Preserved tactile distance estimation despite body representation distortions in individuals with fibromyalgia

Abstract

Our mental representation of our body depends on integrating various sensory modalities, such as tactile information. In tactile distance estimation (TDE) tasks, participants must estimate the distance between two tactile tips applied to their skin. This measure of tactile perception has been linked to body representation assessments. Studies in individuals with fibromyalgia (FM), a chronic widespread pain syndrome, suggest the presence of body representation distortions and tactile alterations, but TDE has never been examined in this population. Twenty participants with FM and 24 pain-free controls performed a TDE task on three Body regions (upper limb, trunk, lower limb), in which they manually estimated the interstimuli distance on a tablet. TDE error, the absolute difference between the estimation and the interstimuli distance, was not different between the Groups, on any Body region. Drawings of their body as they felt it revealed clear and frequent distortions of body representation in the group with FM, compared to negligible perturbations in controls. This contrast between distorted body drawings and unaltered TDE suggests a preserved integration of tactile information but an altered integration of this information with other sensory modalities to generate a precise and accurate body representation. Future research should investigate the relative contribution of each sensory information and prior knowledge about the body in body representation in individuals with FM to shed light on the observed distortions.

Keywords: body image; body schema; chronic pain; multisensory integration; sensory weighting; tactile perception.

Figure 1

The caliper (left panel) and the touch pad (right panel) used for the TDE task.

Figure 2

Median pain intensity of participants with FM, over the UL, the trunk, and the LL. Error bars represent the IQR. * indicates a p < 0.05; other differences are not significant. UL, upper limb; LL, lower limb.

Figure 3

Estimation according to the inter-stimulus distance, for the UL (left panel), the LL (middle panel), and the trunk (right panel). Each thin line represents a participant, of the FM group (in red) or of the CTRL group (blue). The thick line represents the mean for each group. UL, upper limb; LL, lower limb.

Figure 4

Median error of the estimation of the distance in participants with FM (in red) and CTRL participants (in blue), over the UL, the trunk, and the LL. The error bars represent the IQR. No significant differences were found. FM, participants with fibromyalgia; CTRL, control participants; UL, upper limb; LL, lower limb.

Figure 5

Drawings of 3 representative participants with FM et 3 representative CTRL participants. The participants of the FM group are (from left to right): S17, S12, S34; the CTRL participants are (from left to right): S08, S11, S21. The annotations for S17 indicate an “explosion” of the head, “pressure” on the eyes and shoulders, a “depression” of the thoracic cage, abdomen, and ankles, “shooting pain” in the thighs, and “stretching” of the neck. For S12, annotations demonstrate a sensation of having “very small eyes” and a “very stiff” neck. S34's annotations express a “tense” hand and another “looser” hand, a sensation of having a “brick” behind the head, and of having “a knife pulling on all the nerves” in the middle of the back. FM, participants with fibromyalgia; CTRL, control participants.