Fast Mapping: How to acquire new declarative memories independently from the Hippocampus?

Current theories of declarative memory suggest that it is supported by two complementary memory systems: the medial temporal lobe (MTL) which specializes in rapid acquisition of novel associations and the neocortex, which slowly learns through environmental regularities. Gilboa et al. recently reported an extraordinary phenomenon of rapid acquisition of novel arbitrary associations by adults with severe anterograde amnesia due to extensive MTL lesions. These data challenge the accepted view of dual declarative memory systems and offer a radically different mechanism for directly acquiring semantics without enlisting the hippocampus: the Fast Mapping. Fast Mapping refers to a process that supports vocabulary acquisition among children who do not have a mature hippocampus. They actively infer the meaning of novel words by generating hypotheses based on contextual cues or on the way the words are used in a sentence. By using a multidisciplinary approach, this project aims at highlighting the neural substrates and the cognitive mechanisms underlying this type of learning. First, we will explore the neural basis of FM by a clinical approach. We will contrast the performance of patients whose pathology primarily involves the Anterior Temporal Lobe (Semantic Dementia) with that of patients with more pronounced Medial Temporal Lobe pathology (Alzheimer’s disease). In a second experiment we will use Transcranial Magnetic Stimulation in order to highlight the brain regions that are involved in the FM learning. Experiments 3 and 4 aim at investigating the neurocognitive mechanisms underlying FM. Using a Bayesian framework, we will try to demonstrate how knowledge and inference are used in combination with repeated exposures to guide people in learning new words. We will also use MEG to highlight the patterns’ changes of neocortical activity when participant learn through FM. Finally, we will develop new tools for memory rehabilitation based on the FM acquisition.