How does the brain process the experience of pain? Thanks to advances in neuroimaging, we now know the answer lies in a network of brain structures called the pain matrix.
This matrix contains two parallel systems. The medial pain system processes the emotional aspects of pain, including fear and stress, while the lateral system processes the physical sensations - pain's intensity, location, and duration.
Marked by morning stiffness, joint aches, and flare-ups, the pain of arthritis tends to be acute and recurrent, in contrast to many chronic pain conditions. Arthritis pain therefore makes an ideal model for comparing common clinical pain with experimental pain. Inspired by this observation, researchers at University of Manchester Rheumatic Diseases Centre in the United Kingdom conducted the first study to compare directly the brain areas involved in processing arthritis pain and experimental pain in a group of patients with osteoarthritis (OA). Their results, published in the April 2007 issue of Arthritis & Rheumatism (http://www.interscience.wiley.com/journal/arthritis), shed light on the role of emotions in how patients feel arthritis pain.
The study focused on 12 patients with knee OA - 6 women and 6 men, with a mean age of 52 years. All subjects underwent positron emission tomography (PET), to measure and map 18F-fluorodeoxyglucose (FDG) uptake in the brain as an indicator of brain activity. PET scans were performed during three different pain conditions: arthritic knee pain; experimental pain, achieved by heat application; and pain-free. The brain responses to each pain state were then rigorously examined and statistically evaluated and compared for significant differences.