Study Offers Images of Pain’s Effect on the Brain

by Kelli Whitlock Burton

October 11, 2007

Stub your toe and a shock of pain courses through your body, riveting all your attention on the injured digit. It’s a basic survival skill preserved by evolution in all animals, including humans. But despite its advantages, this biological self-awareness comes with a downside. Pain demands full attention from the brain, making it almost impossible to concentrate on anything else.

A team of researchers in Germany have identified which regions of the brain allow pain to affect cognitive thought, work that furthers the understanding of the interactions that take place in the brain.

“If you think about it carefully, it is not really surprising to find that pain influences that ability to concentrate,” says Jan Gläscher, a neuroscientist at the University Medical Center Hamburg-Eppendorf and coauthor of the paper, which appeared in the July 5 issue of Neuron. “Pain is such an important and relevant stimulus that often requires immediate action.”

In the study, participants were scanned using a functional magnetic resonance imager as they performed two tasks. They reviewed slides in groups of 10 images that contained varying backgrounds overlaid with a large, single letter. As a test of subjects’ working memory, they were asked to press a button when the same letter appeared on two consecutive images. Another, more complicated, task required them to press a button when the same letter appeared on every fourth image, creating what scientists call a “working memory load.”

During the test, participants received intermittent relatively harmless zaps to their hands from a laser beam, administered at varying levels of intensity. After the test, they were then asked to identify the background images on the photos they reviewed.

As expected, participants fared worse on the test when they experienced the “pin-prick like” sensation from the laser beam, Gläscher, says. But with and without the zapping, subjects struggled to succeed at the more complex test, suggesting that dealing with a “working memory load” might distract participants as much as pain does.

Reviewing the scans of brain activity taken during the test, the scientists found that pain affects cognition through an area deep within the brain called the rostral anterior cingulate cortex. However, working memory load disturbs cognition through a different region, the inferior parietal complex.

“We can now say that both painful stimulation and working memory are represented in different brain areas and that these areas exert a separate influence of object recognition,” Gläscher says, who adds that this information will help scientists better understand the interconnected nature of the brain. “It helps us to develop an integrative description of cognitive functions and their implementation in the brain.”

The next step in the work will be to examine the impact of chronic pain on cognition.