Why do we sleep? We spend nearly one-third of our lives sleeping. Growing evidence suggests that one purpose of sleep is to strengthen memories formed during the day, particularly if these memories are emotional. With the support of the National Science Foundation, Dr. Elizabeth Kensinger (Boston College), Dr. Jessica Payne (Notre Dame), Dr. Bob Stickgold (Beth Israel hospital), and their students are assessing the role of sleep in memory formation, focusing on how memory for emotional experiences changes over sleep-filled delays. In particular, this research examines how sleep contributes to the maintenance of an emotional trade-off in memory, whereby people have difficulty remembering information presented in close proximity to an emotional item, although they remember the emotional item itself extremely well. This research combines electroencephalography (EEG), functional magnetic resonance imaging (fMRI), and behavioral methods in examing how different phases of sleep can lead to re-wiring of the neural circuits used to retrieve emotional memories, and how such re-wiring is influenced by the way an emotional event is first experienced.
Memory trade-offs are magnified in those with depression and anxiety, and both disorders are associated with dramatic changes in sleep. Understanding the cognitive and neural mechanisms of the development and long-term preservation of these memory trade-offs is thus essential for knowledge of both healthy and dysfunctional emotional processing. Moreover, a longstanding question in cognitive neuroscience is how memory for emotional experiences is consolidated over time, and examining sleep-dependent effects on memory trade-offs provides a rare window through which to view the consolidation processes at work. Examining sleep effects on memory trade-offs also provides a means to answer one of the most mystifying questions in the field in sleep and memory research, which is how sleep-dependent consolidation processes preferentially select some aspects of an experience for long-term storage while allowing other aspects of memory to be forgotten. In addition to contributing to cognitive neuroscience and clinical psychology research, funding of this project enabling the growth of the neuroscience program at Boston College and helping launch a neuroscience focus at the University of Notre Dame. Moreover, this project is facilitating fruitful collaborations between Boston College, Beth Israel hospital, and Notre Dame, allowing students to benefit from training at all three sites. The project offers a rich research infrastructure for undergraduate student learning, providing them with exposure to EEG, fMRI, and behavioral assessment.
The scientific goal of this project was to examine the role of sleep on the "emotional memory trade-off," a phenomenon whereby emotional elements of a scene are often remembered at the cost of other concurrently presented information. Through the research supported by this grant, we reached a number of important conclusions about the role of sleep in this "trade-off" effect. We demonstrated that a night of sleep is sufficient to aide in the selective retention of emotional components of studied scenes. While periods of wakefulness lead to memory degradation of all scene elements, regardless of the emotional content of information, periods of sleep lead to a relative preservation of emotional content from scenes (Payne & Kensinger, 2011; Payne et al., 2012) and to a refinement of the neural processes recruited to retrieve those emotional elements (Payne & Kensinger, 2011; Bennion et al., 2014). Thus, sleep enables the selective maintenance of emotional information in memory. Our work also revealed that, over this night of sleep, processes that act during periods of Rapid Eye Movement (REM) sleep are of particular importance for solidifying emotional memories: The retention of emotional information strongly correlates with the amount of overnight REM sleep achieved. This finding is important because it suggests that the benefits conveyed by sleep are not just due to passive processes that could operate throughout the night of sleep, but rather stem from active processes that selectively preserve emotional content while allowing other content to decay from memory. Our research further showed that the benefits of sleep are relatively long-lasting, and are maximal when sleep follows soon after the encounter with emotional information (Payne, Chambers, & Kensinger, 2012). Our results also began to shed light on the neurobiological processes implicated in these effects of sleep, demonstrating that arousal and stress responses present at the time of processing the emotional information may aide in the creation of a salience signal, allowing sleep to selectively preserve the memories of the salient stimuli (Bennion et al., in press; Cunningham et al., 2014). These studies emphasize that sleep is not a time of dormancy for the brain, and the neural activity that occurs during sleep serves to shape which aspects of our past we remember upon waking. The project had the educational and outreach goals of involving student trainees in the research and in actively discussing research with community members. To meet our educational goals, we established a Cognitive Neuroscience Summer Research Exchange program between Notre Dame and Boston College; each summer, students spent 6-10 weeks at the other university to learn new research methods. We included a high school intern on the project each summer, and we trained multiple graduate students through the conduct of the research. To achieve our outreach goals, we organized and participated in Brain Awareness Week activities each year, gave talks at elementary, middle, and high schools, at other colleges, at senior centers and retirement communities, and for corporations. These outreach activities were geared toward explaining the importance of getting a good night’s sleep for mental health and cognitive function: a message we believe is critical to spread given the high rates of sleep deprivation in our society.
