“Never go to bed on an argument,” so the saying goes. And according to a new study, we should take note of this age-old advice. Researchers have found that going to sleep while still holding on to negative memories can make it harder to suppress them.

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It might be best not to go to sleep on an argument; it could make those bad memories harder to suppress.

Study co-author Yunzhe Liu, of the Institute for Brain Research at Beijing Normal University in China, and colleagues report their findings in the journal Nature Communications.

In recent years, neuroscientists have learned just how important sleep is for learning and memory.

A study reported by Medical News Today earlier this year, for example, uncovered evidence that rapid eye movement (REM) sleep – the cycle of sleep in which dreams occur – is essential for memory consolidation, the process by which information is transferred from short-term to long-term memory.

However, there are some memories we would rather not hold on to, such as those of a traumatic event. While bad memories may never be fully eradicated, studies suggest we are able to voluntarily suppress them to some extent in order to cope with trauma.

“A failure to suppress unwanted memories has been linked to symptoms in a number of psychiatric disorders including the ruminative state found in depression and intrusive memories in post-traumatic stress disorder (PTSD),” note Liu and colleagues.

They add that over time, emotional memories can become increasingly resistant to suppression, which they speculate is down to memory consolidation during sleep.

“However, it remains unknown how consolidation impacts the effectiveness of voluntary suppression of unwanted emotional memories,” say the authors.

With a view to finding out, Liu and colleagues enrolled 73 male college students and asked them to take part in a number of memory suppression tasks over 2 days.

First, subjects were required to learn associations between faces and aversive images, so that when they were reintroduced to each face, memories of the aversive image would arise.

Participants were presented with the faces again – both 30 minutes and 24 hours after learning the associations – and told to suppress any negative memories that came to mind.

During this experiment – called the “Think/No Think” task – participants’ brain activity was monitored using functional magnetic resonance imaging (fMRI).

The researchers found that when presented with the faces 24 hours after the learning task – after having had a good night’s sleep in between – subjects were more likely to remember the aversive images than when they were presented with the faces 30 minutes after the learning task.

Subjects’ brain activity during the tasks may shed light on why it was easier to remember the aversive images after sleeping.

The team found that 30 minutes after the learning task, neural circuits involved in memory suppression were more active in the hippocampus – the brain region linked to learning and memory – while 24 hours after, this activity became widely distributed in the cortex, making bad memories harder to repress.

The authors explain:

“Our findings point towards a neurobiological model through which overnight consolidation assimilates aversive memories into more distributed neocortical representations, and makes these memories more resistant to suppression through the prefrontal-hippocampal inhibitory pathway.

Our study underlines the importance of memory consolidation in understanding the resistance to suppression of emotional memories, which is a cardinal feature of affective disorders.”

They add that information on how brain changes impact memory suppression could give physicians a better understanding of PTSD and other psychological disorders associated with bad memories.

All in all, Liu and colleagues believe there is some substance to the theory that one should not go to bed on an argument.

Talking to The Guardian, the researchers say: “We would suggest to first resolve [an] argument before going to bed; don’t sleep on your anger.”

Read how retrieval practice could help protect memory in stressful scenarios.