PSEN1 and Alzheimer disease: Thus far, STED microscopy has only been used in a handful of AD-related studies, e.g., to visualize amyloid fibrils in vitro [15]; characterize in the cerebrospinal fluid (CSF) of individuals with AD the number and size of Aβ and tau aggregates [16]; determine the localization of γ-secretase in the neuronal synapse in mouse hippocampal neurons in culture [17–19]; examine nanoscale features of spine morphology in the APP/PS1 mouse model of AD amyloidosis [20]; and visualize normal, unaggregated tau protein in the mouse brain [21].