New brain cells in the old stokes debate

People as old as 79 may still generate new brain cells, US researchers said last week, stoking fresh debate among scientists over whether or when our mental capacity ever stops growing.

The report by scientists at Columbia University in New York, published in the journal Cell Stem Cell, runs directly counter to a different study published in Nature last month which found no evidence of new neurons are being created past the age of 13.

While neither study is seen as providing the definitive last word, the research is being closely watched as the world’s population ages and scientists seek to better understand how the brain ages for clues to ward off dementia.

The focal point of the research is the hippocampus, the brain’s centre for learning and memory. Specifically, researchers are looking for the foundations of new brain cells, including progenitor cells, or stem cells that would eventually become neurons.

Using autopsied brain samples from 28 people who died suddenly between the ages of 14-79, researchers looked at “newly formed neurons and the state of blood vessels within the entire human hippocampus soon after death”, said the study.

“We found that older people have similar ability to make thousands of hippocampal new neurons from progenitor cells as younger people do,” said lead author Maura Boldrini, associate professor of neurobiology at Columbia University. “We also found equivalent volumes of the hippocampus across ages.”

The findings suggest that many seniors may retain more of their cognitive and emotional abilities longer than previously believed.

However, Boldrini cautioned that these new neurons might be less adept at making new connections in older people, due to ageing blood vessels.

Animals like mice and monkeys tend to lose the ability to generate new brain cells in the hippocampus with age.

Just how the human brain reacts to ageing has been controversial, though the widely held view is that the human brain does indeed continue to generate neurons into adulthood, and that this “neurogenesis” could one day help scientists tackle agerelated brain degeneration.

A study last month led by Arturo Alvarez-Buylla of the University of California in San Francisco found the opposite, however.

Looking at brain samples from 59 adults and children, “we found no evidence of young neurons or the dividing progenitors of new neurons” in the hippocampi of people older than 18, he said when the study was published.

They did find some in children between birth and one year, “and a few at seven and 13 years of age”, he said.

That study was described by experts as “sobering”, because it indicated the human hippocampus is largely generated during foetal brain development.