Miércoles 24 de Mayo de 2006, Ip nº 154

The Real Pain of Dread
Por Emily Singer

For some people, waiting for a particularly unpleasant event, such as a colonoscopy or root canal, can be just as awful as the event itself, according to a new study on the neurobiology of dread, published in the journal Science.

Scientists found that dread activated brain areas similar to those associated with pain, and that people who rated the waiting period as most unbearable had more activity in a part of the brain's pain circuit that mediates attention. They say the findings could help explain how people make some decisions, such as dieting and buying stocks, which involve a long waiting period before seeing results.

The perception of pain is mediated by a complex neural circuit, known as the "pain matrix." Some parts of the matrix control the physical sensations of pain, such as the pain receptors that react when you accidentally bang your knee. Other parts of the matrix control higher-level perceptions of pain, which vary depending on the level of attention and emotional state. One is less likely to feel the pain in a knee, for example, if the joint is banged while running from a bear.

In the current study, researchers used functional magnetic resonance imaging (fMRI), which measures blood flow in the brain, to determine which parts of the brain were most active as subjects waited for an electric shock. They found that the dread associated with waiting for the unpleasant stimulus activated parts of the pain matrix, especially those involved in attention to pain. "These findings underscore the very real nature of dread," says Gregory Berns, the neuroscientist at Emory University in Atlanta who led the research.

Researchers also found that people react to the prospect of the pain in different ways. While almost all participants preferred to get the physical shock over with quickly, about one-third -- whom the researchers dubbed "extreme dreaders" -- actually chose to receive a more severe shock sooner rather than wait for a less painful shock. "Some people found waiting so unpleasant that they were willing to take a worse shock rather than wait," says Berns. And those "extreme dreaders" had more activity in the attention part of the pain matrix.

In a somewhat surprising finding, the researchers discovered that dread was neurologically distinct from both fear and anxiety. An area of the brain known as the amygdala, which plays a key role in regulating emotions such as fear, was not more active in extreme dreaders.

"The prospect that [dread] has more to do with attention than emotion is interesting," says Elizabeth Phelps, a neuroscientist at New York University who studies emotion and decision-making. "Presumably, if you could distract yourself in some way, you could get rid of some of these responses."

The findings could help in the understanding of how people make decisions. Many choices involve a waiting period -- playing the stock market, for example, often requires waiting years to get returns. Yet most economic models don't take into account that waiting has its own costs and benefits -- such as the dread sometimes felt waiting for something bad to occur or the eagerness in waiting for a happy event. "The current study shows that anticipation itself becomes part of the consumption pattern," says Kevin McCabe, a neuroscientist and economist at George Mason University in Fairfax, VA. "I think if [the findings] hold up, it basically does imply different policies for dealing with losses than the way standard economics models would approach them."

The findings might also help to explain seemingly odd decisions, such as why some people overeat or use addictive drugs, which they know are harmful in the long run. "These findings emphasize the role of immediate emotions rather than abstract trade-offs," says George Lowenstein, an economist and psychologist at Carnegie Mellon University. While scientists aren't yet sure why some people are more likely to overeat or become addicted to drugs, one theory is that they value short-term pleasure over long-term health. But the new study suggests these people may instead be trying to avoid the unpleasantness of waiting, says Lowenstein. "If someone is overeating, it's not that they don't care about being obese. They find it very uncomfortable in the here and now to desist from eating."

Berns and colleagues are now studying different aspects of decision-making, such as how adolescents make choices when faced with rewards and how adults do so when negative consequences are uncertain. Berns points out that the recruiting process for the experiment may have screened out certain types of people, though, such as super-extreme dreaders. "When we told people on the phone that the experiment would involve shocks, many dropped out right then," he says.

McCabe says it would be interesting to see how people with phobias, such as fear of flying or heights, react to dread. "These people do try to avoid the circumstances as long as possible," says McCabe. "It would be interesting to see how this normal circuitry is different in those people's brains."

  18/05/2006. MIT's Technology Review.