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When you’re up late at night, watch out. Your brain might be more likely to slip into sin.

That’s because researchers believe “cognitive tiredness” might escalate throughout the day. In other words, a person’s self-control wears down at the day wears on, increasing the likelihood of lying, cheating, or fraud.

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Isaac H. Smith of Cornell University and Maryam Kouchaki of Northwestern University conducted an experiment on two groups of people—one in the morning and the other in the afternoon—in which participants were given course credit and the opportunity to earn up to $5. In each of 100 trials, they were shown a square on a computer screen containing 20 dots distributed unevenly on either side of a diagonal line. If they reported that the dots were concentrated on the right side of the screen rather than the left, they earned five cents. However, if they reported that there were more on the left side than the right, they earned a mere 0.5 cents. Because participants were not given money based on the veracity of their claims (they were paid solely on what they reported), they could still earn five cents by claiming that the dots were more concentrated on the right even if that was blatantly false. This made it especially tempting for participants to lie in order to receive more money. Smith and Kouchaki—both professors of management—found that the afternoon group was 25% more likely to “cheat” in this way and claim something other than the truth in order to win money.

Cognitive tiredness could make cheating and other immoral acts more tempting.

The study backs up previous claims about the brain’s decision-making and moral judgment centers, but it can’t necessarily be regarded as conclusive. Here’s Matt Richtel, writing for The New York Times:

The latest findings are not without detractors. In July, another group of scholars offered a commentary arguing that the morning morality effect was an oversimplification. They said the research failed to recognize that some people are night owls and might resist temptation better as the day goes on. Their point was that some brains start out tired, then ramp up during the day. Dr. Smith and Dr. Kouchaki countered, in essence, that no matter when you felt most alert, brain depletion happened bit by bit over the course of the day.

Regardless, the new evidence points to the need for all of us to pay more attention to time of day and how it influences our decision-making.