Anterograde amnesia following hippocampal damage involves the loss of the capacity to form new declarative memories but leaves nondeclarative memory processes intact. Current theories of declarative memory suggest the existence of two complementary memory systems: a hippocampal-based system that specializes in rapid acquisition of specific events and a neocortical system that slowly learns through environmental statistical regularities and requires the initial support of the hippocampal system. Contrary to this notion, we demonstrate a neurocognitive mechanism that enables rapid acquisition of novel arbitrary associations independently of the hippocampus. This mechanism has been dubbed "fast mapping" (FM) and is believed to support the rapid acquisition of vocabulary in children as young as 16 mo of age. We used FM to teach novel word-picture associations to four profoundly amnesic patients with hippocampal system damage. Patients were able to acquire arbitrary associations through FM normally, despite profound impairment on a matched standard associative memory task. Most importantly, they retained what they learned through FM after a week's delay, when they were around chance level on the standard task. By contrast, two patients with unilateral damage to the left polar temporal neocortex were impaired on FM, suggesting that this cortical region is critical for associative learning through FM. Left perirhinal and entorhinal cortices might also play a role in learning through FM. Contrary to current theories, these findings indicate that rapid acquisition of declarativelike (relational) memory can be accomplished independently of the hippocampus and that neocortical plasticity can be induced rapidly to support novel arbitrary associations.consolidation | medial temporal lobe | neocortex | semantic memory M emory consolidation is a gradual, time-dependent, reorganization process by which memories become stable. Systems consolidation of declarative memory is thought to occur when memories that are initially supported by both the hippocampus and the neocortex become hippocampus-independent over periods of time that range from weeks to years (1-3). Systems consolidation is thought to be gradual because rapid acquisition of novel information by the neocortex would cause interference with existing knowledge structures ["catastrophic interference" (1)]. Therefore, novel associations always depend initially on the hippocampus, which specializes in rapid representation of novel associations or arbitrary relations. The hippocampus, in turn, supports the gradual changes in neocortical connections that allow for the incorporation of novel information into existing knowledge structures (1-4). We hypothesized that an exception to this rule might be observed in a process called "fast mapping" (FM) (5, 6), which supports the astounding ability of toddlers as young as 16 mo of age (7) to acquire rapidly vast numbers of novel word-referent associations. We predicted that adults with lesions to the hippocampus might be able to lea...