The younger siblings of children diagnosed with autism are at an increased risk for autism themselves. By studying these at-risk babies, we can better understand the development of the condition and this, in turn, may lead to more effective early treatments. It remains challenging, however, to study brain function in a safe and effective way in young babies. Mark Johnson and his colleagues at the University of London have been developing a new method of brain imaging called functional near-infrared spectroscopy (fNIRS), which involves weak beams of light that are absorbed differently in active vs. inactive parts of the brain. Johnson plans to bring together a group of internationally recognized experts to determine how effective this new method is, by directly comparing it to existing methods that are more difficult to use with awake babies (e.g., functional magnetic resonance imaging, or fMRI) or that have inferior spatial resolution (e.g., electroencephalography, or EEG). The researchers aim to assess the reliability and accuracy of the new method in a practical laboratory context by testing and then retesting the same babies one week later. Finally, they plan to gather fNIRS measurements from at-risk siblings and low-risk controls at 6 months of age, and then again about 30 months later. The researchers hope their methods can be used to look for differences in brain function between at-risk and low-risk babies during infancy, which could be related to later-emerging symptoms of autism.