When research subjects under hypnosis are given the suggestion that they will feel extremely severe pain when they plunge their hand into a tub of hot water, their neuronal circuits activate more intensely than if the same subjects are told that the heat will be only slightly painful, or not painful at all. Somewhere between the spinal cord and the brain, the pain signal is changed.

Pierre Rainville, a research associate in the Université de Montréal faculty of dentistry has demonstrated this in the course of a study on the representation of pain in the cerebral cortex, just published in the Journal of Neurophysiology with Gary Duncan and co-researchers at McGill University. "There's no such thing as a center of pain," says the UdeM researcher, who conducted part of his recent projects at the University of Iowa. "No lobotomy makes pain disappear entirely. But recent research conducted using functional cerebral PET imaging (positron emission tomography) clearly shows that certain parts of the brain change when we are afraid of the sensation before it comes. In other words, the response of certain regions of the cortex is directly proportional to the subjective experience of pain."

Pain is a sensation that is crucial for survival. Without a sense of pain there are no protective reflexes, no fear...no control of risks. But the threshold of tolerance varies. The pain you might feel in your stomach after a big meal is different from what a carpenter feels if he bangs his thumb with a hammer. Three experimental conditions were tested. In the first, the subjects were simply lowered for one minute into a tub of water at 47° C (116.6° F). In the second set of conditions, the subjects were hypnotized and the experimenter would suggest that the water was very hot. Under the third set of conditions, the research subjects, again under hypnosis, believed the opposite - that the water temperature was only slightly warm.

Questionnaires completed after each test revealed that the subjects felt much greater pain under the second set of conditions than under the third. This shows that an anticipation that a thing will hurt accentuates pain's severity. "We know that there's an affective component to pain," Pierre Rainville says. "Our research shows that there are physiological signals in the nervous system when we feel pain. The subjects didn't simply react to the suggestions in order to please the experimenter. Their brain activity in several regions that were known to be active at the moment pain occurred suggests that they actually feel more pain, or less, under different experimental conditions."

Twenty-three hundred years ago Aristotle called pain a "passion of the soul" and recognized it as a phenomenon distinct from the "five senses." Pierre Rainville's 21st-century research on the puzzle of pain is finding new answers...and raising new questions.

Researcher: Pierre Rainville
Phone: (514) 343-6111, Local 3935
Funding: Canadian Foundation for Innovation, Aid to Researchers Fund