How to lose friends and alienate people by disrupting the brain

Oscar Wilde once said, "One can survive everything nowadays, except death, and live down anything, except a good reputation." All well and witty, but for those of us who aren't Victorian cads, reputation matters. It's the bedrock that our social lives are built upon and people go to great lengths to build and maintain a solid one. A new study shows that our ability to do this involves the right half of our brain, and particularly an area called the lateral prefrontal cortex (PFC).

Disrupting the neurons in this area hampers a person's ability to build a reputation while playing psychological games. They can still act selflessly, and they still know what they would need to do in order to garner good repute. They just find it difficult to resist the temptation to cheat, even though they know it will cost them their status among other players. Most of us know from personal experience that knowing what's best for us is very different to acting on it - this study shows that this distinction exists at a neurological level.

Daria Knoch and colleages from the University of Basel focused on the PFC because it's a key player in mental abilities that centre around self-control, including planning, decision-making and attention. These "executive processes" must surely play a key part in building a good reputation, for doing so typically involves a cost (such as time, effort or money) and a tradeoff between current and future benefits. For example, I might return a dropped wallet so that I'll be seen in a good light, rather than pocket the cash and be done with it.

Other studies have compared neural activity in the PFC with people's behaviour, but these brain scans can't tell us whether the activity caused the behaviour or vice versa.  To do that, Knoch decided to take the PFC out of the game entirely. She used a technique called transcranial magnetic stimulation (TMS) where rapidly changing magnetic fields induce weak electric currents in specific parts of the brain the suppresses the buzz of the local neurons.

After going through this treatment, 87 volunteers played a "trust game" in pairs. In each round, an investor decides how many points (out of 10) to donate to a trustee. These are quadrupled, and the trustee decides how many of these to give back.  Some games were played anonymously and the investors never knew about the trustees' decisions. With the investor in the dark, the trustees had no strategic incentive to return any points at all, and doing so is a measure of their selflessness.


In other games, the trustee's last three decisions were public knowledge and that brought reputation into play. The trustee could achieve a good reputation by equalising the shares or paying back even more, or shatter their credibility by paying back nothing or very little. The latter option nets big rewards in the short-term, but the trustees needed to override their immediate self-interests for bigger gains in the long-term. And if the initial investment is greater, the trustees also need more self-control for the amount they have to return is greater.

This worked in practice. If trustees always equalised their payoffs, they had a 71% chance of being trusted with the full 10 point investment; if they gave nothing back, this probability fell to 6%. In the long run, those who always cooperated until the last hurdle earned 43% more points than constant cheats. And trustees cared about their reputation - when the game was anonymous, they send back around a quarter of their investment, but if their status was on the line, they gave back 44%. 

TMS didn't affect the trustees' choices in the anonymous games, or in the reputational ones if investments were low. But when big points were on the table, things changed. Targeting their right lateral PFC significantly reduced their likelihood of paying back the investors to 30%, down from 41% for a fake round of TMS, or 48% for a burst directed to the left brain.

In fact, the trustees whose right brains were targeted with TMS behaved in exactly the same way regardless of whether the investors knew about their choices or not. Anonymous or transparent, it didn't matter - even though their reputation was on the line, their behaviour didn't change.


Knoch also found that the TMS didn't affect the volunteers' perceptions of fairness. They knew that hoarding large investments was unfair, and they knew that if they did so, the investors would probably give them fewer points in the future. They knew all of this - they just couldn't put it into useful practice. They couldn't put off the short-term gains of having lots of points, in favour of earning even more in the long-term - a basic skill when it comes to building a reputation.

Of course, the lateral PFC is probably only part of the story. It's fashionable to try and discover the brain region "responsible for" different abilities or behaviours, but the PFC is no more the brain's "reputation centre" than a steering wheel is a car's "driving centre" - clearly other parts like the wheels, axle and engine help too. Knoch (more so than many neuroscientists), is aware of this and says, " In highly complex processes such as reputation formation, brain areas do not act in isolation, but rather must work together as a network." Her next goal is to investigate how different parts of the brain interact when reputation is on the line.

Reference: PNAS 10.1073/pnas.0911619106

More on reputation and coopoeration: 


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