"Long before it's in the papers"
January 27, 2015

RETURN TO THE WORLD SCIENCE HOME PAGE


How the brain chooses between truth and lies

Sept. 3, 2014
Courtesy of Virginia Tech
and World Science staff

What’s the price of your in­tegr­ity? Eve­ry­one has a tip­ping point. Most of us want to be hon­est, but at some point, we’ll lie if the ben­e­fit is great enough. 

Now, sci­en­tists say they have con­firmed the ar­ea of the brain in which we make that de­ci­sion, and gath­ered ev­i­dence that a pref­er­ence for hon­esty over­rides a more bas­ic ten­den­cy to fa­vor self-in­ter­est. The find­ings were pub­lished on­line this week in the jour­nal Na­ture Neu­ro­sci­ence.

Regions of the brain examined in the study. Brain ar­e­as be­hind the fore­head, called the dor­so­lat­er­al pre­fron­tal cor­tex and or­bito­front­al cor­tex, be­come more ac­tive in brain scans when a par­ti­ci­pant is told to lie or to be hon­est. (Im­age cred­it: NIH)


“We pre­fer to be hon­est, even if ly­ing is ben­e­fi­cial,” said Lusha Zhu, the stu­dy’s lead au­thor and a post­doc­tor­al as­so­ci­ate at the Vir­gin­ia Tech Car­il­ion Re­search In­sti­tute. “How does the brain make the choice to be hon­est, even when there is a sig­nif­i­cant cost” to it? She added.

Pre­vi­ous stud­ies have found that brain ar­e­as be­hind the fore­head, called the dor­so­lat­er­al pre­fron­tal cor­tex and or­bito­front­al cor­tex, be­come more ac­tive in brain scans when a par­ti­ci­pant is told to lie or to be hon­est. But there’s no way to know if this oc­curs be­cause an in­di­vid­ual is ly­ing or be­cause he or she pre­fers to be hon­est, said Brooks King-Casas of the in­sti­tute, a co-au­thor with Zhu.

So in the new stu­dy, “we asked wheth­er there’s a switch in the brain that con­trols the cost and ben­e­fit trade­off be­tween hon­esty and self-in­ter­est,” added Pearl Chiu, an­oth­er co-au­thor al­so with the in­sti­tute.

The re­search­ers com­pared healthy vol­un­teers’ choices in an hon­esty game with those of par­ti­ci­pants with dam­age in the brain areas in ques­tion. In one game, par­ti­ci­pants faced an op­tion that gave them more mon­ey at a cost to an anon­y­mous op­po­nent, and an op­tion that gave the op­po­nent more mon­ey at a cost to the par­ti­ci­pant. Un­sur­pris­ing­ly, par­ti­ci­pants chose the op­tion that filled their own pock­ets.

In a dif­fer­ent game, the re­search­ers pre­sented par­ti­ci­pants with the same op­tions but asked the par­ti­ci­pants to send a mes­sage to their op­po­nents, rec­om­mend­ing one op­tion over the oth­er. The par­ti­ci­pants ei­ther lie and reap the re­ward, or tell the truth and suf­fer a loss.

“The av­er­age per­son usu­ally shows lie aver­sion,” Zhu said. “If they don’t need to send a mes­sage, they pre­fer the op­tion that gives them more mon­ey. If they do need to send a mes­sage, they’re more likely” to be hon­est and take the loss.

Par­ti­ci­pants with dam­age in the dor­so­lat­er­al pre­fron­tal cor­tex were not as averse to ly­ing as the two com­par­i­son groups, the study found: they were more likely to pick the prac­ti­cal op­tion and less con­cerned about costs to self-im­age. But when no mes­sage was re­quired, par­ti­ci­pants with dor­so­lat­er­al pre­fron­tal cor­tex dam­age showed the same pat­tern of de­ci­sion-making as the com­par­i­son groups, sug­gest­ing that for each group, the bas­ic ten­den­cy to give to oth­ers is the same.

Thus this brain re­gion, “known to be crit­ic­ally in­volved in cog­ni­tive con­trol, may play a caus­al role in en­a­bling hon­est be­hav­ior,” Chiu said. “Peo­ple feel good when they’re hon­est and they feel bad when they lie,” King-Casas said. “Self-interest and self-im­age are both pow­er­ful fac­tors in­flu­enc­ing a per­son’s de­ci­sion to be hon­est.”

King-Casas added that “one of the real strengths of our study is that we’re able to see how a per­son’s trade­offs change when we add in re­spon­si­bil­ity,” ex­plain­ing that “in past stud­ies, par­ti­ci­pants are typ­ic­ally in­structed by the ex­pe­ri­menter to lie or be hon­est. There’s no con­se­quence for ly­ing; the sub­ject is just comply­ing.”

Anoth­er strength is the measura­ble trade­off, the re­search­ers added – when will an hon­est per­son de­cide ly­ing is worth it?

“We ma­ni­pu­lated the costs and ben­e­fits of hon­esty to quantify the tip­ping point for each per­son,” said Chiu. “We pick­ed tough dilem­mas where, for ex­am­ple, tell­ing a lie might harm the oth­er play­er one cent, where­as be­ing hon­est will cost you $20.” A play­er might then “de­cide that one cent of harm is­n’t so bad.”

The study sheds light on the brain ba­sis and broader na­ture of hon­esty, the in­ves­ti­ga­tors said. 

Phi­loso­phers and psy­chol­o­gists have had long­stand­ing, con­trast­ing hy­pothe­ses about what go­verns the trade­off be­tween hon­esty and self-in­ter­est. The “grace” hy­poth­e­sis sug­gests that peo­ple are in­nately hon­est and have to con­trol hon­est im­pulses if they want to prof­it. The “will” hy­poth­e­sis holds that self-in­ter­est is our au­to­mat­ic re­sponse.

“The pre­fron­tal cor­tex is key to con­trolling our be­hav­ior and helps to override our nat­u­ral im­pulses to be ei­ther hon­est or self-in­ter­ested,” King-Casas said. “Know­ing this, we can test wheth­er ‘grace’ or ‘will’ is dom­i­nant. By in­clud­ing par­ti­ci­pants with le­sions in the pre­fron­tal cor­tex, we were able to test wheth­er hon­esty re­quires us to ac­tively re­sist self-in­ter­est – in which case dis­rupt­ing the pre­fron­tal cor­tex would re­duce the in­flu­ence of hon­esty pref­er­ences – or wheth­er we are au­to­mat­ic­ally pre­dis­posed to­ward hon­esty, in which case dis­rupt­ing the pre­fron­tal cor­tex would in­stead en­hance hon­est be­hav­ior. And our re­sults show a nec­es­sary role for pre­fron­tal con­trol in gen­er­at­ing hon­est be­hav­ior by overriding our ten­den­cies to be self-in­ter­ested.

“Our next step will be to com­bine func­tion­al brain im­ag­ing with eco­nom­ic mod­el­ing to un­der­stand how the brain com­putes the trade­off be­tween the costs and ben­e­fits of ly­ing,” King-Casas added. “Then we can beg­in to un­der­stand the na­ture of hon­esty.”


* * *

Send us a comment on this story, or send it to a friend

Sign up for
e-newsletter
   
 
subscribe
 
cancel

On Home Page         

LATEST

  • St­ar found to have lit­tle plan­ets over twice as old as our own

  • “Kind­ness curricu­lum” may bo­ost suc­cess in pre­schoolers

EXCLUSIVES

  • Smart­er mice with a “hum­anized” gene?

  • Was black­mail essen­tial for marr­iage to evolve?

  • Plu­to has even cold­er “twin” of sim­ilar size, studies find

  • Could simple an­ger have taught people to coop­erate?

MORE NEWS

  • F­rog said to de­scribe its home through song

  • Even r­ats will lend a help­ing paw: study

  • D­rug may undo aging-assoc­iated brain changes in ani­mals

What’s the price of your integrity? Everyone has a tipping point. Most of us want to be honest, but at some point, we’ll lie if the benefit is great enough. Now, scientists say they have confirmed the area of the brain in which we make that decision, and gathered evidence that a preference for honesty overrides a more basic tendency to favor self-interest. The findings were published online this week in the journal Nature Neuroscience. “We prefer to be honest, even if lying is beneficial,” said Lusha Zhu, the study’s lead author and a postdoctoral associate at the Virginia Tech Carilion Research Institute. “How does the brain make the choice to be honest, even when there is a significant cost” to it? She added. Previous studies have found that brain areas behind the forehead, called the dorsolateral prefrontal cortex and orbitofrontal cortex, become more active in brain scans when a participant is told to lie or to be honest. But there’s no way to know if this occurs because an individual is lying or because he or she prefers to be honest, said Brooks King-Casas of the institute, a co-author. So in the new study, “we asked whether there’s a switch in the brain that controls the cost and benefit tradeoff between honesty and self-interest,” added Pearl Chiu, another co-author also with the institute. The researchers compared healthy volunteers’ choices in an honesty game with those of participants with damaged dorsolateral prefrontal cortices or orbitofrontal cortices. In one game, participants faced an option that gave them more money at a cost to an anonymous opponent, and an option that gave the opponent more money at a cost to the participant. Unsurprisingly, participants chose the option that filled their own pockets. In a different game, the researchers presented participants with the same options and but asked the participants to send a message to their opponents, recommending one option over the other. The participants either lie and reap the reward, or tell the truth and suffer a loss. “The average person usually shows lie aversion,” Zhu said. “If they don’t need to send a message, they prefer the option that gives them more money. If they do need to send a message, they’re more likely to send a message that will benefit the other person even at a loss to themselves. They want to be honest, at the cost of their own wallet.” Participants with damage in the dorsolateral prefrontal cortex were not as averse to lying as the two comparison groups, the study found: they were more likely to pick the practical option and less concerned about costs to self-image. But when no message was required, participants with dorsolateral prefrontal cortex damage showed the same pattern of decision-making as the comparison groups, suggesting that for each group, the basic tendency to give to others is the same. Thus “the dorsolateral prefrontal cortex, a brain region known to be critically involved in cognitive control, may play a causal role in enabling honest behavior,” Chiu said. “People feel good when they’re honest and they feel bad when they lie,” King-Casas said. “Self-interest and self-image are both powerful factors influencing a person’s decision to be honest.” King-Casas added that “one of the real strengths of our study is that we’re able to see how a person’s tradeoffs change when we add in responsibility,” explaining that “in past studies, participants are typically instructed by the experimenter to lie or be honest. There’s no consequence for lying; the subject is just complying.” Another strength is the measurable tradeoff, the researchers added – when will an honest person decide lying is worth it? “We manipulated the costs and benefits of honesty to quantify the tipping point for each person,” said Chiu. “We picked tough dilemmas where, for example, telling a lie might harm the other player one cent, whereas being honest will cost you $20.” A player might then “decide that one cent of harm isn’t so bad.” The study sheds light on the brain basis and broader nature of honesty, the investigators said. Philosophers and psychologists have had longstanding, contrasting hypotheses about what governs the tradeoff between honesty and self-interest. The “grace” hypothesis suggests that people are innately honest and have to control honest impulses if they want to profit. The “will” hypothesis holds that self-interest is our automatic response. “The prefrontal cortex is key to controlling our behavior and helps to override our natural impulses to be either honest or self-interested,” King-Casas said. “Knowing this, we can test whether ‘grace’ or ‘will’ is dominant. By including participants with lesions in the prefrontal cortex, we were able to test whether honesty requires us to actively resist self-interest – in which case disrupting the prefrontal cortex would reduce the influence of honesty preferences – or whether we are automatically predisposed toward honesty, in which case disrupting the prefrontal cortex would instead enhance honest behavior. And our results show a necessary role for prefrontal control in generating honest behavior by overriding our tendencies to be self-interested. “Our next step will be to combine functional brain imaging with economic modeling to understand how the brain computes the tradeoff between the costs and benefits of lying,” King-Casas added. “Then we can begin to understand the nature of honesty.”