Yes, your brain can make new neurons, a process called neurogenesis. But the extent to which this happens in adult humans is one of the most hotly contested questions in neuroscience. The best evidence points to new neuron production occurring in at least two specific brain regions, though how much it continues past childhood and whether you can meaningfully boost it remain subjects of genuine scientific disagreement.
Where New Brain Cells Are Born
New neurons arise from stem cells in two specific zones. The first is the subgranular zone, nestled inside the hippocampus, the brain’s memory hub. The second is the subventricular zone, lining the walls of fluid-filled chambers deep in the brain called the lateral ventricles. These two areas are sometimes called “neurogenic niches” because they maintain the rare conditions needed for stem cells to divide and produce new neurons throughout life, at least in many animal species.
The hippocampus gets the most attention because of its role in learning, memory, and mood regulation. In that region, stem cells divide roughly three times over the course of a week, producing about a dozen precursor cells each. Around 80% of those precursors go on to become neurons. The rest become support cells called astrocytes. New neurons are added to the inner surface of the hippocampus’s granule cell layer, the same spot where older neurons naturally die off. This isn’t a wholesale replacement of the entire layer. It’s more like selective patching.
The Scientific Debate Over Adult Neurogenesis
For decades, textbooks stated that humans are born with all the brain cells they’ll ever have. That idea was first seriously challenged in 1998, when researchers detected newly born neurons in the hippocampus of cancer patients aged 58 to 72. Later studies using radioactive carbon dating of neuronal DNA confirmed the presence of adult-born neurons in both the hippocampus and the subventricular zone. The field seemed to converge on the idea that hundreds of new neurons could be added to the adult hippocampus every day.
Then, in 2018, two high-profile studies came to opposite conclusions. A team led by Maura Boldrini at Columbia examined brains from people aged 14 to 79 who had no psychiatric illness. They found that while certain stem cell populations declined with age, the number of immature neurons and mature granule neurons did not significantly drop, even in older adults. Around the same time, Arturo Alvarez-Buylla’s group at UC San Francisco analyzed a larger set of hippocampal samples and reported that neurogenesis drops sharply during the first year of life, with only a few isolated young neurons visible by ages 7 and 13. In adults aged 18 to 77, they could not detect young neurons at all.
How can two credible labs reach such different answers? Technical differences matter enormously. The proteins used to tag young neurons degrade quickly in postmortem tissue, and how long a brain sits before preservation affects what researchers can detect. Boldrini’s group also noted that missing information about psychiatric diagnoses and medications in the other study’s subjects could have skewed the results, since both factors selectively affect neurogenesis. The debate is far from settled, but most researchers accept that some degree of new neuron production continues in the adult human hippocampus, even if it’s far less robust than in rodents.
What New Neurons Actually Do
New hippocampal neurons aren’t just extras filling empty seats. They play a specific role in pattern separation: the ability to distinguish between similar but different experiences. Think of parking in a large garage every day. Pattern separation is what lets you remember where you parked today versus yesterday, even though the two memories are nearly identical. When researchers blocked new neuron production in mice by targeting the hippocampus with radiation, the animals lost the ability to make fine spatial discriminations, though they could still handle large, obvious differences. Increasing neurogenesis had the opposite effect, improving the animals’ ability to tell similar situations apart.
New neurons in the olfactory system play a parallel role, helping distinguish between similar smells. Together, these findings suggest that adult-born neurons serve as fine-tuning instruments, sharpening the brain’s ability to encode new contextual and sensory information rather than simply adding raw processing power.
Exercise Is the Strongest Known Booster
Aerobic exercise is the single most well-supported way to promote new neuron growth. The mechanism centers on a protein called BDNF (brain-derived neurotrophic factor), the most abundantly expressed growth factor in the brain. When you exercise, your muscles release signaling molecules that cross the blood-brain barrier and trigger BDNF production in the hippocampus. BDNF then binds to receptors on hippocampal neurons, activating cascades that promote new cell survival, differentiation, and stronger nerve transmission.
In mice given running wheels, BDNF levels in the hippocampus rose after just a few days of voluntary exercise and stayed elevated for weeks, with corresponding increases in the BDNF protein itself. Mice injected with endurance-related factors from skeletal muscle showed elevated hippocampal neurogenesis and better spatial memory, even without exercising. In humans, aerobic exercise has been shown to increase BDNF gene expression in the hippocampus. Because BDNF also promotes the survival of existing neurons and strengthens the connections between them through a process called long-term potentiation, the cognitive benefits extend well beyond just adding new cells.
Diet and Calorie Restriction
What you eat also influences new neuron production, though the evidence is strongest in animal models. Rodents fed calorie-restricted diets consistently show higher rates of hippocampal neurogenesis than those eating freely, likely through a BDNF-mediated pathway. Omega-3 fatty acids and certain plant compounds called polyphenols have also shown positive effects. A diet enriched in both polyphenols and polyunsaturated fatty acids increased the number of newly generated cells in the hippocampus of mice after 40 days, with significantly more cells expressing markers of young neurons.
Specific polyphenols that have shown promise include compounds found in green tea, turmeric, red grape skin, blueberries, and cocoa. In one study, aged rats treated for four weeks with a combination of blueberry and green tea polyphenols plus the amino acid carnosine showed increased neural stem cell proliferation and better spatial memory, along with reduced brain inflammation. Low concentrations of the turmeric compound curcumin stimulated stem cell differentiation into neurons both in lab dishes and in living mice. These are animal findings, and the doses used don’t always translate directly to humans, but the consistency across multiple compounds and studies is notable.
Chronic Stress Works Against You
If exercise and good nutrition are accelerators, chronic stress is the brake. Stress hormones called glucocorticoids (cortisol in humans, corticosterone in rodents) suppress both the proliferation of new cells and the survival of young neurons in the hippocampus. This effect holds regardless of sex or reproductive status.
The mechanism is somewhat indirect and still not fully understood. New stem cells and young precursor cells don’t actually carry many receptors for stress hormones during their earliest stages. They gain those receptors only after about four weeks of maturation. This means the damage probably happens through neighboring mature neurons that do have stress hormone receptors. When cortisol binds to those mature cells, it may alter the local chemical environment in ways that make it harder for new neurons to survive. Stress hormones might also change the inputs that mature neurons send to their younger neighbors, creating a less hospitable environment for growth.
The Connection to Depression and Mood
The relationship between neurogenesis and depression has fueled one of the more intriguing theories in psychiatry. Common antidepressants, particularly SSRIs, increase the proliferation and survival of new neurons in the hippocampus after about 14 or more days of treatment, a timeline that roughly matches the well-known delay before these medications start working clinically. Shorter treatment periods don’t produce the same neurogenic effect. Mood stabilizers like lithium and valproate have been shown to markedly enhance both cell proliferation and survival as well.
Antidepressants also boost BDNF expression in the hippocampus, creating a similar molecular environment to what exercise produces. This led to the “neurogenesis hypothesis of depression,” which proposes that reduced new neuron production contributes to depressive symptoms and that restoring it is part of how treatments work. The reality is more nuanced. Not every study finds that stress reduces neurogenesis, and not every antidepressant trial shows increased new neuron production. The effect appears to depend on the type of stress, the specific brain region examined, and individual differences. Neurogenesis is likely one piece of a larger puzzle rather than the whole explanation.
How Neurogenesis Changes With Age
Even researchers who believe adult neurogenesis continues agree that it declines substantially over time. The sharpest drop happens early. In primates, proliferation of new neurons in the hippocampus is highest during early postnatal life and diminishes rapidly during juvenile development. Some research suggests that by the first year of human life, the rate has already fallen dramatically. Boldrini’s group found that while certain stem cell populations (quiescent neural progenitors) and blood vessel formation declined in older adults, the number of intermediate progenitors and immature neurons held relatively steady across the lifespan in healthy individuals without psychiatric illness. This suggests the brain may retain some neurogenic capacity even into old age, though the raw output is far lower than in youth.
One major unknown is how long it takes a new human neuron to fully mature and integrate into existing brain circuits. In rodents, this process takes several weeks. In humans, the timeframe has never been precisely measured. New neurons pass through distinct maturation stages before becoming nearly indistinguishable from neurons that were present since development, but exactly how many weeks or months that journey takes in the human hippocampus remains an open question.