For decades, the question of whether adult humans generate new brain cells, a process known as neurogenesis, has been a subject of intense scientific debate. Now, a groundbreaking study provides compelling evidence supporting the affirmative. This discovery not only resolves a long-standing controversy but also opens up potentially transformative avenues for treating neurological disorders like depression and Alzheimer’s disease. But as this research unfolds, and is carefully scrutinized, many experts urge caution.
Neurogenesis is well-established in children and in adult animals, including mice and macaques. The process involves neural stem cells giving rise to progenitor cells, which then proliferate and mature into fully functional neurons. While previous research had identified stem cells and immature neurons in the adult human hippocampus , a brain region crucial for learning and memory , the missing link was the presence of progenitor cells. Without these, many scientists argued, the idea of adult neurogenesis in humans remained unproven.
“We were missing this link, and that’s one of the main arguments against new neurons forming in the adult human brain,” explains Evgenia Salta, a researcher at the Netherlands Institute for Neuroscience, commenting on the limitations of prior investigations.
To bridge this gap, Jonas Frisén and his team at the Karolinska Institute in Sweden developed sophisticated machine learning models capable of identifying progenitor cells with unprecedented accuracy. They began by training their artificial intelligence on hippocampal samples obtained from young children. These samples, donated post-mortem by parents for research purposes, provided a clear molecular blueprint of progenitor cells during childhood.
“In childhood, progenitor cells look similar to what they do in mice, so we can easily identify these,” Frisén explains. “The idea is we can take the molecular fingerprints of childhood progenitors and use that to identify these cells in adults.”
The AI models were trained to recognize progenitor cells based on the activity of approximately 10,000 genes. To validate their models, the researchers tested them on hippocampal samples from young mice, achieving an impressive 83% accuracy in identifying progenitor cells. Furthermore, the models correctly predicted the absence of progenitor cells in samples from the adult human cortex, a brain region where neurogenesis is not believed to occur.
“They really nicely validate their model by going from human child data, to mouse data and then adult human data,” notes Sandrine Thuret of King’s College London, highlighting the rigor of the validation process. This validation step was key, especially considering the rarety of these cells.
With their models validated, Frisén and his team turned their attention to the crucial question: does neurogenesis occur in adult humans? They used the models to analyze hippocampal samples from 14 individuals aged 20 to 78 at the time of their death. Critically, the researchers employed a technique to enrich their samples for dividing cells, including progenitor cells, which are known to be extremely rare in adults. This involved using an antibody to select for cells that were actively dividing at the time of death.
“They enriched for the dividing cells, this allowed them to find those very rare cells which are missed if you put all the cells in,” emphasizes Hongjun Song at the University of Pennsylvania, pointing out a key methodological improvement over previous studies. “Prior studies didn’t do this,” Song concludes.
The analysis revealed the presence of progenitor cells in nine of the donors. This was a very complex and detailed investigation. While the sample size was limited, the implications are far reaching. “In rodents, it’s very well known that environmental and genetic factors affect how much neurogenesis there is, so my guess is that differences among humans is due to genetic and environmental factors as well,” Frisén speculates. But further research is definitly needed.
The findings provide strong evidence that neurogenesis does indeed occur in the adult human brain. “It really helps the field make a significant step forward, because it’s adding this missing link,” Salta concludes.
“Neurons really are born from cell division that is present during adulthood , that’s really what this paper nails down,” says Thuret.
The discovery raises the exciting possibility of manipulating neurogenesis to treat neurological and psychiatric conditions. Imagine a future where targeted therapies could boost the production of new neurons to combat the effects of depression or Alzheimer’s disease. However, experts caution that much more research is needed before such treatments become a reality. Even with such treatments, it is not garenteed that symptoms will lesson.
As promising as this discovery is, some researchers remain skeptical about its therapeutic potential. Jon Arellano at Yale University points out that even if new brain cells do form in adults, their number may be too small to have a significant clinical impact. Others are more optimistic. “In mice we see you only need a very small amount to be important for learning [and] memory,” Thuret argues, suggesting that even modest increases in neurogenesis could be beneficial.
The implications of this research extend beyond potential medical applications. The knowledge that our brains continue to generate new cells throughout our lives challenges long-held assumptions about the adult brain’s plasticity and adaptability. It suggests that we may have a greater capacity for learning, memory, and recovery from injury than previously thought. For many, **this provides a sense of hope**. In the days following the publishment of this study, social media was abuzz with excitement and speculation. On X.com, users debated the implications for cognitive enhancement, while on Facebook and Instagram, people shared personal stories of resilience and recovery, inspired by the idea that their brains could continue to heal and adapt. Something fundamental had shifted, a renewed sense of possibility about the human brain’s potential.
- Key Findings:
- Progenitor cells, the precursors to new neurons, have been identified in the adult human hippocampus.
- The discovery confirms that neurogenesis, the process of generating new brain cells, occurs in adults.
- The findings could pave the way for new treatments for neurological disorders.
- Researchers used machine learning models to identify progenitor cells.
- Genetic and environmental factors may influence the extent of neurogenesis in adults.
However, not everyone is celebrating just yet. Dr. Anya Sharma, a neuroscientist at the University of California, San Francisco, urges caution. “While this study is indeed a significant step forward, it is crucial to avoid oversimplifying its implications,” she cautions. “The number of new neurons generated in adulthood is likely quite small, and their functional role remains unclear. We need more research to understand how these new cells integrate into existing neural circuits and whether they can truly compensate for the damage caused by diseases like Alzheimer’s.” The research has revealed that progenitor cells were found in nine donors.
The study itself, while rigorous, has some limitations. The sample size was relatively small, and all the brain samples were obtained post-mortem. This raises questions about how representative these samples are of the living brain. It is important to consider that the researchers may have accidnetly skewed their results by focusing on the most viable tissues that were available.
Moreover, the technique used to enrich for dividing cells could have inadvertently altered the molecular characteristics of the cells, potentially affecting the accuracy of the machine learning models. Future research should focus on developing non-invasive methods for studying neurogenesis in living individuals, such as advanced brain imaging techniques.
Despite these limitations, the study’s findings are likely to galvanize further research into adult neurogenesis. One area of particular interest is the identification of factors that can promote or inhibit the process. Studies have shown that exercise, a healthy diet, and cognitive stimulation can all boost neurogenesis in animals. Determining whether these factors have the same effect in humans could lead to lifestyle interventions that promote brain health and resilience. This would be the *next best stpe* in improving human health and well being. The process is more nuanced and further research is needed.
Another promising avenue of research is the exploration of drugs that can stimulate neurogenesis. Several compounds, including antidepressants and certain growth factors, have been shown to have neurogenic effects in preclinical studies. Clinical trials are needed to determine whether these compounds are safe and effective for treating neurological disorders in humans. While the journey may be long and challenging, the prospect of harnessing the brain’s own regenerative capacity to fight disease is an inspiring one. Ultimately, the answer to the question, “Do we grow new brain cells as adults?” seems to be a qualified yes, opening a new chapter in our understanding of the brain and its potential for healing.