Research into the molecular changes underlying hippocampus-dependent memory formation has identified an important role of the ERK MAPK (extracellular signal-regulated kinase, mitogen-activated protein kinase) cascade and subsequent induction of the immediate-early genes (IEGs) FBJ murine osteosarcoma (c-Fos), early growth response 1 (Egr-1) and activity-regulated cytoskeleton-associated protein (Arc) (Atkins et al., 1998; Blum et al., 1999; Guzowski et al., 2001; Adams and Sweatt, 2002). The gene discussed is ARC; the disease is osteosarcoma.