Regina Patrick is a freelance medical writer and registered sleep technologist with more than 30 years of experience in the sleep field.
Memory is the ability to store and recall information. Recent research indicates that a certain type of brainwave, called a sleep spindle, may be involved in memory. This finding could someday improve sleep in people with post-traumatic stress disorder (PTSD).
In the first half of the 20th century, many scientists believed that no brain structure was involved in memory. However, in the 1950s, neurosurgeon William Scoville described memory problems in patients whose hippocampus (pronounced "HIP-poh-CAM-pus) had been damaged during brain surgery. After surgery, patients would have problems remembering having performed a recent action, remembering where they had placed an object after using it, or remembering significant past life events such as the death of a loved one.
The hippocampus is a small structure at the base of the brain that relays signals to a nearby structure, the thalamus (pronounced "THAL-uh-mus"). In response, the thalamus relays sleep spindles to the surface the brain. Spindles are short bursts of brainwave activity (12-16 cycles/second) that last about one-half second.
To examine the impact of spindles on memory in humans, scientists can artificially alter the number of spindle bursts occurring during sleep by using the hypnotic drug zolpidem (trade name, Ambien), which increases spindling, or the wake-promoting drug sodium oxybate (trade name, Xyrem), which is used to treat narcolepsy and decreases spindling. After receiving these drugs, a person undergoes memory tasks. For example, in a study at the University of California, San Diego, the study participants (all normal sleepers) first viewed images that were designed to elicit positive or negative responses. After taking zolpidem, the researchers noted that the participants more readily recalled the negative images. This suggests that zolpidem, by increasing spindling, may enhance emotional memory. (Erik Kaestner, who headed this study, reported his findings in the October 2013 issue of the Journal of Cognitive Neuroscience.)
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People who have PTSD experience intrusive negative memories that are connected to a previous traumatic event or series of events. The memories elicit strong emotions such as terror, panic, anxiety, and fear. Dreaming about the event or dreams with themes related to the traumatic event can disrupt sleep or induce nocturnal panic attacks. Zolpidem or benzodiazepine drugs (e.g., diazepam [trade name, Valium], clonazepam [trade name, Klonopin]) are sometimes prescribed to people with PTSD to try to improve their sleep.
Zolpidem, which is a nonbenzodiazepine drug, and benzodiazepine drugs act on the same brain regions. If these regions are also involved in negative emotional memory, then giving people with PTSD these classes of drugs may inadvertently worsen the disorder. However, the apparent link between sleep spindles and memory is a recent finding, and the extent that certain hypnotic drugs may worsen PTSD symptoms needs further investigation. If future studies corroborate that these sleep medications worsen emotional memory and thereby worsen the sleep of people with PTSD, then it may be that using another class of sleep medicine could improve sleep in people with PTSD.
Kaestner EJ, Wixted JT, Mednick SC. Pharmacologically increasing sleep spindles enhances recognition for negative and high-arousal memories. Journal of Cognitive Neuroscience. 2013;25:1597-1610.
Mednick SC, McDevitt EA, Walsh JK, et al. The critical role of sleep spindles in hippocampal-dependent memory: A pharmacology study. Journal of Neuroscience. 2013;33:4494–4504.
Scoville WB, Milner B. Loss of recent memory after bilateral hippocampal lesions. Journal of Neurology, Neurosurgery, and Psychiatry. 1957;20(1):11–21.
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