Rapid acquisition of arbitrary associations independent of the MTL: challenging current neurobiological theories of declarative memory

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Current theories of declarative memory propose two complementary learning systems in the mammalian brain: a hippocampal-centered system that supports rapid learning of arbitrary associations, and a neocortical-centered system that only learns slowly by extracting statistical generalities out of multiple similar experiences. Contrary to this model, we recently demonstrated rapid acquisition of novel arbitrary associations by severely amnesic patients with extensive lesions to the Medial Temporal Lobe (MTL) including the hippocampal complex. This was achieved through "Fast Mapping" (FM): A process that supports vocabulary acquisition in toddlers in whom the MTL is not fully developed. Patients with Anterior Temporal Lobe (ATL) lesions were unable to learn through FM, suggesting that neocortical region is critical for FM learning. The first objective of the proposed set of studies is to further understand the nature of the information learned through FM. Specifically, to further demonstrate that the information learned through FM is declarative I aim to test two central features that distinguish declarative and non-declarative memory: the flexibility of the novel arbitrary associations acquired through FM and the awareness subjects have of the novel knowledge. The second objective of the proposed research is to gather evidence as to whether learning through FM involves consolidation processes or merely neural adaptation. Finally, the third aim is to better understand what makes FM learning unique and allows it to putatively incorporate novel semantic information directly into existing neocortical networks. I would like to test is whether this can only work for completely novel information, but which is embedded within existing categorized knowledge structures. The overall scientific approach will involve behavioural investigations in healthy adults and patients with amnesia following MTL lesions and patients with ATL damage, employing the lesion-deficit as well as functional neuroimaging and network analyses of functional and effective connectivity.