Nuclear Bomb Tests Shed Light On Neurogenesis In The Human Hippocampus
June 9, 2013

New Evidence Suggests Neurons Continue To Grow In Adult Brains

redOrbit Staff & Wire Reports — Your Universe Online

Despite a longstanding view that an adult brain is incapable of generating new neurons, researchers from the Karolinska Institute in Sweden have discovered that a person´s hippocampus is constantly generating more of them — and their discovery comes thanks in part to early Cold War-era nuclear bomb tests.

The research, which has been published in the journal Cell, calculated the growth of new cells in adult brains using a carbon isotope that was picked up by humans from the fallout of above-ground nuclear testing during the 1940s, 1950s and 1960s, explains Geoffrey Mohan of the Los Angeles Times.

“It´s been hard to tell how many neurons are generated and if they are viable cells, because humans are not fond of having their brains removed. So a lot of the research uses mice and other animals,” Mohan said. “Enter dead people and the carbon-14 isotope. The latter is a ℠heavy´ carbon variant produced in nuclear reactions, such as blowing up a nuclear device out in the Pacific Ocean, a practice that was banned by treaty in 1963.”

The Karolinska Institute researchers, led by assistant professor Kirsty Spalding, analyzed the donated brains of deceased men and women. According to Time´s Michael D. Lemonick, they discovered that their hippocampuses had gained about 700 and perhaps as many as 1,400 new neurons each day throughout their adult lives.

“That being the case, you might reasonably wonder why our ability to learn and remember declines with age, given that our central memory organ is constantly growing new cells,” Lemonick said. “Unfortunately, the rate of renewal doesn´t make up for the rate of cell death, which is also going on constantly — and the new cells live for a far shorter time than our original hippocampal neurons.”

“Still, even that limited regeneration can provide a cognitive boost,” the Time reporter said.

The majority of those cells grow in a region of the hippocampus known as the dentate gyrus, and that area could develop unique solutions to computational problems found in parts of the brain responsible for learning, memory, and other important cognitive functions. Of course, this is only speculation at this point, Lemonick noted, but the researchers are confident that their work will help establish continued neuron growth in the adult brain.

“It was thought for a long time that we are born with a certain number of neurons, and that it is not possible to get new neurons after birth,” senior author Jonas Frisén of the Karolinska Institute told “We provide 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.”