Academic CentreCharan Ranganath
Director, UC Davis Memory and Plasticity Program and Professor of Neuroscience and Psychology
Complementary learning systems in Memory and Navigation
Since the pioneering work of Ebbinghaus (1885), researchers have studied memory through lists of items, with the implicit idea that memories are composed of simple items and associations that faithfully represent past experiences. This perspective is difficult to reconcile with almost a century of research that has shown that human memory is dynamic and constructive, such that we do not replay the past, but rather, we rely on prior knowledge about events, along with a small amount of retrieved information to imagine how the past could have been. Drawing from this work, my colleagues and I have embraced a radical alternative to the dominant view in systems neuroscience: Rather than recording every moment of experience, the brain might reconstruct past events from information gathered at moments of high uncertainty or prediction error, or "event boundaries". I will present data consistent with the view that the hippocampus and subcomponents of the neocortical "Default Mode Network" serve as complementary learning systems, with the former playing a role in recording snapshots of cortical activity at event boundaries, and the latter involved in using prior knowledge to understand and reconstruct past events. Our computational modeling and empirical data suggest that this model also can account for the neural mechanisms of spatial navigation. Specifically, our recent modeling suggests that "grid cells" in the entorhinal cortex support disambiguation of similar events in episodic memory, and recent intracranial recordings suggest that cortico-hippocampal interactions occur disproportionately at decision points and goal locations during navigation. These data are consistent with the idea that precisely-timed interactions between the hippocampus and neocortex enable complex online computations that enable event-specific information to be integrated with general knowledge about events, environments, and tasks
Aidan J. Horner
York Episodic Memory Lab, University of York, UK
Tracking the emergence of location-based spatial representations
As we learn new spatial environments we are eventually able to identify specific locations, regardless of our current heading direction. This ability allows us to know where we are independent of our current direction of travel. While previous research has provided evidence for the existence of ‘location-based’ representations in the human brain, we still know little about their formation. I will present a recently developed experimental approach that allows us to track the emergence of location-based representations by assessing neural responses pre- vs post-learning. Participants view individual real-world static scenes during scanning. Some of these scenes are from different viewpoints (e.g., 00 and 1800) from the same real-world location. During scanning, participants also watch videos that pan from one scene to another, providing evidence that specific scenes are from the same spatial location. Using fMRI, we show that the representations of scenes from the same location become more similar post- vs pre-learning, suggesting the emergence of ‘location-based’ representations. I will also present recent MEG data using a similar design to reveal the temporal dynamics of location-based learning. Using a combination of fMRI and MEG data, I will provide insight into the neural mechanisms that allow for the emergence of location-based representations in the human brain.
Nora Newcombe
Laura H. Carnell Professor of Psychology, Research in Spatial Cognition (RISC) Lab, Temple University, USA
Charting Our Way in Space and Time
Episodic memory and navigation are two adaptive functions that share some neural substrates and that develop in humans from fragile beginnings in the first two years to mature competencies (with individual differences) by early adolescence. But how are they related, both in development and maturity? In this talk, I will discuss the two developmental trajectories, and some possible answers to that question.