Acting dishonestly once can make people more likely to be dishonest again, scientists have discovered. They have even identified the neural mechanism associated with this phenomenon, showing that the brain is capable of adapting to dishonest behaviours.

Many studies published in the past have shown that adaptation is a key principle of how the brain processes sensory information – it allows people to progressively adapt to certain stimuli that they find uncomfortable in the first place.

In a study published in the journal Nature, researchers wanted to find out if adaptation also occurs in the context of emotional decision-making, and if humans could become used to acting in ways they find morally dubious, such as acting dishonestly.

Dishonesty has been studied extensively by researchers in the field of psychology and sociology. They have often found that dishonest acts can be traced back to a sequence of smaller transgressions that gradually escalated. Scientists working in this field from University College London have tested this discovery through a series of experiments and have tracked brain response to dishonesty over a period of time.

On the money

The scientists' experiments involved recruiting 80 adults who were given repeated opportunities to act dishonestly. Participants were asked to advise each other about the amount of money in a jar of pennies.

This experiment was repeated a number of times, and in each trial, people were given a different scenario; the jar's contents would either benefit the participant at the expense of their partner, benefit both parties, benefit the partner at the participant's expense, benefit only the participant without affecting the partner, or benefit the partner without affecting the participant.

The researchers found that the participants were more likely to be dishonest about the content of the jar in the scenarios that benefited them. Levels of dishonesty escalated over the course of the trials and served the participants' self-interest.

The researchers then used functional magnetic resonance imaging (fMRI) to see whether the gradual increase of dishonesty could be objectively observed in the brain. They identified the amygdala as a key region involved in the brain's adaptation to dishonesty.

The amygdala is known to respond to various emotion-eliciting situations, such as when we commit acts that we may find immoral. Here, the scientists discovered there was a progressively reduced response in the amygdala to self-serving dishonesty over time, suggesting the brain gradually adapts to dishonesty.

"The act of telling lies reduces our brain's emotional response to dishonesty and encourages us to tell bigger lies in the future. The study highlights the dangers of engaging in small acts of dishonesty because it can escalate to larger ones further down the line," leading brain analyst Neil Garrett concluded.