Why you shouldn't go to sleep angry
Going to bed angry or upset may make it harder to suppress negative emotional memories, according to a study published this week...
Sleep plays an important role in consolidating our experiences in to long term memories, but what if it's a memory you want to forget? Yunzhe Liu and colleagues looked at the effect of a good night's sleep on our ability to block out unpleasant memories, which may help us understand conditions like post traumatic stress disorder (PTSD) and depressive rumination. Conditions like these often involve reliving or fixating on painful experiences, so understanding how sleep affects the brain's ability to suppress memories may help provide an insight into how to better treat them.
In this study, participants were trained to associate various neutral faces with images of upsetting scenes, with different pairs of images on consecutive days. Later, they were shown the neutral faces again, while being asked to either recall the upsetting image or to push it out of their mind, in what is known as a 'Think/No Think' procedure.
Small changes in the conduction of the skin due to sweat gland activity were also used to identify whether the memory was triggered and hence if suppression was successful, in addition to memory recall tests.
For the images shown 30 minutes before the testing phase, participants managed almost 9% conscious suppression relative to a control set. However, image pairs shown 24 hours before testing could only be suppressed by around 3%. Conscious suppression seemed much less effective after a night of sleep.
Brain scans taken during the testing phase shed some light on what was going on. According to Shaozheng Qin, one of the researchers in this work, when you try to push out negative memories, you engage the prefrontal cortex, which sends an inhibiting signal to the hippocampus. More prefrontal cortex engagement was needed to suppress memories acquired the previous day.
Additionally, the patterns associated with a memory were more distributed throughout the brain after 24 hours, which may make them harder to suppress.
These results, announced this week in the journal Nature Communications, were unable to separate whether the memory consolidation was sleep-dependent or simply time-dependent, as all of the participants had a full night's sleep, and the study only included male students in their early 20s who may not be representative of the general population. However, these results do give an interesting insight into how our brain's consolidation of memories changes our ability to suppress them, which may help better treat conditions like PTSD in future.
For now, the message is clear: for the thought to slide away, don't nap in anger...