The connectivity of the human brain—and the development of this connectivity—can be described at coarse, intermediate, and fine levels. At the coarsest level, brain areas are created by the process of , which occurs . At the intermediate level, connections between individual neurons are created by the process of . The number of synapses peaks and then declines as a result of a process called . At the finest level, the strengths of individual neurons are adjusted as a result of experience. This is the primary mechanism of plasticity