“I think these findings help us understand why sleep disturbances and nightmares are such important symptoms in PTSD,” said Sean P.A. Drummond, Ph.D., professor of psychiatry at the University of California San Diego School of Medicine.
“Our study suggests the physiological mechanism whereby sleep difficulties can help maintain PTSD. It also strongly implies a mechanism by which poor sleep may impair the ability of an individual to fully benefit from exposure-based PTSD treatments, which are the gold standard of interventions.”
“The implication is that we should try treating sleep before treating the daytime symptoms of PTSD and see if those who are sleeping better when they start exposure therapy derive more benefit,” said Drummond, also director of the Behavioral Sleep Medicine Program at the VA San Diego Healthcare System.
PTSD is an often difficult-to-treat mental health condition triggered by a terrifying event. Frequently associated with people who have served in war zones, it is characterized by severe anxiety, flashbacks, nightmares, and uncontrollable thoughts.
The latest study builds on previous research on fear conditioning in animals, considered the PTSD of the animal world. In fear conditioning, an animal is trained to associate an averse stimulus, such as an electric shock, with a neutral stimulus, such as a tone or a beep. Researchers have found that this disrupts the animals’ rapid eye movement (REM) sleep, the deep, dream-filled recuperative slumber.
For their study, Drummond and his colleagues investigated the impact of fear conditioning and another form of behavioral training called safety signal learning upon human REM sleep. Safety signals are learned cues that predict an averse event won’t re-occur, scientists explained.
“In PTSD, humans learn to associate threat with a stimulus that used to be neutral or even pleasant,” he said. “Often, this fear generalizes so that they have a hard time learning that other stimuli are safe.
“For example, a U.S. Marine in Iraq might suffer trauma when her personnel carrier is blown up by a roadside bomb hidden in trash alongside the road. When she comes home, she should learn that trash on the side of I-5 does not pose a threat — it’s a safe stimulus — but that may be difficult for her.”
For the study, researchers recruited 42 healthy volunteers who were tested over three consecutive days and nights.
They found that increased safety signaling was associated with increased REM sleep consolidation at night. They also found that the quality of overnight REM sleep was related to how well volunteers managed fear conditioning.
Drummond noted that the stimuli representing safety increased human REM sleep, adding that “helps humans distinguish threatening stimuli from safe stimuli the next day. So while animal studies focused on learning and unlearning a threat, our study showed REM sleep in humans is more related to learning and remembering safety.”
He noted, however, that the findings are not conclusive. “No comparable animal studies have examined the relationship between safety and REM sleep,” he said.
“However, the findings do encourage further investigation, eventually into human PTSD populations where fear, safety, and sleep are on-going and paramount concerns among military veterans and others”, he said.
“A very large percentage of missions in both Iraq and Afghanistan were at night, so soldiers learned the night was a time of danger,” he said. “When they come home, they have a hard time learning night here is a time to relax and go to sleep.”
The study was published in the Journal of Neuroscience.