It’s said that time heals all wounds, but could sleep help to heal the wounds of our past?
The link between healthy sleep and memory is well documented. Sleep is essential for the formation and consolidation of new memories, with a side effect of many sleep disorders being poor brain function and memory loss.
But does the relationship between sleep and memory go deeper than that? Does sleep not only help us to form new memories, but also rewrite the old ones?
A new study suggests that may be the case, revealing just how healing a good night’s rest can be, and how past trauma could be treated through the power of sleep.
The experiment
Conducted by PNAS, the peer-reviewed scientific journal of the National Academy of Sciences (NAS), the study involved 37 volunteers and took place over several days.
These volunteers were first given a set of 48 nonsense words, which were then linked to unpleasant images taken from established databases. These included images of fierce animals and injuries, designed to induce a mild but definitively negative emotional reaction.
After a night of sleep, helping to stabilise the new memories, the volunteers were then given 24 of the same nonsense words and a new set of positive images to associate them with, such as smiling faces and calm, pleasant scenery, designed to evoke a feeling of safety and contentment. The intention was not to erase the initial negative memories, but to interfere with them through the creation of a new, positive emotional connections.
During the second night, while the volunteers were in the deep phase of non-rapid eye movement sleep, the words were quietly played aloud. The non-rapid eye movement phase is known to be essential to memory processing.
The findings
As the words were played, the researchers measured brain activity using electroencephalography. It was noted that, while the nonsense words were played, there was increased theta band activity, a signal associated with emotional memory. Perhaps surprisingly, the signal was notably stronger when the words had been associated with both the positive and negative images rather than solely the negative ones.
This indicates that the sleeping brain is more responsive to positive memories than negative ones, replaying them more actively and thus making them stronger once the volunteers woke up.
In the days following the experiment, the volunteers were asked to fill in a series of questionnaires and memory tests. The results of these tests consistently showed that the volunteers were more easily able to recall the positive memories associated with the second set of images than the negative ones.
This was still the case even when thoughts came involuntarily. Intrusive memories associated with the images tended to be more positive, and the negative association was harder to recall than before.
The negative memories hadn’t disappeared entirely, but they were much weaker, evoking a less potent emotional response.
What could this mean for trauma treatment?
While the results of the research have some promising implications, the researchers were careful to temper them, as viewing unpleasant pictures in a laboratory setting is not the same as real world trauma, which tends to be far more personal, emotional, and visceral.
Even so, the results suggest that positive memories can be made to take up more space during sleep, a time where memories are solidified. It further indicates that there may be a non-invasive way to weaken traumatic memories, one which does not involve medication or direct brain stimulation.
According to this study, one way to deal with traumatic memories may be, not to avoid or suppress them, but to take the sting out of them with new positive associations, aided by the healing power of sleep.