Study: Brain neurons don’t keep growing
New research suggests that the human brain does not add more neurons to its circuitry once it has reached maturity.
The work, published in the journal Nature, contradicts a smattering of earlier studies that found that humans did indeed have the ability to add to their neural networks even after they reached adulthood.
Amar Sahay, a professor at the Harvard Stem Cell Institute not involved in the research, said the new findings are sure to make a splash.
“But that’s science,” he said. “It’s not always a straight line from point A to point B. Sometimes it’s a winding road.”
Researchers have known for decades that many animals — including mice, canaries and monkeys — have the ability to produce new neurons over the course of their lives in the process known as neurogenesis.
A small number of papers had indicated adult humans possessed this capability, specifically in an interior region of the brain known as the hippocampus that is associated with memory.
But after examining brain tissue samples from 59 human subjects ranging from a 14-week-old fetus to a 77-year-old man, the authors found neurogenesis drops off considerably in humans after one year of life.
After adolescence, it appears to stop completely.
The findings came as a bit of a shock to the research team from the University of California at San Francisco
“We went into this work thinking we were going to find evidence of neurogenesis because other groups did,” said Mercedes Paredes, an assistant professor of neurology at UCSF and one of the study leaders.
Neurons are the oddly shaped cells that process and transmit information in our brain. Arturo Alvarez-Buylla, the principal investigator of the study, described them as the semiconductors of the brain.
The vast majority of neurons are generated during fetal development, but scientists have shown that in some regions of the brain, new neurons can continue to be made in adult animals.
“It is really a feat of biology,” said Alvarez-Buylla. “The cell has to be born, then migrate and integrate into the tissue, make new extensions to connect with other cells, and then it has to contribute to the brain function.”
Although this process has been well studied in mice, rats and canaries among other animals, only a handful of studies have sought to discover if neurogenesis also occurs in people after childhood.
“It’s tricky,” Paredes said. “It’s hard to study human brain tissue, not only to get the samples, but to know how to analyze them and have confidence in the result.”