How Cold War Pollution Proved We Keep Making New Neurons

Your brain isn’t just shedding grey matter!

Turns out, the Cold War didn’t just give us nukes and paranoia—it also gave us proof that our brains keep making new neurons well into adulthood.

Scientists have known for a while that rodents crank out new neurons throughout their lives. Enough to impact learning, memory, and decision-making. But what about us humans? Do we keep making brain cells, or does our gray matter just slowly decay into forgetfulness and bad decisions?

Enter a group of international researchers with a bold idea: use the radioactive pollution from Cold War nuclear tests to track the birth of new human brain cells.

Between 1955 and 1963, nuclear tests filled the atmosphere with radiocarbon, which got absorbed by plants and, in turn, by every human who ate them. When an international treaty banned above-ground nuclear testing in 1963, radiocarbon levels began to drop. This environmental catastrophe became an accidental scientific goldmine: researchers could analyze human brain tissue for radiocarbon levels, essentially time-stamping when individual neurons were born.

Spalding et al. (2013) examined brain tissue from 55 human brains stored in Sweden, Hungary, and the U.S. The brains came from individuals aged 19 to 92 who had died between 2000 and 2012. The researchers focused on a brain region crucial for memory—the dentate gyrus region of the hippocampus.

The results? Humans generate about 700 new neurons in the dentate gyrus every day. That means around 1.75% of the neurons in that area are swapped out annually. Translation: your brain isn’t as static as you think. It’s constantly upgrading itself, which might explain why we can keep learning, recognizing patterns, and forming distinct memories well into adulthood.

What Does This Mean for You (and Your Brain)?

Pattern Recognition & Memory: Fresh neurons in the dentate gyrus help distinguish between similar experiences, forming clearer memories. Think of it as upgrading your brain’s filing system so life doesn’t become one big blur.

Mental Health Implications: Neurogenesis may be tied to mental health. Issues with pattern recognition are linked to anxiety and depression. So, continuous neuron production might not just be about memory—it could be about mood, too.

But before you start celebrating your ever-refreshing brain, let’s talk about the fine print.

The Limitations (Because Science is Beautiful But also Messy)

Not everyone is on board with Spalding et al.’s (2013) findings. Other studies, like Sorrells et al. (2018), suggest that adult hippocampal neurogenesis isn’t as robust as we’d like to think—maybe just a few new neurons in childhood before tapering off. Plus, Spalding’s study used post-mortem brain tissue from different countries, which means storage conditions, lifestyle factors, and other environmental differences could have skewed the results.

And the confidence interval on that 35% neuron turnover rate? Massive. Anywhere from 12% to 63%. That’s a wide range. In other words, that’s a 35% turnovers give or take anywhere from 12-63%! If it’s on the lower end, neurogenesis might not be as impactful as we think.

Also, the research assumes that rodent brains work similarly to human brains—a leap of faith that may or may not hold up.

So, What’s the Big Deal?

If Spalding et al. (2013) are right, adult neurogenesis is a key player in brain function. That means:

Memory Disorders: If neurogenesis fuels pattern recognition and memory, then reduced neurogenesis could explain some of the memory impairment in aging and neurodegenerative diseases. Blocking neurogenesis in rodents leads to memory problems (Jessberger et al., 2009), suggesting the same could be true for humans.

Depression & Mental Health: The dentate gyrus isn’t just about memory—it’s also tied to mood regulation. Studies (Sahay et al., 2007) suggest that reduced neurogenesis could be a factor in depression. More neurons, better mood? Potentially.

Lifestyle Choices Matter: The research points to diet (Stangl & Thuret, 2009), exercise (Vivar et al., 2012), and even alcohol consumption (Le Maître et al., 2018) as factors influencing neurogenesis. Translation: what you eat, how often you move, and whether you overdo it on booze could be shaping your brain’s ability to keep itself fresh.

The Takeaway

Unless you whittle away your days glued to a TikTok feed, your brain isn’t just a static lump of cells—it’s a dynamic, ever-evolving system. Whether you keep producing new neurons into old age may depend on factors you can control. The Cold War’s radioactive fallout accidentally gave us a tool to measure this process, but now it’s up to science to refine, challenge, and expand on these findings. In the meantime, maybe skip the extra drink and go for a run instead. Your dentate gyrus will thank you.

References

Dennis, C.V., Suh, L.S., Rodriguez, M.L., Kril, J.J., & Sutherland, G.T. (2016). Human adult neurogenesis across the ages: an immunohistochemical study. Neuropathology and Applied Neurobiology, 42(7), 621-638.

Eriksson, P.S., Perfilieva, E., Björk-Eriksson, T., Alborn, A-.M., Nordborg, C., Peterson, D.A., & Gage, F.H. (1998). Neurogenesis in the adult human hippocampus. Nature Medicine, 4, 1313-1317.

Hainmueller, T., & Bartos, M. (2020). Dentate gyrus circuits for encoding, retrieval and discrimination of episodic memories. Nature Reviews Neuroscience, 21, 153-168.

Jessberger, S., Clark, R.E., Broadbent, N.J., Clemenson, G.D., Consiglio, A., Lie, D.C., Squire, L.R., & Gage, F.H. (2009). Dentate gyrus-specific knockdown od adult neurogenesis impairs spatial and object recognition memory in adult rats. Learning & Memory, 16, 147-154.

Kempermann, G., Song, H., & Gage, F.H. (2015). Neurogenesis in the adult hippocampus. Cold Springs Harbor Perspectives in Biology, 7(9), a018812.

Knoth, R., Singec, I., Ditter, M., Pantazis, G., Capetian, P., Meyer, R.P., Horvat, V., Volk, B., & Kempermann, G. (2010). Murine features of neurogenesis in the human hippocampus across the lifespan from 0 to 100 years. PLoS one, 5(1), e8809.

Le Maître, T.W., Dhanabalan, G., Bogdanovic, N., Alkass, K., & Druid, H. (2018). Effects of alcohol abuse on proliferating cells, stem/progenitor cells, and immature neurons in the adult hippocampus. Neuropsychopharmacology, 43, 690-699.

Sahay, A., Drew, M.R., & Hen, R. (2007). Dentate gyrus neurogenesis and depression. Progress in Brain Research, 163, 697-722.

Schmidt, B., Marrone, D.F., & Markus, E.J. (2012). Disambiguating the similar: The dentate gyrus and pattern separation. Behavioural Brain Research, 226(1), 56-65.

Sorrells, S.F., Paredes, M.F., Cebrian-Silla, A., Sandoval, K., Qi, D., Kelley, K.W., James, D., Mayer, S., Chang, J., Auguste, K.I., Chang, E.F., Gutierrez, A.J., Kriegstein, A.R., Mathern, G.W., Oldham, M.C., Huang, E.J., Garcia-Verdugo, J.M., Yang, Z., & Alvarez-Buylla, A. (2018). Human hippocampal neurogenesis drops sharply in children to undetectable levels in adults. Nature, 555, 377-381.

Spalding, K.L., Bergmann, O., Alkass, K., Bernard, S., Salehpour, M., Huttner, H.B., Böstrom, E., Westerlund, I., Vial, C., Buchholz, B.A., Possnert, G., Mash, D.C., Druid, H., & Frisén, J. (2013). Dynamics of hippocampal neurogenesis in adult humans. Cell, 153(6), 1219-1227.

Stangl, D., & Thuret, S. (2009). Impact of diet on adult hippocampal neurogenesis. Genes & Nutrition, 4, 271-282.

Vivar, C., Potter, M.C., & van Praag, H. (2012). All about running: Synaptic plasticity, growth factors and adult hippocampal neurogenesis. Neurogenesis & Neural Plasticity, 15, 189-210.