MAPK3 and Alzheimer disease: ERK1/2 is highly expressed in the mossy fiber pathway (Hu et al, 2004; Provenzano et al, 2014); has been linked to memory function, fear extinction, and Alzheimer's disease (Sweatt, 2004; Fischer et al, 2007; Kim & Choi, 2015); interacts with the actin cytoskeleton; and translocates to the nucleus upon stimulation (Wang & Hatton, 2007; Berti & Seger, 2017).