Project Summary/Abstract The goal of this project is to identify corresponding ages across postnatal ages in humans and model organisms. This work is needed because scientists often use model organisms such as mice to understand basic biological processes and disorders in humans, but there is currently no resource that enables researchers to find corresponding ages across the lifespan of model organisms and humans. We and others have implemented an easily accessible website to find equivalent developmental ages across 18 mammalian species (http://www.translatingtime.net). This resource is used by a number of researchers who study model organisms (e.g., mice) to translate their findings to humans, but it only finds corresponding ages up to 2 year after birth in humans and its equivalent in model organisms. This is because we focused on sharp changes that occur during neurogenesis (i.e., the production of neurons) as a basis with which to find corresponding ages across species. Neurogenesis occurs largely during fetal development. As a result, we have only identified corresponding ages during fetal and early postnatal development in humans and and model organisms. Yet, many researchers use model organisms to understand human childhood, adolescence, and aging, and there is no resource that enables scientists to find corresponding ages between humans and other species across the lifespan. We will compare the timing of tract (i.e., pathway) maturation and temporal changes in gene expression across species in order to identify corresponding transformations during postnatal and adult ages in humans and their equivalent in model organisms. We will use diffusion MR tractography, which identifies tracts across the brain, to compare the timing of tract maturation across postnatal development in humans, non-human primates, and mice. We will use RNA sequencing to track temporal changes in gene expression across postnatal ages in humans, non-human primates, and mice. Integrating diffusion MR tractography with gene expression is an innovative approach with which to find corresponding ages across the lifespan of humans and model organisms. This project will implement new tools with which to find corresponding ages from model organisms to humans.