Stress at learning interacts with sleep to optimally consolidate emotional memories

Boston College, Chestnut Hill MA

Investigators

Abstract

We spend nearly a third of our lives sleeping, yet research is just beginning to shed light on the multitude of benefits that are conveyed by sleep. One important benefit of sleep is to strengthen the memories we form during the day, particularly if those memories have some future utility. But how is future utility determined? This research tests a new model which proposes that sleep selectively strengthens memories for events that are associated with elevated levels of stress hormones or with elevated physiological arousal, such as changes in heart rate or sweating, when we first encounter them. This research is significant for a number of reasons. In a society in which many people are chronically sleep deprived, and report high levels of stress, it is important to understand how interactions between stress and sleep may influence the ability for the human brain to store and remember information. This research will clarify how stressful situations are remembered over time, which may yield new insights into why sleep disruption often co-occurs with affective disorders (such as depression) and memory problems. The project provides training in the integrated use of functional magnetic resonance imaging (fMRI), stress, and sleep scoring and recording methods; it continues a summer research exchange program between Boston College and Notre Dame; and it supports high school internships, exposing diverse students to neuroscience, a field that is not included in most high school curricula. The project also contains an outreach component that strives to inform community members of the importance of prioritizing sleep and the value of stress management. Emotional memories form the core of our personal histories, marking our greatest achievements and worst defeats. While our ability to remember and learn from these events is critical for survival, how we remember them can also influence the development of affective disorders, such as clinical depression and post-traumatic stress disorder (PTSD). Negative experiences enjoy a privileged status in memory, being better remembered than most neutral events, yet there is a limited understanding of how such memories are consolidated and stored. The PIs' prior research demonstrated that sleep selectively preserves emotional memories, but only if participants had higher resting cortisol levels and elevated psychophysiological responses at the time of encoding. We now propose to directly manipulate encoding levels of stress and to examine how stress at encoding may enhance connectivity within emotional-memory neural networks (Aim 1); how sleep may preserve this enhanced connectivity over time (Aim 2); and how these effects of stress and sleep may combine to enhance emotional memory performance (Aim 3) and neural cohesiveness in emotional memory networks during memory retrieval (Aim 4). It is widely thought that stress disrupts sleep, and sleep affects sensitivity to stress, yet there are few empirical tests of their shared influence on cognition and emotion. However, these interactions are critical to understand given the 1) increase in stress-related illnesses and sleep disruption and the concurrent rise in affective disorders, 2) prevalence of PTSD in the military, and 3) likely impact of stress and sleep disruption in the classroom and workplace. By uniting the traditionally separate fields of sleep and stress, and examining the interactive effects of processes that unfold during encoding and consolidation, this novel research is expected to yield transformative findings. The proposal strengthens a productive collaboration between Elizabeth Kensinger at Boston College (BC), with expertise in affective neuroscience and Jessica Payne at Notre Dame (ND), with expertise in sleep and stress effects on memory.