Reducing activity in specific areas of the brain caused people to become more generous, researchers found.
Researcher Leonardo Christov-Moore, of the University of California-Los Angeles (UCLA), and colleagues publish their findings in the journals Human Brain Mapping and Social Neuroscience.
In the first study, the team set out to identify the brain regions that play a role in empathetic decision-making.
The researchers enrolled 20 participants and asked them to take part in two tasks while undergoing brain scans with functional magnetic resonance imaging (fMRI).
One task involved viewing a video of a hand being pricked by a pin, while the other task involved viewing photographs of faces showing a variety of different emotions - such as happy, sad and angry - and imitating them.
Low generosity linked to high activity in areas of prefrontal cortex
The researchers found that the amygdala, somatosensory cortex and the anterior insula areas of the brain were involved with imitating others and experiencing pain and emotion, while two other areas in the prefrontal cortex - the dorsolateral and dorsomedial regions - played a key role in behavior and impulse control.
Next, the participants took part in a task called the "dictator game," in which they were given $10 each round for 24 rounds and asked whether they wanted to keep their money or share it with a stranger, for whom information on age and income was provided.
On comparing the brain scans of participants with the amount of money they shared in the dictator game, the team found that individuals who demonstrated the greatest activity in the prefrontal cortex parted with the least money, giving away an average of $1-3 in each round.
However, subjects who showed the greatest activity in areas of the brain linked to pain perception, emotion and imitating others gave away an average of 75% of their funds. The researchers say this behavior can be referred to as "prosocial resonance" - a type of mirroring impulse that they believe is a key driver for altruism.
"It's almost like these areas of the brain behave according to a neural Golden Rule," says Christov-Moore. "The more we tend to vicariously experience the states of others, the more we appear to be inclined to treat them as we would ourselves."
Reducing activity in behavior, impulse brain regions increased generosity
The team enrolled 58 participants for the second study, all of whom underwent theta-burst transcranial magnetic stimulation, a non-invasive procedure used to temporarily weaken activity in certain areas of the brain.
Activity in the dorsolateral prefrontal cortex or the dorsomedial prefrontal cortex - the areas linked to behavior and impulse - was blocked for 38 of the participants, while for 20 control participants, activity in an area of the brain linked to sight was reduced.
The participants were then required to play the dictator game, enabling the researchers to assess how dampening activity in these regions affected subjects' willingness to share with others.
Christov-Moore hypothesized that if selfishness was ingrained within an individual, reducing activity in the dorsolateral and dorsomedial prefrontal cortexes would allow them to be even more selfish.
However, the researchers found that reducing activity in these behavior and impulse regions actually increased generosity, with these subjects being an average of 50% more generous with their money than those in the control group.
Reducing activity in the dorsomedial prefrontal cortex appeared to increase overall generosity, while subjects whose activity was reduced in the dorsolateral prefrontal cortex were more likely to share their money with strangers who had higher incomes.
"Normally, participants would have been expected to give according to need," says Christov-Moore, "but with that area of the brain dampened, they temporarily lost the ability for social judgments to affect their behavior. By dampening this area, we believe we laid bare how altruistic each study participant naturally was."
Based on their results, the researchers suggest we may be hard-wired for altruism. What is more, they believe the results indicate that it may be possible to make people less selfish and more generous toward others.
"This is potentially groundbreaking," says Christov-Moore. Senior author Marco Iacoboni, a psychiatry professor at UCLA, adds:
"The study is important proof of principle that with a non-invasive procedure you can make people behave in a more prosocial way."
Last July, Medical News Today reported on a study in which researchers created a computational model that can predict generosity.