Nuclear bomb tests reveal brain regeneration in humans

Nuclear bomb tests carried out during the cold war have had an unexpected benefit.

A radioactive carbon isotope expelled by the blasts has been used to date the age of adult human brain cells, providing the first definitive evidence that we generate new brain cells throughout our lives. The study also provides the first model of the dynamics of the process, showing that the regeneration of neurons does not drop off with age as sharply as expected.

In mammals, most types of brain cell are created at or soon after birth and are never renewed. But studies in rodents and monkeys have shown that in two regions new neurons continue to be created even in adulthood – the hippocampus, which is involved in learning and the formation of new memories, and the olfactory bulb, which processes smell.

However, there has been some controversy over whether the same is true for humans. Fifteen years ago a study found evidence for such neurogenesis in adults up to the age of 72 (Nature Medicine, doi.org/b7hjfz), but the research relied on a chemical called bromodeoxyuridine (BrdU) to label neurons. BrdU was used at the time to track the spread of tumours in people with cancer, but it was banned shortly after and so the study was never repeated, leading some researchers to question the results.

Another study on London taxi drivers suggested that the hippocampus grows with increasing knowledge of the city but this, too, has been controversial.

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