DescriptionThe default mode network (DMN) is a structurally interconnected network of brain regions defined collectively by their high level of intrinsic activity at “rest” and relative decrease in activity while performing a range of cognitive tasks. The functional role of the network's intrinsic activity, as well as the significance of its task-evoked attenuation is unknown. However, aberrations in DMN activity are implicated in many disorders including Alzheimers, depression, autism, and schizophrenia, suggesting it may have a fundamental role in healthy brain function. Using diffusion imaging, I trace the large-scale anatomical connections of the network through the basal ganglia and thalamus, illustrating that the core regions of the network form a distributed cortico-striatal-thalamic circuit. Using Markov chain models of functional MRI, I explore the temporal dynamics of each region of the network during task execution and and present evidence suggesting the DMN may orchestrate switching between bottom up and top down processing in the brain through its connections to the basal ganglia. Subcomponents of the network in parietal cortex may support bottom-up processing while anterior portions in medial prefrontal cortex facilitate top-down. Finally, I classify resting-state data from patients with autism and schizophrenia and find that changes in DMN activity are potential biomarkers for distinguishing between the two disorders.