microstructure, most prominently the superior longitudinal fasciculus, was strongly associated with crystallized (gc) and fluid (gf) abilities. Finally, we used SEM trees to demonstrate evidence for developmental reorganization of gc and gf and their white matter substrates such that the relationships among these factors dropped between 7-8 years before increasing around age 10. Together, our results suggest that shortly before puberty marks a pivotal phase of change in the neurocognitive architecture of intelligence.

Keywords: Crystallized intelligence; Fluid intelligence; Neurocognitive reorganization; Structural equation modelling; White matter.

Fig. 1

Histograms of age distributions for CALM and NKI-Rockland samples.

Fig. 2

Scatterplots of cognitive task scores across age for CALM and NKI-Rockland samples. Lines and shades reflect linear and polynomial fit and 95 % confidence intervals, respectively. Solid lines: CALM. Dashed lines: NKI-Rockland. Abbreviations: matrix reasoning (MR), spelling (Spell), single word reading (SWR), numerical operations (NO), forward digit recall/span (DR), backward digit recall/span (BDR), Peabody Picture Vocabulary Test (PPVT), Dot Matrix (Dot), Mr. X (MRX), N-Back (NB).

Fig. 2

Scatterplots of cognitive task scores across age for CALM and NKI-Rockland samples. Lines and shades reflect linear and polynomial fit and 95 % confidence intervals, respectively. Solid lines: CALM. Dashed lines: NKI-Rockland. Abbreviations: matrix reasoning (MR), spelling (Spell), single word reading (SWR), numerical operations (NO), forward digit recall/span (DR), backward digit recall/span (BDR), Peabody Picture Vocabulary Test (PPVT), Dot Matrix (Dot), Mr. X (MRX), N-Back (NB).

Fig. 3

Scatterplots of FA values for all white matter tracts across age for CALM and NKI- Rockland samples. Note that the age trends are more pronounced in CALM than in the NKI sample, possibly due to lower sample size in the NKI-Rockland sample (N = 65). Lines and shades reflect linear and polynomial fit and 95 % confidence intervals, respectively. Solid lines: CALM. Dashed lines: NKI-Rockland. Abbreviations: anterior thalamic radiations (ATR), corticospinal tract (CST), cingulate gyrus (CING), cingulum [hippocampus] (CINGh), inferior fronto-occipital fasciculus (IFOF), inferior longitudinal fasciculus (ILF), superior longitudinal fasciculus (SLF), uncinate fasciculus (UNC), forceps major (FMaj), and forceps minor (FMin).

Fig. 4

MIMIC models displaying standardized parameter estimates and regression coefficients for all cognitive measures and white matter tracts for complete CALM and NKI-Rockland samples. Dotted, green, and red arrows indicate nonsignificant (>.05), positively significant, and negatively significant path estimates, respectively. Note standardized estimates exceeding 1 in NKI are likely the consequence of highly-correlated factors (Jöreskog, 1999).