In regular cells, like in bone and blood, the cells divide. But brain cells do not normally divide. The great majority will not divide. The neurons you're born with are pretty much what you have at end of life.

Cells become stuck in the process of cell division.

The finding would indicate that there are earlier events that are happening that precede the plaque build-up. The authors have demonstrated in animal models that these changes are happening as early as six months before the first signs of plaque accumulation. This seems to be a separate cellular process unlinked to the plaque process.

It really is going against the central grain of what we know, and it actually may lead to something more promising.

My brain cells are dying in their trillions.

Brain cells are normally not sensitive to light. So by introducing light-sensitive proteins into specific types of neurons, we can now selectively control that specific type of neuron by shining light in the brain.