In the 1990s scientists discovered that the adult mammalian brain is capable of sprouting thousands of new neurons. They allow us to keep learning new things. But most of them don’t stick around long enough to do this. Why is that?
The field of neurobiology was startled to learn a few years ago that the mature brain is capable of sprouting new neurons. Biologists had long believed that this talent for neurogenesis was reserved for young, developing minds and lost with age.1 It isn’t. Elizabeth Gould, then at the Rockefeller University demonstrated that new cells arise in the adult brain—particularly in a region called the hippocampus, which is involved in learning and memory. Old dogs can learn new tricks.
Gould’s work, albeit mostly in rats, reveals that fresh neurons arise in the brain on a daily basis. As Tracey Shors writes in a 2009 Scientific American article, “Studies indicate that in rats, between 5,000 and 10,000 new neurons arise in the hippocampus every day.” What we’re unclear about is how many cells the human hippocampus welcomes each day. We do know these new neurons mean old humans can learn new tricks.
All this would seem to be good news except that most of these new cells disappear within just a few weeks of arising. They don’t stick around long enough to teach us new things. Why not? The answer is in distinguishing between the environmental factors that produce new neurons versus the one factor that makes for retaining them.
The rate of producing new cells can be enhanced by exercise. Rats and mice that log time on a running wheel can kick out twice as many new cells as mice that lead a more sedentary life. But that’s not what makes these new cells stick around.
The retention of these new neurons in the adult brain requires being engaged in solving a challenging problem. “And the more engaging and challenging the problem,” Shors notes, “the greater the number of neurons that stick around.” If adults are cognitively challenged, the cells will linger. “If not, they will fade away.” The key to retaining new neurons is having assumptions continually disrupted while trying to solve problems.
This explains something. I’m 60. Somewhere along the way, most men and women my age stopped learning new things. They’re old dogs doing old tricks. They talk about the same stuff they talked about twenty years ago—weather, gas prices, golf, blah, blah. If they’re Christians, they haven’t learned anything new about God in years. Now they’ve added aches, pains, and retirement to their repertoire. Frankly my dear, I find it boring. The fact that we can retain new neurons indicates to me that God made us to be lifelong learners. This however requires trying to solve a big problem, pursuing a BHAG (Big Hairy Audacious Goal). Got one? If you don’t, and you’re an adult, your new neurons are dying. And so are you, in more ways than you probably ever imagined.
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1 Tracey J. Shors, “How to Save New Brain Cells,” Scientific American, May 2009, pp. 47-48.