In case you hadn’t noticed, Donald Trump lies. A lot.

He’s lied about his own questioning of President Obama’s birthplace. He’s lied about tweeting that climate change is a hoax planted by China. He’s lied about how he’s voiced support for the Iraq War.

Trump is hardly the only politician who gets caught in lies, even if he’s more practiced and prolific than most. We have a much more fact-driven political discourse today than we used to, as journalist and author Lucas Graves told my colleague Tara Golshan this summer.

But how do politicians — or anyone who lies regularly — end up lying so much in the first place? Here’s one suggestion, from psychological science: The more we lie, the easier it becomes to lie in the future. Lying is a skill we get better at. And Trump has a lot of practice.

Lying may be a kind of “emotional adaptation”

Before we dive in, let’s be clear: Psychological research makes predictions about the behavior of groups; it cannot necessarily explain the behavior of an individual. So we can’t say for sure what the source of Trump’s — or any other politicians’ — lies are.

But researchers do have some new insight into how a person might grow more comfortable lying over time.

The authors of a paper published Monday in Nature Neuroscience call this “emotional adaptation.” It’s similar to what happens when you’re exposed to a strong smell. At first the smell is extremely noticeable, but eventually you stop noticing it as much. With time, any stimulus — a loud noise, a strong perfume, etc. — is likely to provoke a smaller response. The same goes with lying.

We get desensitized to our own lying as the areas of our brain that correlate with negativity become less active. This makes it easier for us to lie in the future, the study concludes.

“The first time you cheat — let’s say you’re cheating on your taxes — you feel quite bad about it,” Tali Sharot, a University College London neuroscientist and one of the study’s authors, said on a press call last week. But then the next time you cheat, you’re less likely to get that negative feeling. That makes it easier to lie again. And the cycle escalates from there.

In the study, the researchers had 80 participants play a simple game. The participants played the role of an adviser. They looked at 60 photos of glass jars with differing numbers of pennies, and were told to advise a partner (who was really a researcher in disguise) on how much money the jars contained. The participants were told they’d receive compensation based on the accuracy of their partner’s guesses.

In some of the trials, the participants were incentivized to be honest: If the partner guessed correctly, they’d both get the prize money. In other trials, the participants were incentivized to lie: If the partner overestimated, the participant would get more (the study gave the participant the impression the partner had no idea about this arrangement).

When the participants were incentivized to lie, they lied more as more trials were conducted.

“They started with small lies — let’s say lies of around £1 — but this grew, and they ended up with large lies, of around £8,” Neil Garrett, also a University College London neuroscientist and a co-author of the study, said.

The authors then took the study a step further to understand what this looked like in the brain. A small subset of the participants played this game while undergoing fMRI, a brain scanning technique. It appeared that the more the participants grew accustomed to lying, the less activation there was in the amygdala, a region of the brain associated with negative emotion.

“Arousal is one of the telltales of lying,” Sharot said. It can take the form of sweating and faster heart rate — what polygraph machines look for to detect lies. So if the brain is less aroused by lying, that might mean a person is getting used to it. “If arousal goes down, people may be less likely to catch you in a lie,” Sharot said.

(Caveat: The subject pool for the fMRI section of the study was very small, only 25 participants. So these neuroimaging results would have to be replicated for a firmer conclusion. Also the study design was not preregistered, which increasingly is seen as a safeguard against false-positive results. “We will need to wait for a replication of the fMRI results,” Sharot said. And fMRI results are notoriously hard to interpret: Read more about that in my earlier piece.)

But the participants could also just be learning how to win the game

There may be another way to interpret the results of the study: The participants are simply learning how to be liars.

Oriel FeldmanHall, a neuroscientist who studies morality at Brown University and did not contribute to the Nature Neuroscience study, says the structure of the game may be what’s causing the lies to escalate, since there are no consequences for gaining more money through lying.

“Rather than demonstrating a dishonest snowball effect, [the authors] may just be illustrating successful learning,” she writes me in an email. (They didn’t rule out or mention this alternative interpretation, she adds.)

So it’s not necessarily that the participants stop feeling bad. It’s that they’re figuring out how to succeed in the game.

In her lab, FeldmanHall finds that when she gives her participants negative feedback on their selfish decisions — like showing participants that their actions are harming others — they issue a course correction. They become less selfish. In one experiment, FeldmanHall gave participants an unsettling choice: They could have some money, but the more they took, the more a participant in another room would receive an electric shock. When participants were shown the video of the consequences of their actions (people being zapped), they took less money.

Is there a way to stop people from lying?

It’s clear that some people are more prone to dishonesty than others — and are unlikely to change. Here’s one reason: Research suggests some people have a stronger physiological response to moral dilemmas than others. And extreme forms of lying, like compulsive lying, may be indicative of an underlying personality disorder.

But let’s assume politicians aren’t abnormal in this way, and that they are just normal people who are in an environment that rewards lying. Is there any way to keep them honest?

Sharot, the author of the new study, has a simple suggestion: “Perhaps we can nudge people away from dishonesty by calling them on their lies even if they are small, and try to reproduce an emotional reaction,” she says. In other words, reminding people they’re lying could help revive the negative feeling that may have been lost. Though this could backfire: People can become defensive when being called a liar.

Social norms play a big role, too, for ordinary people at least. David Rand, a Yale University psychologist, has found that when cooperation and truth telling are established upfront as the norm, people are more likely to play fair in the future.

Even politicians may listen to nudges to keep the fibbing to a minimum.

In a small study, political scientists Brendan Nyhan and Jason Reifler found some evidence that down-ballot candidates who were sent letters reminding them "politicians who lie put their reputations and careers at risk, but only when those lies are exposed" were somewhat more truthful in their campaigns, as measured by newspaper fact checks.

A 2015 study in the Quarterly Journal of Political Science also showed this in a straightforward manner: When researchers paid political partisans to be honest, they were more likely to answer questions about the country and the economy correctly.

I asked Sharot if she thinks her work has any bearing on politicians. Can a long public life of small lies make you completely comfortable with lying?

“If someone has been repeatedly engaging in dishonest behavior, it is likely that that person has emotionally adapted to their own lying,” she says.

But what about Trump — is he a special case? Sharot wouldn’t answer. But she says he’s welcome to participate in a future study to find out.