April 2, 2004

Study details brain changes in autism, language disorder

Using advanced imaging technology, an MGH-based research team has identified
specific portions of the brain's white matter that are abnormally large in children with autism and developmental language disorder (DLD). The findings confirm that the previously observed overgrowth of white matter occurs after birth and suggest that it may be related to the process of myelination, in which portions of nerve cells called axons are covered with a material called myelin. The report appears in the April issue of Annals of Neurology.

The researchers noted that the factor most closely associated with the areas showing the greatest volume increase is when the axons in those areas myelinate, a key step in maturation that allows nerve impulses to be transmitted properly. In both autistic and DLD patients, the most enlarged areas were those that myelinate latest in normal development and where myelination takes a longer period of time.

"Knowing that white matter is most enlarged in the area that develops myelin latest will help us narrow the time window in which to look for the cause of these problems and should help focus future research," says Martha Herbert, MD, PhD, of MGH Neurology and the Center for Morphometric Analysis, the paper's lead author.

The current study used advanced techniques for analyzing magnetic resonance imaging (MRI) studies to subdivide white matter into distinct regions related to the pathways taken by nerve fibers. The results showed that in both the autistic and DLD participants, the outer layer of white matter was significantly larger than among controls, while the inner areas were no different. Both groups of children showed the greatest white matter enlargement in the prefrontal area, at the very front of the brain.

Herbert's MGH co-authors are senior author Verne Caviness, MD, DPhil; David Ziegler; Nikos Makris, MD, PhD; Joseph Normandin; and David Kennedy, PhD.