Brain cell renewal lifelong
Older people are often characterized as forgetful, but that isn’t necessarily the case. New Swedish research has found that our brains generate those little gray cells every day until we die.
The study, from Stockholm’s Karolinska Institute, investigated how many neurons, or nerve cells, are generated in the hippocampus. That’s the part of the brain used for memory and the ability to learn.
Studies on mice have shown that they continue to generate these cells, but the human aspect has been debated. Jonas Frisén, professor in stem cell research at Karolinska, led the team. He says it was long thought that humans were born with a certain number of neurons, and it was impossible to get more after birth.
Writing in the latest issue of the journal “Cell”, Frisén and his team say they’ve now found that the human brain generates around 1400 neurons every day, and the process goes on until we die.
The scientists used radioactive carbon-14 dating, the same method used to date archeological finds, to measure when neurons have been created. What made that approach possible were the atmospheric nuclear bomb tests of the 50’s and 60’s, which deposited more carbon-14 into the air.
“When new DNA is created,” Professor Frisén tells Swedish Radio’s Science Department, “carbon-14 is included in the DNA-chain with a concentration corresponding to that in the atmosphere at that time. So there’s a kind of date-stamping in the cell DNA.”
The research team took test samples from the hippocampus from 55 people who had died, between the ages of 19 and 92. Measuring the carbon-14, they found that more than one-third of the neurons in the hippocampus are regularly renewed throughout life. But this only happens in the hippocampus. Similar studies have found no such renewal in the cortex or the part of the forebrain where smells are perceived, for example.
Studies do show, however, that the growth of brain cells is stimulated by exercise and intellectual challenges.
“If you put mice on a hamster wheel,” Jonas Frisén says, “their voluntary running leads to nearly a doubling of their nerve cell renewal.”
Professor Frisén says their discovery can lead to future treatments for mental disorders, like depression, as there is a lot of evidence that there is a link between the growth of new nerve cells and psychological well-being.