"That showed us that we do have the ability to detect them, even in adult cases as well," Paredes said.
After they were convinced that there was nothing wrong with their detection technique, the authors set about making sense of their data.
Their research had shown that there are significantly fewer immature neurons in the 1-year-old brain, compared to earlier stages of life. In addition, the oldest sample where they still saw evidence of young neurons came from a 13-year-old."
"This was a very extensive and detailed undertaking that is critical to the field," Sahay said.
While the authors have some thoughts as to why previous work on neurogenesis in humans do not agree with their findings, they also say that more work needs to be done to understand exactly what is going on in the human brain.
"There are only a handful of studies out there that have already attempted to look at this, and they came to wildly different conclusions," said Shawn Sorrell, a senior researcher in Alvarez-Buylla's lab who co-led the work. "We felt there was room for another voice on this and another set of data that could provide more clues to what is happening in humans."
He added that reconciling all the various findings is "part of the scientific enterprise."
One of the reasons scientists are so interested in the possibility of adult human neurogenesis is that it suggests one way that the human brain might repair itself, said Alvarez-Buylla.
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"A new neuron made in the brain would be an incredible tool to fix brains," he said.
But both the authors and other experts in the field say the new work is no reason to give up on the dream that neurogenesis could one day be harnessed to help humans.
"The takeaway is not that it is pointless to study neurogenesis," Sahay said. "Neuroscience is replete with examples of how to restore plasticity in the brain."
Perhaps future work will reveal what mechanisms animals are using to generate new neurons into adulthood, as well as how the human brain might be taught to master this challenging feat.
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