BERKELEY (CBS SF) – Lack of sleep alters the way our brains read facial expressions and could make friendly faces appear more threatening, according to a new study from UC Berkeley.

The study was published in Wednesday’s edition of The Journal of Neuroscience.

READ MORE: Newsom Unveils State's COVID Recovery Plan; $75B Budget Surplus To Provide For Direct Payments

According to a university statement, the study involved 18 young adults. Participants in the study viewed 70 facial expressions, after getting a full night of sleep and again after being awake for 24 hours. The researchers scanned their brains and measured their heart rates.

Researchers found when the participants were sleep deprived their brains couldn’t distinguish between a threatening face and a friendly one. Sleep deprived participants also interpreted more faces as threatening, including faces that are friendly.

READ MORE: Asian American Attacks: San Francisco Police Investigate Two Separate Assaults on Muni Buses in Tenderloin

“Sleep deprivation appears to dislocate the body from the brain,” said UC Berkeley psychology and neuroscience professor Matthew Walker, the study’s senior author. “You can’t follow your heart.”

The researchers also found higher quality REM (Rapid Eye Movement) sleep or dream sleep increased the participants’ accuracy to read facial expressions.

MORE NEWS: CHP Seeks Driverless Tesla With Man Riding In Back Seat Along Bay Area Roads

According to the National Institute of Neurological Disorders and Stroke, the average person spends around two hours a night in REM sleep.