The granule cells in the dentate gyrus are distinguished by their late time of formation during brain development. In rats, approximately 85% of the granule cells are generated after birth.[23] In humans, it is estimated that granule cells begin to be generated during gestation weeks 10.5 to 11, and continue being generated during the second and third trimesters, after birth and all the way into adulthood.[24][25] The germinal sources of granule cells and their migration pathways[26] have been studied during rat brain development.