A participant in the Pain 2000: An Ancient Problem on the Verge of Solution? symposium to be held Sunday, February 20, 2000, at 3:00 p.m., Dr. Catherine Bushnell Harold Griffith Professor of Anesthesia and Director of the Anesthesia Research Unit at McGill University, will literally show pictures of how we perceive pain.
"Pain is a complex experience, which includes both sensations and emotions," says Dr. Bushnell. "We often use words that describe physical pain to describe emotional pain as well. We say 'my feelings are hurt' or 'I have a heartache,' for example. Because of the complexity and subjectivity of pain, it is difficult to study how nerve signals into the brain lead to the final perception of pain."
In her laboratory, Dr. Bushnell and her team use human brain imaging techniques, such as positron emission tomography (PET scan) and functional magnetic resonance imaging, to study how the human brain is activated when a person experiences pain. "In the cerebral cortex it is the outer layer of the brain that is important for our most sophisticated cognitive experiences," explains Dr. Bushnell. "We find four regions that are particularly important for experiencing pain. Two of the regions (primary and secondary somatosensory cortices) are known to be important for feeling touch as well as pain. Two other regions (anterior cingulate cortex and insular cortex) are part of the limbic system, important for our emotional experiences."
The anterior cingulate cortex appears to be particularly important for determining how much a pain bothers us. When Dr. Bushnell and her team asked subjects to put their hands in painfully hot water and gave hypnotic suggestions to increase or decrease how much the hot water bothered them, they found that activity in the anterior cingulate cortex corresponded to this unpleasantness. However, when they used distraction to take the subject's attention away from the pain and reduce both the burning sensation and the unpleasantness, activity in the somatosensory regions of the cortex was also reduced.
"These findings suggest that the complex experience of pain results from activation in several regions of the cerebral cortex. Further, there appears to be a basis in the cerebral cortex for the observation that psychological state can alter how much pain we feel," Dr. Bushnell concluded.