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 GMV increases in parietal, lateral occipital, and cerebellar regions at 2 h post-learning ( n = 139), which were no longer detectable relative to baseline at 12 h ( n = 96), consistent with rapid renormalization. Critically, GMV changes in left parietal cortex were further linked to how well participants retained the memory, such that greater maintenance of GMV was associated with better retention ( n = 37). By contrast, in a distinct right parietal region ( n = 32; 17 sleep, 15 wake), GMV increased in the sleep group in the control but not in the learning condition, whereas GMV change did not differ between conditions in the wake group. This sleep-related effect was unrelated to memory retention. Our findings suggest that human gray matter undergoes hour-scale changes, with potentially dissociable memory- and sleep-related components.