Washington: Researchers have identified the sleep mechanism that enables the brain to consolidate emotional memory and found that a popular prescription sleep aid heightens the recollection of and response to negative memories.
The findings have implications for individuals suffering from insomnia related to posttraumatic stress disorder (PTSD) and other anxiety disorders who are prescribed zolpidem (Ambien) to help them sleep.
Sara C. Mednick, assistant professor of psychology at UC Riverside, and UC San Diego psychologists Erik J. Kaestner and John T. Wixted determined that a sleep feature known as sleep spindles - bursts of brain activity that last for a second or less during a specific stage of sleep - are important for emotional memory.
Research Mednick published earlier this year demonstrated the critical role that sleep spindles play in consolidating information from short-term to long-term memory in the hippocampus, located in the cerebral cortex of the brain.
Zolpidem enhanced the process, a discovery that could lead to new sleep therapies to improve memory for aging adults and those with dementia, Alzheimer`s and schizophrenia.
It 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, focusing instead on rapid eye movement (REM) sleep.
Using two commonly prescribed sleep aids - zolpidem and sodium oxybate (Xyrem) - 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, she said.
"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.
The study may have even broader implications, the researchers said.
The study appeared in the Journal of Cognitive Neuroscience.