Scientists have found at least a sliver of a silver lining in the radioactive nuclear bomb tests conducted between 1945 and 1963. Researchers were able to “time-stamp” the age of cells as a result of the testing.

A recent study uses the method to offer further proof that adults form new neurons in the hippocampus every day.

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Researchers used carbon isotope 14, which was released into the atmosphere during bomb tests, to time-stamp the age of cells, Gerd Kempermann writes in a Science article published today. Carbon isotope 14 peaked in the Earth’s atmosphere during the above-ground bomb testing, and the isotope made its way into the DNA of all the cells that were dividing at the time.

“There are few positive things to be said about above-surface nuclear bomb tests, but one of their most unexpected fallouts will be the proof of neurogenesis in the adult human brain,” Kempermann wrote. “The long-awaited, more direct proof has finally been provided by (the authors) through an ingenious approach.”

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Because the amount of carbon isotope 14 in one’s chromosomes correlates with the levels of carbon isotope 14 in the atmosphere at the time of cell division, the researchers measured carbon isotope 14 in the DNA to determine the age of the cell. Using a modeling approach, they determined that 1/3 of adult neurons in the hippocampus turn over every day, meaning about 700 new neurons are created on a daily basis.

It’s unclear how — or even whether — new neurons affect brain function, but it’s possible they could contribute to everything from learning and memory to the shaping of personality, Kempermann wrote.

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