Long-term potentiation (LTP) is the most dominant model for neuronal changes that might encode memory. LTP is an elegant concept that meets many criteria set up by theoreticians long before the model's discovery, and also fits the anatomical data of learning-dependent synapse changes. Since the discovery of LTP, the question has remained regarding how closely LTP produced in vitro by artificial stimulation of neurons actually models putative learning-induced synaptic changes. A number of recent investigations have tried to correlate synaptic changes observed after learning with changes...