Intriguingly, some AD mouse models show a decrease in the number of Arc-expressing cells in the cortex (Wegenast-Braun et al., 2009), a reduced Arc mRNA expression following explorative behavior (Palop et al., 2005; Wegenast-Braun et al., 2009), and lower levels of Arc mRNA in Aβ-containing brain regions (Dickey et al., 2004). This evidence concerns the gene ARC and Alzheimer disease.