PSEN1 and Alzheimer disease: APP/PS1 mice showed a 22% reduction in Fos-IR cells in the granular layer of the DG (WT 369.87 ± 20.70 vs. AD 289.76 ± 26.33 cells/mm2, p = 0.0378; Figures 1A–1C), but more than double the number of Fos-IR cells in the pyramidal cell layer (stratum pyramidale; SP) of CA3 and CA1 compared to age-matched wild-type littermates, differences that were highly significant (CA3: WT 64.41 ± 8.77 vs. AD 168.63 ± 23.45 cells/mm2, p = 0.0019; CA1: WT 63.68 ± 6.21 vs. AD 142.48 ± 16.03 cells/mm2, p = 0.001; Figures 1D–1I).