This is a mentored Research Career Development Award to support the career development of clinical investigators in patient-oriented research. The overall research goal of this research is focused on characterizing the development of brain and sensorimotor skills in children with autism. Motor impairments and cellular abnormalities in the cerebellum have been documented in the majority of individuals with autism studied to date. Sixty individuals with autism between ages 5-25 years will be compared with 60 age- and IQ-matched healthy controls. Subjects will perform sustained and ballistic (high-velocity musculoskeletal movement) motor control tasks for both ocular and manual systems. Preliminary evidence indicates that subjects with autism show reduced: a) visual tracking accuracy, b) manual force stability, c) saccade accuracy (quick, simultaneous movements of both eyes in the same direction), and d) ballistic force accuracy. In addition, the variability-reducing function of the cerebellum is implicated by pilot data showing increased trial-wise variability of saccade and ballistic force accuracy. Parallel functional magnetic resonance imaging (fMRI) tasks will assess the development of cerebellar ocular and manual motor circuits in the 45 subjects with autism and 45 controls > age 8 years. Neuropsychological tests of motor skill, as well as clinical neurological examinations of motor function, will be administered. These studies have the potential to elucidate abnormal developmental pathways of motor and cerebellar systems, which in turn could provide clues to pathophysiological mechanisms in autism, assist in more reliable diagnosis, and inform the development of novel treatments targeting cerebellar systems.