Background/Purpose: Fibromyalgia Syndrome (FMS) is a disorder characterized by the presence of widespread pain and tenderness, which is now believed to be, at least in part, a disorder of central pain processing producing hyperalgesia and allodynia. These phenomena might be caused by defective top-down sensorimotor regulation. In order to test this notion, we activated the pain matrix in a top-down manner by presenting pictures of painful situations while recording brain activity using Magnetoencephalography (MEG). We hypothesized that FMS patients will show different responses to pain pictures and will not show normal alpha desynchronization.

Methods: 19 FMS patients (ACR 1990 criteria) and 14 age-matched healthy controls (age 20-60) were recruited from the community as well as from a specialized fibromyalgia clinic. Participants were shown photographs of right hands and feet in situations depicting pain and in control situations with no depiction of pain and were instructed to judge the painfulness of each situation (painful vs. not-painful). A total of 160 pictures (80 each) were presented in random order, displayed for 200ms followed by a “?” that remained on screen until the response was made. A whole-head, 248-channel magnetometer array (4-D Neuroimaging, Magnes 3600 WH) was used in a magnetically shielded room. The data were digitized with a sample rate of 1017Hz and an online 1-400Hz band-pass filter. Data were filtered offline (1-40Hz), segmented into 2s epochs with a 800ms pre-stimulus baseline. Segments containing excessive artifacts were removed. Sources were localized with beamforming (SAM) using alpha-band filtered data from all segments to derive the covariance matrix and weights. Normalized alpha (10-11Hz) power was then estimated separately for each condition and group. Functional images were co-registered with a template MRI adapted to individual head shapes. Statistical analyses were performed using AFNI (3dMVM).

Results: In healthy controls exposure to pictures depicting painful situations induced a decrease in alpha activity (10-12Hz) which was significantly more pronounced than the one induced by non-painful content. However, FMS patients did not show decreased alpha for pain relative to no-pain pictures, indicating abnormal regulation of sensorimotor cortex. Reduction in alpha power at 100-500ms was significant at right Precentral and Postcentral regions, only in the healthy control group [p<0.05, cluster size=37]. Overall, FMS patients showed more alpha activity in bilateral visual areas , left Fusiform, right Precentral and right Inferior Frontal, left Middle Frontal and Anterior Cingulate Gyri [p<0.05, clusters size>20].

Conclusion: Consistent with previous findings, healthy participants displayed stronger alpha desynchronization for pain pictures, indicating automatic disinhibition of the sensorimotor cortices in response to the observation of pain in others. We found evidence for a deficient modulation of sensorimotor cortex in FMS patients. The lack of differential response suggests that they perceived relatively neutral pictures as potentially painful, at least in this setting. Our findings suggest that defective top-down regulation may play a role in the pathogenesis of FMS.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/brain-responses-to-others-pain-in-fibromyalgia-a-magnetoencephalography-meg-study/