First author Jason J. Wolff and senior author Dr. Joseph Piven, both of the University of North Carolina, Chapel Hill, said the study showed differences in brain structure at 6 months of age, the earliest such structural changes have been recorded in those with autism spectrum disorders.
Many early behavioral signs of autism spectrum disorders are not apparent until the first year of age, but autism spectrum disorders are typically diagnosed at age 3 or older, Piven said.
"The difference in the trajectory of brain development between the two groups was dramatic between six and 24 months," Piven said in a statement. "This suggests that the period from 6 to 24 months -- when behavioral studies suggest the symptoms of autism are first appearing -- is a period of dramatic brain changes in autism spectrum disorders."
The researchers recorded brain images of 92 infants, all of whom had an older brother or sister with autism spectrum disorders. Children who have an older sibling with autism spectrum disorders have an increased risk of developing autism spectrum disorders, Piven explained.
The study published online in the American Journal of Psychiatry found at six months, the intensity of white matter connections -- connections between the various brain areas -- was greatest in the group that later developed autism spectrum disorders.
The researchers interpreted the findings to indicate that coherent, organized information pathways developed faster in the children who did not have autism spectrum disorders.