Human beings are more aroused by rewards they actively earn than by rewards they acquire passively, according to brain imaging research by scientists at Emory University School of Medicine. Results of the study, led by first author Caroline F. Zink and principal investigator Gregory S. Berns, MD, PhD, of Emory's Department of Psychiatry and Behavioral Sciences, are published in the May 13 issue of the journal Neuron.

The Emory scientists used functional magnetic resonance imaging (fMRI) to measure brain activity in the striatum, which is a part of the brain previously associated with reward processing and pleasure. Although other experiments have studied and noted brain activity associated with rewards, until now these studies have not distinguished between the pleasurable effects of receiving a reward and the "saliency" or importance of the reward.

Study volunteers in the Emory experiment were asked to play a simple target-detection computer game. During the game, a money bill appeared occasionally and automatically dropped into a bag of money on the screen. The participant was given the amount of money that dropped in the bag at the end of the game, but because receiving the money had nothing to do with their performance on the computer game, it was not particularly arousing or salient to them.

In another version of the game, a money bill occasionally appeared on the screen and the participant had to momentarily interrupt the target detection game and push a button to make the bill drop into the bag. In this case, whether or not the participant received the money did depend on their performance, which made the appearance of the money bill more salient to them.

In yet another version, participants played the same computer game except the bag on the screen did not appear to have money in it and a blank "blob" dropped into the bag instead of money.

The investigators performed fMRI on the subjects while they were playing the game, particularly focusing on the reward centers. They found that some reward centers of the brain were activated whenever the money was received, but that other parts, particularly the striatum, were activated only when the participants were actively involved in receiving the reward.

"Scientists have conducted tests with monetary rewards in the past and noted that the striatum was activated, but it has been unclear whether it was because of the pleasure surrounding the money or the fact that the money was presented to participants in a salient or behaviorally important manner," said Zink. "We differentiated the saliency aspect by having the participants receive money that had nothing to do with their actions and having them receive money through active participation."

The investigators confirmed that the appearance of money that required a response was more salient to participants than money received passively by measuring skin conductance responses during the game -- a measurement of general arousal used as part of lie detector tests. The active participation in receiving the reward was the only condition that elicited a higher skin conductance measure, indicating greater arousal.

"Being actively engaged in the pursuit of rewards is a highly important function for the brain, much more so than receiving the same rewards passively," Dr. Berns explains. "It is like the difference between winning the lottery and earning the same amount of money. From the brain's perspective, earning it is more meaningful, and probably more satisfying."

It makes sense from an evolutionary perspective that the brain is wired up to reward itself for successfully engaging in activities that bring gains to one's position. History has already provided copious quantities of evidence that the political philosophy of Karl Marx is incompatible with human nature. Even before communist revolutionaries swept into power there were older theories of human nature that predicted the failure of a creed based on "from each according to his ability and to each according to his need". But advances in brain imaging technology has produced tools that are allowing reductionist brain scientists to start unravelling the deep seated mechanisms of our brains that alwayts doomed Marxism to failure.

A more general observation here is that by discovering the mechanisms that govern our behavior science is discovering limits to the malleability of human nature. As brain science advances its results are increasingly going to be used to judge whether proposals for changes in social order are going to compatible with human nature as science comes to understand it. Radical advocates of new social orders are going to increasingly be challenged by results from scientific research labs.

However, science will not only play a conservative role in opposition to proposed changes. Some proposals will be found to be compatible with human nature. Also, and more worringly, eventually scientific advances in the understanding of the brain and in ways to manipulate neurons will serve as the foundation for the development of technologies for changing human nature. Any future radicals who manage to seize power will be able to use biotechnologies to rework the brains of their subjects to be compatible with their imagined utopias. We will no longer be able to count on human nature to serve as a source of resistance to radical utopians because human nature will become more malleable.