Relaxing Words Steer Sleep Quality

Summary: The human body, specifically the heart, responds to external auditory stimuli during sleep, challenging the notion that the body is disconnected from the environment during this rest period. The study demonstrates that relaxing words can slow cardiac activity, thereby deepening sleep, unlike neutral words that do not affect heart rate.

This research emphasizes the importance of brain-heart interactions during sleep and suggests that both brain and bodily reactions are crucial for understanding how sensory information modulates sleep functions. The findings not only broaden our understanding of sleep but also open new avenues for enhancing sleep quality through auditory stimuli.

Key Facts:

  1. Heart Rate Affected by Auditory Stimuli During Sleep: Relaxing words heard during sleep can slow down cardiac activity, indicating that the body remains responsive to external stimuli.
  2. Brain-Heart Interactions in Sleep: The study reveals significant brain-heart interactions during sleep, highlighting the role of the heart in processing auditory information and its impact on sleep quality.
  3. Open Science Approach for Future Research: The researchers have shared their methodology openly, encouraging further investigation into the heart’s role in other sleep-related processes, such as emotional memory processing.

Source: University of Liege

A discovery by researchers from the GIGA – Center of Research Cyclotron at University of Liège reveals that the sleeping body also reacts to the external world during sleep, explaining how some information from the sensory environment can affect sleep quality.

Researchers at ULiège have collaborated with the University of Fribourg in Switzerland to investigate whether the body is truly disconnected from the external world during sleep.

This shows a woman sleeping.
Markers of both cardiac and brain activity were then compared to disentangle how much they contributed to the modulation of sleep by auditory information. Credit: Neuroscience News

To do so, they focused on how heartbeat changes when we hear different words during sleep. They found that relaxing words slowed down cardiac activity as a reflection of deeper sleep and in comparison to neutral words that did not have such a slowing effect.

This discovery is presented in Journal of Sleep Research and sheds new light on brain-heart interactions during sleep.

Matthieu Koroma (Fund for Scientific Research – FNRS postdoctoral researcher), Christina Schmidt and Athena Demertzi (both Fund for Scientific Research – FNRS Research Associate) from the GIGA Cyclotron Research Center at ULiège teamed up with colleagues from University of Fribourg led a previous study analyzing brain data (electroencephalogram) showing that relaxing words increased deep sleep duration and sleep quality, showing that we can positively influence sleep using meaningful words.

By that time, the authors hypothesized that the brain also remains able to interpret sensory information in a way that makes our body more relaxed after hearing relaxing words during sleep. In this new study, the authors had the opportunity to analyze cardiac activity (electrocardiogram) to test this hypothesis and found that the heart slows down its activity only after the presentation of relaxing, but not control words.

Markers of both cardiac and brain activity were then compared to disentangle how much they contributed to the modulation of sleep by auditory information. Cardiac activity has been indeed proposed to directly contribute to the way we perceive the world, but such evidence was so far obtained in wakefulness.

With these results, the ULiège researchers showed that it was also true in sleep, offering a new perspective on the essential role of bodily reactions beyond brain data for our understanding of sleep.

“Most of sleep research focuses on the brain and rarely investigates bodily activity”, says Dr. Schmidt.

“We nevertheless hypothesize that the brain and the body are connected even when we cannot fully communicate, including sleep. Both brain and body information need then to be taken into account for a full understanding of how we think and react to our environment”, explains Dr. Demertzi.

“We shared freely our methodology following the principles of Open Science hoping that the tools that helped to make this discovery will inspire other researchers to study the role played by the heart in other sleep functions”, Dr.Koroma advocates.

This work offers a more comprehensive approach about the modulation of sleep functions by sensory information. By looking into the cardiac responses to sounds, we may, for example, study in the future the role of the body in the way sounds influence emotional processing of memories during sleep.

About this sleep and auditory neuroscience research news

Author: Didier Moreau
Source: University of Liege
Contact: Didier Moreau – University of Liege
Image: The image is credited to Neuroscience News

Original Research: Closed access.
Probing the embodiment of sleep functions: Insights from cardiac responses to word-induced relaxation during sleep” by Matthieu Koroma et al. Journal of Sleep Research

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  1. Only IF one can tolerate someone droning on while they are trying to sleep/relax.
    I went to a “relaxation class” years ago, and the bl**dy woman droning on and on and on . . . made me want to get up and kilL her, not too mention the bad migraine I got from it,

  2. Presumably we’re not saying the heart responds to words, but that our autonomic nervous system is still active while we sleep.
    The parasympathetic nervous system in this case of relaxing.
    Isn’t this the same as saying that if, while you’re sleeping, someone shouts your name, or burns things in your room, or slaps you, then you wake up – still the ANS, but the sympathetic nervous system side. Your heart will probably be beating faster. No surprise.
    Just because we’re not conscious, doesn’t mean we’re not thinking, especially given that most of our thought is outside our conscious minds anyway.
    But does this mean you can learn foreign languages in your sleep, or you can be impacted by what surgeons say while you’re under general anaesthetic?!

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