This research proposal will directly test a fundamental hypothesis suggesting that ASD is characterized by an over-abundance of short-distance connections and reduced long-range connections in the cerebral cortex. This imbalance may be more or less severe depending upon functional status of the individual, but it has been difficult, if not impossible, to carry out fMRI on so-called lower-functioning individuals. The investigators have perfected a method that requires very short imaging periods (minutes) for measuring functional connectivity (defined as the degree of synchronization between distant brain regions) that they have shown to be exquisitely sensitive in detecting connectivity differences between typically developing children, adolescents and adults. Preliminary data indicates that this team can detect autism-related differences in functional connectivity in children with high-functioning autism who are between 8-14 years of age. Here, the investigators propose a two-year cross-sectional study to examine such measures of connectivity in young children (between 36 and 60 months of age) with ASD compared to controls. A comparative analysis across cortical regions will allow the investigators to determine whether there is a regional bias that includes frontal cortex, which is most involved in processing social information. The investigators also have included the development of analytical and imaging technologies that will be broadly applicable across imaging sites. The study thus has the opportunity to expand greatly the capacity of neuroimaging research programs around the country to include ASD as a focus of their efforts. What this means for people with autism: Our understanding of the disruption of circuit organization and function in ASD is based on imaging or electrophysiology studies performed mostly on teenage and adult subjects who are characterized as high functioning. This new imaging approach should make it possible to extend functional neuroimaging to include very young children as well as those with severe ASD (e.g., non-verbal, disruptive behaviors), about which we have very little information. If this methodology works, it may provide a biomarker of autism functioning.