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.
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