CNS development

Important Concepts

During the first 6 years of life, the brain undergoes a period of rapid growth, increasing from 10% to 90% of adult volume. Most of this growth occurs before the age of two.
Synaptic density, dopamine receptor density, and cerebral metabolic rates peak in the first 3 years of life and decline over subsequent decades (1).
Significant myelination begins in infancy and is not completed until adulthood. This process corresponds with better motor coordination and faster information processing.

Development of frontal lobes allows school-age children to better inhibit distracting stimuli and maintain focus on a particular task.

Synaptic pruning, or reorganization and elimination of cortical synapses, increases through adolescence. Pruning results in elimination of up to 50% of synapses that existed prior to puberty. This remarkable processes is evidenced by declines in brain glucose metabolism, blood flow, and decreased EEG amplitude.

Pruning is evident in structural changes in the brain:

decreased grey matter density (GMD) in dorsal aspect of frontal and parietal lobes between childhood and adolescence,
further decrease in GMD in frontal cortex between adolescence and adulthood,
there are increases in white matter density and volume until early adulthood.
pruning correlates with ability to inhibit impulses, prioritize, and development of executive functioning.