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“IT’S ALL IN YOUR MIND” is what sufferers of chronic pain hear repeatedly to downplay or even dismiss their difficulties. But these days that charge also brings new truths that can help to corroborate and hopefully one day to better treat both acute and chronic pain.
Using “functional” Magnetic Resonance Imaging (fMRI) of the brain, a computer algorithm recognizes a complex pattern of activation in the brain using signals dependent on blood oxygen levels.
Researchers led by Tor Wager at the University of Colorado Boulder observed the effects in the brain of “painful and non-painful” heat applied to the forearm; defined a pattern of activity that correlated with the subjects’ pain scores; and were then able to predict a “signature response” of pain in a new group of subjects. The magnitude of the response correlated with both the temperature and intensity of self-reported pain.
Wager’s group also showed that “looking at pictures of an ex-partner after an unwanted romantic breakup” activated similar brain regions as physical pain and that this “signature response” matched that of physical pain. Responses to both physical and emotional pain decreased after treatment with an opioid analgesic, a response that also decreased for subjects who didn’t know they were receiving the drug – indicating that the “signature response” may occur independently of self-reports.
According to the “gate control theory of pain” that emerged in the early 1960s, “pain messages originate in nerves associated with damaged tissue and flow along the peripheral nerves to the spinal cord and on up to the brain,” William Deardorff writes on the website Spine-health. En route to the brain, the pain messages encounter “nerve gates” in the spinal cord that open and close, although the details of this process are not completely understood.
Among the different types of message-sending nerve fibers, some carry faster responses to sudden pain while others carry slower signals. After a blow to the elbow or head, rubbing the area can provide relief by activating the sensory nerve fibers that send faster signals than those responding to the sudden pain, and that can thereby override the sudden pain messages.
For chronic pain, differing actions of various nerve fibers helps explain why treatments such as massage, hot or cold packs or acupuncture can be effective, according to Deardorff. These treatments can stimulate endorphins and other factors that close nerve gates so that the pain signal never reaches the brain; conversely, in times of anxiety or stress, descending messages from the brain can amplify the pain signal.
Sensory, cognitive and/or emotional factors can help open or close pain gates as messages move up and down the spinal cord. Sensory factors that can increase suffering include injury, inactivity and long-term narcotic use; while those that can ameliorate it include increased physical activity, relaxation training, meditation, biofeedback and hypnosis.
Cognitive factors range from focusing on pain to using visual imagery and other thoughts as distractions to help cope with the pain. Emotional factors include feeling more or less in control of one’s chronic pain and life, as well as stress management and having a positive attitude.
Wager used fMRI images to identify which factors are involved in an individual’s pain by seeing exactly where in the brain their pain signals go — with the eventual goal of determining which therapy is best for each sufferer.
Another “functional” imaging technique uses Positron Emission Tomography (fPET) to more accurately map inflammation when there’s no obvious tissue damage: in the neck to show whiplash, or near the elbow for “tennis elbow.”
Aware of the risk that imaging could someday be misused as a lie detector, however, medical experts emphasize that pain is still “by definition a subjective experience, and so the self-report of the pain experience is what tells us if someone is in pain,” according to Karen Davis, pain specialist at the University of Toronto in Ontario.
–Mary Carpenter
