My parents have been married for nearly 50 years. For the longest time my father would tell me that the key to a healthy marriage is to never go to bed angry under any circumstances, but what pops said all those years wasn't unique to just him. It's long been thought that going to bed angry or with hard feelings will turn into resentment. Now, science has evidence that support these claims.
A study published in the journal Nature Communications suggests that the brain reorganizes the way that negative memories are stored during sleep and makes these associations more difficult to suppress in the future. Over the course of two days the study used “think/no-think,” a psychological technique used to gauge how successfully 73 male students could suppress memories.
The men first learned to associate pairs of neutral faces and unsettling images like injured people, dead bodies, and crying children. The men were then showed the images again and told to either think of the image or consciously avoid thinking of it. Just 30 minutes after the session ended participants were nine percent less likely to remember the image they were instructed to avoid compared to the image they were supposed to remember. Twenty-four hours after the session they were three percent less likely to recall the image.
Functional MRI scans shed light on why memories may be tougher for people to recall once they have been consolidated by sleep. Recent memories were seen in brain activity tightly centered on the brain's memory center known as the hippocampus, while overnight memories were redistributed across the cortex. What that means is your brain is storing those bad memories.
Moral of the study? Don't let your brain store memories of that last fight by going to bed angry.