Relaxing Words During Sleep: A Heartbeat Slowing Discovery

Discover how the sound of relaxing words during sleep soothes the mind.

Recent advancements in sleep research have illuminated a fascinating aspect of our sleep cycle, our bodies’ responsiveness to external auditory stimuli, even in the depths of slumber. 

A collaborative study conducted by the University of Liège, alongside the University of Fribourg, Switzerland, delves into this phenomenon by examining the impact of relaxing versus neutral words on cardiac activity during sleep. 

Their findings reveal that the soothing tones of calming words significantly decelerate heart rate. This indicates a more profound and restorative state of sleep. This research not only challenges the long-held belief that the body is completely disconnected from the external environment during sleep but also opens new avenues for understanding the intricate relationship between the brain and the heart in sleep physiology.

The Heart’s Response to Words

The core of this research centred on the intriguing question: How does the heart respond to auditory stimuli during sleep? By meticulously analysing the cardiac activity of participants exposed to relaxing and neutral words while asleep, the researchers uncovered a remarkable finding. Relaxing words, characterised by their soothing and calming nature, led to a significant reduction in heart rate compared to neutral words, which lacked this effect. 

This pivotal highlights the heart’s sensitivity to the type of words heard during sleep. It also highlights a deeper sleep state induced by calming auditory stimuli. The study offers a new perspective on the synergistic relationship between the auditory environment and sleep physiology.

A Collaborative Effort

The research into the effects of relaxing words on sleep and cardiac activity marks a significant collaborative effort between the University of Liège’s GIGA Cyclotron Research Center and the University of Fribourg. This partnership brought together experts in various fields, including Matthieu Koroma, Christina Schmidt, and Athena Demertzi from the University of Liège, who were pivotal in leading the investigation. Their previous work had already hinted at the potential for auditory stimuli, specifically relaxing words, to enhance sleep quality by influencing brain activity. This foundation spurred the team to explore further how these stimuli could also affect cardiac activity during sleep.

Building on their initial findings, the team embarked on this new study with a hypothesis that the heart, much like the brain, remains responsive to external auditory stimuli during sleep. This hypothesis was grounded in their understanding of the brain’s capacity to process sensory information in a way that promotes relaxation and enhances sleep quality upon exposure to calming words. The investigation aimed to extend this understanding to include the heart’s response, exploring how auditory stimuli during sleep could influence cardiac activity.

The research highlights the necessity of considering both brain and cardiac responses to fully comprehend the impact of auditory stimuli on sleep quality. By doing so, it provided a more holistic view of the sleep experience, suggesting that the interplay between the brain and heart is crucial for understanding how external stimuli affect sleep. The collaboration between the University of Liège and the University of Fribourg exemplifies the importance of interdisciplinary research in uncovering the complex mechanisms underlying sleep and highlights the potential for novel approaches to enhancing sleep quality through auditory stimuli.

Insights into Cardiac and Brain Activity

The study’s innovative approach to understanding sleep involved a comprehensive analysis of both cardiac and brain activity. It revealed a nuanced view of how auditory stimuli during sleep affects the heart and mind. It employed electrocardiogram (ECG) to monitor cardiac responses and electroencephalogram (EEG) for brain activity.  Researchers could discern the distinct but interconnected roles these physiological responses play in sleep modulation. The finding that relaxing words can slow down highlights a symbiotic relationship between the heart and brain during sleep.

This dual-focus methodology provides compelling evidence supporting the hypothesis that the heart is not just a passive recipient of brain commands during sleep but an active participant in sleep quality and depth regulation. The research aligns with a growing body of evidence suggesting that sleep is a more dynamic and interactive state than previously understood, involving complex interactions between various physiological systems.

By bridging the gap between cardiac and neurological research in sleep studies, this work opens up new therapeutic avenues. Understanding how specific types of auditory stimuli, like relaxing words, can modulate this brain-heart interaction points towards innovative approaches to improving sleep quality. For individuals suffering from sleep disorders, this could mean the development of non-pharmacological interventions that leverage auditory stimuli to induce a deeper, more restorative sleep.

Implications and Future Directions

The implication that auditory stimuli, specifically relaxing words, can induce deeper sleep and slow heart rate presents a novel avenue for sleep therapy. This could lead to the development of targeted sleep enhancement programs. Such non-pharmacological interventions could be particularly beneficial for individuals with insomnia or other sleep disorders. By offering a complementary or alternative approach to traditional sleep medications, which often come with side effects.

Beyond clinical applications, this research has practical implications for the general public. It suggests that the careful curation of sleep environments. This includes the auditory landscape, can significantly impact sleep quality. Individuals may explore the use of sound machines, apps, or other devices that emit calming words or sounds, potentially improving sleep hygiene and overall well-being.

The study also paves the way for future research into the mechanisms underlying the observed effects of relaxing words on sleep quality. Questions remain about the specific characteristics of words or sounds that elicit the most beneficial responses, such as tone, volume, and frequency. Furthermore, investigating the long-term effects of auditory stimuli on sleep patterns and the potential differences in response among different populations could provide deeper insights into personalised sleep therapy.


  1. Matthieu Koroma, Jonas Beck, Christina Schmidt, Björn Rasch, Athena Demertzi. Probing the embodiment of sleep functions: Insights from cardiac responses to word‐induced relaxation during sleep. Journal of Sleep Research, 2024; DOI: 10.1111/jsr.14160
  2. Hearing relaxing words in your sleep slows your heart down. (2024, February 24). ScienceDaily.

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