April 15, 2003 Volume 39 Issue 15

Brain images lend new insight into pain control

Work showing emotional and psychological states can alter perception of pain garners award for Montreal researcher

By Jenny Manzer

CHICAGO – Dr. Catherine Bushnell, like many scientists, used to regard hypnosis as bit "airy fairy."

Then, she tried incorporating the technique into her pain research and some surprising brain images changed her mind.

The experiment involved having normal subjects submerge their hands in hot, circulating water. Once under hypnosis, the subjects were given different suggestions intended to alter their response to the pain.

Their brain scans showed their pain signals changed dramatically depending on what type of hypnotic suggestion they were given—even though the stimulus stayed the same.

Dr. Bushnell (PhD) is director of the anesthesia research unit at McGill University in Montreal, where she investigates how the brain transforms sensory input into pain.

Her team decided to use hypnotic suggestions to try to tease out the sensory and emotional aspects of pain. They used positron emission tomography (PET) to scan every subject, before and after different conditions were tested.

In one test, the subjects were put into a hypnotic state, then given hypnotic suggestions intended to alter their emotional response to the pain.

During the hypnosis, they were told it was a sunny day at the beach, and that their hand was in warm water from the Gulf of Mexico. "They could feel this burning sensation, but they felt it as not unpleasant," said Dr. Bushnell.

The stimulus was kept at the same temperature, and the same subjects were given suggestions describing the water as scalding and unpleasant.

They found that when subjects were told the burning sensation was unpleasant, their PET images showed high activation in their anterior cingulate cortex, part of the limbic system.

Conversely, they found pain signals to the brain were decreased when subjects were given the pleasant suggestions. The decreased activation was also evident in scans of the limbic system, which is associated with emotion.

Interestingly, the subjects' somatosensory cortex, which is associated with skin sensation, was not altered by the suggestions geared to emotion.

The team then tried giving the same subjects a hypnotic suggestion describing the intensity of the heat sensation.

In one test, the hot stimulus was described as burning and stinging. In another, it was described as warm and benign.

They found when subjects perceived the heat sensation to be stronger, activation in the somatosensory cortex was remarkably higher, said Dr. Bushnell.

"I have to tell you, I didn't believe for a second that hypnosis was worth anything until I actually saw the images, and I thought, 'Wow, are you kidding? We are doing something!' "

The hypnosis study is just one of several done at McGill in recent years showing emotional and psychological states can not only change perception of pain, but derail the pain signal en route to the brain.

Last month, she received the Frederick W. L. Kerr award for basic research at the American Pain Society, given to pain professionals who have made outstanding contributions to the field.

Speaking at the society's annual meeting here, she declared the honour beyond her "wildest dreams."

The recognition from her peers in pain medicine aside, Dr. Bushnell said she suspects most physicians are not aware of the growing imaging data suggesting patients can alter their pain.

For example, Dr. Bushnell and colleagues have found strong evidence that attention can modulate pain.

Their work on attention has shown that when subjects concentrate on a modality other than the pain stimulus, such as a visual, auditory or olfactory stimuli, they report less pain.

The distraction actually dampens the pain signal before it gets to the higher centres of the subject's brain, she said, adding it affects both the limbic and the somatosensory cortex.

"You are actually reducing that pain, just as if you'd given them a shot of morphine."

She noted that a group in Germany studied spousal relationships in people with chronic pain. They found pain sufferers whose spouses constantly inquired about their health had more pain than those with less solicitous spouses—a difference which was apparent in their brain images.

In another recent study, Dr. Bushnell found the brain could be tricked into believing a benign stimulus was burning hot.

Her team used a "thermal grill," a device consisting of a column of silver bars with individually controlled temperatures.

Subjects placed their hands on the columns, then rated the pain as the temperature was adjusted.

Researchers found that when all the bars were made warm or cool at the same time, subjects did not report pain. However, when the bars alternated between warm and cool, subjects perceived a burning pain.

Dr. Bushnell said the illusion can be traced back to pain receptors that are modulated by skin temperature.

The thermal grill works by stimulating cells in the spinal cord that respond to cool and are inhibited by warm. The cells that respond to cool inhibit pain information. For example, if all the bars were set at a cool temperature, pain cells in the spinal cord would be activated.

At the same time, the cool temperature activates another set of cells that inhibits the activation of the pain cells, and they cancel each other out, said Dr. Bushnell.

By adding in warm bars and alternating them with the cool, it's possible to dampen activation of the inhibitory cells without dampening activation of the pain cells, she added.

"You've changed the balance of the pain and the inhibition."

Using PET, the researchers found the subjects' anterior cingulate cortex was activated when the thermal grill warm-cool illusion was presented, showing a real perception of pain, even in the absence of painful stimuli.

Dr. Bushnell said they suspect some patients with brain damage, such as those recovering from stroke or with diseases such as multiple sclerosis, may have a similar kind of imbalance in their pain cells.

"A cool breeze to them will feel like a horrible burning-pain sensation. We think what has happened to those people is very similar to what you can create with this illusion."

Dr. Bushnell said they hope that ultimately tests such as the thermal grill can be used to distinguish different dysfunctions in patients' brains, and better direct their therapy.

Neurologist Dr. HÃ¥kan Olausson, from Gothenburg, Sweden, worked in Dr. Bushnell's lab for two years as a postdoctoral student. He said her work has contributed much to understanding the mechanism of pain.

"We are now about to study the underlying mechanism for the individual patient, to try to find out for one individual what is the cause of the pain, and from that choose the best method for treatment," he said.

Dr. Olausson, a clinician and pain researcher, said while the new insights on pain from brain imaging have not yet trickled down into clinical practice, there are exciting possibilities.

"There are various ways of modifying the pain experience. Many more ways than were previously thought," he said.

Dr. Bushnell said doctors need to inform patients that through interventions such as cognitive behavioural training, or even focusing their attention elsewhere, they can change the pain signal to their brain.

"Making these suggestions does not mean their pain is not real," she stressed.

Both doctors and patients need to realize that emotional and psychological factors have a powerful influence on the way we feel, she said. "And we have a lot more control over our own pain than most of us realize."