Study Finds Adult Neurogenesis Occurs in Human Hippocampus

A recent study published in Science provides new evidence that neurons continue to form in the hippocampus, the brain’s memory center, well into late adulthood. This research, conducted by a team at Karolinska Institutet, addresses a longstanding question about the adaptability of the human brain.

The hippocampus is crucial for learning, memory, and the regulation of emotions. In 2013, Jonas Frisén’s research group at Karolinska Institutet demonstrated that new neurons could form in the adult human hippocampus by measuring carbon-14 levels in DNA from brain tissue, allowing them to determine when cells were generated.

Despite these findings, the extent and significance of adult neurogenesis have remained topics of debate, particularly concerning whether neural progenitor cells—the precursors to new neurons—exist and divide in adults. According to Dr. Frisén, “We have now been able to identify these cells of origin, which confirms that there is an ongoing formation of neurons in the hippocampus of the adult brain.”

In the new study, researchers analyzed brain tissue from individuals aged 0 to 78 using samples from multiple international biobanks. They employed single-nucleus RNA sequencing to assess gene activity in individual cell nuclei and flow cytometry to examine cell properties. Machine learning techniques enabled the identification of various stages of neuronal development, from stem cells to immature neurons, with many cells observed in the process of division.

To pinpoint the location of these cells, the team used RNAscope and Xenium, two methods that reveal where specific genes are active within tissue. These approaches confirmed that new neurons are formed in the dentate gyrus, a region of the hippocampus involved in memory, learning, and cognitive flexibility. 

The study found that the progenitor cells in adult humans are similar to those in mice, pigs, and monkeys, though some differences in gene activity were noted. There was also significant variation between individuals in the number of neural progenitor cells present.

Jonas Frisén noted, “This gives us an important piece of the puzzle in understanding how the human brain works and changes during life. Our research may also have implications for the development of regenerative treatments that stimulate neurogenesis in neurodegenerative and psychiatric disorders.”