Mapping how 100 billion cells in the brain all fit together is the brave new world of neuroscience

A few months back there was a very interesting report on using Rabies to map the brain connections, the Rabies virus infect neurons but it doesn't spread indiscriminately to other cells close by, instead it replicates inside the infected neuron and uses the synapses to travel to the next neuron. By making recombinant virus that stain the cells they infect scientists can see which other neurons are connected to the ones infected and even get full neural pathways that can be mapped that way.

There are about 100,000,000,000 brain cells in each of us.

Brain cells would normally die by around 3,000,000 daily after we are 20 years old, without hardly any replenishment.

How many will be left when we are 100? Enough to allow us to keep thinking clearly or efficiently?

Brain cells would normally die by around 3,000,000 daily after we are 20 years old, without hardly any replenishment.

That's not the current accepted science:

https://japantoday.com/category/features/health/mapping-how-the-100-billion-cells-in-the-brain-all-fit-together-is-the-brave-new-world-of-neuroscience#comment-2732226

Good news, because it needs brain to make brain mapping. So there’s still some left.