A simple hypothesis which could explain this might be that the plaques cause effectivelt permanent brain damage. The question is whether degenerative patterns ceased or slowed after substantial clearing of plaques from the brain.

I would expect this test (and therefore the hypothesis) to fail if the plaques themselves are a byproduct rather than the cause of degradation in brain function. That said, I'm surprised I haven't read much in Gates' Notes or other funding sources on potential ties to HSV1 considering all the increasingly supportive research between the two.