For release: Wednesday, April 4, 2007
It’s an enduring mystery that taunts neuroscientists and evolutionary biologists. If the human brain evolved to maximize its owner’s survival, why are we motivated to help others, even when it incurs some personal cost?
One pat answer is that when we help someone in need, we expect him to return the favor. But some kinds of altruism aren’t easy to explain away as mere reciprocity. For example, tax incentives aside, donating money to a charitable cause is unlikely to bring the donor any foreseeable return – except perhaps the "joy of giving."
Two new studies shed light on why it feels good to give by examining how and where altruism originates in the brain.
In both studies, functional magnetic resonance imaging (fMRI) was used to visualize the brain's activity while people played computer games that enabled them to earn money for real-life charities. The researchers also tied the results of these imaging experiments to the subjects’ everyday behaviors, by asking them about their involvement in charitable work, or about their general capacity for altruism. Both studies conclude that areas of the cerebral cortex – the outer layer of the brain that serves highly evolved cognitive functions, such as abstract thought and self-awareness – are key mediators of altruistic behavior.
One study, published in the Proceedings of the National Academy of Sciences,* involved about 20 people, each of whom had the potential to walk away with a pot of $128. They also were given a separate pool of funds, which they could choose to distribute to a variety of charities linked to controversial issues, such as abortion and the death penalty. A computer presented each charity to the subjects in series, and gave them the option to donate, to oppose donation, or to receive a payoff, adding money to the pot. Sometimes, the decision to donate or oppose was costly, calling for subjects to take money out of the pot.
It turned out that a similar pattern of brain activity was seen when subjects chose either to donate or take a payoff. Both types of decisions were associated with heightened activity in parts of the midbrain, a region deep in the brain that is known to be involved in primal desires (such as food and sex) and the satisfaction of them. This result provides the first evidence that the "joy of giving" has an anatomical basis in the brain – surprisingly, one that is shared with selfish longings and rewards.
Jordan Grafman, Ph.D., the scientist who led the work, was more interested by what happened when subjects donated, or opposed donation, at a cost to themselves. In either case, an area of the brain toward the forehead, known as the anterior prefrontal cortex, lit up. When Dr. Grafman and his team asked subjects to rate their charitable involvement in everyday life, he found that those with the highest ratings also had the highest level of activity in the prefrontal cortex.
"There’s a lot of controversy about what the prefrontal cortex does," said Dr. Grafman, a senior investigator in the intramural research division of the National Institute of Neurological Disorders and Stroke (NINDS). "We’re interested in how this uniquely human part of the brain represents and processes information."
Studying how the prefrontal cortex influences altruistic behavior is likely to yield insights into other kinds of complex decision-making "where the end-result is not going to be immediately apparent," he said.
Meanwhile, a study in Nature Neuroscience** connects altruism to the posterior superior temporal cortex (pSTC), an area in the upper rear of the brain that’s known to enable us to perceive goal-directed actions by someone or something else.
About 45 subjects were asked to play a computerized reaction time game or, on some trials, to simply watch as the computer played it. Faster reactions earned money for the subject or for a charity, and subjects were told at the beginning of each trial where their earnings would go. They also completed assessment scales designed to measure their altruism in real-world situations.
Among subjects who scored high on the altruism scale, the pSTC became more active during "watching" sessions and less active during "playing" sessions. Moreover, this link between pSTC activation and watching was strongest when the charity, not the subject, was designated to receive the game's winnings. Among low-altruism subjects, pSTC activation was not significantly altered by the conditions of the game – that is, whether the subject played or watched, and who received the winnings.
The results suggest that altruism depends on – and may have evolved from – the brain's ability to perform the relatively low-level perceptual task of attributing actions to others, said senior author, Scott Huettel, Ph.D.
"Our findings are consistent with a theory that some aspects of altruism arose out of a system for perceiving the intentions and goals of others," said Dr. Huettel, a neuroscientist and NINDS grantee at Duke University Medical Center in Durham, North Carolina. "To be altruistic, you need to see that the people you’re helping have goals, and that your actions will have consequences for them," he said.
Although his study and Dr. Grafman's study link altruism to different brain regions, Dr. Huettel sees the results as complementary rather than contradictory. "There are certain to be multiple mechanisms that contribute to altruism, both in individuals and over evolutionary time," he said.
Dr. Grafman's team included Jorge Moll, Ph.D., and Frank Krueger, Ph.D., who are both postdoctoral fellows in his lab at NINDS. Dr. Huettel’s team included Dharol Tankersley, a graduate student in his lab at Duke, and C. Jill Stowe, Ph.D., a professor at Duke's Fuqua School of Business.
*Moll J et al. "Human Fronto-Mesolimbic Networks Guide Decisions About Charitable Donation." Proceedings of the National Academy of Sciences, October 17, 2006, Vol. 103(42), pp. 15623-15628.
**Tankersley D et al. "Altruism is Associated with an Increased Response to Agency." Nature Neuroscience, February 2007, Vol. 10(2), pp. 150-151.
By Daniel Stimson, Ph.D.
Last Modified April 4, 2007