During the third trimester of human brain development, the cerebral cortex undergoes dramatic surface expansion and folding. Physical models suggest that relatively rapid growth of the cortical gray matter helps drive this folding, and structural data suggests that growth may vary in both space (by region on the cortical surface) and time. In this study, we propose a new method to estimate local growth from sequential cortical reconstructions. Using anatomically-constrained Multimodal Surface Matching (aMSM), we obtain accurate, physicallyguided point correspondence between younger and older cortical reconstructions of the same individual. From each pair of surfaces, we calculate continuous, smooth maps of cortical expansion with unprecedented precision. By considering 30 preterm infants scanned 2-4 times during the period of rapid cortical expansion (28 to 38 weeks postmenstrual age), we observe significant regional differences in growth across the cortical surface that are consistent with patterns of active folding. Furthermore, these growth patterns shift over the course of development, with non-injured subjects following a highly consistent trajectory. This information provides a detailed picture of dynamic changes in cortical growth, connecting what is known about patterns of development at the microscopic (cellular) and macroscopic (folding) scales. Since our method provides specific growth maps for individual brains, we are also able to detect alterations due to injury. This fully-automated surface analysis, based on tools freely available to the brain mapping community, may also serve as a useful approach for future studies of abnormal growth due to genetic disorders, injury, or other environmental variables.Cortex | growth | strain energy | registration | development D uring the final weeks of fetal or preterm brain development, the human cerebral cortex dramatically increases in surface area and undergoes complex folding (Fig. 1). This period represents an important phase of neurodevelopment, as crucial brain regions undergo changes in connectivity and cellular maturation (1, 2). Physical simulations suggest that folding may result from mechanical instability, as the outer gray matter grows faster than underlying white matter (3, 4). Such models accurately predict stress patterns within folds and explain abnormal folding conditions such as polymicrogyria and pachygyria. However, recent models, which consider uniform cortical growth on a realistic brain geometry, do not fully reproduce highly conserved (primary) folding patterns observed in the human brain (4). This suggests a role for other hypothesized factors such as axon tension in white matter (5), regional di erences in material properties, or regional di erences in growth (6).Advances in magnetic resonance imaging (MRI) and cortical reconstruction have enabled detailed quantification of brain structure and connectivity during brain development (7-9). Nonetheless, measuring patterns of physical growth over time presents a unique challenge, as quan...