Offering something to help someone relax after having a nasty shock seems natural, but careful they don't go to sleep. According to a new study, going to sleep directly after witnessing a traumatic event may be what ties the unpleasant experience to emotional memories that may lead to post traumatic stress.
Researchers from the University of Massachusetts Amherst showed 106 volunteers ages 18 to 30, 30 highly disturbing and 30 neutral images and found that the group of people with who stay awake after initially seeing the images were less likely to be disturbed if they saw the image again in contrast with the group who slept shortly after.
"From a clinical standpoint, insomnia following trauma might not necessarily be bad," said study lead author Rebecca Spencer, a psychologist at the University of Massachusetts Amherst. "It may be the appropriate biological response and might help you forget something traumatic."
The volunteers were asked to rate on a scale from one to 9 how calm or excited each image made them feel. They then divided 82 of the volunteers into two groups, one that slept after being shown the images the other group were not allowed to sleep or given any alcohol. Twelve hours later, the researchers mixed the original 60 pictures in with 120, and showed each group asking if they remembered seeing the each picture before.
To understand if the time of day the test was done had any effect on participants' memory performance the researchers assigned 24 of the remaining volunteers to sessions that were only 45 minutes apart, carried out in both the morning and the evening.
Published in the The Journal of Neuroscience the researchers found that sleep improved the participants' recollection of both negative and neutral images, but the group that had not slept found the images less disturbing the second time they were shown.
"Sleep protected their emotional reactivity," Spencer said suggesting it helped to seal in those negative emotional responses.
Spenser and her team found that even after a long period of sleep which involved dreaming during REM, memory was not affected, but it did affect emotional response. In fact the longer they slept the higher they rated the images as disturbing the second time seeing them.
These results contrast with previous research by UC Berkeley who found that nearly all mood disorders and emotional experiences are processed during sleep to help take the edge off painful memories.
View related article: Deep sleep takes the edge of trauma
But while scientists agree that the brain consolidates memories and ties in an emotional response during sleep, the actual connection between both hasn't been explored until now.
"There are profound implications for preventing post-traumatic stress disorder," Spenser says. "Should we have people sleep or should we sleep deprive them?"
One study "essentially didn't find what another study has found," said Stephan Hamann, who studies the relationship between sleep, memory and emotion at Emory University in Georgia. Although Hamann was not involved with the research, he told LiveScience that "very little research has been devoted to teasing out the relationship between sleep and emotional memory, but the new study will stimulate more interest in the topic."
View gallery: Tips for a good night's sleep
While more research is needed into sleep and emotional balance, we can at least use the findings that memory improves with more sleep.