Between when President Donald Trump assumed office in January 2017 and the end of April, the average number of public false or misleading statements he has made per day has been increasing. According to the Washington Post’s fact checkers on May 1, "for the president’s first 100 days, he averaged 4.9 claims a day... since we last updated this tally two months ago, the president has averaged about 9 claims a day."

This is a significant rise. Our calculations suggest that if the current escalation rate remains steady, by the end of his term the president could be making as many as 19 public false statements a day, on average.

To psychologists interested in the science of lying, Trump’s increasing mendacity presents an interesting question: What might be causing this growth?

We first considered whether the increase could be explained by reporting bias. In other words, perhaps more falsehoods have been reported over time, rather than actually presented by the president. We found this explanation to be unlikely, as the Washington Post fact checkers stated they have scrutinized every single tweet, speech, statement and interview by the president since last January. (Importantly, this analysis is confined to public statements and it is difficult to know whether there has been a change in Trump’s total falsehoods.)

Emotion plays an important role in constraining dishonesty. If we feel bad when we lie, we are less likely to do so.

So if not reporting bias, what can explain the temporal increase of these falsehoods? Perhaps past lies needed to be covered up by more lies, or repeated falsehoods were eventually perceived as true making subsequent repetition likely. Or maybe falsehoods led to positive consequences, reinforcing such behavior further. These are all plausible explanations. But our research points to yet another intriguing explanation — a biological process called emotional adaptation.

Emotion plays an important role in constraining dishonesty. If we feel bad when we lie, we are less likely to do so. But if this uncomfortable feeling were to magically disappear, research suggests we would in turn lie more. In one study, students who were given a pill called a beta-blocker, which reduces emotional arousal, were more likely to cheat on an exam than students who were given a placebo. In other words, without that uncomfortable physiological feeling that accompanies dishonest behavior, people were more likely to cheat.

Research we conducted at University College London with our colleagues Dan Ariely and Stephanie Lazzaro, which was published in 2016 in the journal Nature Neuroscience, showed that the intensity of the emotional response people experience when they act dishonestly is reduced every time they lie. And this reduction (which scientists call emotional adaptation) makes them likely to lie more over time.

In our experiment, which was funded by the Wellcome Trust and the Center for Advanced Hindsight, we gave a group of 80 individuals the opportunity to lie again and again in a financial task in order to gain money at another person’s expense. We found that the volunteers started with relatively small lies, cheating by only a few cents, but slowly over the course of the experiment lied more and more. While they were doing so we recorded their brain activity using a brain imaging scanner. We found that the emotional network in the brain responded less with each additional lie. The greater the drop in the brain’s sensitivity to dishonesty, the more people lied the next time they had a chance.

Repeated dishonesty is a bit like a perfume you apply over and over. At first you easily detect the powerful scent of a new perfume. But over time and with more applications you can hardly sense its presence, so you apply more liberally. This happens because neurons in your olfactory bulb desensitize to the smell of the perfume. Similarly, it appears that our response to our own acts of dishonesty is strong at first, but over time decreases. Like students taking beta-blockers, your capacity for being dishonest increases.

Repeated dishonesty is a bit like a perfume you apply over and over. At first you easily detect the powerful scent of a new perfume. But over time and with more applications you can hardly sense its presence.

The picture becomes more alarming when we consider that individuals adapt not only to their own dishonesty but also to that of others. Research Harvard professors Francesca Gino and Max Bazerman shows that people are less likely to criticize the unethical actions of others when such behavior increases gradually over time. Politically speaking, this suggests that voters (and perhaps even the president’s own advisors) may desensitize to the president’s falsehoods in the same way that they do to overused perfume, making them less likely to act to correct this pattern of behavior. The absence of sanctions could in turn be interpreted as a “green light” by the president.

Indeed, in a recent study of 2,500 U.S. citizens, the psychologist Birony Swire-Thompson found that Trump supporters’ intentions to vote for him were not affected by learning that the president had provided false information. And a recent Gallup poll showed that while the percentage of Americans who believe the president is “honest and trustworthy” has decreased from 46 percent in February to 36 percent in April, his approval ratings remained relatively stable. Indeed, in the past few months his approval rating continues to rise.

It is thus likely that we will observe a continuing increase in the number of falsehoods emanating from the Oval Office, accompanied by less and less outrage from the public.

Tali Sharot is an associate professor of Cognitive Neuroscience at University College London, the director of the Affective Brain Lab and author of "The Influential Mind: What the Brain Reveals About our Power to Change Others."

Neil Garrett is a postdoctoral researcher at The Princeton Neuroscience Institute.