One of the enduring mysteries of neurogenesis - the process of creating new neurons in the brain - is the purpose of all these new cells. After all, one of the reasons scientists believed that neurogenesis didn't exist (this was the scientific dogma for most of the 20th century) was that newborn neurons seemed so disruptive. How do untutored cells slot into the intricate networks of the brain? The idea was that, at some point in our distant past, mammals traded the ability to give birth to new neurons for the ability to retain plasticity in old neurons. We don't need new cells because we're able to tweak the ones we already have.
This is why many scientists continued to argue that, even if neurogenesis existed, it was probably unimportant, a vestigial legacy of infancy. You don't really need these new cells, you just never bothered to stop making them.
But now, in the latest Nature Neuroscience, there's exciting evidence that neurogenesis is actually necessary for the formation of new memories. Using a really nifty experimental setup, the scientists were able to selectively ablate these newborn neurons. While the absence of neurogenesis didn't shrink the hippocampus, it did dramatically interfere with the performance of the hippocampus on spatial memory and associative learning tasks. When put in a new maze, mice without fresh brain cells always got lost.
Now, I'm a neurogenesis partisan - I just find the idea of birthing brain cells so lovely and optimistic that I want them to be functional - but I do think this adds something important to the growing body of research showing that the absence of neurogenesis has important consequences. It won't just make you depressed, it might also make you forgetful.
For more, check out my profile of Elizabeth Gould.
Update: Mo's got a great writeup if you want to learn more about genetic labeling and Cre mediated recombination.
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Gerd Kempermann who studied under the mentoring of Fred H. Gage and others sustains a "neurogenic reserve hypothesis" for the newly formed nerve cells in the brain.
And according to this hypothesis, the birth of new neurons help already stablished neural networks to adjust themselves to challenging demands. New neurons are not necesarily implicated in replacing cell necrosis or cell loss, but in learning (and also memory and emotional behaviour)and improving cognitive functions that otherwise decline with age.
Jonah, your featured article of Dr. Gould is insultantly precocious, perfectly waving the tribulations of maverick ideas at the begining that turn into solid scientific ideas, with personal touchs of the scientists behind the ideas, and the facts.
The last paragraph is perfect, really!
Great article. Do you have any information on the role of dreaming and neurogenesis? Consolidation of the waking day's memories occurs in our sleep, and I was wondering whether the process of neurogenesis is promoted by dream activity. Thanks.
Fascinating article, Jonah!
"I just find the idea of birthing brain cells so lovely and optimistic that I want them to be functional"
Ha. I've heard this exact sentiment from 2 of my neuro professors at Hopkins. One of them says it's the only reason he gets out of bed every morning. I am 80% sure he was joking.
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I wonder if there is a limit to fluid intelligence gains. Has anyone heard of dual n back? I have been using dual n back for 3 months now and I have noticed my reasoning ability has dramitically increased. I believe that working memory has a larger component to fluid intelligence than what is currently known. Please let me know your thoughts.