Dr. Giedd and the NIMH team screened healthy children for MRI scanning, as well as children with specific disorders. MRI studies help us to determine that brain structural development is different in autism, ADHD, childhood schizophrenia, dyslexia, eating disorders, Tourette syndrome, and Sydenham's chorea. All show reliable developmental anatomical differences from control children in brain scans. Studying control children is very important. Brain size is highly variable and as a whole does not change much from age 4 to 18.
Most brain development occurs in utero.
Parts of the brain develop more during childhood, during adolescence, or throughout life, such as small areas of cortical development, myelination and dendritic arborization. For example, although overall brain size changes little during childhood, individual components of the brain change a lot. These moving parts change in a sexually dimorphic way. The corpus callosum does not differ between males and females. The amygdala has more androgen receptors, and the hippocampus has more estrogen receptors.