A recent study in adult mice indicates that new neurons in the memory-forming part of the brain have only a narrow time window, about three weeks, in which they can be saved. How were the saved from death? ... by providing a stimulating environment. Rather than being raised in standard laboratory cages as were the controls, the test mice lived in groups in cages that had various toys and things to do. These neurons survived if they were born one-to-three weeks earlier, but not if the enriched environment was available later.The spared neurons survived throughout the four-month observation period.
People also presumably are birthing new neurons, but learning experiences and mental activity are probably needed to help these new neurons to get incorporated into existing circuitry. If new neurons don't get included in circuitry, they will die.
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