With repeated lies, the brain becomes less and less sensitive to dishonesty, supporting ever larger acts of dishonesty. But why do we lie and is it such a terrible thing if we do?

STEVE INSKEEP, HOST:

If you ever tell a lie, it would be normal for your conscience to bother you. But here’s a question. If you tell many lies, does that voice inside go quiet? Neuroscientists recently explored this idea. And our colleague Rachel Martin sat down to talk about it with NPR’s social science correspondent Shankar Vedantam.

RACHEL MARTIN, HOST:

Hi, Shankar.

SHANKAR VEDANTAM, BYLINE: Hey, Rachel.

MARTIN: So we’re talking about neuroscientists. They were studying the brain, as they are known to do.

VEDANTAM: (Laughter).

MARTIN: Who are they, and what did they find?

VEDANTAM: So that’s right. If you buy the idea that all behavior stems from the brain, Rachel, this prick of conscience that we often experience obviously has something to do with what’s happening in the brain. Some months ago, Neil Garrett, Stephanie Lazzaro, Dan Ariely, and Tali Sharot conducted a very interesting study. I talked to Dan Ariely. He studies economics and psychology at Duke University. And he said that the premise of the study was actually a very old idea.

DAN ARIELY: The brain is really a mechanism for detecting surprising things, right? The brain is basically working on adaptation. You get to a certain level of flight. In the beginning it’s surprising, and then you get used to that environment.

VEDANTAM: Ariely and his colleagues wanted to know if the same thing happens when you tell a lie. Just as your brain and your eyes adapt to being out in bright sunlight, does your conscience adapt to you being deceitful?

MARTIN: All right, so how did they go about testing this?

VEDANTAM: Well, they scanned the brains of volunteers using what’s known as an fMRI machine. It picks up dynamic changes in the brain as you’re thinking. And they had volunteers participate in a series of experiments where they were given the opportunity to tell lies in order to improve the rewards they received. The researchers found something that you won’t find surprising. Once participants told the first lie, the second lie became easier to tell. And the magnitude of lies increased over time.

When the researchers scanned the brains of the volunteers, they found an explanation for this behavior.

ARIELY: It turns out that the brain also reacts very strongly to a first act of lying. But then as we keep on lying more and more, the brain kind of stops reacting to it. So we start by being aware of this maybe being a dishonest act, and we’re at least aware of it. But over time, it just goes into the background and we don’t pay attention to it.

VEDANTAM: So as volunteers lied repeatedly, Rachel, brain activation in a region of the brain known as the amygdala slowly decline. So in exactly the same way as your eyes react to being in bright sunlight, there was less brain reaction to each new act of deception.

MARTIN: And I’m going to assume that there were no consequences to these lies…

VEDANTAM: (Laughter).

MARTIN: …‘Cause these people who were telling lies, there were no negative effects that would convince them that maybe they shouldn’t keep telling them.

VEDANTAM: That’s absolutely right. So if you tell lies at work or at home, eventually those lies are going to catch up with you and presumably, you will face negative consequences. Your brain’s going to notice those negative consequences, and that’ll change your behavior. This experiment is just talking about how the slippery slope works. The first step down the path of deception makes every subsequent step easier.

MARTIN: Shankar Vedantam is NPR’s social science correspondent. He’s also the host of a podcast exploring the science of deception and other topics related to human behavior. It’s called Hidden Brain. Shankar, thanks so much.

VEDANTAM: Thanks, Rachel.

(SOUNDBITE OF RJD2 SONG, “THE PROXY”)

INSKEEP: Everything Shankar said, definitely true. He’s speaking with our own Rachel Martin.

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