Brain cells can’t grow, right?
Written by Mashiyat Ahmed
Illustrated by Rebecca Parvaneh
For the longest time, scientists believed that part of what made the brain so unique was that its cells couldn’t regenerate themselves in adulthood like other cells could. But since the 1990s, scientists have confirmed that the cells in our brains can multiply.¹ Our bodies are composed of an assortment of cells with different functions to maintain our diverse needs. Some cells are specialized to pass on information to other cells, while others come in delicate branching star-like shapes to traffic blood and nutrient flow to important centers of the brain (astrocytes).
Every other cell type in the human body is capable of creating copies of itself — a process known as mitosis — using the genetic information it already has, and must do so regularly to continue functioning normally.
Brain cells — neurons — communicate signals between the brain, body, and external environment, and compose the basic functional building blocks of our nervous system.² Everything that our brains do, such as movement, emotion, language, and cognition (e.g., thinking, decision-making, and perception) relies on electrical and chemical “communication” lines between cells as they transmit necessary information from one region of the brain to the other to accomplish a task (e.g., speaking a language or picking up a pencil). Neurons and other cells hold up this communicative infrastructure through essentially priming each other to “tightly hold hands.”
But neurons are unique in that they are, for the most part, incapable of creating new copies of themselves after the first year of life, meaning the number of neurons stay relatively the same throughout one’s lifetime.³ This is the reason brain injuries and lesions are so damaging. The inability of brains to regenerate new cells means that once we lose neurons, we can’t get them back.
Can brain cells multiply?
Neurons — all 86 billion of them that make up our brains — are the largest cells in the human body and come in various, asymmetrical shapes which makes creating copies of itself difficult since mitosis produces cells that are exactly the same in shape, size, and function.⁴˒⁵ One of the ways the brain produces new neurons, however, is by using a pre-existing stock of cells that have not undergone specialization.⁶ Known as neural stem cells (SCs), these entities can change into neurons in certain parts of the brain. On top of this, SCs in the brain also produce copies of themselves (known as symmetric division), thereby creating a reserve of SCs that in the future, will specialize into whatever cells (e.g., neurons, astrocytes, glia) the brain needs.⁶
While we develop in the wombs of our mothers and shortly after we’re born, our cells undergo transformation to serve specialized functions. So, even though our neurons don’t multiply like other types of cells, the reserve of SCs in the brain, often referred to as basal progenitor cells, are always poised to give birth to new neurons in times of need.⁶
Research shows that fungal species can grow brain cells
Fungi are truly fantastic. Encompassing various species of yeasts, rusts, molds, and mushrooms, fungi can thrive in the harshest radioactive environments, are incredible agents of ecological health, while also providing unexpected health benefits to us humans.⁷ But relevant to our prior conversation about the production of new neurons, research shows that certain fungi species can facilitate new neurons in specific brain regions essential to learning and memory, such as the hippocampus.
And just like our incredible bodies, the brain also relies on different sources of “food” to thrive and stay fit. Known as neurotrophins, this family of proteins promote brain health by strengthening pre-existing neuronal connections, prompting new connections to grow (a process known as synaptogenesis), and most surprisingly, stimulating the growth of entirely new neurons — a phenomena otherwise believed to be impossible or at best, highly unlikely.
In 2023, scientists from South Korea and Australia teamed up to explore whether Hericium erinaceus, or colloquially known as lion’s mane mushroom for its shaggy, off-white appearance, could act as a neurotrophin, or brain food.⁸ Lion’s mane is an edible mushroom species abundant in North America and Eastern Asia. Their shaggy bush-like existence can be seen on the trunks of hardwood trees, and the edible portions of the shroom is used in traditional Chinese medicine as herbal medication, primarily based on the belief that it can reduce negative emotions.
The scientists hypothesized that if lion’s mane contained neurotrophins, neurons and their delicate connections would grow and strengthen in response to consuming this mushroom, which would positively affect the brain by enhancing learning and memory processes.⁸ After isolating these nutrient compounds found in lion’s mane, and feeding them to mice, scientists found that the shroom not only stimulated new brain cells to grow in the hippocampus (central to learning and memory), but encouraged more efficient growth patterns to enhance brain function.⁸ In this study, mice which were fed lion’s mane showed better memory by navigating multiple tunnels of a maze on several test runs, as opposed to the same tunnel each time. Trying out different tunnels, hypothesized the scientists, meant that the mice could remember what tunnels they have previously already visited, which indicates a robust memory and learning happening in the hippocampus.⁸
While it’s important to note that the world of neuroscience has known for the last fifty years that cells could indeed be regenerated in the hippocampus, it’s still astounding that an innocuous mushroom species can also aid in these critical processes.
Beyond the laboratory
There’s still a lot of scientific and ethical exploration to be done in the world of fungi. We know that fungal species have been used for medicinal purposes for centuries, but could they provide a novel avenue into treating brain diseases like mild cognitive decline or something more severe like dementia? It’s a well-established fact that physical activity can stimulate neurons to grow in the hippocampus as well, but for now, mushrooms are also lending robust support to the fact that certain substances can improve cognitive abilities through altering the number of cells. The world of neuroscience is excited to see what other wonders lie in the world of fungi and neuroscience!
Sources:
- Gulati A. 2015. Understanding neurogenesis in the adult human brain. Indian Journal of Pharmacology. 47(6):583–584. https://pmc.ncbi.nlm.nih.gov/articles/PMC4689008/
- Ludwig PE, Reddy V, Varacallo M. 2023. Neuroanatomy, Neurons. Treasure Island (FL): StarPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK441977/
- Sorrells SF et al. 2018. Human hippocampal neurogenesis drops sharply in children to undetectable levels in adults. Nature. 555: 377-381. https://doi.org/10.1038/nature25975
- A New Field of Neuroscience Aims to Map Connections in the Brain. 2023 Jan 19. Harvard Medical School. https://hms.harvard.edu/news/new-field-neuroscience-aims-map-connections-brain
- Frade JM, Ovejero-Benito CM. 2014. Neuronal cell cycle: the neuron itself and its circumstances. Cell Cycle. 14(5): 712–720. https://doi.org/10.1080/15384101.2015.1004937
- Masahiro Yamaguchi et al. 2016. Neural stem cells and neuro/gliogenesis in the central nervous system: understanding the structural and functional plasticity of the developing, mature, and diseased brain. The Journal of Physiological Sciences. 66: 197–206. https://doi.org/10.1007/s12576-015-0421-4
- Case NT et al. 2022. The future of fungi: threats and opportunities. Genes, Genomics, Genetics. 12(11): unknown. https://doi.org/10.1093/g3journal/jkac224
- Martinez-Marmol R et al. 2023. Hericerin derivatives activates a pan-neurotrophic pathway in central hippocampal neurons converging to ERK1/2 signaling enhancing spatial memory. Journal of Neurochemistry. 165(6): 791-808. https://doi.org/10.1111/jnc.15767