The tangles in some areas of the brain were getting to be so thick it was like trying to kick a soccer ball through a chain-link fence.

Ultimately, many of the neurons would die, and the brain would begin to shrink. Because the brain is highly specialized, the strangulation of each clump of neurons would restrict a very specific function — the ability to convert recent events into reliable memories, for example, or the ability to recall specific words, or to consider basic math problems. Or, eventually, to speak at all, or recognize a loved one. Or to walk or swallow or breathe.