Final answer:
The statement regarding neuronal pruning and increased myelination during adolescence is true, with these processes contributing to improved brain efficiency and functionality in cognitive tasks and executive functions.
Step-by-step explanation:
The statement that during adolescence, two significant changes in the brain are the pruning away of some neurons and the increasing myelination of brain cells is true. During adolescent brain development, a process known as synaptic pruning occurs, where the brain eliminates unused neural pathways to increase efficiency and functionality. At the same time, there is an increase in myelination, which involves the addition of a myelin sheath to neurons, thereby improving the speed and efficiency of nerve impulse conduction.
This complex remodeling enhances the brain's capacity to perform various cognitive functions such as decision-making, information processing, and abstract reasoning, which continue to mature as the prefrontal cortex develops during adolescence. Notably, the prefrontal cortex is associated with so-called executive functions, which include planning ahead and impulse control.