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A DYNAMIC MODEL OF MEMORY FORMATION AND RETRIEVAL

A fundamental question in the study of memory is why we remember some events and not others. Researchers have tended to approach this question by isolating discrete memory events from the backdrop of ongoing cognitive and neural processing. Despite its many successes, this approach neglects the processes that occur both before and after an event. Our research explores the possibility that this ongoing processing influences the fate of a memory. Specifically, we test how neuromodulators, like dopamine and acetylcholine, and the experiences that trigger their release, establish prolonged cognitive states, which facilitate either memory encoding or retrieval.

How do salient events change memory?
  • We study how salient and behaviorally relevant events, such as noveltyreward, and uncertainty, change the way we form and retrieve memories. It has been shown in animals that these events evoke the release of slow acting neuromodulators. These chemicals affect neural processes in the hippocampus, such as synaptic plasticity and memory reactivation, over the time scale of seconds to minutes. We leverage these basic neuroscience discoveries to test biologically-informed predictions about which aspects of human memory should be influenced by recent salient experiences.  For example, I have shown that recent exposure to novelty makes people better at identifying subtle changes to an image, whereas recent exposure to familiarity makes people better at retrieving unrelated past experiences.


How does the hippocampus support memory encoding and retrieval?
  • Our research explores the possibility that the hippocampal processes that support one phase of memory can hinder another. For example, the computational process of pattern separation is thought to be necessary for the formation of distinctive memories, however it also suppresses associative retrieval. Similarly, memory encoding and retrieval differ in the extent to which they rely upon or would be hampered by synaptic plasticity and the competitive processing of internally or externally generated information.  One solution to these trade-offs is that the hippocampus could operate in different states, which either facilitate memory formation or retrieval. For example, we have shown that successful encoding and retrieval are associated with distinct patterns of functional connectivity both within the hippocampus and between the hippocampus and dopaminergic midbrain nuclei.


How do neuromodulators influence human memory?
  • Research in animal models has uncovered the critical role that neuromodulators, such as dopamine, acetylcholine, and norepinephrine, play in hippocampal processing. Our research aims to translate these findings into predictions about human cognition. To do this, we use pharmacological manipulations and we study patient populations who have dysregulation in neuromodulatory systems. For example, I have previously tested how d-amphetamine influences memory formation and retrieval in healthy young adults. Importantly, this research has the potential to guide new treatment development and testing for memory disorders in addition to providing new insights into fundamental memory questions.