Ever heard of neurogenesis? Unless you’re well versed in science, it isn’t likely. Well, to put it simply, it’s the act of growing new nerve cells, and it’s most active during fetal development. In fact, classic neuroscientific dogma in the early 20th century held that no neurons could be added to the adult brain.
However, research by Joseph Altman in the 1960s showed the neuroscience community newly developed nerve cells in adult rat brains(1). Nevertheless, interest in this field only picked up when these findings were thrust into the spotlight in the early 1990s, when neurogenesis was proven to also occur in adult human brains(2).
Now, that doesn’t mean neurons have the regenerative capacity of other types of cells in the body, such as skin or gastrointestinal cells. To highlight the difference, let’s use an example. Person A loses nerve cells (such as in a stroke), while Person B loses skin cells (through burns). In both cases, let’s say the same amount of cells are killed. Person B only takes a few days to regenerate new skin, while Person A may take up to 6 months to recover, and they may never fully do so.
The difference between these 2 cases makes neurons a precious commodity. In fact, only around 700 neurons are generated every day, making up a minuscule 1.75% annual turnover rate. Compare that to our skin, which is made up of an estimated 2 trillion cells and is replaced entirely every 47-48 days (4,5). To make matters worse, adult neurogenesis declines with age. It decreases sharply after the first year of life and suffers a four-fold reduction across the entire lifespan.
New neurons arise from neural stem cells. Neural stem cells are undifferentiated cells that can mature to various types of cells in the brain, including neurons and supporting cells (known as glial cells). As we age, these stem cells do not die, rather, they become increasingly quiescent and therefore less likely to sprout new nerves(6).
A lack of neurogenesis has been associated with a myriad of conditions such as Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease(7). These neurodegenerative disease have a predilection for attacking regions rich in neural stem cells—as evidenced by symptoms of mood changes (hippocampal damage) and changes in sense of smell (olfactory area damage).
Why does adult neurogenesis matter?
Evidence suggests that adult neurogenesis contributes to long term, adaptive benefits. This is because newly formed neurons are not ready to work immediately after their birth. They have to mature, migrate to their new home in the body, form new synapses, then integrate into the existing brain network(8). New neuron formation in the hippocampus is thought to be important for learning and pattern separation—the ability to discriminate between very similar stimuli, like telling apart two people who have similar facial features or remembering small details that distinguish different memories(9).
Besides learning, adult hippocampal neurogenesis is important in mood regulation10. Neurogenesis is attenuated in depression, and is increased with antidepressant treatment. Furthermore, stress, which is often a component of depression, increases cortisol hormone levels that go on to suppress nerve growth.
With that, we come to the million dollar question—does boosting neurogenesis really make a difference? Well, the jury’s out. Scientists are at odds when debating if selectively increasing neurogenesis is able to selectively stimulate cognition. Yes, it’s been proven true in mice, but that doesn’t always translate to humans, because our neurological range and cognitive abilities far outstrip our rodent friends.
In any case, preserving the limited neural stem cells would be well worth it. Even if enhanced cognitive abilities is beyond their skillset, boosting neurogenesis could be used as a means to treat those with neurodegenerative diseases like the ones mentioned above, and that would be a game-changer for millions of people around the world.
To wrap it all up, adult neurogenesis exists, and boosting it could result in a multitude of benefits, especially in the elderly. So, are you ready to grow more brain cells?
In the meantime, GENEius can help you make the most of the brain you have. Click here to see how.
1. Altman J, Das GD. Autoradiographic and histological evidence of postnatal hippocampal neurogenesis in rats. J Comp Neurol. 1965;124:319–335.
2. Eriksson PS, Perfilieva E, Björk-Eriksson T, et al. Neurogenesis in the adult human hippocampus. Nat Med. 4 (11): 1998 Nov;1313–7. doi:10.1038/3305. PMID 9809557.
3. Ming G, Song H. Adult Neurogenesis in the Mammalian Brain: Significant Answers and Significant Questions. Neuron. 2011;70(4):687-702. doi:10.1016/j.neuron.2011.05.001.
4. Bianconi E, Piovesan A, Facchin F, Beraudi A, Casadei R, Frabetti F, Vitale L, Pelleri MC, Tassani S, Piva F, Perez-Amodio S, Strippoli P, Canaider S. An estimation of the number of cells in the human body. Ann Hum Biol. 2013 Nov-Dec;40(6):463-71. doi: 10.3109/03014460.2013.807878. Epub 2013 Jul 5.
5. Iizuka H. Epidermal turnover time. J Dermatol Sci. 1994 Dec;8(3):215-7.
6. Ahlenius, H., Visan, V., Kokaia, M., Lindvall, O. & Kokaia, Z. Neural Stem and Progenitor Cells Retain Their Potential for Proliferation and Differentiation into Functional Neurons Despite Lower Number in Aged Brain. J Neurosci. 2009.29:4408–4419, 10.1523/Jneurosci.6003-08.2009
7. Winner B, Winkler J. Adult Neurogenesis in Neurodegenerative Diseases. Cold Spring Harbor Perspectives in Biology. 2015;7(4):a021287. doi:10.1101/cshperspect.a021287.
8. Stangl D, Thuret S. Impact of diet on adult hippocampal neurogenesis. Genes & Nutrition. 2009;4(4):271-282. doi:10.1007/s12263-009-0134-5
9. Swan AA, Clutton JE, Chary PK, Cook SG, Liu GG, Drew MR. Characterization of the role of adult neurogenesis in touch-screen discrimination learning. Hippocampus. 2014;24(12):1581-1591. doi:10.1002/hipo.22337.
10. Becker S, Wojtowicz JM. A model of hippocampal neurogenesis in memory and mood disorders. Trends Cogn Sci. 2007 Feb;11(2):70-6. Epub 2006 Dec 14.