Some cheating spouses, corrupt financiers and dishonest politicians learn this the hard way: Lies that start small often spiral into something much bigger.

But what they may not know is that this could be because the human brain adapts to repeated acts of dishonesty, according to research published Monday in the journal Nature Neuroscience.

“Whether it’s evading taxes, being unfaithful, doping in sports, making up data or committing financial fraud, deceivers often recall how small acts of dishonesty snowballed over time,” Tali Sharot, an associate professor of cognitive neuroscience at University College London and a co-author of the study, said in a press teleconference.

Many environmental and cultural factors can explain dishonest acts, but Sharot and her colleagues decided to look at the brain to understand escalating lying behavior from a neurological standpoint.

“We suspected there might be a basic biological principle of how our brain works that contributes to this phenomenon,” Sharot said. “It’s called emotional adaptation.”

In the same way we may gradually lose our sensitivity to a specific perfume, we seem to become desensitized to negative emotions associated with telling a lie, the research team found. Even small, self-serving lies, if told enough times, may blunt the negative response of the amygdala, a tiny structure in the brain that processes fear and other emotions.

When we lie for personal gain, our amygdala produces a negative feeling that limits the extent to which we are prepared to lie. However, this response fades as we continue to lie. Researcher Tali Sharot

“When we lie for personal gain, our amygdala produces a negative feeling that limits the extent to which we are prepared to lie,” Sharot said in a press statement. “However, this response fades as we continue to lie, and the more it falls the bigger our lies become. This may lead to a ‘slippery slope’ where small acts of dishonesty escalate into more significant lies.”

To see the neurological effects of repeated lies, Sharot’s team designed an experiment in which one participant was asked to advise another about how many pennies were in a glass jar. Sometimes, the researchers told the participants that they would benefit from overestimating the number of coins and lying to their partners.

And sure enough, the idea of a personal benefit pushed the participants to lie more often. And the size of their lies ― that is, the degree to which they overestimated ― also grew over several trials.

Meanwhile, the researchers used brain scans to monitor the participants’ brain activity, particularly in the amygdala. The increase in lying went hand-in-hand with a decline in the response of the amygdala.

“First [the amygdala] responded strongly when the participants lied. But as time went on it responded less and less,” said Neil Garrett, a doctoral student at University College London and a co-author of the study.

Researchers could predict how large a person’s next lie would be just by looking at how much the amygdala’s activation had dropped.

The results supported the idea that we undergo an emotional adaptation as we tell more and more lies, and that a numbed amygdala may lead us to hesitate less before telling bigger lies.

“The same mechanism may also underlie all sorts of escalations, such as escalation of risk-taking and violent behavior,” Garrett said.

These findings could offer policymakers insights for designing strategies for deterring people — particularly those who work at financial and political institutions — from going down the spiral that leads to committing acts of dishonesty with large consequences.

“They may open possible avenues to curbing dishonesty, such as finding ways to reproduce a negative emotional reaction to stop of from engaging in such acts,” Garrett said.

But until then, the best way to avoid getting caught in a large lie would be not telling a small one.