The team knew from the work of others that lying causes stress for the person telling the lie. The anxiety from knowing you're doing something wrong and being afraid of getting caught activates an area of the brain called the amygdala. So, for their study, the researchers hooked up each participant to a brain-scanning device that would monitor the activity of the amygdala during testing. Each participant in the test group was shown an image of a glass jar containing pennies and was told to help a partner, who could not see the jar as clearly, to estimate the amount of money. Now, here's the twist: In some trials. the participants were told they would receive a reward if their partner's estimate were either too high or too low This gave the participants a reason to lie to their partners about the pennies they were seeing​