A new study from Sleep researchers at University of California campuses in Riverside and San Diego has identified the sleep mechanism that enables the brain to consolidate emotional memory, and the study results indicate a broader role for sleep in the processing of emotional stimuli with differing effects based on arousal and valence, and raises the possibility that sleep spindles causally facilitate emotional memory consolidation.
The study — “Pharmacologically Increasing Sleep Spindles Enhances Recognition for Negative and High-arousal Memories” is published in the Journal of Cognitive Neuroscience.
In the study the researchers experimentally increase non-REM sleep features, sleep spindle density, and SWS, with pharmacological interventions using Zolpidem (ambien) and sodium oxybate (xyrem) during daytime naps. The researchers also use a full spread of emotional stimuli to test all levels of valence and arousal and found that increasing sleep spindle density increases memory discrimination (da) for highly arousing and negative stimuli without altering measures of bias (ca).
Using two commonly prescribed sleep aids — zolpidem and sodium oxybate (Xyrem) the studys authors Mednick, Kaestner and Wixted were able to tease apart the effects of sleep spindles and rapid eye movement (REM) sleep on the recall of emotional memories. They determined that sleep spindles, not REM, affect emotional memory.
The researchers gave zolpidem, sodium oxybate (Xyrem) and a placebo to 28 men and women between the ages of 18 and 39 who were normal sleepers, allowing several days between doses to allow the pharmaceuticals to leave their bodies. The participants viewed standardized images known to elicit positive and negative responses for one second before and after taking supervised naps. They recalled more images that had negative or highly arousing content after taking zolpidem, a finding that also suggests that the brain may favor consolidation of negative memories.
The study may have even broader implications, the researchers said. Clinical guidelines of the U.S. Department of Veterans Affairs and Department of Defense recommend against the routine use of benzodiazepines to treat PTSD, although their use increased among men and women with PTSD between 2003 and 2010. The effects of benzodiazepines on sleep are similar to those of zolpidem. The U.S. Air Force uses zolpidem as one of the prescribed “no-go pills” to help flight crews calm down after taking stimulants to stay awake during long missions, the researchers noted in the study.
“In light of the present results, it would be worthwhile to investigate whether the administration of benzodiazepine-like drugs may be increasing the retention of highly arousing and negative memories, which would have a countertherapeutic effect,” they wrote. “Further research on the relationship between hypnotics and emotional mood disorders would seem to be in order.”