A study published in the latest issue of Science provides compelling evidence that the hippocampus, the brain region in charge of memory, can continuously generate new neurons in adulthood and even old age. Conducted by Sweden's Karolinska Institutet, this research addresses a core long-standing controversy: whether the adult human brain retains plasticity.
The hippocampus is a crucial brain region for learning, memory, and emotional regulation. As early as 2013, a high-impact study led by Professor Jonas Frisén from Karolinska Institutet found that new neurons can still be generated in the adult hippocampus. They inferred the timing of cell formation by measuring the carbon-14 content in brain tissue DNA.
However, the scientific community has remained contentious due to the lack of direct evidence for the existence of "neuronal precursor cells" in the adult human brain—these are the source cells that generate new neurons.
In this new study, the team analyzed brain tissues from individuals aged 0 to 78 from multiple international biobanks. They employed a method called "single-nucleus RNA sequencing" to analyze gene activity in individual cell nuclei and combined it with flow cytometry to study cell characteristics. By introducing machine learning algorithms, they tracked the development of neurons from stem cells to immature stages and identified multiple cell subpopulations that are still in a dividing state.
To locate these cells, the team used two spatial transcriptomics techniques, RNAscope and Xenium, to visualize the locations of active genes in the tissue. The results showed that these newly generated cells are concentrated in the "dentate gyrus" of the hippocampus, a key structure responsible for memory formation, learning, and cognitive flexibility.
The study revealed that the precursor cells of adult human neurons are similar in many aspects to those of mammals such as mice, pigs, and monkeys, but there are differences in gene activity. Additionally, there are significant individual variations—some adult samples have an abundance of neural precursor cells, while others have nearly zero.
Frisén pointed out that this research provides a crucial piece of the puzzle for understanding how the human brain changes and adapts throughout life. The findings also offer new ideas for regenerative therapies for neurodegenerative and mental disorders, such as repairing brain function by stimulating neural regeneration mechanisms.