Sleep Drugs Heighten Recollection of Bad Memories

The popular prescription sleep aid zolpidem appears to heighten the recollection of and response to negative memories. This finding may have implications for patients who experience insomnia related to posttraumatic stress disorder (PTSD) and other anxiety disorders.

“Drugs used as sleep aids such as zolpidem and benzodiazepines are under-studied. There are many side effects that may be subtle and unexpected,” Sara C. Mednick, PhD, Assistant Professor of Psychology at the University of California at Riverside, told ConsultantLive.

Dr Mednick and University of California at San Diego psychologists used a pharmacological intervention to modulate a specific sleep feature, sleep spindles, which are bursts of brain activity that last for a second or less during a specific stage of sleep and are important for emotional memory. “Then we examined what modulating that feature did to memory performance,” she said.

Earlier this year, Dr Mednick published research that 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 disease, 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,” Dr Mednick said. “We don’t know exactly how sleep drugs influence the brain to consolidate negative memories, but the leading hypothesis is that the memories get transferred from short-term to long-term memory storage areas (hippocampus to cortex) during sleep via sleep spindles.”
 
Until now, researchers had not considered sleep spindles as playing a role in emotional memory, focusing instead on rapid eye movement (REM) sleep, Dr Mednick said. Using 2 commonly prescribed sleep aids-zolpidem and sodium oxybate-she and her colleagues were able to determine that sleep spindles, not REM, 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,” Dr Mednick noted. “These are people who already have heightened memory for negative and high-arousal memories. Sleep drugs might exacerbate their symptoms and improve their memories for things they don’t want to remember.”

In light of the present results, Dr Mednick suggests 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. "Further research on the relationship between hypnotics and emotional mood disorders would seem to be in order,” she said.

“To be on the safe side, I would suggest that primary care physicians reduce the use of benzodiazepines and zolpidem-like drugs in their patients who have anxiety disorders and recommend that these patients use caution when taking these drugs.”

The researchers presented their results online on June 14, 2013, in the Journal of Cognitive Neuroscience.