How does the brain change across childhood?

The brain weighs about 350 grams at birth and about 1,450 grams by adulthood. The increase in weight is mainly due to growth in dendritic branches. This is because the basic structures of the brain are in place at birth, but the connections between neurons are still under developed.

The synaptic connections between neurons are highly dependent on experience. In other words, the firing of neurons greatly influences the creation and strengthening of synaptic connections. When our brain responds to its environment—be it a sensory, perceptual, emotional, or motor response—we are activating all the neurons in the relevant brain circuitry and causing them to fire. This activation then strengthens the synaptic connections between them. As the saying goes, “Neurons that fire together, wire together.”