Interrupted sleep disrupts mood more than late bedtime, according to experts at the Johns Hopkins University School of Medicine.
The study, published in the journal Sleep, involved 62 healthy men and women, with self-reported good sleeping patterns.
They were divided into 3 groups: the first got to enjoy sleep as much as they wanted, the second had to stay up late, while the third was subjected to constant sleep interruptions.
More precisely, in the last category, every night, volunteers were awaken for 20 minutes every hour, on 7 different occasions, as well as for one full hour the 8th time.
“It was pretty harsh. It was a sledgehammer approach. It would be more severe than clinical insomnia”, declared Patrick Finan, study lead author and assistant professor of psychiatry and behavioral sciences at Johns Hopkins University School of Medicine.
However, it must be noted that overall the total amount of sleep for this group was the same as among those who had been required to have delayed bedtimes.
The experiment lasted for 3 days, and after each night the participants were surveyed regarding their overall moods, based on how strongly they felt certain emotions, like anger or cheerfulness.
At the end of the first night, there was a similar decrease in positive states of mind, and an increase in negative feelings, among those who had experienced abbreviated or fragmented sleep.
Following the second night of the trial however, the effects of sleeping patterns on psychological well-being became apparent among the three groups.
More precisely, those who had been awaken forcibly several times per night experienced a 31% drop in positive emotions, which was much higher than the 12% decrease reported by those who had been required to stay up late. This downward trend continued after the last night of the experiment as well.
On the other hand, there was no statistically significant difference between delayed sleep and fragmented sleep subjects when taking into account negative emotions.
Therefore, researchers now believe that sleep interruptions are more likely to negatively impact positive moods, than to accentuate negative states of being. These effects are much greater than those produced when a person falls asleep at late hours, but rests continuously until morning.
Prior research had focused mostly on the quantitative aspects of sleep, but this new research points out that it’s even more important if nightly rest is consolidated, and suffers no interruptions.
The findings may not come as a surprise to new parents or to those who are affected by chronic pain, insomnia or other sleep disorders.
These people have to deal with sudden awakenings on a nightly basis, and can no longer achieve deep “slow-wave” sleep, which is the third stage in the non-rapid eye movement (NREM) sleep.
Slow-wave sleep has been proven essential for the cognitive function, because it assists in processing and consolidating new memories, and it allows the brain to recover, preventing the build-up of free radicals.
By using polysomnography in order to identify sleep stages based on brain and body functions, it was proven that indeed slow-wave sleep was much more infrequent among the participants who had gone through interrupted sleep.
This study therefore provides further proof that failure to benefit from the restorative powers of deep sleep can result in depression, and it can also make people more likely to be hostile or unsympathetic towards others.
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