Formation and evolution of gyri and sulci in fetal brains: A growth-release model

During human prenatal development, the cerebral cortex undergoes a remarkable morphological transformation characterized by the formation and evolution of gyri and sulci. The biomechanical mechanisms underlying the unique cerebral cortical folding remain inadequately understood. In this paper, a growth-release model is proposed, through a combination of theoretical and numerical efforts, to investigate the morphological evolution of fetal brains. Compared with existing numerical frameworks, our model yields cortical morphology predictions that better align with experimental observations and measurements by accounting for the differential growth of soft tissues and growth-accommodated stress release. The effects of growth-accommodated stress release in brain tissues on cortical folding patterns are revealed. We find that, due to the stress release, the gyri are widened, and the sulci are sharpened. The degree, timing, and number of stress releases have distinct influences on cortical folding patterns-specifically, sulcal depth and mode number of the convoluted surface. The results demonstrate that growth-accommodated stress release plays a crucial role in the prenatal development of the human brain. The presented growth-release model can be extended to explore the morphological evolution of other biological soft tissues and organs. This work provides a new understanding of the gyrification of the human brain, offering a scientific basis for the diagnosis and treatment of cortical malformations. STATEMENT OF SIGNIFICANCE: Cortical gyrification is a critical process in human brain development, involving the formation and evolution of gyri and sulci, yet its underlying biomechanical mechanisms remain inadequately understood. This work develops a growth-release model that incorporates differential growth of soft tissues and growth-accommodated stress release to investigate the morphological evolution of fetal brains. Compared with existing numerical frameworks, the proposed model predicts more similar cortical folding patterns to those of real brains. By combining theoretical, numerical, and experimental approaches, we demonstrate that the stress release significantly influences key folding characteristics, such as gyral width, sulcal depth, and folding mode. This work provides mechanistic insight into brain gyrification and establishes a biomechanical framework for understanding cortical malformations.