Here is the original draft ofa featured article I wrotePronew scientist, in adult neurogenesis in the human brain. You need to register to read the magazine version, but registration is free and only takes a minute.
Neurogenesis refers to the production of new nerve cells. Everyone would like to believe that the human brain creates new cells throughout life, but as you will see in this article, the evidence for this is scant and several prominent researchers are very skeptical.
I'm sitting on a long lab bench in theMRC Center for Developmental Neurobiology, View through a microscope of the hindbrain of a three-day-old chicken embryo. The egg had already been injected with bromodeoxyuridine (BrdU), a compound whose structure is similar to that of thymidine, one of the four main components of DNA, and which is incorporated into newly synthesized DNA.
The embryo was then removed, the hindbrain dissected and treated with an antibody that binds to BrdU. Now split across the top and spread out on a slide, this is how it looksDivided into eight compartments, each revealing their newborn cells with their DNA stained dark brown.
andres lumsden, director of the center, explains that each segment expresses a unique combination ofgenetic patternand that the boundaries of the segments restrict the movements of immature cells. Neurons in each segment are given a unique identity: those arising in the anterior segment fuse to form the nucleus of the fifth cranial nerve, while those further back form other cranial nerves.
At this stage of development, the nervous system is a hollow tube that runs along the back of the embryo. Its walls contain wedge-shaped cells that divide near the inner surface to produce neurons that migrate outward. This happens at different speeds along the length of the tube, creating three bulges at one end that eventually form the brain. Successive waves of migrating cells populate the developing brain to give the cortex its characteristic layered appearance. Once at the target site, they differentiate into the three main cell types of the brain (neurons, astrocytes, and oligodendrocytes) and then sprout connecting branches to form functional tissue.
fountain of eternal youth
For much of the last century, it was thought that the production of new neurons, neurogenesis, was restricted to embryonic development. “Once development is complete,” wrote Santiago Ramón y Cajal, the father of modern neuroscience, “the sources of growth … are irrevocably dry. In the adult, neural pathways are... immutable. Everything can die, nothing can die regenerated."
This became the central tenet of neuroscience, but the view began to change in the 1980s, whenfernando nottebohmof Rockefeller University published the first unambiguous evidence of adult neurogenesis in the vertebrate brain. Nottebohm showed that the brain of an adult canary undergoes seasonal changes in size. Males sing to serenade females, but the regions of the brain that produce the song drastically decrease in size after the breeding season. The following spring, they regenerate through neurogenesis to allow the male to learn new songs.
Indeed, Joseph Altman of the Massachusetts Institute of Technology reported evidence of adult neurogenesis in the hippocampus of adult rats and guinea pigs and in the cortex of cats in the 1960s, but his work was ignored and later ridiculed. “Altman started with the idea of adult neurogenesis, but his data were not convincing,” says Nottebohm. "Our results showed beyond a shadow of a doubt that neurons are born in adulthood and are built into existing circuits. They broke most of the resistance to the idea."
Evidence for adult neurogenesis in mammals quickly followed. 1992,Samuel Weissand Brent Reynolds of the University of Calgary isolated neural stem cells from the brains of adult mice and showed that they can generate neurons and astrocytes when grown in a petri dish. This was confirmed byFred Gagefrom the Salk Institute. Working with several colleagues, Gage also showed that exercise and environmental enrichment increase the rate of adult neurogenesis and that the number of new cells produced decreases with age. Thousands of studies have been published and it is widely accepted that adult mouse brains continue to producenew neurons.
In all mammalian embryos, neurogenesis takes place along the neural tube. In the adult, the tube cavity has turned into brain chambers filled with cerebrospinal fluid, and neurogenesis is confined to two brain regions, each containing a niche with different types of stem cells.
The largest C-shaped niche in the walls of the lateral ventricles produces immature neurons thattravel in chains within the rostral travel current(RMS) to the olfactory bulb. Some differentiate into mature neurons that integrate into local circuits andparticipate in odor information processing🇧🇷 The other produces cells that integrate into the dentate gyrus of the hippocampus and play an important role in learning and memory. It's not clear exactly how the new cells are involved in processing information. They can replace dying cells or be added to existing circuits to provide additional information processing capabilities.
Other regions of the lateral ventricles contain dormant stem cells that can be activated after brain injury to produce new cells that migrate to the site of injury.
From rats to monkeys and humans.
In the late 1990sElizabeth Goldfrom Princeton University reported evidence of adult neurogenesis in the monkey hippocampus and showed that stress reduced stem cell division in the dentate gyrus. However, the monkey brain is much larger than that of rodents and the process takes time. Fewer cells are produced, travel greater distances and take longer to mature. According to a recent study by researchers at the University of Illinois, new cells occupy the monkey's dentate gyrusat least six months to full maturity.
Adult neurogenesis is implicated in depression and Alzheimer's disease, both of which involve contraction of the hippocampus. The antidepressants Prozac and imipramine stimulate hippocampal neurogenesis in adult mice, and some of their effects depend on new cells. They also cause immature hippocampal cells derived from human embryos to divide in the petri dish.
It is now taken for granted that adult neurogenesis occurs in humans, and the idea has revolutionized the way we think about the brain. It is widely believed that physical and mental exercise can stimulate hippocampal neurogenesis, which reverses age-related cognitive decline and may protect against depression and Alzheimer's disease. "Everyone would like to believe that functional neurogenesis occurs in adult humans," says Lumsden. "Everyone would like to believe that we can fix damaged brains, but there is very little evidence for that."
The biggest skeptic isPasko Rakic, who discovered how newborn cells migrate to the developing brain in a series of classic experiments in the early 1970s: Rakic injected monkey fetuses with radioactive thymidine and sliced their brains into hundreds of ultrathin slices. He identified the migrating neurons from his newly synthesized radioactive DNA and carefully reconstructed the sections to show that the cells ascend into elongated cells called radial glial cells, which traverse the thickness of the tube to touch its inner and outer surfaces and then crawl out. like an amoeba. ., along the radial glial fibers towards the outer surface. His hand-drawn diagrams describing the process appear in textbooks to this day.
Now Chair of the Department of Neurobiology at Yale and Director of theKavli Institute of NeuroscienceCasting a long shadow, Rakic is extremely critical of some research on adult neurogenesis. He claims that BrdU can induce cell division, and alsomark dying cells, which synthesize DNA near death, cannot therefore provide accurate counts of newborn cells in adult brain tissue. This can be overcome by double staining with other antibodies to confirm that the BrdU-labeled cells are dividing.
Rakic has published evidence for and against adult neurogenesis in monkeys. He estimates that neurons added to the adult human hippocampus take a year to mature and argues that antidepressants cannot work to stimulate neurogenesis because their effects take about a month to become effective.
“Rakic reasonably requested higher levels of evidence,” says Nottebohm, “but he attacked adult neurogenesis so aggressively that it struck many as a defense of ancient dogma.” As a participant in the battles, I found it very negative.” and not particularly insightful. His own work used animals raised in conditions that inhibit the formation and survival of new neurons.”
Nottebohm and others say that Rakic held back neurogenesis research in adults, but according to Gage, he was "one of the main drivers in making the field more rigorous. He challenges the weaknesses of his work and relies on researchers in the field to solve them." However, Gage notes that immature neurons in mouse stem cells are more active than their mature counterparts, so a longer maturation time could actually be beneficial. "I'm not surprised that maturation takes longer in humans, but the other way of looking at it is that newborn cells have a longer period of plasticity."
However, Rakic's skepticism is supported by scientific evidence, or rather the lack of it.
1998 Gage and the late Peter Erikssonexamined the brains of five cancer patientswho had been injected with BrdU for diagnostic purposes. They treated hippocampal tissue with antibodies against BrdU and proteins synthesized by immature neurons and found some staining in the dentate gyrus. This was the first evidence that the adult human brain contained newborn neurons, but the researchers emphasized that it did not prove that the cells were functional.
Others have isolated stem cells from different regions of the adult human brain. These cells have a limited capacity for self-renewal when grown in the laboratory, but they can produce mature astrocytes, oligodendrocytes, and neurons with normal electrical properties.
Em 2006,jonah's friezefrom the Karolinska Institutet and colleagues examined the cortex in the autopsied brains of seven adults. They looked for radioactive carbon from Cold War atomic bomb tests accumulating in newly synthesized DNA, but only detected atmospheric levels and came to the conclusion.Neurogenesis does not occur in the cortex..
More recentlyGerd Kempermannof the Center for Regenerative Therapies in Dresden and colleagues examined the brains of 54 people aged up to 100 years with antibodies against various proteins and foundsmall number of newborn hippocampal cellsIn all. "It appears to be the same as in rodents," says Kempermann. “There is a very sharp decline early in life, but towards the end it remains a very low level. We saw small numbers of cells, but we saw them until very late in life."
butArturo Alvarez-Buylla, a professor in the Department of Neurological Surgery at the University of California, San Francisco, is not entirely convinced. "Gage and Erikkson provided evidence that some proliferation occurs in the adult hippocampus," he says, "but this should be treated with caution, as some of the labeled cells may have died."
Alvarez-Buylla earned her Ph.D. worked with Nottebohm on songbirds before turning to rodents, where he showed that newborn neurons travel long distances to the olfactory bulb. He has since published several studies suggesting that this migration is unlikely to occur in adult humans. Work withNader Sanai, director of the Barrow Brain Tumor Research Center in Phoenix, Arizona, examined the brains of about 100 people of all ages and a similar number of tissue samples collected during neurosurgery.
identifieda 'ribbon' of astrocytesin the walls of the lateral ventricles producing immature neurons, astrocytes and oligodendrocytes and which has not been observed in other species. They also identified the RMS in infants and found that it contains a small number of migratory cells, as well as a previously unidentified migratory pathway that branches off the RMS to invade the prefrontal cortex.
According to their data, migration in both streams occurs after birth, but declines abruptly by 18 months of age and disappears almost completely by early adulthood. "We concluded that if there is migration, it is very little", says Alvarez-Buylla, "and that the cells do not form large bundles that migrate towards the olfactory bulb".a 2007 study by Erikkson and Maurice Curtis, which saw a robust RMS containing large numbers of migrating cells, but were confirmed last year by Chinese researchers who foundlow number of migratory neurons in adult RMS, but in the olfactory bulb itself there are no new cells.
"How much neurogenesis occurs in older people and how much it contributes to local plasticity are still open questions," says Alvarez-Buylla. “There is controversy about how much cell turnover takes place in the hippocampus and how durable stem cells are over a lifetime. If they shrink with age, they don't really regenerate."
In general, the few available studies indicate that the fountain of youth in adults is thinning. There is no evidence of adult neurogenesis in human cortex; The existence of RMS in adults is still controversial, and evidence of hippocampal neurogenesis in this area is very scarce. When the hippocampus produces new cells, are they enough to be significant?
Kempermann finds it this way: "The network requires very few cells that need to be added and is still functionally relevant," he says. Like other adult neurogenesis researchersa small number of cells may be relevant to hippocampus function🇧🇷 But that question remains unanswered, and the possibility that the number of cells produced is not large enough to be functionally significant has serious implications for popular claims, such as that exercise can improve memory, and also for new brain discoveries. who did this. were suggested. accepted so quickly.
"A side effect of having a big, complex brain is that you don't want naive newcomers breaking in," says Lumsden. “How would new neurons be meaningfully integrated into complex neural networks? At the very least, evolution would have provided mechanisms to eliminate these invaders. The lack of neurogenesis after completion of the brain-wiring scheme would be a selective advantage.”
The brain may therefore prefer stability to plasticity. Adult human neurogenesis may be an evolutionary relic and comes at a very high cost, as stem cells in the adult human brain likely contribute to the formation of brain tumors.
There is still hope
"Rakic was almost right," says Nottebohm. "So far, the overwhelming evidence is that most neurons form early in development, even shortly after birth." But even if functional adult neurogenesis does not occur in the human brain, or if the number of cells produced is too small to be significant, there is still hope that neural stem cells may have therapeutic value.
"Rakic missed the plot point," continued Nottebohm. “There is a rich collection of neural stem cells that produce new neurons well into adulthood. This is extremely important. This shows, in principle, that this reservoir can be used for brain repair purposes.”
To that end, researchers are investigating two approaches to developing neural stem cell-based therapies for neurological disorders, although these treatments still have a long way to go. One approach is to trick brain stem cells into creating neurons that travel to sites of injury or disease. The other is to transplant laboratory neurons of certain types directly into the brain. Indeed, neurons derived from human neural stem cells can, and now can, differentiate into fully functional neurons when transplanted into the brain of a mouse fetus.monitored in live animals using MRI.
“We found the first evidence of replaceable neurons,” says Nottebohm, “and I have no doubt that a whole new field will develop around this concept. I'm sure sooner or later this will have a profound impact. This is just the beginning." ." 🇧🇷
Can your brain make new brain cells If yes explain? ›
The brain can produce new cells
Neurogenesis is now accepted to be a process that occurs normally in the healthy adult brain, particularly in the hippocampus, which is important for a learning and spatial memory.
This is where that rumour comes from that neurons can't regenerate, and scientists actually believed this to be true for a long time. However! Science has since discovered that neurons can actually regenerate using a really unique method if an area of the brain gets damaged – we call this method neurogenesis.Why does your body not produce new brain cells? ›
Nerve Cells Do Not Renew Themselves
They do not divide at all. There are very few exceptions to this rule – only two special places in the brain can give birth to new neurons. For the most part though, the brain cannot replenish dead neurons.
According to one recent study by researchers from the University of Illinois, new cells in the macaque dentate gyrus take at least six months to mature fully. Adult neurogenesis is implicated in depression and Alzheimer's disease, both of which involve hippocampal shrinkage.Can the brain grow new cells? ›
New hippocampal neurons continue to form in older adults, including those with MCI, Alzheimer's. Neurogenesis—the process of forming new brain cells—appears to continue in people well into old age, according to a recently published study funded in part by the NIA.Can the human brain make new cells? ›
Neurons are born in areas of the brain that are rich in concentrations of neural precursor cells (also called neural stem cells). These cells have the potential to generate most, if not all, of the different types of neurons and glia found in the brain.At what age do you stop producing brain cells? ›
Your brain has peaked by age 13. The creation of new brain cells in the hippocampus ends before we even reach adulthood, according to a study published Wednesday in the journal Nature.How can I regenerate my brain cells naturally? ›
- Get plenty of sleep.
- Try intermittent fasting.
- Follow a healthy diet.
- Indulge in dark chocolate.
- Get moving.
- Exercise your brain.
- Drink green tea.
- Get outside.
Permanent cells are cells that are incapable of regeneration. These cells are considered to be terminally differentiated and non-proliferative in postnatal life. This includes neurons, heart cells, skeletal muscle cells and red blood cells.What helps make new brain cells? ›
- Learning new skills.
- Intermittent fasting.
- Calorie restriction.
- Resveratrol (found in red wine)
- Curcumin (found in turmeric)
Can lost brain cells be replaced? ›
All of these studies suggest that the injured adult brain can support the production and incorporation of new neurons. Even if the numbers are small, these results show the adult brain can regenerate neurons after injury.Why can liver cells regenerate but not brain cells? ›
Which organs aren't very good at regenerating? The brain actually can't regenerate itself well because when the brain is damaged its cells find it harder to make new ones. This is because the brain has very few of the special cells, or stem cells.How many brain cells do you need to live? ›
The average adult human has about 100 billion brain cells. About 85,000 brain cells die each day. Approximately 1,400 new brain cells are produced each day.Can the brain continue to grow? ›
Researchers have discovered that, in fact, we continue to grow new brain cells (neurons) as we age – perhaps even well into our 90s!Can brain cells regenerate after lack of oxygen? ›
Without oxygen, brain cells die, and a brain injury can occur. It can happen even when enough blood reaches the brain, such as when you breathe in smoke or carbon monoxide. Treatments can help people who have brain injuries from cerebral hypoxia. But no one can bring back dead brain cells or reverse a brain injury.Can aging brain reversed? ›
Regular aerobic exercise in combination with a heart-healthy diet appears to reverse some effects of brain aging and might reduce the risk of dementia, according to a new study that reinforces the value of lifestyles changes for keeping both heart disease and dementia at bay.Do we all lose brain cells? ›
He explained that around a quarter of all microglia, which make up about 10% of the glial cells in the brain, are replenished every year. “When you do the maths, that means that each day about 4 million microglial cells die. But they are replenished, so there is a loss, but no 'net loss',” he told us.Is alcohol killing brain cells? ›
Alcohol does kill brain cells. Some of those cells can be regenerated over time. In the meantime, the existing nerve cells branch out to compensate for the lost functions. This damage may be permanent.What foods make new brain cells? ›
- Wild caught Fish.
- Grass fed Beef.
- Grass fed Dairy (milk)
- Pastured chicken & eggs.
- Saturated fats : Coconut oil, lard, ghee.
An amino acid called taurine plays an important role in creating new brain cells. Researchers found that taurine increased the growth of brain cells by activating “sleeping” stem cells. Taurine also increased the survival of new neurons, resulting in an increase in adult brain cell creation.
What feeds the brain cells? ›
The brain needs energy to work, and its main source of energy is glucose. This simple sugar, found in many foods, is carried in the bloodstream and converted into energy by tissue cells throughout the body.What is the only organ that can grow back? ›
The liver has a unique capacity among organs to regenerate itself after damage. A liver can regrow to a normal size even after up to 90% of it has been removed.What helps cell repair? ›
While healthy fats and protein bolster our cellular walls or membranes, vitamins, minerals and plant chemicals called phytonutrients help to protect and repair our cells from damage.What cells regenerate the fastest? ›
The most frequently replaced cells in the human body are the cells that line the stomach walls and intestine. They typically last around five days before regeneration. Skin cells are replaced every two to four weeks.How long do brain cells live? ›
Adult neurons survive for a lifetime and remain malleable for several years. This is one reason kids are especially adept at learning new languages, explained W.A. Harris (left), who was joined by Joshua Sanes, director of the Center for Brain Science at Harvard.What damages brain cells? ›
Many habits contribute to poor brain health, but four areas can have the most influence. They are too much sitting, lack of socializing, inadequate sleep, and chronic stress.How many brain cells does a human have? ›
This was accomplished by Azevedo et al. (2009), who found that the adult male human brain, at an average of 1.5 kg, has 86 billion neurons and 85 billion non-neuronal cells – numbers that deviate from the expected by 7 and 24% only.What is the only organ that Cannot regenerate itself? ›
However, this is not the case with all patients; some will require a liver transplant following the resection because their liver tissue does not re grow.Which organ Cannot regenerate itself? ›
Teeth are the ONLY body part that cannot repair themselves. Repairing means either regrowing what was lost or replacing it with scar tissue.What organ can you live without? ›
You can still have a fairly normal life without one of your lungs, a kidney, your spleen, appendix, gall bladder, adenoids, tonsils, plus some of your lymph nodes, the fibula bones from each leg and six of your ribs.
Is changing brain possible? ›
Experts previously believed that after a given point in life, your brain could no longer change or develop further. Now they know this isn't true. With a bit of time and patience, you can rewire your brain, which may help with certain mental health symptoms and protect against cognitive decline.Can Your mind Change Your brain? ›
The overall conclusions from these studies are that one can transform the mind through meditation and thereby alter the brain and the periphery in ways that may be beneficial for mental and physical health, and for well-being.Do you get smarter as you age? ›
Aging may also bring positive cognitive changes. For example, many studies have shown that older adults have more extensive vocabularies and greater knowledge of the depth of meaning of words than younger adults. Older adults may also have learned from a lifetime of accumulated knowledge and experiences.At what age does the brain stop developing? ›
The brain finishes developing and maturing in the mid-to-late 20s. The part of the brain behind the forehead, called the prefrontal cortex, is one of the last parts to mature.What are 5 ways of making your brain grow? ›
- Do Brain Training.
- Extend Your Education. ...
- Maintain High Levels of Mental Activity. ...
- Stay Healthy. ...
- Meditate. ...
- Eat Well. ...
- Get Quality Sleep. ...
- Think Positive. ...
In fact, Dr. Lipton's research illustrates that by changing your perception, your mind can alter the activity of your genes and create over thirty thousand variations of products from each gene.How to reset your brain? ›
- Develop Healthy Sleep Habits. Sleep is our body's method of resetting and replenishing itself—including (and especially) the brain. ...
- Eat a Healthy Diet. There's a deeper connection between the brain and the gut than most people realized. ...
- Meditation/Mindfulness Exercises. ...
- Get Outside. ...
When your mind seems to be playing tricks on you, it can be unsettling—sometimes terrifying. Everyone's brain has glitches every now and then. But feeling like your brain is constantly messing with you is often a sign of a mental health condition that needs attention and treatment.