Sleeping Can Reinforce Negative Memories, Too

Several recent studies have been produced purporting to show the healing power of sleep to overcome trauma and successfully process the routine trials of every day. A new study from the University of Massachusetts Amherst, however, suggests that might backfire, and sleep might "protect" and solidify negative emotional memories as well.

A total of 106 young adults from ages 18 to 30 were shown a series of happy or sad photographs and asked to rate their emotional responses to each. They were shown the same photos twelve hours later and asked to repeat the process. The timing of the viewings was arranged such that some participants were able to remain awake and others were expected to sleep.

As expected, sleeping after the first viewing improved recall during the second viewing. But while the researchers anticipated that sleep would dampen the emotional resonance of the negative photos, what they discovered was in fact the opposite: the sleeping group maintained their negative feelings about the sad photos much more strongly than did the waking group. An important conclusion from this is that memory and emotion can be affected differently by sleep.

From an evolutionary standpoint, preserving memories of traumatic experiences may have helped our ancestors learn from negative events and avoid them in the future. On the other hand, say the scientists at Amherst, people who witness something terrible often find it difficult to fall asleep immediately afterward. The study could then indicate that this wakefulness could be a defensive mechanism, equivalent to the brain refusing to perform an action (i.e., sleep) that will cause the prolonging of a negative experience.

The Amherst team expects their findings to have particular relevance to those suffering from post-traumatic stress disorder and individuals offering eye-witness testimony in court. Knowing how the brain handles both the memory of events and the ongoing emotional impact of those events may improve a person's ability to face and overcome bad experiences.

Source: The University of Massachusetts Amherst