Imaging Infant Brain Development from Birth to 2 Years

Background:  The first years of life are the most dynamic and perhaps the most critical phase of postnatal brain development.  Concurrent with the rapid pace of structural brain growth is an equally rapid development of a wide range of cognitive and motor functions.  Abnormalities in early postnatal brain development have been implicated in neurodevelopmental disorders, including overgrowth of gray matter volumes and abnormal white matter development in autism.  In spite of its importance for understanding normal brain development and the early origins of neurodevelopmental disorders, our knowledge of human brain development in this crucial time period is still not well developed.  The Early Brain Development Study at UNC
focuses on early childhood developmental trajectories and their relationship to cognitive development in typically developing children, in twins, and in children at high risk for psychiatric disorders.

Objectives:  To summarize early childhood brain development in the first 2 years of life.

Methods:  Over 800 children have had structural, diffusion tensor, and resting state functional MRI scans at birth, with follow-up scans and cognitive assessments at ages 1, 2, 4 and 6 years.  DNA has been collected on most children as well.

Results:  There is  rapid growth of overall brain size, driven mainly by gray matter development, attaining almost 85% of adult volume by age 2 years.  Cortical thickness reaches 95% of adult values by age 2 years and surface area reaches 69%.  There are marked regional differences in cortical gray matter growth, consistent with temporal patterns of sensory/motor and higher integrative function development.  Most white matter tracts, including short cortico-cortical fibers, arise during prenatal brain development and are present at birth.  There is rapid tract-specific maturation as reflected in diffusion tensor properties.  Cortical gyrification and folding at birth is very similar to that observed in adults and we have found very little change in the first years of life.   We have conducted a series of resting state fMRI studies in our cohort and found that most resting state networks including the default, attention control, visual, and sensorimotor networks are established by age two years.

Conclusions:  The picture is emerging that overall cortical structure and “hard wiring” of the brain is well developed at birth. By age 2 years, the structural and functional network stage is largely set for future learning, neuroplasticity, and “fine tuning” of major structural connections already in place.  Thus, we believe that the first two years of life are critically important for establishing the infrastructure for future cognitive development, are likely a major critical or sensitive period for psychiatric disorders risk, and suggest that the window for effective interventions may need to be before the age of two years.