If you're having a rough day, popping a sleeping pill and hitting the sack could be the worst thing you could do--it could help you recall bad memories even better than usual. Ambien has been shown to boost your brain's ability to store and consolidate memories. But it appears to work explicitly for negative emotional memories, according to new research from psychologists at the University of California.
During stage 2 sleep, sleep spindles--little flashes of brain activity--help the brain process short-term memories into long-term memories. A previous study by psychologist Sara Mednick of UC Riverside found that sleep spindles play a role in processing explicit memory, or specific facts, and a greater density of sleep spindles can enhance verbal memory.
In a new study published in Journal of Cognitive Neuroscience, Mednick and her team show sleep spindles also affect how we recall emotional memories, an area that had been associated with rapid eye movement (REM) sleep before.
Researchers gave 28 participants two different sleep aids--zolpidem (Ambien), which has been shown to increase the density of sleep spindles, and sodium oxybate (Xyrem) which decreases spindle activity. They then viewed one-second images designed to provoke a positive or negative response, before taking supervised naps. (Science: Just like kindergarten!) After taking zolpidem, their memory was enhanced--but it only increased their ability to remember the negative images, specifically those that were considered "high arousal" (like pictures of a hairy car wreck or a snake poised to attack, rather than an image of people standing around a grave). Somewhat surprisingly, sodium oxybate did not lead to a decrease in the ability to recall negative emotions, despite the decrease in spindle activity.
This could be a result of our natural tendency to recall the bad, rather than the good. "We do seem to have a stronger memory for negative emotions," Mednick told me. This could be a result of the multiple parts of the brain involved in consolidating memories of fear--it not only activates the hippocampus, but also involves the amygdala. "The more brain areas you can recruit, the better your processing," she explains. If we naturally recall these negative feelings better anyway, by increasing the mechanism by which we process memories during sleep, Ambien helps usher more negative memories into our long-term recall.
Mednick says this could impact Ambien users who suffer from anxiety disorders and PTSD. "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," she said in a statement. It could also have implications for the use of benzodiazepines, a class of drugs (including Valium) used to treat anxiety and insomnia, with similar effects on sleep.