MAPT and Alzheimer disease: Just as the risk of stroke is now reduced by giving blood pressure lowering drugs prophylactically, we expect the long-term future of AD therapy to involve—at least partly—prophylactic agents that prevent pericyte-mediated capillary constriction, and thus prevent both direct effects of CBF decreases and the amplification of Aβ production and tau phosphorylation that a fall in CBF generates.