The tradeoff between honesty and self-interest isn't always blatantly apparent, but it plays a role in a wide range of personal and professional decisions. One example is selling a car. If you're trying to sell a car, do you tell potential buyers that the A/C sometimes doesn't work? Or that the CD player skips? That the brake pads need replacing? How much information do you reveal when you know that that information will affect the buyer's willingness to purchase the car and how much they're willing to pay for it? You could lie, or even simply withhold information, hoping to sell the car for a higher price, but that would be dishonest. You could provide the buyer with complete information on the car, but that will limit your chances of selling it or reduce the price you get for it. Studies have shown that, in general, individuals are willing to give up some economic benefits and personal gain in favor of honesty, even when there's no risk of punishment or repercussions for dishonesty. So even if they could sell the car with complete anonymity and finality, most people choose to reveal more information about it than they have to, fully knowing that it will decrease the price. What's keeping us honest? How do our brains actually make that decision?
Neural imaging and developmental studies have shown that this sort of decision involves two major parts of the brain: the dorsal lateral prefrontal cortex (DLPFC) and the orbital frontal cortex (OFC), both of which are part of the larger prefrontal cortex. The prefrontal cortex, or PFC, is known to be responsible for planning complex behavior, decision making that accurately weighs the possible outcomes, and our ability to put ourselves in other peoples' shoes. In humans, the ratio of PFC weight to total brain weight is much higher than it is in any other animal. That and the PFC's contribution to rational thinking and empathy make many people believe that it is what separates us from other animals and makes us uniquely human. Choosing to be honest over acting in your own self-interest could be seen as an aspect of that.
There are two prevailing theories of exactly what role the OFC and DLPFC play in honesty. The first is that the PFC promotes honesty concerns over self-interest, and the second it that the PFC promotes consideration for self-interest over altruistic considerations, raising the question: Is your PFC helping you be more honest or encouraging you to be less honest? A paper published a few weeks ago in Nature Neuroscience attempts to answer just that.
Lusha Zhu at Virginia Tech, and other researchers in neuroscience and economics, had several patients with brain lesions, as well as several healthy individuals, partake in economic decisions designed to measure honesty versus self-interest. Six patients with DLPFC lesions and seven patients with OFC lesions participated. Surprisingly, the patients with OFC lesions performed identically to the healthy controls. The patients with DLPFC lesions, however, were significantly less willing to sacrifice monetary benefits in the interest of being honest, without being significantly different in their base altruistic tendencies. This tells us not only that the DLPFC has a causal effect in these situations but that it is the promoter of honesty, not the promoter of self-interest.
The latter of these conclusions might be obvious to anyone who remembers being a teenager. The PFC is one of the last brain regions to finish developing, so, for a period in our adolescence, we all have what is essentially a natural PFC lesion. The implication from this study is that teens are less willing to sacrifice personal benefit in favor of being honest than healthy adults are. While there's nothing anyone can do to change that, it should be taken into consideration when designing anything that may interact with teens. Things like jumpable subway turnstiles or unlocked movie-theater doors marked "exit only" may not be enough to keep teenagers honest. Knowing this can help us predict behavior and build better, more effective systems.