Rapid expansion and renormalization of parietal gray matter volume following associative learning

The human brain exhibits rapid structural plasticity following learning, yet its temporal dynamics and behavioral relevance remain elusive, particularly for declarative forms of learning. In this study, we tested whether T1-weighted MRI captures rapid structural reorganization following associative memory formation and whether such changes follow an expansion-renormalization trajectory. We combined three independent datasets (N = 198) to quantify gray matter volume (GMV) changes following an associative memory task using voxel-based morphometry across baseline, 2 h, and 12 h post-learning. We observed transient GMV increases in parietal, lateral occipital, and cerebellar regions at 2 h post-learning, which returned to baseline by 12 h, consistent with rapid renormalization. Critically, GMV changes in left parietal cortex were associated with memory retention, such that greater maintenance of GMV was associated with better retention. Sleep further facilitated renormalization of GMV, suggesting that the sleeping brain regulates structural changes in task-relevant areas. Our findings provide evidence that human gray matter undergoes hour-scale, behaviorally relevant structural reorganization after associative learning.