We used to think that the human brain was unchanging once a person reached maturity. Not true. One of the things that helped debunk this idea was the most destructive weapon ever created. This is what nuclear bombs proved about the human brain.
Early brain research indicated that, although other cells in the body regenerated after they were damaged, and continued to grow and change throughout a person's life, the brain was remarkably resistant to change. Once you were grown, you essentially were stuck with the brain configuration you had. In the 1960s, that thinking began to change. The brain cells didn't divide the way other cells might. Neural stem cells sat around for some indeterminate amount of time, before they sprang into action. They turned into neuroblasts, which migrated around, then split into full-fledged neurons.
That was the theory, at least, but it was hard to find ways to prove it. No one knew exactly how to stimulate the generation of brain cells, so the process often involved putting markers in rat brain cells, waiting for rats to die, and dissecting their brains. When it was discovered that the markers themselves might cause mutations, scientists had to come up with something new.
Enter the atom bomb. Sometime, tens of thousands of years into the future, the atom bomb is going to be a real annoyance to scientists. Scientists use carbon-14 dating to determine the age of organic matter. There's a certain amount of carbon-14, a specific isotope of carbon, in the atmosphere. It gets incorporated into living cells as they are made. Once the cell dies, the carbon decays, slowly, over thousands of years. Measuring the amount of decay allows scientist to get a rough estimate of when the cell lived and died.
Above-ground testing of the atom bomb caused a huge spike in the amount of carbon-14 in the atmosphere. For the years during which there were above-ground tests, the amount of the isotope incorporated into new cells went way up. Someday, that's going to be a source of ambiguity to scientists. For now, it's a source of information. By studying the amount of carbon 14 in different cells in human brains, scientists are able to see what neurons were newly-made between the years of 1945 and 1963. The difference in carbon 14 levels shows that some adults did make new cells, especially in certain parts of the brain. So there's one positive side of above-ground nuclear testing.
Image: U.S. Army Photographic Signal Corps
[Via Physics Central]