APP and Alzheimer disease: Here, we investigated ongoing activity of neurons in the visual cortex (V1) of a genetic mouse model of AD carrying the mutated human amyloid precursor protein (APP) gene as well as human mutated presenilin 1 (5xFAD, APP K670N, M671L, I716V; PS1 M146L,L286V;37), prior to the onset of apparent neurodegeneration and pronounced plaque formation.