MAPT and Alzheimer disease: In AD, ultrafast fMRI has determined that the cardiovascular pulse propagation inside the brain parenchyma is more variable, and that the main driver for increased CVBOLD is intracranial cardiorespiratory pulsation: this is thought to link with glymphatic clearance.35,37 The impulse speeds were mostly increased in narrowed peripheral arteries but, importantly, a reversed impulse propagation was detected in (para)hippocampal areas known to present increases in the permeability of the blood brain barrier (BBB) irrespective of β-amyloid/tau depositions in early AD.29,37,41