By introducing arrays of microelectrodes into hippocampal, thalamic, and neocortical areas of freely behaving rodents, we have characterized the detailed structure and content of memory patterns across ensembles of individual neurons as they are formed during spatial behavior, and reactivated during quiet wakefulness, and sleep. I will describe the contributions of these brain systems to the expression and coordination of memory reactivation, including recent results demonstrating the ability to influence reactivated memory content during sleep.