Recent research has provided compelling evidence that the human brain is capable of generating new neurons well into adulthood, a discovery that could potentially resolve decades of debate on the subject.
This phenomenon, referred to as “neurogenesis,” primarily occurs in the hippocampus, an essential region of the brain associated with learning, memory, and emotions.
Marta Paterlini, co-lead author of the study and a researcher at the Karolinska Institute in Stockholm, stated, “In short, our work puts to rest the long-standing debate about whether adult human brains can grow new neurons.”
Experts in the field have corroborated the study’s findings, asserting that it presents substantial evidence in favor of adult neurogenesis.
Dr. Rajiv Ratan, CEO of the Burke Neurological Institute at Weill Cornell Medicine, emphasized that while no single study provides absolute proof, this research supports the idea that stem cells and precursors to new neurons exist in the adult human brain and are proliferating.
He described the study as a valuable opportunity for the clinical neuroscience community, noting, “This is a perfect example of great science teeing up the ball for the clinical neuroscience community.”
To conduct their research, the team utilized advanced techniques, including single-nucleus RNA sequencing and machine learning, to analyze brain tissue samples sourced from international biobanks. RNA, a counterpart to DNA, indicates which genes are active within cells, while machine learning offers powerful tools to process large datasets.
Since the 1960s, it has been established that new brain cells are produced in the dentate gyrus of the hippocampus in various animal species, such as mice and rats, throughout their lives. However, obtaining quality brain tissue samples from adult humans poses significant challenges.
Paterlini noted that human tissue often comes from autopsies or surgeries, and factors like handling, the time before fixation in preservatives, the chemicals used, and the slicing thickness can obscure the presence of new cells.
The incorporation of new technologies allowed the research team to overcome these obstacles. They examined over 400,000 individual cell nuclei from the hippocampus of 24 individuals and also analyzed 10 additional brains using alternative methods. The samples encompassed a wide age range, from zero to 78 years old, including six children and four teenagers.
By employing two cutting-edge imaging techniques, the researchers successfully mapped the locations of newly formed cells within the tissue. They noted clusters of dividing precursor cells situated adjacent to fully developed neurons, precisely where previous animal studies have identified adult stem cells.
Paterlini stated, “We didn’t just see these dividing precursor cells in babies and young kids — we also found them in teenagers and adults. These include stem cells that can renew themselves and give rise to other brain cells.”
The new technologies allowed the researchers to identify new brain cells in various developmental stages—insights that would have been difficult to achieve just a few years prior, according to Ratan.
The team also employed fluorescent markers to distinguish proliferating cells, enabling them to create a machine learning algorithm capable of identifying likely neurogenic stem cells based on insights gathered from previous rodent studies. Ratan referred to this as a “clever approach” that effectively addressed the complexities associated with investigating brain cell formation in older adolescents and adults.
The analysis revealed that while children’s brains exhibited a greater production of new cells compared to those of adolescents and adults, a notable nine out of fourteen adult brains studied with one technique showed signs of neurogenesis. Furthermore, all ten adult brains examined with a second technique demonstrated the presence of new cells.
Paterlini commented on the few adult brains without documented new cell growth, stating that it is premature to draw definitive conclusions about the differences observed among the adult samples.
Looking ahead, the researchers aim to investigate whether the generation of new brain cells in adults is a response to neurological conditions such as Alzheimer’s disease, or if adult neurogenesis signifies robust brain health. Dr. W. Taylor Kimberly, chief of neurocritical care at Massachusetts General Brigham, not involved in the study, expressed that understanding these cells could facilitate tracking their progression over time and their relation to various diseases.
He envisions research that juxtaposes dementia patients with “super agers,” individuals who exhibit exceptional cognitive resilience in old age. Identifying potential links between neurogenesis and disease could pave the way for novel treatments.
Paterlini articulated the transformative implications of their findings, stating, “Although the precise therapeutic strategies in humans are still under active research, the very fact that our adult brains can sprout new neurons transforms how we think about lifelong learning, recovery from injury and the untapped potential of neural plasticity.”
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