Understanding the Relationship Between Sleep and Emotions

Many individuals experience occasional nights of poor sleep, often managing to push through the next day and compensating with an early bedtime. However, for those battling psychiatric conditions like depression, anxiety, or PTSD, the consequences of a restless night can be profound.

Recent research published in Current Biology indicates that a particular type of disrupted sleep may be more detrimental than total sleep deprivation when it comes to managing emotions. This investigation, which incorporated karaoke performances, unusual scents, and MRI imaging, took a fresh look at the emotional functions of sleep. The findings imply that not all sleep is beneficial for our mental health.

“It’s particularly challenging for individuals with insomnia or other sleep disorders to alleviate emotional turmoil,” explains senior study author Eus van Someren, a neuroscientist at the Netherlands National Institute for Neuroscience. Previously, his team established a link between REM sleep—characterized by vivid dreaming—and emotional recovery. In this study, they engaged 30 participants to explore the specifics of this connection.

To assess emotional recovery, the researchers first needed to induce distress. They had participants sing a challenging karaoke track while listening to a loud playback, which made it difficult to hear their own voices. “In such situations, people often end up singing off-key and out of sync,” notes van Someren.

After capturing recordings of their less-than-stellar performances, participants were made to listen to these recordings in silence. “I was among the initial participants,” van Someren recalls, “and I could feel the sweat on my palms, dreading how poorly I performed.”

Days later, subjects returned for MRI scans while listening to their embarrassing recordings. Their amygdalae—the brain's emotional response center—activated, signaling significant emotional distress. To enhance the memory of this embarrassment, researchers introduced a specific scent during the listening session, leveraging the strong link between olfactory cues and memory.

Participants then spent the night in a sleep lab where their brain activity was monitored, with the triggering scent introduced during the night. The following morning, they re-entered the MRI and listened to their karaoke renditions once more.

Those who experienced uninterrupted REM sleep—up to 20 minutes—reported feeling significantly less embarrassment compared to the previous day. This mirrors the common experience of feeling relief after a good night’s sleep following an upsetting event. Conversely, individuals who experienced fragmented REM sleep, a common issue for those with depression or PTSD, reported heightened embarrassment.

While the karaoke trigger during REM sleep appeared to aid those with uninterrupted REM, it seemed counterproductive for individuals with disrupted REM patterns. As a control, researchers also paired a different scent with a skilled singer to test reactions.

According to Gina Poe, a UCLA neuroscientist specializing in sleep, memory, and trauma, the locus coeruleus—a small area in the brainstem—plays a crucial role here. This region produces noradrenaline, a brain-specific form of adrenaline, and is linked to the fight-or-flight response. It remains active during wakefulness and most sleep stages, but becomes inactive during uninterrupted REM sleep, allowing the brain to process and store memories effectively.

In individuals with fragmented REM sleep, however, the locus coeruleus may not deactivate. This ongoing release of noradrenaline can keep embarrassing memories vivid, making them feel as though they just occurred.

While this theory remains to be thoroughly validated in human studies, the current research provides initial supporting evidence. It shows that participants who experience uninterrupted REM sleep connected to negative emotions (like shame) can recover better than those with disrupted REM sleep, who end up feeling more embarrassed. The prevailing explanation is indeed linked to noradrenaline, according to van Someren.

“We have begun to assume that sleep universally benefits us,” he states. This study suggests that assumption may not hold true in every case.

Exploring the Effects of Sleep on Memory and Emotions