“In a groundbreaking study conducted by researchers from the GIGA – Center of Research Cyclotron at the University of Liège, in collaboration with the University of Fribourg, it has been discovered that the human body, even while asleep, is not entirely disconnected from the external world. This study, published in the Journal of Sleep Research, reveals that our hearts respond to different types of words heard during sleep, with relaxing words causing a slow down in cardiac activity, reflecting a deeper state of sleep compared to neutral words.
During nights when relaxing words were played, participants’ heartbeats slowed down significantly, indicating a deeper level of sleep. This effect was not observed during the control nights. Furthermore, the study found that the heartbeats were modulated around the presentation of each word, with a more significant modulation for relaxing words than for neutral or reversed words.
The researchers also explored whether cardiac activity provided additional information about sleep depth beyond what could be gleaned from brain activity alone. By comparing cardiac and brain indices, they concluded that cardiac activity indeed holds unique information about sleep functions that brain markers alone cannot capture. This suggests a more complex interaction between our hearts and brains during sleep than previously understood.”
source: https://www.psypost.org/hearing-relaxing-words-during-sleep-slows-down-your-heart-rate/