We’ve all done it: someone asks us our opinion, and we tell a little white lie. But a new study suggests that while lying is difficult at first, it gets easier and easier the more we do it. And it’s all explained by blood flow to an area of the brain.

The study, which was published in the journal Nature Neuroscience, suggests that telling self-serving lies may turn into bigger and bigger lies, and make it easier for the liar to continue lying. Basically, repeated lying desensitizes your brain to the typical adverse emotions that come when someone lies for the first time, and it opens the door to being more comfortable with bigger and bolder lies, according to a University College London statement.

The findings were based on functional MRI scans that measured blood flow int he brain as they participated in tasks where they could benefit from lying. They found that the amygdala region of the brain associated with emotion got greater blood flow during the first lies, but each lie decreased the response of the amygdala, even when the magnitude of the lies increased.

“When we lie for personal gain, our amygdala produces a negative feeling that limits the extent to which we are prepared to lie,” explains senior author Dr Tali Sharot (UCL Experimental Psychology). “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.”

“It is likely the brain’s blunted response to repeated acts of dishonesty reflects a reduced emotional response to these acts,” says lead author Dr Neil Garrett (UCL Experimental Psychology). “This is in line with suggestions that our amygdala signals aversion to acts that we consider wrong or immoral. We only tested dishonesty in this experiment, but the same principle may also apply to escalations in other actions such as risk taking or violent behaviour.”