University of California sleep researchers have identified how the brain consolidates emotional memories during sleep and found that widely-used sleeping pills heighten the recollection of, and response to, negative memories.
The findings, reported in the Journal of Cognitive Neuroscience, have implications for individuals suffering from insomnia related to posttraumatic stress disorder (PTSD) and other anxiety disorders.
The study, led by researcher Sara C. Mednick (pictured), focused on a sleep characteristic known as sleep spindles - bursts of brain activity during sleep that last for only a second. She had previously investigated the role that sleep spindles play in consolidating information from short-term to long-term memory and found that the drug zolpidem (marketed as Ambien and Stilnox) enhanced this process. Hers was the first study to show that sleep can be manipulated with pharmacology to improve memory.
"We know that sleep spindles are involved in declarative memory - explicit information we recall about the world, such as places, people and events," she explained. But until now, researchers had not considered sleep spindles as playing a role in emotional memory.
Using two commonly prescribed sleep aids - zolpidem and sodium oxybate (marketed as Xyrem and Alcover) - Mednick was able to tease apart the effects of sleep spindles and REM sleep on the recall of emotional memories. She determined that sleep spindles directly affect emotional memory.
"I was surprised by the specificity of the results, that the emotional memory improvement was specifically for the negative and high-arousal memories, and the ramifications of these results for people with anxiety disorders and PTSD," Mednick said. "These are people who already have heightened memory for negative and high-arousal memories. Sleep drugs might be improving their memories for things they don't want to remember."
The study may have even broader implications, according to Mednick and her co-researchers. They warn that the effects of widely prescribed benzodiazepines (Xanax, Valium, Paxal) on sleep are similar to those of zolpidem.
"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," Mednick said. "Further research on the relationship between hypnotics and emotional mood disorders would seem to be in order."
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Source: University of California, Riverside