New research suggests that the human brain does not add more neurons to its circuitry once it has reached maturity.
The work, published Wednesday in 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 who was 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 that adult humans also possessed this capability, specifically in an interior region of the brain known as the hippocampus that is associated with memory.
However, after examining brain tissue samples collected from 59 human subjects ranging in age from a 14-week-old fetus to a 77-year-old man, the authors found that 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, 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 leaders of the study. "So we were actually surprised when we didn't see any evidence of it in our adult samples."
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.