Neuro-Cognitive Studies of Sleep and the Generalization of Emotional Learning and Threat Detection

点击翻译按钮获取中文摘要

The ability to encode emotionally laden memories and exploit them efficiently in novel situations is among the most important learning capabilities of an individual. From correct recognition of facial expressions in emotionally-charged social situations, to discrimination between threatening and safe signals in fight-or-flight scenarios, the way we build on our past emotional experiences to decipher unfamiliar conditions strongly determines our ability to survive and function adaptively. Contemporary research on sleep and memory indicates that sleep plays a key role in the generalization of past experiences to novel situations, a process involving core brain regions such as the hippocampus, amygdala and medial prefrontal cortex. However, significant inconsistencies exist between findings regarding the effect of sleep on emotional versus non-emotional memories. These inconsistencies pose a significant obstacle for reaching a comprehensive understanding of how sleep affects memory and learning in general, and how it differentially affect fear memories in particular. Understanding how sleep assists processing of emotional memories can bridge those gaps, as well as contribute broader knowledge to inform any future developments in prevention and treatment of anxiety disorders that involve both sleep and memory generalization disruptions, specifically post-traumatic stress disorder for which sleep irregularities have been emphasized as a key factor.Current studies suggest that generalizing acquired associations of non-emotional stimuli to novel situations is influenced by a specific sleep stage termed Slow-Wave-Sleep (SWS). Processing of emotional stimuli, on the other hand, was shown to be influenced mostly by another sleep stage, Rapid-Eye-Movement (REM) sleep. These potential inconsistencies raise the question of how sleep influences processes requiring a combination of the two, namely, generalization of emotional memories. These issues, however, were only sporadically addressed in human studies, and were mainly concentrated on a narrow definition of memory generalization. The current project will attempt to elucidate the mechanism involved in the way sleep affects fear generalization and threat detection in humans, addressing the empirical and theoretical gaps by: (1) Employing long-term monitoring of sleep stages prior to, and following, fear learning, that may be more sensitive in detecting relations between cognitive mechanisms and sleep characteristics compared to studies using only single-night monitoring (2) Using novel neurocognitive assessments of fear generalization processes, focusing on discriminative learning of threat and safe stimuli, accompanied by functional neuroimaging (fMRI); (3) Studying computational network models of the key brain regions known to be involved in fear learning to simulate and interpret the experimental findings. These three approaches will allow establishing how fear generalization is affected by individual baselines of sleep patterns, whether it is differently affected by the type of stimuli generalization (discriminative versus similarity-based) required by the behavioral task, and what the level of involvement of the key brain regions is in each type of generalization task and in relation to the individual sleep patterns.