From The Quarterly, Fall 2013

Researchers used a very innovative methodology to quantify, for the first time, the number of new neurons formed in the human brain throughout life (a process called “neurogenesis”). The work supports the view that the brain’s capacity for change over time––its “plasticity”––persists throughout life, supporting cognitive functions and offering the potential for targeted treatments to recover healthy brain function in patients with a broad range of psychiatric disorders.



The current study was published in the June 6th issue of the journal Cell by 2007 NARSAD Young Investigator Grantee Kirsty L. Spalding, Ph.D., of Sweden’s Karolinska Institutet, and colleagues. Dr. Spalding and team found physical evidence in the postmortem brains of people aged 19 to 92 by identifying the “birth date” of neurons in the brain samples. They discovered that new neurons are born in the brain’s hippocampal region over the lifespan and estimate that the average adult generates 1,400 new hippocampal neurons every day in the prime of life, a rate that does not vary greatly over time and corresponds with a turnover of almost two percent every year. This turnover does not occur across the brain. Neurogenesis was confirmed in a single brain region, the hippocampus, and only in one subregion within it called the dentate gyrus. Reduced neurogenesis in this region is believed to be associated with depression, bipolar disorder, schizophrenia and some anxiety disorders.



A particularly novel method was used to obtain this important result. Beginning in 1945 with the birth of the atomic age, and lasting until 1963, nuclear weapons were tested openly at above-ground sites. This resulted in increased atmospheric levels of Carbon-14 (14C). The Karolinska team reasoned they could “carbon-date” neurons in preserved postmortem brains since the DNA of these and all cells are essentially “stamped” with 14C (and other elements in the atmosphere) at the time of their birth. 14C levels spiked in 1963 and have fallen steadily ever since at a known rate, making it possible to determine the birth date of neurons based on 14C levels in a cell’s DNA. The team has used this methodology over the past decade to test a variety of cells, including fat cells, and was able to refine it to a point that it became sensitive enough to measure tiny amounts of 14C in small hippocampus samples.  



Because the hippocampus is a region heavily implicated in many brain and behavior disorders, the new findings offer exciting proof of the brain’s potential to recover from dysfunction throughout life. For researchers working on new treatment approaches to promote neuroplasticity and neurogenesis, this new work offers crucial evidence necessary for their further development.