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Why Is Synaptic Pruning Important for the Developing Brain?

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Why Is Synaptic Pruning Important for the Developing Brain? ASK THE BRAINS Experts answer questions from readers Why is mon misconception is that neurons have dif culty recovering from a trau- that do not make the cut are defec- matic brain injury: eliminating synaptic synaptic pruning tive. Although some may indeed be redundancies diminishes our ability to important for the damaged, most simply fail to con- develop alternative pathways to bypass developing brain? nect to their chemically de ned tar- the damaged region. —Rowena Kong via e-mail gets. In a series of brilliant studies In addition, many major mental ill- performed during the latter half of the nesses start to emerge in adolescence, 20th century, researchers discovered which may be caused by aberrant syn- Irwin Feinberg, professor how pruning works. They found that aptic pruning. In 1982 I hypothesized emeritus of psychiatry and newborn neurons migrate along chemi- that disordered synaptic pruning could behavioral sciences at the Univer- cally de ned routes and that when the explain the age of onset of schizophre- sity of California, Davis, replies: neurons arrive at their genetically as- nia, and in 2016 researchers published signed locations, they compete with One of the grand strategies nature uses their “sibling” neurons to connect with to construct nervous systems is to over- predetermined targets. produce neural elements, such as neu- Victorious neurons receive trophic, rons, axons and synapses, and then or nourishing, factors that allow their prune the excess. In fact, this overpro- survival; unsuccessful neurons fade Streamlining duction is so substantial that only about away in a process called apoptosis, or neural circuits could half of the neurons mammalian em- cell death. The timing of cell death is bryos generate will survive until birth. genetically programmed and occurs explain the boost Why do some neural connections at different points in the embryonic persist, whereas others do not? A com- development of each species. in cognitive skills For decades neuroscientists that occurs in our believed that neural pruning ended shortly after birth. But in 1979 the late teens late Peter Huttenlocher, a neurolo- Other factors may contribute to a gist at the University of Chicago, or early 20s. person’s success in music and mathe- demonstrated that this excess matics. It is possible that noncognitive production and pruning strategy variables—socioeconomics or educa- actually continues for synapses tion—are involved. If, for example, you long after birth. Using electron grow up in a household with signi cant microscopy to analyze carefully genetic and experimental evidence sup- nancial resources, you may be more selected autopsied human brains, porting this association in Nature. likely to attend a top-rated school or be he showed that synapses—the Although we are only beginning to able to afford music lessons. tiny connections between neu- unravel the rami cations of synaptic Although the precise connection be- rons—proliferate after birth, pruning in the human brain, this pro- tween music and mathematics training reaching twice their neonatal lev- cess clearly has signi cant consequenc- has not yet been untangled, this line of els by mid- to late childhood, and es for normal human brain function inquiry raises intriguing questions about then decrease precipitously dur- and may provide key insights into the the relation between these two subjects. ing adolescence. causes of some devastating and mysteri- To determine whether music training in- These changes at the synapse ous neuropsychiatric diseases. M uences aptitude in math, or vice versa, level cause neural restructuring researchers would need to conduct long- that very likely has important term studies that measure one ability be- consequences for normal and ab- Do you have a question fore and after studying the other. But re- normal brain function. Streamlin- about the brain you would like gardless of how these skills are connect- ing neural circuits could explain an expert to answer? ed, it is clear that studying math and the boost in cognitive skills that Send it to music provides a range of bene ts, such occurs in our late teens or early editors@sciam.com as improving mood, memory and focus. 20s. The loss of redundant path- ways could help elucidate why we MIND.SCIENTIFICAMERICAN.COM SCIENTIFIC AMERICAN MIND 75 miq317Brns3p.indd 75 3/6/17 4:36 PM.
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