The human brain reaches peak synaptic density—that’s when the most neurons are the most wired to other neurons—when we’re around two.[*24] Then the brain starts violently pruning itself back, like an overzealous master gardener. Glial cells move in and gobble up synapses. Inhibitory cells start damping signals in some pathways, effectively increasing the strength of signals traveling nearby paths, a bit like redirecting traffic. The brain of a standard toddler is effectively rewiring itself, dramatically reshaping the material it just built.
