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There are two conflicting stories about our neurons: (1) we shouldn't kill our brain cells because they’re the only ones we've got, and (2) neurogenesis—the birth of neurons—continues throughout our lives. What's the scoop?

Until the 1960s, scientists believed that whatever neurons we had at birth were all we’d get. But about that time, experiments on rats and monkeys showed otherwise; and still other experiments on canaries showed that they developed new brain cells when they learned new songs. Researchers wanted to know if people also developed new neurons—but since it's a little tricky to dissect the brain of a learning human, they couldn't find out that way for sure.

Move ahead thirty years to the ‘90s, when scientists conducted research on terminal cancer patients who were given certain drugs labeled with fluorescent dyes in their medical treatment. After the patients died, their brains were examined. The examinations showed that the patients had generated new neurons—right up until death. They indicated that the human hippocampus, a memory center of the limbic system, retains its ability to generate neurons throughout life.¹¹

The Myth of Limited Brain Use

Is it true that we use only 10% of our brain? Do we have 90% that's just twiddling its proverbial thumbs, wishing it had something to do already? Does that idle 90% mean we are really psychic or could move mountains if we used it?

No, that's a myth, says neuroscientist Eric Chudler, director of education and outreach at the University of Washington and developer of the informative Neuroscience for Kids website.¹² Images from PET scans and MRI have shown that if someone loses 90% of her brain—or of any part of her brain—she will not just continue living as if nothing had happened. From the perspective of evolution, it does not make a whole lot of sense to build and maintain a massively underutilized organ.

Researchers still have questions about neurogenesis. New neurons in rat brains travel from the hippocampus to other parts of the brain, but researchers have not yet proven whether the same thing happens in human brains. Some camps question whether the new brain cells are neurons or glial cells and what purpose they serve.¹³

For us nonscientists, the important thing to know is that even though we get almost all our neurons at birth, our brains continue to change and grow, supporting our learning with new neurons, new connections, or both.