early growth spurt is followed by several years of slower expansion, giving the autistic child an adult-size brain by the age of 4 or 5. During adolescence and adulthood, autistic brains are generally no larger than normal ones. Unfortunately, they exhibit a range of other anomalies, including dense clusters of underdeveloped cells in the hippocampus and amygdala—structures that are critical for integrating emotional and sensory information. Courchesne believes it can be summed up in three words: “growth without guidance.� Normal brain development is not a monologue but a dialogue, in which the brain generates neural circuits and the child’s experiences determine which ones survive. The first year of life is a critical period for this “experience-guided growth�—and it’s not hard to see how a sudden shift into high gear might derail it. The brain’s circuitry would expand haphazardly as cell growth outpaced experiencePredicting Autism: "Autism, the new findings suggest, is not a sudden calamity that strikes children at the age of 2 or 3 but a developmental problem that can be traced back to infancy"