For instance, Bushnell could tell you about a case she was involved with, in which a young neuro-scientist felt pain in her left leg during a daily jog. The woman took a hiatus from her training, but the pain worsened.

"The most disturbing thing was that when she went into an air-conditioned room, the sudden cold caused a burning pain radiating throughout the left side of her body. She went to a number of doctors who couldn't decide what was wrong with her, and who even suggested that she may have been imagining the pain. Eventually, a neurologist discovered a rare syndrome known as 'central pain,' caused by damage to the pain pathways in the nervous system."

As Bushnell notes, central pain patients exhibit no obvious tissue damage, so their symptoms are often dismissed by physicians as psychosomatic.

"Yet these people have excruciating pain that does not respond to normal pain medications. Very many of the patients eventually commit suicide."

Bushnell herself is quick to acknowledge both the psychological and physiological components of any painful experience.

"The meaning of any injury depends upon your particular emotional state at the time. If you have a pain in your stomach and you've just had a great French meal, you may think it's just indigestion and it won't bother you. But if you have the same pain and you've been diagnosed with intestinal cancer, that pain might bother you a lot, even if it were not intense. This is all part of the pain experience."

Bushnell is making a name for herself in pain research with papers published recently in such influential journals as Science and Nature. Mainstream media such as the Washington Post and the Discovery Channel are increasingly seeking out her expertise.

During her undergraduate and graduate career, Bushnell studied psychology, and became increasingly interested in the influence of people's psychological states over their perceptions.

"Pain seemed like an experience that is particularly dependent on cognitive and emotional factors, so I became interested in understanding how this psychological modulation of pain is processed in the brain."

She now conducts research to identify pain pathways, with the ultimate aim of developing effective pain therapies.

"Understanding the physiological mechanisms of pain helps us target brain regions and neurotransmitter systems for pain treatments. For example, there are brain receptors for opiates  the most effective pain control medication available  but only some of these receptors are involved in pain modulation. Knowing which cells make up the pain pathways will help us develop opiate therapies directed towards the specific receptor subtypes."

In work published last year in Nature, Bushnell determined that a specific area of the brain  the anterior cingulate cortex  is involved in pain processing. She employed a "thermal grill," a device used to create the illusion of pain. The grill consisted of a column of silver bars in which the temperature of each bar was individually controlled. Subjects placed their hands across the column, and rated the degree of pain induced by the specific temperature presented.

The illusory aspect arose when hot and cold bars were interlaced. When all bars were either warm or cool, subjects scored a non-painful experience. When, however, subjects were presented with alternating warm and cool bars, they felt and reported sensations of burning pain.

Positron emission tomography (PET) showed the anterior cingulate cortex was activated when either painfully hot or painfully cold stimuli were applied and when the illusory thermal grill pain was presented. In other words, a real perception of pain occurred in the absence of genuinely painful stimuli, and the anterior cingulate cortex was involved in this level of pain processing.

In a recent Science article, Bushnell provided more evidence. Again using PET, subjects under hypnosis had their hands placed in hot water. With the level of physical pain static (the temperature was held constant), the subjects' psychological experience of the unpleasantness caused by the pain was manipulated by hypnotic verbal suggestion.

Activity in the anterior cingu-late cortex paralleled the level of hypnotically suggested unpleasantness  not the intensity  of the pain. Bushnell believes this further implicates the anterior cingulate in the emotional aspect of the pain experience.

"The anterior cingulate cortex may be very important for our emotional response to pain. In cases where we cannot heal the tissue damage causing the pain, such as in advancing cases of cancer, being able to reduce the suffering caused by the pain through pharmacological or surgical treatment aimed at the anterior cingulate cortex may be the best treatment available."

Bushnell holds the Harold Griffiths Chair in Anesthesia along with appointments in the Dentistry, Neurosurgery, Physiology and Anesthesia Departments. Access to such a wide range of scientists and clinicians is a boon to her research.

For instance, working with Drs. Fiset, Plourde and Backman from the Department of Anesthesia, Bushnell is examining links between pain and consciousness.

"The brain circuitry involved in the loss of consciousness and absence of pain during anesthesia is unknown. We want to examine the parts of the brain involved in loss of pain perception during anesthesia, as well as the parts of the brain involved in pain-evoked arousal from an unconscious state."

This research involves several techniques, including electroencephalo-graphy (reading the brain's electrical activity), psychophysical measures (noting subjects' verbal or written responses to various stimuli), and PET.

Bushnell also studies the long-term use of opiates in chronic pain patients, collaborating with Dr. Anneli Vainio of the Department of Anesthesia and the Pain Clinic at the Montreal General Hospital.

"There is no clear criterion at this moment about which chronic pain conditions respond well to long-term morphine use, so we are studying the effectiveness of morphine in reducing pain and improving quality of life in patients whose pain originates from a number of different sources, including nerve damage, arthritis and musculoskeletal injury."

Ultimately, Bushnell hopes the theoretical knowledge she produces will have practical applications. "Getting to understand the physiological mechanisms of pain processing is interesting in itself, but it's gratifying to know that the work could be used to help patients."