Most modern theories assume that memories are stored in the brain in the form of changed patterns of synaptic connections within ensembles of neurons, although it remains debated whether such patterns are stable once formed or subject to dynamic change. Any such growth or reorganization of synapses requires the synthesis of the molecules comprising them, especially the proteins and lipids of the synaptic and dendritic membranes. The idea that memory formation involves protein synthesis has been around for a long time—certainly since the days of Santiago Ramón y Cajal (Spanish histologist, 1852-1934) at the beginning of the twentieth century—but serious experimental tests of the idea became possible only with techniques available beginning in the 1960s. The adult brain has one of the highest rates of protein synthesis of any body organ, and also...