Staying awake after experiencing a traumatic event greatly mitigates its effect, but falling asleep only worsens such an impact.
If the traumatic scene is revisted or a flashback memory occurs, it will be just as upsetting as the first time for those who have slept after viewing compared to those who have not.
Neuroscientists Rebecca Spencer, Bengi Baran and colleagues from the University of Massachusetts Amherst, say that from an evolutionary perspective, it would provide survival value to our ancestors by preserving very negative emotions and memories.
“Today, our findings have significance for people with post-traumatic stress disorder, for example, or those asked to give eye-witness testimony in court cases,” Spencer says.
“We found that if you see something disturbing, let’s say an accident scene, and then you have a flashback or you’re asked to look at a picture of the same scene later, your emotional response is greatly reduced, that is you’ll find the scene far less upsetting, if you stayed awake after the original event than if you slept. It’s interesting to note that it is common to be sleep-deprived after witnessing a traumatic scene, almost as if your brain doesn’t want to sleep on it,” adds Spenser.
In their experiments involving 68 healthy female and 38 male (total 106) young adults between 18 and 30 years old, Spencer and colleagues set out to explore, among other ideas, an assumption that the well-known enhancement of memory that occurs during sleep is tied to a change in emotional response to the memory.
Spencer and colleagues found that sleep had significant effects on participants’ memories and feelings. Recognition memory for the pictures was better following sleep compared with an awakened state.
Importantly, the researchers found that contrary to previous assumptions, sleep was tied with participants’ maintaining the strength of their initial negative feelings compared to a period of wakefulness.