Figure 5. Interregional asymmetry correlations.

Interregional correlations between (A) areal asymmetries and (B) thickness asymmetries for each replication dataset (AI’s residualized for age, sex, scanner). Individual AI’s in rightward clusters are inversed, such that positive correlations reflect positive asymmetry-asymmetry relationships, regardless of direction of mean asymmetry in the cluster (i.e. higher asymmetry in the population-direction). Yellow and blue brain clusters/colours denote leftward and rightward asymmetries, respectively (clusters numbered for reference). A consistent covariance structure was evident both for areal (r ≥ 0.97) and thickness asymmetry (r ≥ 0.46; results above matrices). Black box in A highlights relationships between opposite-direction asymmetries (i.e. leftward vs rightward regions). (C) For areal asymmetry, asymmetry in opposite-direction cluster-pairs that were closer in cortex was more positively correlated (datapoints show cluster-pairs; geodesic distance in mm). (D) A single component explained 21.9% variance across thickness asymmetries in UKB (inset plot). Accordingly, we found a correlation of r=–0.61 (p<2.2e^–16) in UKB between mean asymmetry across leftward clusters (Y-axis) vs. mean asymmetry across rightward clusters (X-axis; AI’s in rightward clusters inversed). Lines of symmetry (0) are in dotted grey (see also Figure 5—figure supplements 1–3).

Figure 5—figure supplement 1. Annotated covariance matrices.

Interregional correlations between (A) areal asymmetries and (B) thickness asymmetries for each replication dataset (AI’s residualized for age, sex, scanner). Individual AI’s in rightward clusters are inversed, such that positive correlations reflect positive asymmetry-asymmetry relationships, regardless of direction of mean asymmetry in the cluster (i.e. higher asymmetry in the population-direction). Yellow and blue brain clusters/colours denote leftward and rightward asymmetries, respectively (clusters numbered for reference). A consistent covariance structure was evident both for areal (r ≥ 0.97) and thickness asymmetry (r ≥ 0.46; results above matrices). Black box in A highlights relationships between opposite-direction asymmetries (i.e. leftward vs rightward regions). Interregional correlations for thickness asymmetry in the lower left quadrant of UK Biobank matrix are visualized in Figure 5—figure supplement 2.

Figure 5—figure supplement 2. UK Biobank lower quadrant.

Thickness asymmetry interregional correlations between opposite-direction asymmetries (lower left quadrant of the UK Biobank correlation matrix in Figure 5—figure supplement 1; N=38,171) are visualized to describe whether negative asymmetry-asymmetry correlations pertained to reduced or reversed thickness asymmetry. Lines of symmetry (0) are shown in grey. X-axis and Y-show raw AI data after removing the fixed effects of age and sex. AI’s in rightward clusters are inversed, such that positive correlations would reflect positive asymmetry-asymmetry relationships regardless of direction of mean asymmetry in the cluster (i.e. higher asymmetry in the population direction). Order of cortical locations is in Figure 5—figure supplement 1.

Figure 5—figure supplement 3. Global thickness asymmetry relationships.

Principal components analysis across AI’s in all leftward and rightward thickness asymmetry clusters revealed a single component explained 21.9% of the variance in UK Biobank, and there was evidence of a relatively stronger first component in LCBC and HCP (inset scree plots). Scatter plots show the partial correlation of the mean asymmetry across all leftward vs. all rightward clusters (means weighted by cluster size) plotted for each cohort, after AI’s were corrected for age, sex and (where applicable) scanner. Lines of symmetry (0) are shown as dotted grey. Individual AI’s in rightward clusters are inversed, such that positive correlations would reflect positive asymmetry-asymmetry relationships regardless of direction (i.e. higher asymmetry in the population direction).

Figure 5—figure supplement 4. HCP outliers discarded.

Two outliers (black) were detected in the cortical thickness data of HCP and subsequently discarded for all analyses following the vertex-wise delineation of cortical asymmetry (in which their inclusion had negligible effect on the derived mean asymmetry maps). The plot shows mean thickness asymmetry across all leftward vs. mean thickness asymmetry across all rightward clusters.