UC Davis

The hippocampus has been recognized as critical for several memory processes, but current theories disagree about how to characterize its role. Some theoretical models suggest that the hippocampus forms memories that capture relationships between different experiences (“integration”), whereas others suggest that it forms distinct representations of otherwise similar events (“differentiation”). Different computational models of hippocampal function propose different mechanisms for hippocampal integration and differentiation, and it is unclear whether a single model can explain both processes. In the first chapter of this dissertation, I consider evidence suggesting that the prefrontal cortex might mediate the tradeoff between memory integration and differentiation, flexibly modulating hippocampal functioning depending on task goals. The second chapter describes a proposed proof-of-concept hippocampal-prefrontal model that is able to handle a switch in task goals from integration to differentiation. The third chapter describes possible ways in which items may be relating to each other in a real-world environment, I present a study on the testing effect and event boundaries. We know through extensive literature that retrieval practice, or repeated recall through testing, enhances long-term memory retention. By introducing a manipulation of event boundaries, I show behaviorally, through the use of virtual reality environments, that retrieval practice or restudy of items within an event can cause forgetting of other items within the same event. In the future, this work can be related to the hippocampal and prefrontal findings associated with both the testing effect and event segmentation. Finally, the last chapter introduces an example of a disorder population, namely individuals with schizophrenia, who have deficits in memory processing, possibly related to hippocampal and prefrontal dysfunction. This chapter showcases a study of temporal sequence processing in schizophrenia, which reveals a deficit in the functioning of both the hippocampus and dorsolateral prefrontal cortex. Together, the work described in this dissertation shows literature from multiple fields of research, empirical studies, and computational modeling of the interplay between the hippocampus and prefrontal cortex.