We know that the quality of the sleep we get at night sleep has a strong impact on our waking lives. However, what we don’t know is how the different sleep stages contribute to how we process life experiences and memories.

New research out this week in the journal eNeuro has used an unusual method to try and understand this more.

Our sleep consists of different stages that help us to process our day. Deep sleep, also known as slow wave sleep (SWS) is associated with memory consolidation and helps to make our memories longer lasting. Rapid eye movement (REM) sleep is the period of sleep where we dream and consolidate our memories. It is less well understood, but thought to be associated with the way that we process emotions and how we remember experiences that are more emotionally charged.

To try and understand this better, scientists took 29 volunteers and asked them to sing Abba’s Dancing Queen on karaoke while wearing headphones that meant they couldn’t hear their own voice. They then took this recording of their singing, removed the background music and played the out-of-tune singing back to the volunteer right before bedtime. The volunteers reported feeling embarrassed when they heard the recording. The volunteers then went to sleep while being monitored and the researchers woke them up during the night either during their SWS or their REM sleep stage. The volunteers were then replayed the bad singing tape the next morning after their disrupted sleep and 5 days later.

Every time they were played the tape, the scientists measured the physiological stress response of the volunteers through a skin conductance level test and measured their reported stress level through a subjective embarrassment rating test.

The researchers found that the volunteers who had been disrupted during their SWS sleep phase but kept their REM sleep intact had higher measured stress levels every time they listened to their embarrassing tape compared to those who were disrupted during their REM stage.

They concluded that the REM stage of sleep plays a crucial role in preserving and even strengthening how emotionally charged a stressful memory is.

The study could help those suffering from anxiety disorders to use sleep therapy that disrupts their REM stages of sleep to help them to reduce some of their negative emotions.

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