During the first 12 months of development in human infancy, the emergence of cognitive and the emergence of motor skills are interconnected. These skills are subsequently applied to most domains of development, including language. Thus, cognitive and motor skills to be achieved during early infancy serve as an essential based for developmental outcome. However, cognitive, linguistic and gross motor domains express the fewest and least consistent gains actualized through early intervention for individuals with Down syndrome (DS) (Connolly et al., 1993; Gibson and Harris, 1988; Piper et al., 1986). It is the working hypothesis of this project that most phenotypic expressions of DS are first actualized as atypical cognitive and motor development during the first year of life. Accordingly, this research project will investigate brain-behavior relationships during cognition and movement among infants with DS that are 1 to 12months of age. Neural measures of attention, stimulus encoding, learning, memory and movement preparation will be recorded in both cross-sectional and longitudinal studies. Results will, for the first time, provide new knowledge concerning brain-behavior relationships during early cognitive and motor development. A group of infants without known risk of developmental difficulties (matched on age, sex and SES) will serve as a comparison group to provide sensitive examination of neurobehavioral expressions in the dysfunction of the nervous system due to DS genetic status. Moreover, characterization and evaluation of the impact of Trisomy-21 upon cognitive and motor functions will be observed before confounding impacts of language impairments are manifested in the development of an individual with DS. At the conclusion of the 5-year project, application of brain-behavior measures in establishing developmental trajectories of cognitive and motor skills will provide new and sensitive methodologies to assess developmental status and, accordingly, the effectiveness of early intervention Thereafter, application of such techniques may provide the foundation for subsequent specialization and refinement of early intervention, particularly with respect to cognitive and motor abilities.