![]() But in 1979 the late Peter Huttenlocher, a neurologist at the University of Chicago, demonstrated that this excess production and pruning strategy actually continues for synapses long after birth. The timing of cell death is genetically programmed and occurs at different points in the embryonic development of each species.įor decades neuroscientists believed that neural pruning ended shortly after birth. Victorious neurons receive trophic, or nourishing, factors that allow their survival unsuccessful neurons fade away in a process called apoptosis, or cell death. They found that newborn neurons migrate along chemically defined routes and that when the neurons arrive at their genetically assigned locations, they compete with their “sibling” neurons to connect with predetermined targets. In a series of brilliant studies performed during the latter half of the 20th century, researchers discovered how pruning works. Although some may indeed be damaged, most simply fail to connect to their chemically defined targets. Why do some neural connections persist, whereas others do not? A common misconception is that neurons that do not make the cut are defective. ![]() In fact, this overproduction is so substantial that only about half of the neurons mammalian embryos generate will survive until birth. ![]() One of the grand strategies nature uses to construct nervous systems is to overproduce neural elements, such as neurons, axons and synapses, and then prune the excess.
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