Remembering Events Pasts: Items, Conjunctions. Inference, and Errors in the Human MTL

Declarative memory permits an organism to bridge the past with the present, providing information about prior events that serves to inform present decisions and action. Declarative memory critically depends on the medial temporal lobe (MTL), which is composed of the hippocampal formation and the surrounding entorhinal, perirhinal, and parahippocampal cortices. Though decades of research have aimed to characterize the role of MTL in declarative memory, fundamental questions remain regarding the functional contributions of specific MTL substructures. In this talk, I will discuss fMRI and MEG data bearing on the relative contributions of hippocampus and the surrounding MTL cortices. These data support three central conclusions. First, a functional gradient exists within the MTL circuit, wherein memory for items and memory for conjunctions differentially depend on processes within MTL cortex and hippocampus, respectively. Second, the conjunctive memories built by hippocampus are flexibly addressable, enabling memory-based inferences. Third, the circuitry of the hippocampus enables it to signal novelty via the detection of conjunctive prediction errors. Through its role in multiple forms of learning and remembering, the MTL not only empowers organisms to learn from the past to predict the present, but also to acquire new knowledge when its predictions are violated.