Early Adulthood Signatures of Motherhood in Brain Aging

Major life transitions have been proposed to influence trajectories of brain aging, yet the timing and cognitive correlates of such divergence remain unclear. Motherhood has been associated with younger brain-predicted age in midlife, but whether similar signatures are already observable in early adulthood-and whether such signatures coincide with differences in cognitive performance-remains unknown. In over 1000 young adults (ages 22-37), brain-predicted age was estimated from structural MRI scans and cognition was assessed across fluid and crystallized domains. Mothers exhibited significantly younger brain-predicted age than non-mothers after adjustment for chronological age, intracranial volume (ICV), socioeconomic status and body mass index (BMI); no comparable association was observed between fathers and non-fathers. Regional analyses revealed a spatially distributed signature, with directionally consistent reductions across all 10 lobar regions, of which bilateral frontal, left parietal, and bilateral subcortical/cerebellar regions survived false discovery rate correction. The younger brain-age profile in mothers did not exhibit a graded association with number of children or the duration of parental experience, providing no support for a strictly linear cumulative exposure pattern in early adulthood. Despite younger-appearing brain anatomy, mothers did not exhibit superior cognitive performance. Instead, crystallized cognition was modestly lower in mothers after covariate adjustment, and a parallel pattern was observed in fathers, whereas fluid cognition did not significantly differ from non-parents in either sex. This cross-sex convergence in crystallized cognition, combined with the brain age effect observed only in mothers, suggests that structural and cognitive correlates of parenthood may have partially distinct origins. Collectively, these findings indicate that motherhood-related differences in brain predicted age are already observable within years of childbirth, albeit without concomitant cognitive advantages.