New Neurons. Use Them or Lose Them

Many studies have demonstrated that new neurons are continuously being born in the hippocampus, the part of the brain that forms new memories. Learning increases the survival of neurons born up to a week before the learning. In other words, use them or lose them.

Source: Drapeau, E. et al. 2007. Learning-induced survival of new neurons depends on the cognitive stateus of aged rats. J. Neuroscience. 27 (22): 6037-6044.

Read more about it at http://thankyoubrain.com/PracticalMemoryResearch.htm
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