Synaptogenesis

making a synapse, the site of chemical-to electrical transmission between neurones. Synapses are generated in both development and adulthood. Synaptogenesis begins in week 12 and is mostly completed by prior to birth. The cerebral cortex and basal ganglia, however, continue to manufacture synapses postnatally, with the most period being from birth to about 5-6 years of age. 

See Basal ganglia (development), Cerebral cortex (development), MECP2 gene, Olfaction, Synapse, Synapse elimination, Synapse stabilization