Residue from Nuclear Bomb Testing Shows That Contrary to Earlier Reports, Neurogenesis Occurs in the Brains of Adults
In 2013 we reported that according to Pasco Rakic, professor of neuroanatomy at Yale University, neurogenesis (the production of new neurons) occurs only in rodents, and not in any significant amount in the brains of adult primates. However, a new carbon-dating procedure shows that the adult human brain does actually continue to create new neurons.
According to an article by Spalding et al. published more recently in the journal Cell, such neuroplasticity occurs to a much greater degree than previously thought. The authors base their research on levels of carbon isotope 14 (14C) that were released into the atmosphere during aboveground nuclear bomb tests between 1945 and 1963. Dividing cells require carbon, so the 14C released into the atmosphere during the era of nuclear testing made its way into the cells of people who were alive at the time. Levels of 14C that were incorporated into the DNA of dividing cells correlate with levels of 14C in the atmosphere at the time the cells divided, and since carbon levels have declined at a predictable rate since the nuclear tests, measuring the 14C in cells can show how old they are.
Spalding et al. show that neurogenesis in humans occurs only in the hippocampus. They found evidence that a subpopulation of hippocampal neurons continually renews itself at a rate of about 700 new neurons per day, while other hippocampal cells are non-renewing. The annual turnover rate of about 1.75% is the same for men and women and declines slightly with age.
The researchers were able to determine that the renewing cells play an important role in certain types of brain function. Long-term potentiation, the process by which learning and memory can occur, depends heavily on new cells produced in the part of the hippocampus knows as the dentate gyrus.
