Even during sleep, the body remains partially connected to the external world. A groundbreaking study, titled "Probing the embodiment of sleep functions: Insights from cardiac responses to word-induced relaxation during sleep" published in the Journal of Sleep Research, highlights that the human heart responds to words heard during sleep, slowing down in cardiac activity when exposed to relaxing words, signifying a deeper sleep state compared to neutral words.
Unraveling the Role of Cardiac Activity in Sleep Quality and Memory Enhancement
Traditionally, the relationship between bodily functions and cognitive processes like memory, emotion, and perception has been extensively explored during wakefulness.
This concept termed the embodiment of cognitive functions, proposes that our bodily states impact cognitive processes. Previous studies have emphasized the role of cardiac activity in enhancing overnight memory, indicating a connection between heart activity and sleep quality.
But the ways in which cardiac activity affects cognitive functions during sleep have been mostly unexplored. This gap, along with the common neglect of ECG analysis in sleep studies, prompted the current research to examine how the heart's responses during sleep can reveal information about sleep quality and cognitive processing.
Christina Schmidt, one of the researchers, pointed out that the majority of sleep studies concentrate on the brain, neglecting bodily activity. Co-author Athena Demertzi supplemented, expressing the hypothesis that the brain and body remain connected even during sleep when full communication is not possible.
They suggest that a comprehensive understanding of how we think and respond to our environment requires considering information from both the brain and the body.
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How Words Impact Heartbeat and Deepen Sleep
Researchers from the GIGA - Center of Research Cyclotron at the University of Liège, in collaboration with the University of Fribourg in Switzerland, explored whether the body remains connected to the external world during sleep.
Their focus was on how the heartbeat reacts to different words heard during sleep. Relaxing words were found to slow down cardiac activity, indicative of deeper sleep, compared to neutral words. This discovery provides new insights into the interplay between the brain and the heart during sleep.
In a prior study, the researchers analyzed brain data and found that relaxing words increased deep sleep duration and quality. This led to the hypothesis that the brain can interpret sensory information during sleep, influencing the body's relaxation.
The recent study allowed the analysis of cardiac activity, confirming that the heart slows down only after hearing relaxing words, not control words. By comparing markers of both cardiac and brain activity, the researchers demonstrated the significant role of bodily reactions, extending beyond brain data, in understanding sleep modulation.
This research offers a comprehensive approach to understanding how sensory information modulates sleep functions. Analyzing cardiac responses to sounds may open avenues for studying the body's role in the impact of sounds on the emotional processing of memories during sleep.
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