The patterned reduction in the number of functional connections among nerve cells or between multiple neurons and muscles that occurs as a normal process of neural development following neural proliferation. In early development, there are many more synaptic connections than at maturity and the process of elimination (involving the loss of up to 50% of connections in some parts of brain), though not completely understood, involves functional activity and learning processes. Identifying the precise mechanisms by which synaptic targets regulate the development of the motor and sensory cells that innervate them is one of the most intensively researched issues in contemporary neuroscience, and for which Rita Levi-Montalcini, partly based on her work with Viktor Hamburger (!900-2001), won the Nobel prize for Physiology or Medicine in 1986 together with Stanley Cohen.
See Apoptosis, Cell death, Cerebral cortex (development), Quantitative and qualitative regressions, Regressive event, Synapse, Synapse stabilization