Final answer:
During childhood, the growth and development of the brain primarily occurs by increasing neuron size and the number of dendrites and synapses. Synaptic pruning also plays a crucial role in this process, making the brain more efficient. Even though the brain reaches most of its adult size early on, the complexity of connections continues to develop into adolescence.
Step-by-step explanation:
The primary process by which growth and development of the brain occurs during childhood is through the increase in neuron size and the number of dendrites and synapses.
This developmental phase is characterized by a fast pace of neural growth known as blooming, where neural pathways are rapidly formed. Alongside the growth of neural pathways, synaptic pruning takes place, which is the process of eliminating unused neural connections. This leads to an increase in the brain's functional efficiency during adolescence, furthering cognitive development.
Although the brain does reach about 90% of its adult size by age six, most neuronal changes post-birth relate to the complexity of connections rather than an increase in the number of neurons. This complexity is mainly due to growth in dendrites, the branching structures of neurons that receive signals, and synapses, the junctions between neurons where signals are transmitted.
Through childhood and into adolescence, neurogenesis or the formation of new neurons does occur, but it is a more limited process compared with the extensive network formation and pruning. These changes are critical for the development of cognitive abilities like memory, learning, and impulse control.