PITTSBURGH -- Using a new form of brain imaging known as diffusion tensor imaging (DTI), researchers in the Center for Cognitive Brain Imaging at Carnegie Mellon University have discovered that the so-called white matter in the brains of people with autism has lower structural integrity than in the brains of normal individuals. This provides further evidence that the anatomical differences characterizing the brains of people with autism are related to the way those brains process information.
The results of this latest study were published in the journal NeuroReport. The scientists used DTI -- which tracks the movement of water through brain tissue -- to measure the structural integrity of the white matter that acts as cables to wire the parts of the brain together. Normally, water molecules move, or diffuse, in a direction parallel to the orientation of the nerve fibers of the white matter. They're aided by the coherent structure of the fibers and a process called myelination, in which a sheath is formed around the fibers that speeds nerve impulses. The movement of water is more dispersed if the structural integrity of the tissue is low -- i.e., if the fibers are less dense, less coherently organized, or less myelinated -- as it was with the participants with autism in the Carnegie Mellon study. Researchers found this dispersed pattern particularly in areas in and around the corpus callosum, the large band of nerve fibers that connects the two hemispheres of the brain.
"These reductions in white matter integrity may underlie the behavioral pattern observed in autism of narrowly-focused thought and weak coherence of different streams of thought," said Marcel Just, director of the Center for Cognitive Brain Imaging and a co-author of the latest study. "The new findings also provide supporting evidence for a new theory of autism that attributes the disorder to underconnectivity among brain regions," Just said.