Role of REM Sleep in Emotional Memory Consolidation with Implications for Post-Traumatic Stress Disorder
Abstract
Sleep confers a special benefit for learning and memory consolidation: For a variety of tasks, subjects who sleep for 8 hours at night between learning the task and being tested on it perform much better than those who learn the task in the morning and are tested 8 hours later. Rapid eye movement (REM) sleep, the stage of sleep during which vivid dreams occur, has been implicated in the consolidation of both procedural memories (e. g., memories for the performance of motor tasks) and emotional memories. With respect to emotional memories, which are the focus of this proposal, it is thought that REM sleep consolidates the content of an emotional memory while at the same time reducing the emotional charge of the memory. The goal of the proposed research is to understand the neural dynamics responsible for emotional memory expression and suppression during awake behavior, the dynamics responsible for emotional memory consolidation during REM sleep, and the aberrant REM sleep dynamics that are associated with the symptoms of post-traumatic stress disorder (PTSD). Experimental studies suggest that rhythmic interactions between the prefrontal cortex and the limbic structures (in particular the amygdala, a brain structure critical for emotional processing, and the hippocampus, which is important for many memory processes and provides contextual information) are key for the expression and consolidation of emotional memories. In addition, our recent work using intracranial recordings from humans resulted in the exciting discovery that beta (15-35 Hz) and theta (4-8 Hz) oscillations are prominent in both the dorsolateral prefrontal cortex (DLPFC) and the anterior cingulate cortex (ACC) during REM sleep and that these oscillations are coherent between the ACC and the DLPFC, two relatively distant structures that are both important for memory processes and implicated in emotional regulation. We will achieve our research goals by building the first ever biophysically detailed large-scale model of the ACC, DLPFC, hippocampus, and amygdala. Plasticity mechanisms will be incorporated into the entire circuit, and our findings concerning the dynamics of beta and theta oscillations in the prefrontal cortices and the limbic system during REM sleep will be incorporated. We will employ our model in three ways. First, we will use it to gain insight into the mechanisms by which emotional memories are expressed during awake behavior. Though rhythmic interactions between the prefrontal cortex and limbic structures are known to be important, the mechanisms by which those neural dynamics translate to the expression of emotional memories at the circuit and biophysical level remain largely unknown. Second, we will modify our model to capture REM sleep processes by making changes to mimic the neurotransmitter levels (for example, lower levels of serotonin and norepinephrine) during REM sleep. This will allow an exploration of how the content of an emotional memory is strengthened while the emotional charge is reduced during REM sleep. We will examine the interplay of oscillatory dynamics in the various network structures, determine which dynamics are critical for the transformation of emotional memories and how this transformation is brought about at a biophysical level, and pinpoint the changes in the connectivity patterns that are essential for emotional memory consolidation. The results of this investigation will provide us for the first time with a systems level and mechanistic understanding of how memories are expressed and suppressed during waking activity and how emotional memories are consolidated during REM sleep. It will also provide a baseline against which neural dynamics in diseases like depression and PTSD can be compared. This will allow the identification of biomarkers that may be used to flag aberrant dynamics in such diseases...
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 11, 2018
- Source ID
- W911NF1710300
Entities
People
- Nancy Kopell
Organizations
- Army Contracting Command
- Boston University
- United States Army