Older people used to say the proverb that we shouldn't go to bed angry. It appears the words of wisdom hold scientific credence as a new study shows that it's harder to suppress bad memories if we sleep on them.

The study reveals that there may be new and other ways to treat people with conditions such as PTSD, and it reinforces an idea that it may be possible to suppress bad memories with the opposite of sleep -- sleep deprivation.

Christoph Nissen at the University of Freiburg Medical Center in Germany told New Scientist that a work such as this will spark new interest to those who want to rid of unwanted memories or memories of traumatic events. Nissen was not involved in the work.

The study involves 73 male students that memorized 26 mugshots, each paired with a disturbing image such as a multilated body, a corpse or a crying child. The next day they were asked to recall the images associated with half the mugshots.

The group were then directed to memorize the 26 pairs and half an hour later they again thought about half the associated images.

Finally, they were asked to describe the image associated with each of the now 52 mugshots. The idea was to see if suppressing memory works better before or after sleep.

The participants struggled most to forget the disturbing images were the ones that came the first day. This means that sleep may make it hard to erase bad memories.

Yunzhe Liu, who worked on the study at Beijing Normal University, said that it may be possible for people to get a bad memory out of their minds by not thinking about it much and not sleeping on it.

In fact, scans on the students' brains showed that different regions were involved in actively "dispelling" these images away from their heads. For instance, when they tried to forget images they learned half an hour ago, the task relied on the hippocampi or the brain's memory storage. After sleeping, the task required activity in a much more diverse set of regions.

This implies that bad memories get consolidated across several brain regions during sleep, making them harder to erase. It also suggests that sleep deprivation could be used to prevent these memories from sticking around.

However, another key factor may be the passage of time, not just sleep deprivation. Nissen said future research is needed to check whether the event is time-dependent or sleep-specific.