Towards The Objective Measurement Of Pain: Fibromyalgia And Brain Networks
Posted Aug 07, 2010
Resting brain activity as measured by functional magnetic resonance imagine (fMRI) is associated with spontaneous pain in fibromyalgia patients, it was recently reported. Have researchers finally found a truly objective tool to measure pain?
Dr. Napadow appears to feel so, as he reports in this month's edition of "Arthritis and Rheumatism". Specifically, "resting-state functional-connectivity MRI is a recent adaptation of fMRI that may be promising for the assessment of associations of spontaneous functional pain with specific brain network activity".
The researchers attempted to establish the degree of connectivity within multiple brain networks in fibromyalgia patients. They then searched for any correlation between network activity and spontaneous pain.
There were only a total of 36 subjects in this study: 18 patients with fibromyalgia and 18 healthy subjects matched for age. Each subject was evaluated for resting (intrinsic) connectivity in three brain networks:
1. The default mode network (DMN), which is most active at rest; it is deactivated during the performance of externally focused tasks.
2. The executive attention network (EAN), which is involved with the processing of memory and maintaining attentiveness.
3. The medial visual network, which was the "control" in this study; it is involved in the processing of visual information.
It was found that fibromyalgia patients had greater connectivity in the DMN and the right EAN, and greater connectivity between the DMN and the insular cortex-that part of the brain that processes evoked pain. Further, the researchers found a direct link to ratings of self-reported spontaneous pain during the MRI scan and the degree of right EAN and DMN connectivity to the insula. When the EAN is distracted by pain, it may account for some of the cognitive complaints offered by the fibromyalgia patient.
Based on this, the researchers concluded that the insular cortex appears to be a key "node" in the increased intrinsic connectivity in patients with fibromyalgia. There is evidence of disrupted intrinsic connectivity within multiple brain networks in fibromyalgia patients. Perhaps we are all one step closer to the definitive discovery of the "neural correlates of spontaneous clinical pain".
Prior research had shown that fibromyalgia sufferers feel a given amount of pain more intensely than healthy controls. This recent study was novel in that pain responses were measured at "rest", and without exposure to painful stimuli.
Rheumatologists and those given the medico-legal task of rating impairment have always struggled with translating human suffering into a spreadsheet. Ultimately, prejudices, inclinations and beliefs are applied to the determination of the degree of pain a given individual is suffering. Injury in fibromyalgia has always been in the eyes-and at the mercy-of the beholder.
Will we ever be ready to trade unreliable (and, alas, fakable) tender points for intrinsic connectivity? Perhaps more time and more research will one day answer that question.