Our thoughts during sleep influence sleep itself. This has been shown by researchers from the University of Fribourg. The study lays an important foundation for the development of new interventions to optimize sleep quality even while we are actually sleeping.

It was not clear to date how thoughts before sleep can influence the deep sleep that occurs later. As part of the ERC project «MemoSleep» conducted by Prof. Björn Rasch, researchers developed a theory which assumes that certain mental concepts such as «sleep”, «relaxation», «safe environment» or also «stress», «pressure to perform» or «unfamiliar environment» remain active during the unconscious sleep state and have an influence on sleep quality.

Mental concepts with a prolonged effect
If these concepts are activated while falling asleep, they can still directly influence the depth of sleep hours later. This is because these concepts are closely linked with physical relaxation responses such as a decrease in heart rate or lower blood pressure. In a study newly published in the journal «Sleep», the researchers now find initial evidence for the application of the theory during sleep: «We were able to show that the activation of psychological concepts for relaxation during sleep can deepen sleep both subjectively and objectively and thus improve the recovery function of sleep», explains PhD student Jonas Beck who carried out the study at the Department of Psychology.

Relaxation words for deeper sleep
50 healthy young sleepers took part in the Unifr study and spent two nights in a sleep laboratory. On one night the researchers played quiet, relaxing words such as «relax» or «sea» over loudspeakers while the participants were sleeping. On the other night, control words were played softly. To objectively measure their sleep, the electrical activity of their brains was measured with an electroencephalogram (EEG). The focus was on the amount of deep sleep. In addition, the researchers examined the EEG signals in the 5 seconds after a word was played during sleep. The next morning, the test subjects stated how they had slept that night and how awake they felt.

The sleep researchers Jonas Beck and Björn Rasch were able to show that when the relaxation words were used, the test subjects spent more time in deep sleep compared to the night with control words. In addition, they were able to show that in the 2 to 3.5 seconds following the playing of a relaxation word during sleep, a higher proportion of the slow EEG waves that are vital for the restorative function of sleep occurred. Hearing relaxation words during sleep not only deepened sleep in an objectively measurable way, but also in the subjective assessment in the morning: the participants rated both their sleep quality and their alertness the next morning as significantly higher.

The results of the study provide initial evidence that the activation of mental concepts such as «relaxation» is able to influence sleep physiology and the subjective assessment of sleep quality.

More recovery through new interventions
«We assume that the words played at night activated the concept of «relaxation» and the associated bodily functions, thereby changing the depth of sleep. This could also explain why, for example, when we brood over an upcoming exam the night before, we sleep less well and are less rested. The mental concept of «examination» or «stress» remains present at night and activates the bodily reactions associated with stress, leading to lighter sleep and possibly making us wake up more often or earlier», says Beck. Most importantly, the study results are a step towards explaining how mental activity prior to sleep can influence how we subsequently sleep. This study could also create an important starting point for the development of new interventions to optimize the quality and restfulness of our sleep while we are actually sleeping.

References:
Beck J., Loretz E., Rasch B.: Exposure to relaxing words during sleep promotes slow-wave sleep and subjective sleep quality. Sleep. 2021; zsab148; DOI: https://doi.org/10.1093/sleep/zsab148
Publication date: 11 June 2021