CONCEPT
Synaptic Pruning
The developmental process by which unused neural connections are eliminated and heavily used ones strengthened — not a failure of development but its mechanism.
Synaptic pruning is the neurobiological operation through which the developing brain transitions from an early period of exuberant connection formation to the refined architecture of mature cognition. A toddler's brain forms approximately fifteen thousand synapses per neuron by age three — a six-fold expansion over birth — and then systematically eliminates the connections the environment did not reinforce while fortifying those it did. By age ten, roughly half of peak synaptic connections have been pruned. The brain does not become more capable by adding indiscriminately; it becomes capable by sculpting. This makes the environment during sensitive periods constitutive rather than decorative: it determines which connections survive and which are eliminated, calibrating the resulting instrument to match the world encountered.
In The You On AI Field Guide
The mechanism of pruning is use-dependent in a precise sense: synapses that fire together in response to environmental stimulation strengthen through long-term potentiation, while those that do not are progressively weakened and eventually eliminated by microglial cells. This is not metaphor. The physical substrate