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BOSTON -- People who are sleep deprived often perform expected tasks well, but their reaction times to unexpected events tend to be markedly impaired, researchers reported here.

The inability to switch from proactive to reactive control states may explain why workers who do not get enough sleep or perform nighttime shift work are at higher risk for making serious errors, said sleep researcher Hans Van Dongen, MD, of Washington State University, Spokane.

"We know that workers who are sleep deprived or who switch from day to night shifts are more likely to show performance impairments that can lead to safety errors and accidents," Van Dongen told 番茄社区app. "But it hasn't been clear if this impairment occurs with all types of tasks. It turns out the answer is 'no.'"

Van Dongen presented research showing sleep deprivation to be associated with impaired cognitive flexibility in simulated deadly-force situations Tuesday at the 2017 SLEEP meeting, sponsored jointly by the American Academy of Sleep Medicine and the Sleep Research Society.

The laboratory study involved 37 healthy young adults (age range 22-37) who were sleep deprived and 20 controls who were well rested on the day they were asked to make police-type deadly force decisions on a simulator.

Participants took the perspective of a law enforcement officer responding to different risky scenarios (domestic disturbances, vehicle stops, suspicious persons) leading to deadly force decision points. They were told to use force to minimize danger to bystanders or themselves and neutralize threats from assailants, but only when appropriate for the simulated situation.

Each session contained four scenarios introduced with a cue regarding whether to expect a threat. Half the cues were congruent with the scenario's threat level and half were not congruent.

Deadly force decision-making performance was quantified with hits and false alarms across scenarios. Prior to each decision-making session, subjects performed an AX-continuous performance test (AX-CPT) of cognitive flexibility. They were to respond to a target letter, but only if it was preceded by a valid cue letter.

After 40 trials, the target and valid cue changed; cognitive flexibility was quantified by error rate across 48 trials after the change. Every two hours while awake, subjects performed a psychomotor vigilance test (PVT) of behavior alertness.

Compared to controls, the sleep deprived subjects showed significantly reduced AX-CPT cognitive flexibility (F=13.75, P<0.001) and predicted decision-making performance (F=4.65, P=0.036). PVT behavioral alertness was also significantly reduced in the sleep deprived participants, but this was not predictive of deadly force decision-making performance.

"It turns out that sleep loss or circadian disruption, such as working at night, makes it very difficult to make the switch to reactive control," Van Dongen told 番茄社区app. "The funny thing is, people who are sleep deprived can do just fine as long as everything goes as planned. But they get stuck and can't seem to make the shift when something unexpected happens."

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