Dynamic arousal and mental states construct memories of time and events
Even though our lives unfold continuously, our personal narratives don’t strictly mirror this constant stream of information. Instead, our memories reflect the passage of discrete and meaningful episodes, much like chapters in a book. Our work shows that dynamic fluctuations in arousal - physiological states characterized by alertness and mental stimulation – promote this transformation of continuous experience into individualized and meaningful memories. In our lab, we use eye-tracking techniques to measure pupil size, an index of arousal, and eye gaze, an index of where attention is directed, to study how memories are formed and structured. Currently, we are examining how stress and emotional experiences influence these memory-structuring processes as well as our subjective sense of time.
Putting the 'episode' in 'episodic memory'
As time unfolds, even the simplest changes in the world, such as crossing through a doorway, can lead individuals to perceive a 'boundary' between adjacent events. Interestingly, these context shifts (e.g., spatial change) also have reliable consequences for how memories become organized later on. In the lab, we examine how the ebb and flow of experience - including changes in our thoughts, feelings, and surroundings - guide the creation of new 'episodes' in memory; that is, memories linked to a specific time and place. The role of context in memory may in part explain why our memories and subjective sense of time have melted away during the COVID-19 pandemic. While working from home on a daily basis, we lack the variety in contexts, novelty, and excitement that normally enable the brain to effectively acquire and store new memories. We use various neuroimaging tools, such as fMRI, to study the brain mechanisms that support these important memory processes, with an especially strong focus on the brainstem and a region known as the hippocampus.
Norepinephrine amplifies selectivity in attention and memory under arousal
Eyewitnesses to a crime often remember the perpetrator's weapon at the expense of remembering the perpetrator's face. How do we explain these types of attention- and memory-narrowing effects that occur under emotional circumstances? Our work suggests that a surge in arousal triggers the release of norepinephrine, a stress hormone, across most of the brain. This neuromodulator, in turn, interacts with local brain activity to enhance processing of important information while also suppressing processing of more mundane or distracting information.
Emotion and neuromodulators determine what we recollect
It often feels as if we are 're-living' past experiences when they are called to mind. This seems to be especially true for emotional events, which tend to become our most vivid and enduring memories. But which details of those experiences give rise to this rich sense of recollection? In collaboration with Dr. Vishnu Murty, we propose that a balance between noradrenergic and dopaminergic activity may determine which information is re-experienced when we retrieve emotional or motivationally-significant memories.
Dr. David Clewett will be accepting graduate student applications in Fall 2021.