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Telling little fibs leads down a slippery slope to bigger lies — and Watch Ava Onlineour brains adapt to escalating dishonesty, which makes deceit easier, a new study shows.

Neuroscientists at the University College London's Affective Brain Lab put 80 people in scenarios where they could repeatedly lie and get paid more based on the magnitude of their lies. They said they were the first to demonstrate empirically that people's lies grow bolder the more they fib.

The researchers then used brain scans to show that our mind's emotional hot spot — the amygdala — becomes desensitized or used to the growing dishonesty, according to a study published online Monday in the journal Nature Neuroscience.

"You can think of this as a slippery slope with what begins as small acts of dishonesty escalating to much larger ones," said study lead author Neil Garrett, now a neuroscience researcher at Princeton University. "It highlights the potential dangers of engaging in small acts of dishonesty on a regular basis because these can escalate to much larger ones further down the line."

And during this lying, brain scans that show blood supply and activity at the amygdala decrease with increasing lies, said study co-author and lab director Tali Sharot.

"The more we lie, the less likely we are to have an emotional response" — say, shame or guilt — "that accompanies it," Sharot said.

Garrett said he suspects similar escalation factors happen in the "real world," which would include politics, infidelity and cheating, but he cautioned that this study was done in a controlled lab setting so more research would be needed to apply it to other situations.

University of Massachusetts psychology and brain sciences professor Robert Feldman wasn't part of the study but praised it: "The results provide clues as to how people may become more convincing liars with practice, and it clearly suggests the danger of tolerating small, white lies, which can escalate into greater and greater levels of deception."

Garrett, Sharot and colleagues arranged for 80 people to go through an experiment where they would see a photo of a jar full of pennies. The subject would advise a partner in another room — someone who was looking at a photo that was less clear — how much money they should guess was in the jar. But the more the partner overestimated the bonus, based on the subject's advice, the higher the reward.

The researchers did a couple variations of the experiment. In one version the test subject was told he and the partner would share in overestimating rewards; in that case, the subject's lies were even bigger.

But in another scenario, the test subject would benefit more from overestimating and the partner would benefit less.

That second scenario showed the increase in the magnitude in lying. The people went from lying on average worth 4 British pounds (about $5) at the beginning to about 8 pounds ($10) near the end of about 80 repetitions — thus going from "little lies to bigger and bigger lies," Sharot said.

And of those 80 test subjects, 25 of them, chosen randomly, did their estimates while an MRI machine scanned their brain. It showed how we get used to the lying, much like someone no longer noticing the smell of their own perfume over time and thus using more, Sharot said.

It shows people's brains adapting to their own wrongdoing. It was so noticeable that the researchers were able to predict growing dishonesty based on the dropping activity in the amygdala.

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Shaul Shavi, who runs the Behavioral Ethics Lab at the University of Amsterdam, said scientists had long suspected this slippery slope in lying existed, but there was limited proof until this "elegant" and "important" study. And the brain scan showing a neurological link with increased lying is novel, added Maurice Schweitzer, who studies deception at the University of Pennsylvania's Wharton School of Business.

The study found that there is a segment of people who don't lie and don't escalate lies, but Sharot and Garrett weren't able to determine how rare those honest people are. It also found that people lie more when it benefits both them and someone else than when they just profit alone.

"That's sort of a good thing," Sharot said.