For decades, we all thought that the human brain stopped forming new neurons after childhood, but a landmark new study subverted this dogma, providing the clearest evidence yet that the brains of older people continue to form new neurons.
In the early 1900s, Santiago RamónY Cajal, the first scientist who detailed the structure of neurons and was recognized as the father of modern neuroscience, proposed that the adult nervous system has almost no regenerative ability, which guided the main research context of neuroscience in the following years. Although neuroscientists later realized that the brain will continue to develop after birth, this is different from brain nerve regeneration. The brain matures around the age of 30, and most neuroscientists still believe that the brain nerve regeneration process ends in childhood.
Later, more and more research began to challenge authority. For example, some researchers observed from animal experiments that the centers of Dentate gyrus (DG) in mice, rats, and non-human primates will produce new brain neurons.
In 2013, a team led by Jonas Frisén, a neuroscientist at the Karolinska Institute in Sweden, assessing neuronal age with innovative carbon dating technology, publishing evidence that adult hippocampus can form new neurons, making headlines at the time, but some neuroscientists remained skeptical and unconvinced.
Adult brain tissue samples are basically obtained from autopsy or surgery, and the sample treatment method – how long before preservatives are put, chemicals used, slice thickness, etc., may make it difficult to detect new cells. Therefore, it is still very challenging to obtain high-quality adult brain tissue samples for research. For example, in the spring of 2018, two different nerve regeneration studies published only one month later came to completely opposite conclusions.
Recently, the Karolinska Academy team has used new technologies to overcome challenges, with clear evidence that the adult brain still carries neural stem cells that grow and divide eventually become new mature neurons.
Newborn nerve cells originate from the brain region responsible for memory
If the brain continues to grow new neurons as we age, we should be able to discover neural progenitor cells, but there is no direct evidence in the past. In order to find these cells, the team combined a variety of advanced methods to clarify the characteristics of individual brain cells, track the expression genes of single-cell nucleus, and analyzed post-mortem brain samples between 0 and 78 years old.
Overall, the researchers examined more than 400,000 independent nuclei from these samples and found that despite differences between individuals, nerve cells at different developmental stages were identified, while confirming that the neonatal nerve cells originated from the dentate gyrus within the hippocampal gyrus.
The hippocampus gyrus is part of the brain’s limbic system and plays an important role in short-term memory, long-term memory, spatial positioning and other functions. During the memory consolidation process, the hippocampus gyrus helps to stabilize the storage of new memories in the long-term memory area of the cerebral cortex, while the dentate gyrus is part of the hippocampus structure.
This study found clear evidence of nerve regeneration, which could end the long-term debate on whether new neurons can grow in adult brains. What is particularly interesting is the obvious differences between individuals. The researchers said that some adult brain tissue samples are rich in neural progenitor cells, but some adults are relatively few, which may help explain the different levels of risk of people suffering from neurological and psychological diseases.
If you can find safe ways to improve the growth capacity of new nerve cells in the brain in adults, you can try to treat related diseases, such as Alzheimer’s disease.
The new paper is published in the journal Science.
(First picture source: pixabay)
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