Proof that our brains are not stagnant comes from a very strange source: a process based on the amount of carbon-14 found in humans as a result of nuclear testing in the 1960s.
Here's how it works:
Thanks (or rather, no thanks!) to the above-ground nuclear bomb testing we did in the 1960s, we've had more carbon-14 in our atmosphere. But when they banned nuclear tests in 1963, the carbon-14 started decreasing.
But when we eat plants or meat (and I presume, fish), we absorb the carbon-14 and the EXACT atmospheric concentration of that moment is stamped in our DNA when a new neuron is born. It's like carbon dating for genetics!
So, researchers from the Karolinska Institute measured the carbon-14 in the DNA from brain cells in the hippocampus of deceased adults. They found that more than one-third are regulary renewed throughout life!
In fact they got it down to how many neurons are "born" each day during adulthood: about 1,400. And the even better news is that the number only decreases modestly as we age.
Here's the summary:
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