The authors suggest that previous reports of adult cortical neurogenesis might be technical artifacts.
The authors first established that there is a relationship between the C14 content of DNA and the atmospheric C14 in the local area when that DNA was made.
Unlike many other macromolecules in a cell, DNA is chemically stable once laid down, so its C14 levels are not expected to change even if the DNA ages.
While they found that total DNA C14 levels in these samples are younger than the donor, indicating cell turnover, they found that the cortical neurons are always as old as the individual donor.
This was true for people born prior to, during, or after the spike in atmospheric C14.
The development and application of new methods is clearly needed to resolve the debate about adult neurogenesis in neocortex and other “non-neurogenic” brain regions.
The recent publication in Cell by Spalding and colleagues (29) reported the use of a novel and highly innovative method to search for adult neurogenesis in human postmortem brain tissue.
Because of its extremely long half-life (over 5,000 years), carbon 14 content has typically been used to date only very old artifacts or fossils.
The method has traditionally failed to resolve dates of samples that differ in age by less than a few hundred years—accurate enough perhaps to date the youngest and oldest parts of the most ancient redwood trees, but not to tell how many newborn cells might be present in the human brain.
As Paola Arlotta and Jeffrey Macklis from the Harvard Medical School write in an accompanying Cell perspective, historically, methods to label newborn cells, such as the use of tritium, bromodeoxyuridine (Brd U), or other halogenated urides, are toxic and cannot be used in humans, so the strategy developed by Spalding and colleagues “enables a more direct understanding of cell turnover, aging, and lifespan throughout the human body and those of other long-lived animals.” There is one small caveat, however.