1960s nuclear testing helps determine if adult brains generate new neurons

Washington: The birth of new neurons in the adult brain sharpens memory in rodents, but it has long been debated if the same holds true for humans.

A study reveals that a significant number of new neurons in the hippocampus - a brain region crucial for memory and learning - are generated in adult humans.

The findings suggest that new neurons are born daily in the human hippocampus, offering the tantalizing possibility that they may support cognitive functions in adulthood.

Senior study author Jonas Frisen of the Karolinska Institute said that it was believed that people are born with a certain number of neurons, and that it is not possible to get new neurons after birth.

He said that they have provided the first evidence that there is substantial neurogenesis in the human hippocampus throughout life, suggesting that the new neurons may contribute to human brain function.

Frisen and his team developed an innovative method for dating the birth of neurons.

This strategy took advantage of the elevated atmospheric levels of carbon-14, a nonradioactive form of carbon, caused by above-ground nuclear bomb testing more than 50 years ago.

Since the 1963 nuclear test ban treaty, atmospheric levels of "heavy" carbon-14 have declined at a known rate.

When we eat plants or animal products, we absorb both normal and heavy carbon at the atmospheric ratios present at that time, and the exact atmospheric concentration at any point in time is stamped into DNA every time a new neuron is born.

Thus, neurons can be "carbon dated" in a similar way to that used by archeologists.

By measuring the carbon-14 concentration in DNA from hippocampal neurons of deceased humans, the researchers found that more than one-third of these cells are regularly renewed throughout life. About 1,400 new neurons are added each day during adulthood, and this rate declines only modestly with age.

A study has been published in the journal Cell.