Scientists Discover a Portion of the Human Brain that Continues to Make New Neurons Well into Adulthood

A small portion of the human brain involved in memory called the hippocampus makes new neurons well into adulthood.

Scientists from Lawrence Livermore National Laboratory made the discovery using data derived from nuclear weapons testing of the 1950s and 1960s.

Specifically, the team used carbon-14 dating techniques to date cells in the hippocampus the same way archaeologists date artifacts.

The method is based on the spike in global levels of the isotope as a result of extensive above-ground nuclear weapons testing during the Cold War. Because plants absorb carbon-14 via carbon dioxide during photosynthesis, animals that eat them also take in radioactive carbon.

For this reason, the researchers argue, the level of carbon-14 in the human body reflects that of the atmosphere. Then, when a cell divides, newly-synthesized DNA integrates a trace amount of the isotope that is proportional to the level of the environment at the time.

Ultimately, what this means is the radioactivity of a cell nucleus can be used as a time stamp of the cell’s genesis.

Using middle-aged mice, the scientists found that one-third of hippocampal neurons are subject to exchange with an annual turnover rate of 1.75 percent in adults, meaning 1,400 new neurons are added every day. Only a modest decline was present in older individuals.

Seeing this, the team tested tissue from postmortem hippocampi of human subjects.

The results, said Bruce Buchhoz who performed the radiocarbon dating, led the researchers to “conclude that neurons are generated throughout adulthood and that the rates are comparable in middle-aged humans and mice, suggesting that adult hippocampal neurogenesis may contribute to human brain function.

The discovery, the researchers believe, may have profound impacts on human behavior and mental health and supports the importance of investigating the therapeutic potential of applying adult neurogenesis, the process by which neurons are generated from neural stem and progenitor cells, to the treatment of age-related cognitive disorders.

The research appeared in the June 6 edition of the journal Cell.