The investigators will focus on three cohorts of brain tumor patients aged, 4-18 years, to answer two critical questions: 1) Can the investigators acquire high quality data relevant to cognitive function during the peri-diagnostic period and, 2) can the investigators develop predictive models for cognitive outcomes using serial examination of functional imaging and cognitive function. Any patient with a newly diagnosed brain tumor aged 4-18 will be eligible for enrollment in cohort 1. Only patients with previously diagnosed tumors of the posterior fossa will be eligible for cohort 2. For cohort 3, eligible patients will include patients with a clinical diagnosis of posterior fossa syndrome with physical impairments that prohibit completion of the NIH Toolbox Cognitive Battery. The investigators have decided to expand the eligible tumor types to better capture the most significant deficit variability that can be caused by tumors outside the posterior fossa. Thus, this focus will provide a platform to analyze the impact that different tumor types and different standard treatments have on cognitive dysfunction. The rationale for inclusion of subjects on cohort 3 is that posterior fossa syndrome is one of the most cognitively devastating diagnoses following a posterior fossa surgery. The causes of posterior fossa syndrome and unknown and there are currently no interventions to improve symptoms. RsfcMRI would offer a novel and non-invasive assessment of posterior fossa syndrome patients by assessing connectivity within and outside of the cerebellum. Expanding the tumor eligibility will allow us to further explore the effect tumor location will have on cognitive testing and rsfcMRI. Here, repeated evaluations on and off therapy will provide the necessary data points to establish trajectories of cognitive development and recovery in this population.