Sleeping less than usual affects how we feel the next morning. Response time and other performance metrics are also affected, according to a study by the Norwegian University of Science and Technology (NTNU).
“Not in the sense that we have more negative feelings, like down or depressed. But participants in our study experienced a flattening of emotions when they slept less than usual. They felt less joy, enthusiasm, attention and satisfaction,” says associate professor Ingvild Saksvik-Lehouillier at NTNU's Department of Psychology.
Most sleep research is done in labs, but Saksvik-Lehouillier and the NTNU research team studied participants who slept at home. The participants first spent seven nights in their own bed and slept as long as usual. Three of the mornings they ran a series of tests. Subsequently, the participants slept two hours less than usual for three nights. They underwent the same tests on two mornings.
“We all have different sleep patterns. The aim of the participants to sleep at home was to keep everything in daily life as much as possible. In the imposed sleep deprivation phase, the participants crawled under their covers two hours later than usual, and had to get up at their usual time," says Saksvik-Lehouillier.
The practical tests took place about an hour and a half after the participants got up - and without drinking coffee.
They were shown 365 different pictures with random letters on a computer screen for 14 minutes. If the image didn't contain the letter x, they would have to press the spacebar and if there was an x in the image, they would do nothing.
“We tested the responsiveness and accuracy. The reaction time decreased after the participants were sleep deprived, but the error rate increased. It seems that we react faster to compensate for a lower concentration. Then there will be more errors. It can be smart to avoid activities that require a high degree of accuracy in the morning after sleeping less than usual,” says Saksvik-Lehouillier.
Previous studies have shown that sleep deprivation has about the same effect on driving as alcohol. While the participants improved every day they took the test after sleeping normally, they scored worse on accuracy every day after a night of insufficient sleep.
“We know that sleep is important for learning. Maybe we'll see that here," says Saksvik-Lehouillier.
In the second part of the test, participants answered a questionnaire to identify 20 positive and negative emotions.
“We found no clear differences for the negative emotions, but there were clear differences for the positive ones. Positive feelings scored worse after just one night of reduced sleep and dropped even more after three nights. I think this is a very interesting find. We already know that less positive emotions have a major impact on mental health. We also know that poor sleep is included in virtually all mental health diagnoses,” said Saksvik-Lehouillier.
In terms of how long the lack of good feelings lasts after sleep deprivation, she says the study didn't address that, but the research team plans to investigate the duration of this mood.
It's not just in Norway that people sleep less than they used to – it's an international trend, especially for people who work full-time.
"It's easy for us to go to bed later than we should, especially when we're thinking, 'I just need to finish this series.' But we still have to get up to work, study or take our kids to school. This contributes to our lack of sleep. How long we sleep is only part of the picture, but when we sleep is also important. An irregular circadian rhythm can be worse than sleeping too little. Going to bed and getting up at the same time is recommended,” says Saksvik-Lehouillier.
