Currently we have multiple ongoing NIH funded studies at the University of Delaware (UD) to examine the effects of various behavioral interventions developed for pediatric and adult neurologically affected special populations. We feel there is an urgent need to understand the neural mechanisms of change underlying the behavioral improvements we notice in our populations of interest. Additionally, we are interested in studying the neural substrates for a wide range of behaviors that are an area of emphasis for NIH including working memory in children with Autism, interpersonal synchrony in children with Autism and Oppositional Defiant Disorder, balance in children with Cerebral Palsy, mobility in children with Down Syndrome, arm function in infants with Brain Injury, locomotion in patients with Stroke, and psychosocial symptoms related to Chronic Low Back Pain in older adults. In this proposal, we are requesting funds to purchase a Hitachi functional infrared spectroscopy (fNIRS) system (Model: ETG-4000) to advance our clinical and translational research programs as well as interdisciplinary collaborations between researchers working in the areas of pediatric/adult neurorehabilitation, developmental psychopathologies, and motor, social, and cognitive neuroscience. Common neuroimaging approaches such as functional Magnetic Resonance Imaging (fMRI) and electrophysiological approaches such as Electroencephalography (EEG) are limited to tasks in reclined or seated positions with minimal to no movement, making these applications ineffective in obtaining brain activation data in the presence of movement and during naturalistic interactions. If the fNIRS system were to become available at UD, it would allow us to examine part or whole brain activation during a variety of functional motor tasks such as reaching and walking as well as naturalistic and play-based interactions between individuals. This makes the fNIRS technology truly translational and transformational in understanding brain-behavior relationships within real-world settings when working with a diverse set of pediatric and adult special populations including Adult with Stroke and Chronic Low Back Pain, Children with Autism, Cerebral Palsy, Oppositional Defiant Disorder, and Down Syndrome as well as High-risk infants.