Synaptic pruning

Synaptic pruning, a phase in the development of the nervous system, is the process of synapse elimination that occurs between early childhood and the onset of puberty in many mammals, including humans.^[1] Pruning starts near the time of birth and continues into the late-20s.^[2] During the pruning of a synapse, both the axon and the dendrite decay and die off. Synaptic pruning was traditionally considered to be complete by the time of sexual maturation, but MRI studies have discounted this idea.^[3]

The infant brain will increase in size by a factor of up to 5 by adulthood, reaching a final size of approximately 86 (± 8) billion neurons.^[4] Two factors contribute to this growth: the growth of synaptic connections between neurons and the myelination of nerve fibers; the total number of neurons, however, remains the same.^{[citation needed]} After adolescence, the volume of the synaptic connections decreases again due to synaptic pruning.^[5]

Pruning is influenced by environmental factors and is widely thought to represent learning.^{[5][need quotation to verify]}