Schematic view of the assessment for conditioned pain modulation.

Schematic view of the assessment for conditioned pain modulation.</p

Thermal grill illusion on the basis of tri-allelic 5-HTTLPR genotype and gender.

<p>Based on our expectations of gender differences, the genotype groups were further divided into females (panel A) and males (panel B). Females differed significantly in ratings of unpleasantness for the thermal grill, *  =  significant at p<0.05.</p

Validation of the thermal grill illusion for affective and sensory dimensions, all subjects.

<p>The thermal grill illusion was tested along with its constituent temperatures, in a randomized and counterbalanced order. Subjects provided VAS-ratings of both the affective-motivational (i.e. unpleasantness, see panel A) and sensory-discriminatory (i.e. pain, see panel B) dimensions for each condition. Validation of the thermal grill illusion, for all subjects: ***  =  significant at p<0.001, **  =  significant at p<0.01, ns  =  not significant.</p

Descriptives of study population.

Descriptives of study population.</p

Contingency table for heat-pain thresholds.

<p>Number of subjects above or below median temperature for heat-pain threshold.</p

Genotype frequencies of the polymorphisms <i>rs1799971</i> (OPRM1), <i>rs6296</i> (5-HT_1A) and the triallelic 5-HTT for the whole group, as well as fibromyalgia (FM) patients and healthy controls (HC) separately.

Genotype frequencies of the polymorphisms rs1799971 (OPRM1), rs6296 (5-HT1A) and the triallelic 5-HTT for the whole group, as well as fibromyalgia (FM) patients and healthy controls (HC) separately.</p

Conditioned pain modulation (CPM) score based on OPRM1 genotype in the study group.

Fig 2A. Fibromyalgia patients and healthy controls pooled together split by OPRM1-AA versus G-genotype. Results showed significantly reduced CPM score in OPRM1 G-allele carriers (p = 0.019). Fig 2B. CPM score for HC and FM patients separately split by OPRM1-AA vs G-allele. A significant difference was seen for FM patients (p = 0.045) but not for HC. Notable, FM patients with the OPRM1 G-allele had the lowest CPM score among all four groups (indicating less efficient CPM).</p

Thermal pain thresholds.

<p>A) Heat-pain thresholds. The difference between average heat-pain threshold for the high- versus the low 5-HTT-expressing groups was significant [U = 155.0, z = −2.03, p = 0.02, one-tailed test]. B) Cold-pain thresholds. The difference between average cold-pain threshold for the high versus the low 5-HTT-expressing groups was significant [U = 162.0, z = −1.91, p = 0.03, one-tailed test].</p

Normalized pressure pain thresholds (PPTs) (mean ± SEM) at start, middle, end and 5 minutes after a standardized tourniquet test.

The conditioning pain was applied in the upper left arm and PPTs were assessed at the contralateral m. quadriceps in FM patients and healthy controls. There was a statistically significant difference between the groups at end (p<0.001) and after (p = 0.041) the assessment.</p

The thermal grill.

<p>The thermal grill consisted of 8 individual silver plates housed in a PVC unit. The subjects placed their ventral forearm against the grill's surface, orthogonally to the long axis of the silver plates. Temperatures of odd and even numbered plates were set to 41.0°C–42.0°C and/or 15.0°C–16.0°C.</p