We’re more negative after five nights of less sleep
by Jessica Hamzelou
We know that sleep deprivation can affect the way a person thinks and functions. But sleep restriction, in which a person gets less sleep than is normal for them, is far more common.
To find out how it might affect our cognition, Daniela Tempesta at the University of L’Aquila in Italy and her colleagues asked 42 volunteers to restrict how much sleep they got for five days.
First, each participant wore a device on their wrist that tracked their normal sleep for five consecutive nights, during which they typically slept for around 7 to 8hours a night. The volunteers filled out questionnaires to assess their mood, sleepiness, energy and concentration.
They then looked at a series of cartoon images of people expressing a range of emotions and scored them on a scale of one to nine, based on how positive or negative they thought the image was.
The following week,the volunteers were told to stay awake until 2 am,then go to sleep and wake up at 7 am. Tempesta and her colleagues confirmed when the participants were asleep and awake by checking data from the wrist devices and called the participants if they failed to wake up at the designated time.
At the end of the five days of restricted sleep,the volunteers repeated the questionnaires and image scoring tasks. Unsurprisingly, these indicated that they were more tired and sleepy after the restricted sleep. They were also less alert, and in a more negative mood.
In addition, the volunteers ranked positive and neutral images more negatively when they hadn’t had enough sleep. This suggests that restricting sleep dampens our ability to experience pleasure, says Jason Ellis at Northumbria University, UK.
“The likelihood is that people [who aren’t getting enough sleep] are going to be less appreciative of general niceties and less responsive to compliments,” says Ellis. A lack of sleep will leave us more likely to misinterpret other people’s reactions, including over video calls platforms like Skype and Zoom, which often solely show a person’s face, he says.
“If you’ve not slept very well, you may end up feeling less happy about a meeting or a response to a question, because you won’t be able to interpret pleasantness from someone else’s response,” say Ellis.
This is probably because we get less REM sleep when our sleep is restricted. This phase of sleep tends to occur more towards the end of a sleep period, and is when we typically have our most vivid dreams. It is thought that REM sleep is important for processing emotions. Recent research suggests that we have our most intense dreams when our brains are processing emotionally powerful experiences.
More of us are likely to be affected during the covid-19 pandemic, says Ellis. This may be because the increased stress and anxiety during the lockdown can affect sleep.Key workers doing long shifts may also not get enough rest.