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Gracely RH, Petzke F, Wolf JM, Clauw DJ. Functional magnetic resonance imaging evidence of augmented pain processing in fibromyalgia. Arthritis Rheum. 2002;46(5):1333-43. PMID 12115241

One-paragraph summary

Sixteen right-handed patients with fibromyalgia (FM) and 16 right-handed matched controls received pressure to the left thumbnail bed during functional MRI. The design's decisive feature was that controls were tested under two conditions: a "stimulus pressure control" condition delivering the same pressure given to patients, and a "subjective pain control" condition in which pressure was raised until controls reported the same pain intensity as patients. When stimulation produced similar pain in both groups, 19 regions of increased signal appeared in controls and 12 in patients, with 7 regions of increase and 1 of decrease in common. When controls received the same pressure that was painful for patients, only 2 regions of increased signal appeared, neither coinciding with any patient activation. Direct group comparison at matched stimulus pressure showed 13 regions of greater activation in patients versus 1 region greater in controls. The authors concluded that FM is characterized by cortical or subcortical augmentation of pain processing.

Key findings

  • Equal subjective pain → largely convergent activation maps (7 common regions of increased signal, 1 common region of decreased signal), i.e. equal pain produces equal brain response in both groups.
  • Equal stimulus pressure → divergent maps: 2 regions in controls, none overlapping patient activations; 13 regions greater in patients on direct comparison versus 1 greater in controls.
  • The dissociation is the evidence: the difference lies in the transfer function from stimulus to percept, not in the reporting of pain.

Limitations

  • n = 16 per group, single site, single stimulus modality (blunt pressure at one body site).
  • Cross-sectional: cannot distinguish cause from consequence of chronic pain, sleep disruption or distress.
  • Healthy controls only — no chronic-pain comparison group. Subsequent work showed the same remote-stimulus augmentation in vulvodynia using FM as a positive control (Hampson 2013, PMID 23578957), and the FM neuroimaging meta-analysis states explicitly that the field cannot yet say whether these findings are FM-specific or generic to chronic pain (Dehghan 2016, PMID 26864780).
  • Psychological state modulates the same signal: in a 29-patient follow-up from the same group, catastrophizing residualized for depression correlated with activation across attentional, anticipatory and affective regions (r = 0.40–0.51) (Gracely 2004, PMID 14960499).
  • Region-of-interest and thresholding conventions of the early-2000s fMRI era were less conservative than current standards; "number of significant regions" is a fragile summary statistic.

Why it matters

This is the study that moved fibromyalgia from "pain without a lesion" to "pain with a measurable central signature", and it did so with a design that pre-empts the obvious objection — that patients simply report more pain. Because the same stimulus produced more brain activation, and the same pain produced comparable activation, the finding is hard to explain by report bias alone. It became the empirical anchor of the central-sensitization model and, later, of the nociplastic-pain construct. Its unresolved weakness — specificity — remains the central open question of the whole central-mechanism literature.

Cited by wiki pages

  • pathophysiology-central