The link between callosal thickness and intelligence in healthy children and adolescents

Abstract

The link between brain structure and intelligence is a well-investigated topic, but existing analyses have mainly focused on adult samples. Studies in healthy children and adolescents are rare, and normative data specifically addressing the association between corpus callosum morphology and intellectual abilities are quite limited. To advance this field of research, we mapped the correlations between standardized intelligence measures and callosal thickness based on high-resolution magnetic resonance imaging (MRI) data. Our large and well-matched sample included 200 normally developing subjects (100 males, 100 females) ranging from 6 to 17 years of age. Although the strongest correlations were negative and confined to the splenium, the strength and the direction of intelligence-callosal thickness associations varied considerably. While significant correlations in females were mainly positive, significant correlations in males were exclusively negative. However, only the negative correlations in the overall sample (i.e., males and females combined) remained significant when controlling for multiple comparisons. The observed negative correlations between callosal thickness and intelligence in children and adolescents contrast with the positive correlations typically reported in adult samples. However, negative correlations are in line with reports from other pediatric studies relating cognitive measures to other brain attributes such as cortical thickness, gray matter volume, and gray matter density. Altogether, these findings suggest that relationships between callosal morphology and cognition are highly dynamic during brain maturation. Sex effects on links between callosal thickness and intelligence during childhood and adolescence are present but appear rather weak in general.

Figure 1. Correlations between callosal thickness and intelligence (overall sample)

Top Panel: Illustrated are correlation coefficients (r-maps) color-coded with respect to effect sizes: small (r ≥ 0.1), medium (r ≥ 0.3), and large (r ≥ 0.5). Cyan and yellow indicate where negative and positive correlations remained below the threshold for relevant effect sizes. Bottom Panel: Illustrated are significance values (p-maps). The color bar encodes the uncorrected significance of negative correlations. White regions indicate significant positive correlations. The smaller callosal maps indicate in pink where significant correlations survived FDR-corrections. Gray indicates where no significant correlations were detected. The callosal posterior section is located on the left; the callosal anterior section points to the right. FS-IQ = full-scale IQ; P-IQ = performance IQ; V-IQ = Verbal IQ.

Figure 2. Age-specific correlations between callosal thickness and intelligence

Top Panel: Illustrated are significant age interactions (in green) at p≤0.05, uncorrected. Bottom Panels; left: Illustrated are correlation coefficients (r-maps) color-coded with respect to effect sizes. Medium effects are indicated by arrows. Bottom Panels, right: Illustrated are significance values (p-maps). The color bar encodes the uncorrected significance of negative correlations. White regions indicate significant positive correlations. The smaller callosal maps indicate where significant correlations survived FDR-corrections. Gray indicates where no significant correlations were detected. FS-IQ = full-scale IQ; V-IQ = Verbal IQ. G1–G4 = Groups 1–4.

Figure 3. Sex- and age-specific correlations between callosal thickness and intelligence

Left Panel: Illustrated are significant sex interactions (in green) at p≤0.05, uncorrected within age groups. Middle Panels: Illustrated are correlation coefficients (r-maps) color-coded with respect to effect sizes. Medium and large effects are indicated by arrows. Right Panels: Illustrated are significance values (p-maps). The color bar encodes the uncorrected significance of negative correlations. White regions indicate significant positive correlations. The smaller callosal maps indicate where significant correlations survived FDR-corrections. Gray indicates where no significant correlations were detected. FS-IQ = full-scale IQ; V-IQ = Verbal IQ. G1–G4 = Groups 1–4.