Many people use relaxing sounds or voices to help them fall asleep. Now it turns out keeping those sounds on while resting could be just as helpful in keeping one asleep. New research reveals that the body continues responding to external stimuli during sleep, with relaxing words slowing heart rate and contributing to deeper, better rest.
The findings help overturn the notion that people become wholly disconnected from their surroundings while sleeping. Instead, the sleeping brain keeps processing sensory information in ways that can influence sleep’s restorative quality.
Published in the Journal of Sleep Research, the study was led by scientists at the University of Liège, Belgium along with partners at the University of Fribourg, Switzerland.
Measuring Words’ Impact on Slumber
Previous research showed that playing relaxing vocabulary during sleep increased time spent in deepest stages and improved reported sleep quality upon waking.
Scientists hypothesized that accompanying physical changes, specifically in cardiac activity, might also occur—indicating the body was still attuned to the sleeping environment.
They tested this by monitoring study participants’ heart rhythms via electrocardiograms along with brain waves during an afternoon nap. Acoustic recordings of words hypothetically labeled “relaxing” or “neutral” were played at random intervals.
Analyzing the results revealed that heart rates decelerated after exposure to relaxing words versus neutral ones. Slower beats signify bodily calm and are associated with deeper non-REM sleep.
Integrating Brain and Body
The findings reinforce a view of sleep as an integrated brain-body process—not just switched “on” or “off” states.
Measuring cardiac activity along with neural signals better captures sleep’s multidimensional nature, the authors said.
“We nevertheless hypothesize that the brain and the body are connected even when we cannot fully communicate, including sleep,” said study author Athena Demertzi, GIGA Cyclotron Research Center at ULiège. “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.”
Hidden Influences on Slumber
Most sleep research focuses squarely on brain signals like waves and electrical rhythms. While crucial, this singular approach excludes potential impacts from the broader bodily ecosystem.
Immune activity, cardiovascular and metabolic states, hormone levels, and more can subtly shape sleep architecture from moment to moment—for better or worse.
Monitoring multiple systems simultaneously is admittedly challenging. But the Liège findings suggest a more holistic analysis better captures how sleep remains dynamic, responsive, and regulated by a symphony of internal feedback loops.
By tracking changes over time across neural circuits, organs, and tissues, scientists can better expose hidden connections between mind, body, and the outside environment that continue modulating sleep behind the scenes.
Open Methodology
The research team also published their experimental protocols and custom analysis scripts. This transparency will help other groups reproduce or extend the work to investigate impacts of music, white noise, vibrations, and more on the sleeping body.
Ultimately, the project reveals that the sensory world continues exerting its influence even after the lights go out and eyes close. The body keeps reacting under the surface, with positive or negative consequences.
Understanding these hidden dimensions of sleep offers new avenues for improving health and wellness during the roughly third of human life spent at rest.
