There’s overwhelming evidence that sleeplessness can make us irritable and moody.

But researchers at the University of California, Berkeley in connection with Harvard Medical School, say it can also have another effect: short-term euphoria.

Puzzled as to why people with depression may temporarily feel more positive after a sleepless night, researchers studied the brains of 27 healthy young adults, half of whom pulled all-nighters. They found that the brain’s pleasure circuitry got a big boost after a missed night’s sleep.

But the neural pathway that stimulates feelings of euphoria, reward and motivation after a sleepless night can also lead to poor judgment and risky behavior, researchers said. Sleep deprivation shuts down the brain’s key planning and decision-making regions—namely the prefrontal cortex—while activating more primal neural functions.

“When functioning correctly, the brain finds the sweet spot on the mood spectrum. But the sleep-deprived brain will swing to both extremes, neither of which is optimal for making wise decisions,” said Matthew Walker, lead author of the study, which was published in the Journal of Neuroscience. “We need to ensure that people making high-stakes decisions, from medical professionals to airline pilots to new parents, get enough sleep.”

Journal of Neuroscience study.

UC Berkeley Article