Neurogenesis is the creation of new neurons in the brain. Some scientists think that it may improve memory and help with anxiety and depression , though this is still an active area of research. One thing’s for sure: the brain continues to birth new neurons throughout life. Get reading to finally understand the science behind it. What is Neurogenesis?
Neurogenesis is the birth and growth of new neurons , which was originally believed to be absent in the adult brain [ 1 ].
Pioneering neuroanatomists like Raymon y Cajal believed the central nervous system, like the peripheral nervous system, was static [ 2 ]
“In adult centers, the nerve paths are something fixed, ended, immutable. Everything may die, nothing may be regenerated.” – Raymon y Cajal (doctrine of late 19th to early 20th century)
This was taken for granted late into the 20th century, and any opposing findings were met with skepticism [ 3 ]. Image: the first evidence of hippocampal neuron generation in an adult mammalian brain [ 4 ].
A 1961 study showed that neurogenesis occurs in the brains of adult mice. Two years later, neurogenesis was found to occur in the hippocampus of adult mice and cats. This discovery was mostly ignored, though, as it seemed just too far-fetched to dogma-entrenched scientists of the days [ 5 , 6 ].
With the development of new technologies in the 1990s, hippocampal neurogenesis was finally proven to happen in monkeys and humans. Centuries-old dogma was crushed once and for all. Neurogenesis was established as a scientific concept [ 7 ].
Nowadays – having neuroimaging and other modern technologies at our disposal – neurogenesis is far easier to measure. It’s opened a whole new field of research important for advancing our knowledge of the brain in both health and disease [ 7 ].
We now know that neurogenesis occurs in two areas of the adult human brain: the dentate gyrus (DG) of the hippocampus and the subventricular zone (SVZ) of the lateral ventricles [ 8 ].
The function of the SVZ is still relatively unknown in humans. Researchers think that new neurons travel from there through other brain areas to reach the olfactory bulb, where they can become interneurons – neurons placed between other neurons to strengthen the brain circuitry and ensure good communication [ 9 , 10 ].
The olfactory bulb is critical for detecting and distinguishing smells [ 11 , 12 ]. It also seems to be used to process pheromones [ 13 ] and monitor amino acids ( leucine , tryptophan, etc.) [ 14 ].
Interestingly, some scientists think that olfactory impairment may be a marker of presymptomatic Alzheimer’s disease, though this hasn’t been sufficiently proven [ 15 ]. Still, an experimental hypothesis posits that impaired neurogenesis may be implicated in Alzheimer’s and other neurodegenerative diseases.
Studies suggest that stem cells and precursor cells (similar to stem cells but more restricted in what they can turn into) are needed for neurogenesis. They are essentially “blank slates” that are able to develop into neurons and other brain cells [ 16 ]. Adult rodent brain highlighting these two main areas that show active adult neurogenesis. Recent research suggests neuronal proliferation and differentiation might occur in other parts of the brain too. The evidence is still highly inconclusive and most scientists consider it insufficient [ 17 ].
One group of scientists found cells similar to those collected from the hippocampus and SVZ in the cerebral cortex, septum, striatum, spinal cord, hypothalamus and white matter [ 18 ]. Based on these findings, they suggested the occurrence of the first stages of neurogenesis in other brain areas.
Various scientists have suggested that neurogenesis may also happen in the neocortex [ 19 , 20 , 21 ], striatum [ 22 ], and amygdala [ 21 ], and spinal cord [ 23 ].
The evidence for new neurons in areas other than the two established regions is controversial.
Scientists explain that this is due in part because of the difficulties that come with analyzing the neuronal cells that divide slowly or infrequently. There are questions of what constitutes proof that a cell is newly born and if it is, in fact, a neuron [ 17 , 24 ].
This post explores associations between neurogenesis and aspects of health.
The majority of studies we discuss deal with associations only, which means that a cause-and-effect relationship hasn’t been established.
For example, just because mood problems have been linked with low hippocampal volume (suggesting less neurogenesis) doesn’t mean that mood disorders are caused by low hippocampal volume.
Nor does it mean that increasing neurogenesis (and consequently, hippocampal volume) will improve mood, unless clinical data about a direct link are available. However, data are lacking to make such claims.
Additionally, even if a study did find that poor neurogenesis contributes to depression, a lack of neurogenesis is unlikely to be the only cause. Complex mood disorders like depression always involve multiple possible factors – including brain chemistry, environment, health status, and genetics – that may vary from one person to another. Neurogenesis Is Not Just the Birth of New Neurons
More broadly, neurogenesis is not just the birth of new neurons. The term can also encompass neuronal differentiation, survival, maturation, and the integration of new neurons [ 2 ]
Science suggests that this process is most active during prenatal development and has a lot to do with neuroplasticity, an umbrella term for the brain’s way of reorganizing itself and forming new neural connections [ 2 ].
Researchers think that children’s high neuroplasticity is why they have such an easy time learning languages, and why it’s a hot field of research. Still, the link between neuroplasticity and neurogenesis is not so straightforward. One does not necessarily equal the other, and most of the research is still is the very early stages [ 2 ].
Different compounds are hypothesized to play critical roles in adult neurogenesis [ 25 ]: Morphogens are molecules that may regulate the maintenance, survival, and development of precursor cells Neurotrophic factors are molecules that protect neurons and help new neurons grow and mature Transcription factors […]