Neuroscience reveals why some people are selfish jerks

Some people are just manipulative jerks.

They deceive people for their own benefit, they see others as weak and untrustworthy, and they ignore moral codes.

Psychologists have dubbed these people Machiavellians, after the Italian political philosopher Niccolo Machiavelli, whose book "The Prince" includes many examples of this sort of unsavory character.

Now, a recent study published in the journal Brain and Cognition reveals what goes on in the brains of these social deviants when they're around others who are acting fairly.

Machiavellianism - which is part of the "dark triad" of personality traits, along with narcissism and psychopathy - falls on a spectrum, from low Machs (aka normal people) to high Machs (aka jerks).

Tamas Bereczkei and his colleagues at the University of Pecs in Hungary gave 38 university students (20 men and 18 women) a 20-item questionnaire consisting of short statements about the rules and principles involved in relationships with others. People who scored less than or equal to 88 were defined as low Machs, while those who scored greater than or equal to 114 were defined as high Machs. (You can take a similar test yourself here, but it's on a different scale.)

Twenty-two of the students scored as low Machs and 16 were high Machs.

The trust game

The students played a two-round trust game while their brains were scanned by an MRI machine. The machine measures the amount of blood flowing to different parts of the brain, which corresponds to which parts are most active at one time.

In the first round, a student was given a small sum of real money and allowed to "invest" some portion of it in a trustee (which was actually a computer algorithm). The trustee then returned some of that money to the investor.

In the second round, the investor became the trustee, and vice versa. Now, the student received an investment, and had the choice of how much to give back to the investor.

An offer was considered "fair" if the return was the same amount as the first player's offer, give or take 10%. An unfair offer returned only 30% of the original offer, give or take 10%.

When the high Machs received a fair offer in the first round, they returned an unfair offer, whereas the low Machs returned fair offers with fair offers of their own.

What a selfish brain looks like

High Machs exhibited higher brain activity in certain areas when their partner made a fair return offer, as opposed to an unfair offer.

Specifically, they had increased activity in two parts of their brain: The anterior dorsolateral prefrontal cortex, a region thought to be involved in suppressing emotional responses, and the inferior frontal gyrus, an area responsible for evaluating social behavior and cooperation, as shown below.

Those who scored high on the Machiavellian scale also earned more money in the game than their less manipulative colleagues, the researchers found.

The researchers think the reason the high Machs has these spikes in brain activity was because they had to use more mental energy to respond to their partner's cooperative behavior (in order to take advantage of it).

These findings agree with previous studies that show Machiavellians act in their own self-interest and manipulate others for personal gain.

Future studies will be needed to understand how Machiavellians control their emotions and what brain structures are involved in their cold and calculating behavior, the researchers reported.