Selective Age-Related Changes in Brain Network Connectivity During Young Adulthood: Sensory Networks Decrease While Hub Networks Remain Stable

Young adulthood (ages 22-35 years) represents an important period for brain development, yet mechanisms underlying age-related connectivity changes remain poorly understood. We examined developmental trajectories in 66 healthy young adults (22 per age group: 22-25, 26-30, 31-35 years) using resting-state functional magnetic resonance imaging from the Human Connectome Project. Contrary to expectations of global increases, we found selective age-related changes: sensory networks (visual and auditory) showed significant decreases in connectivity with age (visual: slope = -0.0133, p = 0.038; auditory: slope = -0.0184, p = 0.012), while hub networks (default mode and frontoparietal) and other networks remained stable (all p > 0.15). Network coupling analysis revealed a mechanistic explanation: sensory networks decouple from hub networks with age (DMN-AUD: change = -0.77; DMN-VIS: change = -0.56), while sensory networks show increased coupling with each other (VIS-AUD: +0.18). This decoupling explains why only sensory networks show age-related changes, as they become independent from hub networks during young adulthood. Importantly, total IQ showed no significant association with network connectivity (all |r| < 0.10, all p > 0.43), strengthening the developmental interpretation. Machine learning revealed the somatomotor network was most predictive of age. All effects remained consistent after controlling for head motion and across sexes. These results demonstrate selective, network-specific developmental trajectories during young adulthood, with sensory networks becoming independent from hub networks and showing age-related decreases, while hub networks maintain stability.