Reactivation of memory: role of medial temporal lobe and prefrontal cortex.

Memory retrieval is to bring the remembered information on-line or to reactivate the information. The critical determinant of memory retrieval mechanisms is whether the information has been maintained on-line or off-line, regardless of whether it is long-term memory or short-term, working memory. Similar reactivation processes occur during retrieval from long-term memory and from working memory when online maintenance has been interrupted. The reactivation is achieved by interactions between the posterior association areas, medial temporal lobe and prefrontal cortex. Posterior association areas maintain the representations of remembered information and are reactivated at retrieval. The medial temporal lobe is primarily involved in retrieval from off-line memory and triggers the reactivation by associating a whole set of features and episodes during encoding of the information. The prefrontal cortex is involved in retrieval from both on-line and off-line memory. It controls reactivation by setting up retrieval mode, starting retrieval attempt, and monitoring the contents of reactivated information. The prefrontal cortex also controls the selection of task-relevant information from information maintained on-line.