Losing sleep puts you in danger... and not in the way you might think

It’s no news to anyone that not getting enough sleep does bad things to your brain, but a new Berkley University study has found that sleep deprivation could affect a life-saving ability to perceive threat.

The study found that sleep deprivation impairs our ability to accurately read facial expressions, an essential skill humans have relied on throughout evolution to determine friend or foe.

“Recognising 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,” says the study’s senior author Matthew Walker, a professor of psychology and neuroscience at University of California Berkeley.

The consequences of not being able to read people’s facial expressions range from mistaking a friendly stranger for a potential mugger, not recognising  that a child is unwell, or constantly accusing your loved ones of being grouchy.

Professor Walker says, “These findings are especially worrying considering that two-thirds of people in the developed nations fail to get sufficient sleep.”

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“Consider the implications for students pulling all-nighters, emergency-room medical staff, military fighters in war zones and police officers on graveyard shifts,” adds fellow researcher Andrea Goldstein-Piekarski.

During the study, volunteers viewed 70 facial expressions ranging from friendly to threatening after a full night of sleep, and again after 24 hours of being awake. Researchers scanned participants’ brains and measured their heart rates as they looked at faces.

Face strip

The scans revealed that the sleep-deprived brains could not distinguish between threatening and friendly faces and that their heart-rates did not respond normally. Worryingly, researchers found a disconnection in the neural link between the brain and heart that typically enables the body to sense distress signals.

“Sleep deprivation appears to dislocate the body from the brain,” says Professor Walker.

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Interestingly, those who lacked sleep were more likely to view friendly or neutral faces as being hostile.

“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,” says Professor Walker.

The study found the more good-quality shut-eye people got – by slipping into REM or dream sleep – the better they were at interpreting the facial expressions.

“The better the quality of dream sleep, the more accurate the brain and body was at differentiating between facial expressions,” Professor Walker said. “Dream sleep appears to reset the magnetic north of our emotional compass. This study provides yet more proof of our essential need for sleep.”

Do you find yourself feeling a bit more defensive when you haven’t had enough sleep?