Can Netflix keep you from sleeping soundly?

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 (Image: Pixabay CC0)
(Image: Pixabay CC0)
Watching suspenseful TV series with cliffhangers before going to sleep has only minor effects on sleep. That’s what scientists at the University of Freiburg have shown. The study reveals what happens in our brains when we sleep after a binge-watching session.

Does binge-watching suspenseful TV series before going to sleep have a real impact on our sleep? This is the question that Professors Björn Rasch and Andreas Fahr from the University of Fribourg asked themselves in a project entitled ’Excessive Media Use in Times of Netflix’, funded by the Swiss National Science Foundation (SNSF). They studied the new phenomenon of binge-watching series, the underlying motivations and experiences, and the effects on sleep. In a study recently published in the journal Sleep Medicine, they were particularly interested in the exciting effect of this activity on sleep.

Cliffhangers increase excitement before sleep
An excited feeling is associated with more difficulty sleeping, longer time to sleep or more fragmented sleep. Indeed, the symptoms of excitement, such as increased heart rate or ruminations, are totally opposite to the physical and mental states that promote good quality sleep. The recently published study shows that binge-watching a suspenseful series before going to bed increases feelings of stress. However, the physiological aspects of arousal, such as increased heart rate and cortisol levels, are only observed when the series ends with a cliffhanger’, explains Sandrine Baselgia, PhD student at the Department of Psychology.

Only minor effects on sleep
50 healthy young sleepers participated in the Unifr study. They spent two nights in a sleep laboratory. One night, they watched 3-4 episodes of a suspenseful television series before going to bed. The other night, they watched a neutral documentary series for the same amount of time before going to sleep. For one group of participants, the suspenseful series ended with a cliffhanger just before going to sleep, while for the other group, the end of the suspenseful series was manipulated to end in a calm situation. To objectively measure their sleep, the electrical activity of their brains was measured using an electroencephalogram (EEG). The focus was on the time it took to fall asleep and the quality of sleep. The latter was measured both subjectively - according to the participants’ report the next morning - and objectively - with the amount of deep sleep and the ratio between slow and fast EEG oscillations, a higher ratio indicating more restful sleep.

Despite the clear increase in arousal before sleep, Sandrine Baselgia and Björn Rasch showed that the effects of a thriller series on sleep quality were not significantly different from those of a neutral documentary. The differences in the subjective evaluation of sleep quality were only minor. To the scientists’ surprise, sleep latency was even significantly reduced after the series. On the other hand, it was also observed that the test subjects spent less time in deep sleep when the series ended with a cliffhanger, compared to a series without one. This effect was particularly visible in the first two sleep cycles (about three hours). The same result appears in the EEG oscillations: the ratio between slow and fast waves is lower after binge-watching a suspenseful series ending with a cliffhanger compared to a series without one and with a neutral documentary, indicating a less restful sleep.

Stopping before the cliffhanger
We hypothesize that the suspense associated with open endings after watching cliffhanger TV series is spontaneously reactivated during sleep. This reactivation could trigger associated body functions and brain regions that promote wakefulness, thereby reducing the depth of sleep," explains Björn Rasch. More importantly, the study results show that TV series ending in a cliffhanger may increase arousal and reduce the recovery function of sleep. Therefore, it is recommended to reduce the use of cliffhangers in TV series or at least stop the episode beforehand, if one wants to enjoy a healthy sleep.

Baselgia S., Combertaldi S.L., Fahr A., Wirz D.S., Ort A. & Rasch B.: Pre-sleep arousal induced by suspenseful series and cliffhangers have only minor effects on sleep: A sleep laboratory study. Sleep Medicine, 102. 2023