Before the Limited Test Ban Treaty of 1963 barred all aboveground, sea and orbital nuclear weapons testing, the world's nations were popping off nukes like champagne bottles on New Year's. Surprisingly, that sprinkling of high-energy particles was actually quite beneficial, to science at least, as it's just helped solve a long-standing dispute in human physiology -- can the brain regrow neurons? Short answer: sort of.
Nuclear tests didn't just give Nevada its iridescent glow. At the heart of these explosions, where temperatures top that of the surface of the sun, numerous isotopes were generated and released -- like carbon-14, a relatively-benign isotope often used in archeological carbon dating techniques. This is important because biological systems, from algae on up to humans, consume and incorporate environmental carbon during cell division (including bits of atmospheric C14 from the tests). Now, since the human brain supposedly stops developing around age two, the amount of C14 incorporated into neural DNA should be roughly constant across all regions of the brain. It's not.
In a recent study published in Cell today, a team at the Karolinska Institute led by Jonas Frisén examined 120 cadaver brains and sampled C14 concentrations in its various regions, using the C14 as an indicator of cellular age, and modelled the results. They found that concentrations varied greatly, especially within the hippocampus. This suggests that the lower-concentration cells were formed after the 1963 testing halt.
In fact, only a tiny portion of the hippocampus known as the dentate gyrus exhibited new cellular growth after the age of two. These cells replaced 700 of themselves (roughly 1.5 per cent of the region) annually, though they live three years less than other neurons. No regrowth was discovered elsewhere in the organ.
Why just this one minuscule lump of flesh renews itself and not the rest of the brain remains a mystery. However, unlocking that secret could provide a quantum leap in the search for curing alzheimer's, dementia, and a host of other degenerative neural diseases. [Cell via Ars Technica]