In the human brain, a great deal of synaptic pruning occurs in early childhood. This pruning appears to be:
1) the unfortunate result of home and school environments that provide only limited stimulation.
2) an adaptive process that allows children to deal more efficiently with typical tasks in their environment.
3) due to an imbalance of important nutrients, and especially to low levels of the B vitamins in many children's diets.
4) the result of the cortex's gradual takeover of responsibility for functions that have previously been controlled by other parts of the brain.