Final answer:
The corpus callosum maintains its size and shape up to approximately 20 years of age, during which the brain continues to develop through processes like myelination and synaptic pruning, leading to a gradual increase in white matter.
Step-by-step explanation:
The corpus callosum is a dense band of neural fibers that connects the left and right hemispheres of the brain, enabling communication between the two. Through childhood and adolescence, the brain undergoes significant developmental processes, such as synaptic pruning and myelination, leading to a more efficient and functionally enhanced brain. While the brain's size may stabilize early in life, the internal structure and complexity continue to evolve well into adolescence.
Specifically, changes in the cerebrum are marked by an increase in white matter due to increased myelination and a concurrent decrease in gray matter as synaptic pruning occurs. This can be visualized on MRI scans showing the developmental trajectory of the brain from 5 to 20 years of age. Evidence indicates that although the brain maintains its general size and shape up to around 20 years of age, there's a gradual shift in the ratio of gray to white matter.