- New neurons in adults continue to form in the hippocampus, which is key to memory and emotion processing.
- Chronic stress and aging significantly suppress adult neurogenesis, potentially accelerating cognitive decline.
- Aerobic exercise and mental stimulation noticeably increase new neuron growth in adults.
- Certain antidepressants may work partly by enhancing brain plasticity through promoting neurogenesis.
- Scientific disagreement continues regarding how much neurogenesis actually persists into later adulthood.
Most of us grew up believing that our brains stopped developing in early adulthood. Significant discoveries in recent decades have changed our understanding of brain development. We now know that some areas of the adult brain continue to generate new cells through a process known as adult neurogenesis. This has important implications for learning ability, emotional control, and how well our brains resist cognitive decline.
Where New Neurons Are Born in Adults
Adult neurogenesis is not a widespread process across the entire brain. Instead, it is restricted to very specific regions that have high functional significance, particularly for memory, learning, and olfactory processing. The two primary areas of adult neurogenesis are:
The Hippocampus
The hippocampus, which is in the medial temporal lobe, is very important for memory formation, spatial navigation, and emotional control. It is the area where adult neurogenesis has been studied the most. Here, new neurons form in the dentate gyrus, a subregion of the hippocampus known to be involved in the discrimination and encoding of different memory patterns.
In 1998, an important study by Eriksson et al. confirmed the existence of adult neurogenesis in the human hippocampus, giving solid proof that even older human brains are not biologically fixed.
The Subventricular Zone (SVZ)
This area lines the lateral ventricles and is another place where new neurons are made in adults. In rodent studies, these cells mainly moved to the olfactory bulb, affecting their sense of smell. However, in humans, this movement is less clear, and what SVZ-made neurons do in adults is still being researched.
The Function of Adult-Born Neurons
New neurons made in adulthood do more than just fill spaceāthey have a job in the brain’s workings. Studies on rodents and primates, and observations in humans, show that adult-born neurons are connected to several important brain functions
Pattern Separation
New neurons help the brain differentiate between similar but distinct memoriesāa process called pattern separation. For example, remembering where you parked your car today versus yesterday depends on the ability to create a distinct memory trace each time.
Emotional Regulation
New neurons that are created help control stress and worry. Research indicates that adult neurogenesis lowers overactivity in the hypothalamic-pituitary-adrenal (HPA) axis, which helps protect against long-term stress.
Spatial Learning
Studies with animals show that when neurogenesis is reduced, they don’t do well on tasks that need spatial learning, like finding their way through mazes. This suggests that adult neurogenesis helps create a mental map of our surroundings and helps with directions.
These aspects have major implications for understanding disorders such as PTSD, anxiety, and memory-related diseases, where neurogenesis might be impaired or dysregulated.
The Role of the Hippocampus in Memory
The hippocampus does more than store memoriesāit actively works with new experiences and what we already know. Neuroscientists now think that making and recalling new memories relies a lot on brain flexibility, which is supported by adult neurogenesis.
Memory Formation and Recall
New neurons integrate into existing hippocampal circuits and appear to play a special role during the encoding of new information. These immature neurons are more excitable than mature ones, allowing them to quickly respond to novel stimuli and encode experiences into long-term memory.
Enriching Neuroplasticity
Adding new cells makes neural networks more flexible, which supports the idea that adult neurogenesis helps us adaptāthis is important for dealing with new situations or recovering after brain damage.
In animals, enhancing neurogenesis has been directly correlated with better performance in memory tests. Some scientists suggest that increasing neurogenesis could improve memory consolidation and recall even in humans, although more studies are needed in human subjects.
Neurogenesis and Cognitive Decline: A Promising Link
Aging brains are often accompanied by memory loss, reduced attention span, and lower cognitive flexibility. This age-related cognitive decline is a growing concern globally, particularly with the projected rise in dementia and Alzheimer’s disease cases.
New Neurons and Protection Against Decline
There is strong evidence to suggest that continued production of new neurons may serve as a buffer against memory loss and cognitive deterioration. One study estimated that about 700 new neurons are generated daily in the adult human hippocampusāan amount substantial enough to sustain neuroplasticity over time.
Integration is Key
But it’s not just about how many new neurons there are. These neurons must fit correctly into the brain’s existing networks. If they don’t fit well, it can cause problems and possibly make thinking worse instead of better.
Hope for Alzheimer’s and Dementia
Preliminary data suggest that strategies aimed at maintaining or boosting hippocampal neurogenesis could help delay the onset or reduce the severity of neurodegenerative disorders. Clinical therapies may one day target this process as a part of early interventions.
Epilepsy and Neurogenesis: A Double-Edged Sword
Epilepsy research reveals one of the more complex aspects of adult neurogenesis.
Rebuilding or Risk?
After seizures, particularly in temporal lobe epilepsy, neurogenesis can increase as the brain tries to fix itself. But, if the new neurons don’t connect properly, they could create bad connections. This bad wiring might add to āseizure circuitsā that increase the chance of more seizures.
Balancing Act
Thus, while enhancing neurogenesis could potentially aid in recovery after seizures, unchecked growth poses a serious risk. Therapeutic efforts need to strike a balance between encouraging regeneration while maintaining structural and functional integrity.
Exercise, Learning, and New Neurons
Fortunately, supporting your brainās capacity to produce and maintain new neurons doesnāt always require medical intervention. Lifestyle plays a powerful role.
Aerobic Exercise
One of the strongest natural stimuli for adult neurogenesis is aerobic activity, especially cardiovascular exercises such as running, swimming, or brisk walking. Numerous animal and human studies show increased hippocampal volume and improved cognitive function among physically active participants.
Mental Engagement
Challenging the brain with new information also boosts neuron integration. Learning a new language, picking up a musical instrument, or solving puzzles are all effective ways to stimulate neurogenesis.
Enriched Environments
Studies in animals have shown that being in different places with social interaction, new things, and chances to learn can increase neuron development. For people, this could be traveling, socializing, or doing new things regularly.
These natural interventions show promise not only for sustaining cognitive function but also for improving mental health outcomes.
Stress, Aging, and Neurogenesis Inhibition
While the brain has immense potential to grow and change, certain factors actively inhibit adult neurogenesis.
Chronic Stress
One of the most harmful things for neurogenesis is long-term stress, which raises cortisol. High cortisol levels can hurt the brain over time, damaging neurons in the hippocampus and reducing the creation of new ones.
Aging
The aging process naturally slows down stem cell activity in all tissues, including the brain. Although adult neurogenesis appears to continue into old age, levels decline. However, this decline can vary significantly among individuals and may be slowed through healthy lifestyle practices.
Sleep and Diet
Sleep deprivation has been shown to reduce the proliferation of neural stem cells, while certain dietsāespecially those high in sugar and saturated fatsāare linked to lower hippocampal volume. Conversely, diets rich in flavonoids, omega-3 fatty acids, and antioxidants may support neuron health and encourage neurogenesis.
A 2018 study by Sorrells et al. argues that adult neurogenesis in humans sharply decreases after childhood. The claim remains controversial and underscores how complex and nuanced this field continues to be.
Controversy in the Scientific Community
Adult neurogenesis is not without debate. Results across laboratories vary, leaving scientists divided on just how much neurogenesis persists into adulthoodāand especially into late life.
Methods Matter
A lot of the disagreement is about how studies are done. Things like how brain tissues are kept, colored, and looked at can really change the results. It’s very hard to study human brain tissue after death without changing important cell details.
The Need for Biomarkers
There is a critical need for non-invasive biomarkers or imaging techniques that could allow scientists to measure neurogenesis in real time in humans. As of now, most direct evidence comes from post-mortem analysis and animal studies.
This lack of consistent methodology makes it harder to design therapies targeting adult neurogenesis. Nonetheless, the search continues.
Implications for Mental Health: Depression and PTSD
Neurogenesis is not just relevant to learningāitās also intricately connected to mood and emotional well-being.
Depression and Neurogenesis
Some studies have found that people with depression and PTSD have a smaller hippocampus. Less neurogenesis might play a role in these changes. Also interesting is what antidepressants might do: many SSRIs seem to encourage neurogenesis as well as affect serotonin.
Experimental Evidence
In animal models, blocking neurogenesis diminishes the therapeutic effects of antidepressants. This suggests that promoting neurogenesis may be a necessary component of recovery from depression.
The Emotional Circuitry Link
New neurons help modulate the amygdala and hippocampusātwo key regions in emotional regulation. A healthy cycle of neurogenesis may improve emotional resilience and reduce the depth and duration of depressive episodes.
Future Horizons: Targeting Neurogenesis in Therapy
As we learn more, adult neurogenesis could go from being just an interesting biological fact to a useful tool in medicine.
Pharmacological Tools
Researchers are experimenting with growth factor-mimicking compounds such as BDNF (Brain-Derived Neurotrophic Factor) agonists that may directly stimulate neuron growth and survival.
Device-Based Strategies
Methods such as transcranial magnetic stimulation (TMS), deep brain stimulation (DBS), and even ultrasound treatments are being studied to improve certain brain networks and maybe indirectly encourage neurogenesis.
Holistic Interventions
Practices that connect mind and body, like yoga, mindfulness, and diet changes, might directly affect brain flexibility. Combined with lifestyle changes and planned cognitive-behavioral therapies, these could be several ways to improve adult brain health.
Rewiring Hope Through Neurogenesis
Finding out about adult neurogenesis has greatly changed how we see the brain. It shows that instead of being set, the adult brain is changeable, flexible, and can renew itself. Even though we still have many questions, especially about using this process in treatments, knowing that you can grow new neuronsāat any ageāis encouraging. As we learn more about adult neurogenesis, it creates opportunities for new ways to improve learning, mental health, and slow down cognitive decline for a better brain future.
Citations
- Eriksson, P. S., Perfilieva, E., Bjƶrk-Eriksson, T., Alborn, A. M., Nordborg, C., Peterson, D. A., & Gage, F. H. (1998). Neurogenesis in the adult human hippocampus. Nature Medicine, 4(11), 1313ā1317. https://doi.org/10.1038/3305
- Spalding, K. L., Bergmann, O., Alkass, K., Bernard, S., Salehpour, M., Possnert, G., … & FrisĆ©n, J. (2013). Dynamics of hippocampal neurogenesis in adult humans. Cell, 153(6), 1219-1227. https://doi.org/10.1016/j.cell.2013.05.002
- Sorrells, S. F., Paredes, M. F., et al. (2018). Human hippocampal neurogenesis drops sharply in children to undetectable levels in adults. Nature, 555, 377ā381. https://doi.org/10.1038/nature25975
- GonƧalves, J. T., Schafer, S. T., & Gage, F. H. (2016). Adult neurogenesis in the hippocampus: From stem cells to behavior. Cell, 167(4), 897ā914. https://doi.org/10.1016/j.cell.2016.10.021
