The Surprising Consequence of Not Getting Enough Sleep 

Bad news for anyone who's not catching enough Zzs.

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Decreased productivity, impaired judgment, drowsiness, and weight gain are all telltale signs that you're not getting enough sleep (not to mention just being plain-old tired). And now new research has added a new one for the list: a decreased ability to distinguish friends from foes. 

According to the University of California-Berkeley study, sleep deprivation impairs our ability to accurately read facial expressions. This can affect everyone from parents—who may have trouble telling when their child is sick—to exhausted students cramming for exams or doctors working in emergency rooms, according to the study's lead author, Andrea Goldstein-Piekarski. The findings were published in the Journal of Neuroscience

Eighteen healthy young adults participated in the experiment. They viewed 70 facial expressions ranging from friendly to threatening after getting a full night of sleep, and then again after being awake for 24 hours. Brain scans revealed that the brains deprived of sleep could not distinguish between the expressions, suggesting that sleep-starved people may perceive harmless gestures as aggressive or threatening.

The researchers also found that the participants' heart rates didn't respond normally to friendly and unfriendly faces after a poor nights' sleep.

“Recognizing the emotional expressions of someone else changes everything about whether or not you decide to interact with them, and in return, whether they interact with you,” study senior author Matthew Walker said in a statement. "Insufficient sleep removes the rose tint to our emotional world, causing an overestimation of threat. This may explain why people who report getting too little sleep are less social and more lonely."

Sleep quality matters, too. During the participants' full night of sleep, those with higher quality Rapid Eye Movement (REM) were able to more accurately read facial expressions.

"Dream sleep appears to reset the magnetic north of our emotional compass," Walker said. "The study proves yet more proof of our essential need for sleep."