Where in the brain does adult neurogenesis happen, and how much is there?
New neurons are born in two specific 'neurogenic niches' in the adult brain: the subgranular zone of the dentate gyrus in the hippocampus and the subventricular zone of the lateral ventricle, from which they migrate to the olfactory bulb [3][6]. The hippocampus is the region most studied in humans because of its role in learning and memory.
However, the rate of new neuron production in adult humans is very low. A 2024 study using spatial transcriptomics on postmortem brain tissue from males aged 2 to 43 years found 'very few cells expressing neural stem cell and proliferative markers' in the dentate gyrus at any age [1]. In contrast, they did find a 'substantial number' of cells expressing DCX, a marker of immature neurons, at all ages, though most of these cells had an inhibitory (GABAergic) phenotype rather than becoming excitatory granule cells [1]. This suggests that while the machinery for neurogenesis exists, the actual production of new functional neurons is minimal in adulthood.
Does age or disease affect adult neurogenesis?
Yes, both aging and neurodegenerative diseases dramatically reduce the brain's ability to generate new neurons. The 2024 study found that even by middle age (mean 43.5 years), the number of neural stem cells and dividing cells was extremely low [1]. This aligns with the general understanding that neurogenesis declines with age due to depletion of the neural stem cell pool [3].
Neurodegenerative diseases make things worse. A 2021 study examined postmortem brain tissue from patients with Alzheimer's, Parkinson's, Huntington's, and other conditions and found that adult-born dentate granule cells showed 'abnormal morphological development' and changes in differentiation markers [4]. The ratio of quiescent (resting) to proliferating neural stem cells was shifted, and the supportive 'neurogenic niche' (including microglia and blood vessels) was damaged [4]. This means that in diseases that already impair memory and cognition, the brain's limited capacity for self-repair is further compromised.
Can we boost adult neurogenesis to repair the brain?
Researchers are actively exploring ways to stimulate neurogenesis for brain repair after injury or in neurodegenerative disease, but the approaches are still experimental and face major hurdles. After a stroke or traumatic brain injury, neurogenesis is naturally stimulated, but the resulting repair is 'usually insufficient' to restore function [2].
Three main strategies are being investigated: (1) stimulating the brain's own neural stem cells with drugs or molecules, (2) transplanting exogenous stem cells, and (3) converting other brain cells (like glia) into neurons. Each has drawbacks. For example, stem cell transplantation shows promise in animals but has 'poor long-term survival and inefficient neuronal differentiation' in humans [2]. The glia-to-neuron conversion strategy is 'still controversial' [2]. A 2026 review notes that while lifestyle interventions like exercise and cognitive training can enhance neurogenesis in animals, translating these to robust, clinically meaningful effects in humans remains a challenge [5]. So while the potential is exciting, we are not yet at the point where we can reliably boost neurogenesis to repair a damaged human brain.
Sources used in this answer
Spatial transcriptomic analysis of adult hippocampal neurogenesis in the human brain
Found very few neural stem cells or proliferating cells in the human dentate gyrus from childhood to middle age, but a substantial number of cells expressed the immature neuron marker DCX, mostly with an inhibitory phenotype.
Versatile strategies for adult neurogenesis: avenues to repair the injured brain
Concluded that while endogenous neurogenesis is stimulated by brain injury, it is insufficient for repair; exogenous stem cell transplantation and glia-to-neuron conversion are promising but face significant challenges.
Adult neurogenesis
Confirmed that adult neurogenesis is restricted to the subgranular zone of the dentate gyrus and the subventricular zone, and that it declines with age due to neural stem cell depletion.
Impact of neurodegenerative diseases on human adult hippocampal neurogenesis
Found that adult hippocampal neurogenesis is disrupted in neurodegenerative diseases (Alzheimer's, Parkinson's, Huntington's), with abnormal development of new neurons and damage to the neurogenic niche.
Adult Neurogenesis: Cellular Mechanisms, Regulatory Pathways, and Therapeutic Prospects in Neurodegenerative Diseases
Noted that evidence for persistent, functionally relevant adult neurogenesis in humans is limited and heterogeneous, and that therapeutic strategies (exercise, drugs, stem cells) face translational challenges.
Adult Neurogenesis: A Review of Current Perspectives and Implications for Neuroscience Research
Summarized that adult neurogenesis occurs in the subgranular zone and subventricular zone, is vital for neural plasticity, and that advanced imaging techniques are aiding its study.