A power plant in the city runs worse and worse, but the lights in the homes have not gone out yet. The same goes for the brain: mitochondria, the cellular power plants, are losing capacity, while the neurons are still alive.
Scientists studied mice with shortened telomeres, the protective caps at the ends of chromosomes. In the memory area, the hippocampus, mitochondria began producing 20% less energy. It is as if the voltage in the city grid dropped by a fifth, but the bulbs are still glowing.
Neurons do not die right away, because they have reserves. But over time the energy deficit grows, and in some parts of the brain cells begin to die. Previously it was unclear why the brain becomes vulnerable long before cell death. Now it is clear: first the mitochondria weaken, and then the neurons go out. These data will help search for early signs of brain aging and for drugs that support mitochondria.
The brain makes up only about 2% of body mass but consumes roughly 20% of all oxygen. A 20% drop in mitochondrial activity in such an organ is equivalent to mild hypoxia.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.