Lack of sleep can make it difficult to decipher another person’s facial expressions, according to a new study at the University of California (UC), Berkeley. In fact, the sleep-deprived brain often perceives neutral or even friendly faces as threatening.
“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,” said study senior author Dr. Matthew Walker, a professor of psychology and neuroscience at UC Berkeley.
“These findings are especially worrying considering that two-thirds of people in the developed nations fail to get sufficient sleep,” Walker added.
Indeed, the results do not bode well for chronically sleep-starved groups, said study lead author Dr. Andrea Goldstein-Piekarski, a postdoctoral fellow at Stanford University, who started the study as a Ph.D. student at UC Berkeley.
“Consider the implications for students pulling all-nighters, emergency-room medical staff, military fighters in war zones and police officers on graveyard shifts,” she said.
The study involved 18 healthy young adults who were asked to view 70 facial expressions that ranged from friendly to threatening. They did this once after a full night of sleep and then once after 24 hours of being awake. As the participants looked at the pictures, researchers scanned their brains with functional magnetic resonance imaging (fMRI) and measured their heart rates.
The brain scans revealed that the sleep-deprived brains could not distinguish between threatening and friendly faces, specifically in the emotion-sensing regions of the brain’s anterior insula and anterior cingulate cortex.
Furthermore, the heart rates of sleep-deprived study participants did not respond normally to threatening or friendly facial expressions. The findings also showed a disconnection in the neural link between the brain and heart that typically allows the body to sense distress signals.
“Sleep deprivation appears to dislocate the body from the brain,” said Walker. “You can’t follow your heart.”
As a result, sleep-deprived participants interpreted more faces as threatening, even the friendly or neutral ones.
“They failed our emotional Rorschach test,” Walker said. “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.”
On the other hand, when researchers recorded the electrical brain activity of the participants during their full night of sleep, they found that the quality of Rapid Eye Movement (REM) or dream sleep correlated with the participants’ ability to accurately read facial expressions.
Prior research by Walker has found that REM sleep reduces stress neurochemicals and tends to soften painful memories.
“The better the quality of dream sleep, the more accurate the brain and body was at differentiating between facial expressions,” 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.”
The findings are published in the Journal of Neuroscience.