Everyone lies once in a while, but according to a new study people who tell small, self-serving lies are likely to progress to bigger falsehoods, and over time, the brain appears to adapt to the dishonesty. The finding, the researchers said, provides evidence for the “slippery slope” sometimes described by wayward politicians, corrupt financiers, unfaithful spouses and others in explaining their misconduct.

Participants in the study were asked to advise a partner in another room about how many pennies were in a jar. When the subjects believed that lying about the amount of money was to their benefit, they were more inclined to dishonesty and their lies escalated over time. As lying increased, the response in the brain (amygdala) decreased. And the size of the decline from one trial to another predicted how much bigger a subject’s next lie would be.

The findings suggest that the negative emotional signals ssociated with lying decrease as the brain becomes desensitized. As one of the researchers said, “Think about it like perfume. You buy a new perfume, and it smells strongly. A few days later, it smells less. And a month later, you don’t smell it at all.”