Neurodevelopment of autism: The first three years of life

The unfolding of behavioral features associated with autism spectrum disorder (ASD) occurs in the latter part of the first and in the second years of life. This dramatic shift in symptom presentation suggests underlying neuroanatomical and functional brain changes that either precede or cooccur with the emergence of aberrant behavioral features. In this chapter we will review recent literature on the neurodevelopment of ASD, particularly focusing on longitudinal studies since brain development is nonlinear during this time period. Key results to date include findings indicating that sometime before two years of age the brain undergoes a period of overgrowth. Infant-sibling research studies have identified abnormal development of white matter fiber tracts, corpus callosum size, and extra-axial fluid as early as six months of age. These findings indicate that it may be possible to use brain features in the first year of life to predict ASD, providing a means to identify infants for very early intervention studies with the hope of improving long-term outcomes.