Sleep Loss Impacts Emotions in an Annoying Way, Psychologists Find

"These consequences reach into really unique pockets of human nature."

For those of us with personalities prone to anger or hostility, there are plenty of things to be annoyed about: terrible work meetings or the world’s microplastic problem, for instance. Most of the time, we get over these irritants — unless we’re sleep deprived. When that’s the case, a study published in Experimental Psychology shows that it’s even harder to shake it all off.

Zlatan Krizan, Ph.D., a professor of psychology at Iowa State and first author on the new study, doesn’t confine his analysis of sleep to evening hours. In the experiment on 142 “community members,” he and his co-authors highlighted the connection between sleep deprivation and anger during the day, showing that with four fewer hours of sleep per night, participants not only were more easily frustrated, they also lost the key ability to manage that frustration over time.

“If we lose sleep over a couple of days we slow down, our alertness shifts,” Krizan tells Inverse. “This has all kinds of consequences on everything we do without our awareness of it. And a lot of these consequences reach into really unique pockets of human nature.”

sleep deprivation
Krizan's experiment showed that losing sleep had effects emotion management during the day

For two days, 67 of the “community members” adhered to a restricted sleep schedule — they were told to go to bed two hours later than their normal sleep time and rise two hours earlier. These tired souls were then subjected to 12 online product surveys while obnoxious static-like noises played in the background. Krizan was clearly provoking his subjects.

Unsurprisingly, both the sleep-deprived and rested subjects were frustrated by these noises — though the sleep-deprived subjects had reported slightly higher anger scores. But this paper’s important finding isn’t that the sleep-deprived people got angry; it’s that they stayed angrier than the control group.

“When individuals who just maintained their sleep schedules did [the product rating task], their negative experiences and emotions went down a lot over those two days. That suggests that these things weren’t so annoying and frustrating the second time around,” Krizan says.

This adaptation, he explains, is what we typically expect from humans. Called hedonic adaptation (or sometimes, the hedonic treadmill), it describes our ability to adjust to both good and really bad scenarios. When we get a new car, we’re initially excited by the smell or the shiny new features, but that eventually fades. Conversely, when we experience something frustrating or sad the pain usually fades with time.

When we’re sleep-deprived, Krizan’s work suggests that we struggle with hedonic adaptation. He demonstrated this on a small scale with his annoying noises: He found that over time his control subjects got used to the noise, but his sleep-deprived subjects never adapted to it.

“In fact, they showed a trend of showing more frustration the second time around,” he says. “That was really a fascinating finding here, because it suggests that sleep could really wreak havoc on these adaptation processes that are important for all kinds of things: short term, for a study, or long term, for how people adjust to adverse life circumstances for example.”

In terms of an explanation for his current results, Krizan thinks it might come down to sleep’s effect on learning and memory. Previous work has shown that sleep helps us consolidate information — the process by which new memories or information are moved to into “long term memory storage in the brain.”

anger sleep
Both the rested (solid lines) and sleep deprived (dotted lines) participants were annoyed by the noise, but the sleep deprived participants got angrier over time

“You can think about it as sleep interrupting consolidation of those negative experiences,” Krizan says. “So the next time you encounter it, its more new than it normally would have been. That’s emotionally more significant and more frustrating in this case.”

With this working hypothesis, Krizan’s forthcoming work looks to demonstrate how this relationship he noticed experimentally plays out in the real world. He’s working on a follow-up paper that analyzes the diary entries of roughly 200 college students who tracked hours of sleep and their daily experiences. But with the latest experiment he’s laying the groundwork for further research on how sleep impacts some of the more complex aspects of human social life:

“Things that have to do with emotion control, self-control, empathy, these kind of higher cognitive functions that are unique to humans really seem to take a hit with sleep loss,” Krizan says. “That’s one of the more fascinating aspects of why sleep is so important for understanding the state of society and humanity at this point.”