'Never go to bed angry': Sleep makes it harder to forget bad thoughts

The age-old advice to "never go to bed angry" is getting some support from new research.

Researchers found that men in the study were less able to suppress a negative memory after they slept than they were before they slept.

Normally, sleep helps people process information from the day and store it in their memory . The new finding suggests that this process of solidifying memories during sleep also makes it harder to suppress negative memories, which people may not want to recall.

The results suggest that people should try to resolve any arguments before going to bed and not sleep on their anger, said study co-author Yunzhe Liu, a Ph.D. student in neuroscience at University College London.

In the study, the researchers asked 73 men in England to look at 26 neutral photos of people's faces. The photos were neutral, meaning they were not associated with either positive or negative emotions . But each of these neutral photos was paired with an upsetting image, such as a photo of corpses, crying children and injured people. This way, the men learned to associate each face with an upsetting image.

Shortly after, the researchers showed the participants some of the photos of faces again and asked them to try to suppress, or forget, their memories of the associated unsettling images. Specifically, the people were 9 percent less likely to recall the upsetting images compared with other, baseline images that the researchers had shown the participants earlier on in the study to test their memory performance .

The researchers repeated the memory-suppression task the next day, after the participants got a night's sleep, and found that this time around, the participants reported that they had more trouble forgetting the upsetting images that had been paired with the faces. Specifically they were just 3 percent less likely to recall the upsetting images compared with other, baseline images that the researchers has shown their earlier on during the study to test their memory performance.

These results suggest that sleep may make it harder for people to forget things they'd rather not remember, the researchers said.

The researchers also scanned the people's brains during the memory-suppression task, and compared the participants' brain activity when they tried to suppress the negative memory before they slept with their memory-suppression activity after they slept.

There was a difference: When the men were asked to suppress their memory of the negative image before they slept, the hippocampus — the brain's memory center — was the part of the brain that was most involved in the task of suppressing memories. But after the men got a night's sleep, other regions of the brain became activated in the task as well, according to the study, published today (Nov. 29) in the journal Nature Communications.

This last finding may lead to a better understanding of conditions such as post-traumatic stress disorder , in which people cannot suppress traumatic memories , the researchers said.

One limitation of the study was that it conducted only in men. Liu told Live Science that she thinks that the mechanisms of memory suppression before and after sleep should work the same way in women, but more research would be needed to confirm this.

Originally published on Live Science .