Hearing relaxing words in your sleep slows your heart down

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. 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.