Washington, Feb 19 (IANS) Autism first begins to show up as a significant difference in the brains of six-month-old babies and develops as they age, as compared to babies who are free of the disorder.

The study, conducted by scientists from Washington (St Louis) and North Carolina (Chapel Hill) Universities, involved infants at high risk for autism because they had an older sibling with the diagnosis.

The new research, which relied on brain scans acquired at night while infants were asleep, suggests that autism doesn't appear abruptly, but instead develops over time during infancy, the American Journal of Psychiatry reports.

"We were surprised that there were so many differences so early in infancy," says co-author Kelly N. Botteron, who is leading the study at Washington, according to a Washington University statement.

"As this study moves forward, we may want to scan babies at even younger ages so that we can try to see how early this pattern is emerging," adds Botteron.

The new findings involved brain scans from 92 infants who had completed diffusion tensor imaging (DTI), a type of MRI scan, at six months and behavioral assessments at 24 months of age. Most also had additional scans at 12 months or 24 months or both.

By 24 months, 28 of the infants (30 percent) met the diagnostic criteria for autism spectrum disorders. Scans of the infants with autism revealed changes in the pathways that connect brain regions to one another. In particular, the researchers found changes in multiple fibre pathways in the brain's white matter.