The brains of children with autism are the same size as those of mentally retarded children and children with speech impairments; there are also no differences in brain metabolism.
This is the conclusion of Mijke Zeegers in her doctoral thesis. Using MRI scans, Zeegers studied the brains of children with autistic disorders, mental retardation, and speech impairments. Almost half of the children studied had an abnormality, which varied from a relatively harmless defect in the shape of the corpus callosum to an 11-month lag in the development of the myelin sheath in a 21-month-old girl.
Mijke Zeegers: "Toddlers with autism; metabolic, radiologic, and volumetric aspects of brain development"