For those who dread a colonoscopy or a root canal so much that they avoid it altogether, scientists have good news.
The first study ever to look at where sensations of dread arise in the brain finds that contrary to what is widely believed, dread does not involve fear and anxiety in the moment of an unpleasant event. Instead, it derives from the attention that people devote beforehand to what they think will be extremely unpleasant.
So the solution to dread, the researchers say, is self-distraction.
"We sort of knew that things like self-hypnosis help relieve dread, but now we know why," said Dr. Gregory S. Berns, a professor of psychiatry and behavioral sciences at Emory University, who led the study.
The research, being published today in the journal Science, is "terrific, " said a leading expert on brain imaging, Dr. Read Montague, a professor of neuroscience at Baylor College of Medicine who was not involved in the study. It demonstrates that the brain "assigns a cost to waiting for something bad, so that the bad thing is worse when it's delayed farther in the future," Dr. Montague said.
"Hence," he said, "the 'let's get it over with' bit when we're at the doctor's office waiting to get a shot."
The research also sheds light on economic behavior, said George Loewenstein, a behavioral economist at Carnegie Mellon University. According to standard economic models of human behavior, choosing more pain in the short run is irrational, Dr. Loewenstein said: if you know something bad is going to happen, you should postpone it as long as possible, and if something good is going to happen, you should want it right away.
In real life, people often do the exact opposite, he said. They delay gratification to savor a sweet sense of anticipation, and accelerate punishment just to get it over with. The new study sheds light, he said, on how the act of waiting can be used to describe economic behavior more accurately.
For the study, Dr. Berns put 32 people into a brain scanner and applied brief electric shocks to the tops of their left feet. After their maximum pain threshold was determined, meaning the most pain they could withstand, they were each presented a series of 96 cues. Each cue stated how much voltage they were about to experience and how long they would have to wait for it. For example, one cue might say they were about to receive 60 percent of their maximum pain after 27 seconds. Another might warn of a 30 percent maximum shock after 9 seconds.
Next the subjects were given options involving various combinations of voltage and how long they had to wait for it . For example, they could choose between getting 90 percent of their maximum voltage after three seconds or 60 percent after 27 seconds. Then they received the chosen shock to the foot.
The scanner detected the brain activity involved in waiting for shocks, providing a road map for understanding the dread response.
Twenty-three of the people, termed "mild dreaders," chose as short a delay as possible for any given voltage but were not willing to accept more pain just to get it over with, Dr. Berns said. The nine others, called "extreme dreaders," always took the highest voltage if it was sooner rather than later. They gladly accepted more pain to reduce their dread time.
In comparing the brain scans of both groups, Dr. Berns found only one difference. During the waiting period, extreme dreaders showed high activity in a part of the brain's so-called pain matrix that involves attention.
The pain matrix is a set of brain regions that become active when people experience pain, Dr. Berns said. Parts of it deal with sensing the body, while other regions are involved in intuition, emotions, fear or attention. Extreme dreaders, he said, deploy more attention to their soon-to-be-shocked foot than do mild dreaders. Above all else, dread involves attention to unpleasant things to come, making it quite different from anxiety or fear.
When it comes to a root canal or a colonoscopy, it is not really the procedures themselves that people dread, but the waiting time, Dr. Berns said. For extreme dreaders, finding distraction is probably the best way to cope.