In this 2-year R21 grant entitled “Elucidating the three-dimensional organization of the human cerebellar cortex using histological and ultra-high resolution structural MRI approaches”, we will use advanced 3D histology and ultrahigh resolution multimodal structural MRI techniques to determine the 3D ground truth organization of the human cerebellar cortex and relate it to 3D structure in the same tissue samples as shown by high resolution MRI. The cerebellum is a large brain region appended to the brainstem and consisting of a thin three-layer cerebellar cortex, and underlying white matter. The cerebellum contains three main divisions, the vestibulocerebellum, the spinocerebellum and the cerebrocerebellum, each which has distinct afferent and efferent connections, as well as distinct functions. Moreover, these divisions are often differentially affected by disease states. There have been limited anatomical studies of the intrinsic connections and three-dimensional architecture of the human cerebellum and specifically the cerebellar cortex, largely due to methodological constraints in the human. Most of the information about intrinsic connectivity and cerebellar cortical architecture is derived from rodent and cat models. Emerging information from animal models have indicated considerable heterogeneity in the cerebellar cortex of the distinct functional divisions of the cerebellum, but this assumption has never been explicitly tested in the human cerebellar cortex. Anatomical ground truth information about the human cerebellar cortex in three dimensions and in the different divisions has not yet been achieved. The goal of the proposed research is to conduct the first detailed histological analysis of the human cerebellar cortex and relate the results to structural MRI findings and thereby validate MRI results. To accomplish this goal, we will first use advanced 3D histological techniques such as CLARITY-based tissue clearing and SWITCH immunohistochemistry to reveal the neuronal organization of the Purkinje cell layer and granule cell layer as well as the architecture of the Purkinje cell dendrites and granule cell parallel fiber axons in the molecular layer of the human cerebellar cortex. This work will be performed in samples from the distinct functional regions of the cerebellum, namely the vestibulocerebellum, the spinocerebellum, and the cerebrocerebellum to determine whether the neuronal organization and architecture of the processes in the molecular layer differs across these regions. Second, and in the identical samples used for histological analysis, we will carry out ultra-high resolution ex vivo multimodal structural MRI analysis to compare structural and diffusion MRI results to anatomical ground truth in the human cerebellar cortex. These data will provide a histologically validated MRI dataset of the human cerebellar cortex using state of the art methodologies from both histology and MRI. The elucidation of this human intrinsic cere...