Final answer:
In middle childhood, the brain becomes more efficient and functional due to increased complexity, particularly in the prefrontal cortex, which enhances cognitive functions and executive decision-making abilities.
Step-by-step explanation:
Changes in the functions of the brain in middle childhood lead to increased brain efficiency and cognitive functions. During adolescence, there is not much increase in brain size but rather enhancements in brain complexity, such as the cerebral cortex becoming more folded, which is associated with various executive functions. The process of synaptic pruning allows the removal of unused brain pathways, while increased myelination contributes to the efficiency of neural communication.
Consequently, the prefrontal cortex, which is critical for decision-making and impulse control, undergoes development that supports cognitive advancements like abstract reasoning and problem-solving.