Fig. 1: Study flow chart.

fMRI contrasts across 17 task epochs were analyzed for 989 healthy young adults from the Human Connectome Project (HCP; a). Left (L) and right (R) hemisphere fMRI signals were assessed independently at 32,492 cortical vertices per participant and contrast to quantify functional interhemispheric asymmetry, Δ using Eq [1] (b). Individual maps of fMRI signal amplitude and asymmetry were averaged across 12 predefined network partitions³¹ for each participant and contrast (c). The sample was divided into Discovery (n = 504) and Replication (n = 485) subsamples to examine the reproducibility of the functional asymmetry index. Functional networks were ranked by root-mean-square values of asymmetry, and task contrasts by mean asymmetry values across participants within each subsample (d). Partial least squares (PLS) regression (e) was applied to extract principal components of fMRI signal amplitude and asymmetry (f). These components were used to predict asymmetry from fMRI signal amplitude, and task accuracy independently for amplitude and asymmetry (g), and assessed the effects of age and sex on PLS regression scores from amplitude and asymmetry (h).