FIG. 2. Palimpsest. Vellum scraped and written over, lit from the side. Extinction learning writes a new memory beside the old one and does not erase it: Bouton, Learning & Memory 11:485-494 (2004); Quirk and Mueller, Neuropsychopharmacology 33:56-72 (2008). On the desk: Cajal's Purkinje cell drawing, a redacted CIA release, a telegraphers' trade paper, an engraving of Edison's stock ticker, and teletype film from Prelinger Archives. The vellum grain comes from a scan of a medieval palimpsest. Credits.