Does lack of sleep impair judgment?
We’re often advised to sleep on a big decision, and science bears out this piece of folk wisdom.
Our sleep has a profound effect on the way we process information. Because the brain is so complex and interconnected, this is a difficult area to research, and scientific findings vary—as do individual sleep needs. Research shows that going for only 17 hours without sleep can impair cognitive performance (including reaction time) nearly as much as being at some countries’ legal alcohol limit for driving.
Neuroscientists do know that insufficient sleep has a particular impact on the brain’s prefrontal cortex, the area that enables us to problem-solve, reason, organize, plan, and perform other higher cognitive tasks. The medial prefrontal cortex, which also acts to regulate emotions, may be less able to “talk down” the amygdala, which processes feelings (especially fear), reacts to stress, and triggers the body’s “fight-or-flight” stress response.
Sufficient sleep is essential for efficient storage of the information that may help you make decisions: the brain consolidates different types of learned information into memories during the different stages and cycles of sleep. Sleep loss may also hamper cognitive flexibility—the ability to rapidly adjust to new information or changing events. Not only does poor sleep impair your thought processes, but there’s evidence that it also prevents you from recognizing that your thinking might be impaired. One study found sleep-deprived participants tended to claim that they were still functioning well—even when tests showed their cognitive abilities had significantly declined.
The sleep-deprived brain
A variety of brain regions play a part in decision making and communication—all need good sleep to function optimally.
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Prefrontal cortex: Controls logical thinking. Poor sleep can lead to unnecessary risk-taking
Parietal cortex: Scientists think that this multitasking area is called on to assist other areas when we are sleepy, affecting its efficiency
Amygdala: The emotional center of the brain becomes more active and less stable following sleeplessness
Hippocampus: Sleep is essential to the memory-processing region, as it performs some key tasks during sleep only
THE MORNING AFTER
In daily life, the cognitive consequences of a poor night’s sleep will usually only cause us minor irritation. Sometimes, however, lives depend on sharp and accurate judgment; the US space shuttle Challenger fell to earth after a postlaunch explosion, killing its crew. An official report found some key managers got less than two hours’ sleep the night before, and sleep loss and early morning shift work contributed to some poor decisions.
Misreading the signs
Sleep-deprived people tend to see the world in a more negative light. In one study, participants were shown a series of images of people with different expressions. Sleep-deprived individuals consistently attributed more negative emotions to the faces than well-rested participants.
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Well-rested people interpreted the expression correctly
Participants were asked to judge the mood of the person in an image
Sleep-deprived people interpreted the expression wrongly