Altered visuomotor integration in complex regional pain syndrome

Visuotactile integration in individuals with fibromyalgia

Our brain constantly integrates afferent information, such as visual and tactile information, to perceive the world around us. According to the maximum-likelihood estimation (MLE) model, imprecise information will be weighted less than precise, making the multisensory percept as precise as possible. Individuals with fibromyalgia (FM), a chronic pain syndrome, show alterations in the integration of tactile information. This could lead to a decrease in their weight in a multisensory percept or a general disruption of multisensory integration, making it less beneficial. To assess multisensory integration, 15 participants with FM and 18 pain-free controls performed a temporal-order judgment task in which they received pairs of sequential visual, tactile (unisensory conditions), or visuotactile (multisensory condition) stimulations on the index and the thumb of the non-dominant hand and had to determine which finger was stimulated first. The task enabled us to measure the precision and accuracy of the percept in each condition. Results indicate an increase in precision in the visuotactile condition compared to the unimodal conditions in controls only, although we found no intergroup differences. The observed visuotactile precision was correlated to the precision predicted by the MLE model in both groups, suggesting an optimal integration. Finally, the weights of the sensory information were not different between the groups; however, in the group with FM, higher pain intensity was associated with smaller tactile weight. This study shows no alterations of the visuotactile integration in individuals with FM, though pain may influence tactile weight in these participants.

Correctly establishing evidence for cue combination via gains in sensory precision: Why the choice of comparator matters

Studying how sensory signals from different sources (sensory cues) are integrated within or across multiple senses allows us to better understand the perceptual computations that lie at the foundation of adaptive behaviour. As such, determining the presence of precision gains - the classic hallmark of cue combination - is important for characterising perceptual systems, their development and functioning in clinical conditions. However, empirically measuring precision gains to distinguish cue combination from alternative perceptual strategies requires careful methodological considerations. Here, we note that the majority of existing studies that tested for cue combination either omitted this important contrast, or used an analysis approach that, unknowingly, strongly inflated false positives. Using simulations, we demonstrate that this approach enhances the chances of finding significant cue combination effects in up to 100% of cases, even when cues are not combined. We establish how this error arises when the wrong cue comparator is chosen and recommend an alternative analysis that is easy to implement but has only been adopted by relatively few studies. By comparing combined-cue perceptual precision with the best single-cue precision, determined for each observer individually rather than at the group level, researchers can enhance the credibility of their reported effects. We also note that testing for deviations from optimal predictions alone is not sufficient to ascertain whether cues are combined. Taken together, to correctly test for perceptual precision gains, we advocate for a careful comparator selection and task design to ensure that cue combination is tested with maximum power, while reducing the inflation of false positives.

Behavioral and Electrocortical Response to a Sensorimotor Conflict in Individuals with Fibromyalgia

People with fibromyalgia have been shown to experience more somatosensory disturbances than pain-free controls during sensorimotor conflicts (i.e., incongruence between visual and somatosensory feedback). Sensorimotor conflicts are known to disturb the integration of sensory information. This study aimed to assess the cerebral response and motor performance during a sensorimotor conflict in people with fibromyalgia. Twenty participants with fibromyalgia and twenty-three pain-free controls performed a drawing task including visual feedback that was either congruent with actual movement (and thus with somatosensory information) or incongruent with actual movement (i.e., conflict). Motor performance was measured according to tracing error, and electrocortical activity was recorded using electroencephalography. Motor performance was degraded during conflict for all participants but did not differ between groups. Time-frequency analysis showed that the conflict was associated with an increase in theta power (4-8 Hz) at conflict onset over the left posterior parietal cortex in participants with fibromyalgia but not in controls. This increase in theta suggests a stronger detection of conflict in participants with fibromyalgia, which was not accompanied by differences in motor performance in comparison to controls. This points to dissociation in individuals with fibromyalgia between an altered perception of action and a seemingly unaltered control of action.

Normal manual straight ahead pointing in Complex Regional Pain Syndrome

There is evidence to suggest that people with Complex Regional Pain Syndrome (CRPS) can have altered body representations and spatial cognition. One way of studying these cognitive functions is through manual straight ahead (MSA) pointing, in which participants are required to point straight ahead of their perceived body midline without visual feedback of the hand. We therefore compared endpoint errors from MSA pointing between people with CRPS (n = 17) and matched controls (n = 18), and examined the effect of the arm used (Side of Body; affected/non-dominant, non-affected/dominant). For all participants, pointing errors were biased towards the hand being used. We found moderate evidence of no difference between Groups on endpoint errors, and moderate evidence of no interaction with Side of Body. The differences in variability between Groups were non-significant/inconclusive. Correlational analyses showed no evidence of a relationship between MSA endpoint errors and clinical parameters (e.g. CRPS severity, duration, pain) or questionnaire measures (e.g. body representation, "neglect-like symptoms", upper limb disability). This study is consistent with earlier findings of no difference between people with CRPS and controls on MSA endpoint errors, and is the first to provide statistical evidence of similar performance of these two groups. Our results do not support a relationship between clinical or self-reported measures (e.g. "neglect-like symptoms") and any directional biases in MSA. Our findings may have implications for understanding neurocognitive changes in CRPS.

Validation of the Bath CRPS Body Perception Disturbance Scale

The Bath Complex Regional Pain Syndrome Body Perception Disturbance Scale ("B-CRPS-BPDS") measures alterations in body perception. We assessed its internal consistency, known group validity, construct validity, and associations with demographic and clinical characteristics. We also evaluated changes in, and baseline predictors of B-CRPS-BPDS scores at follow-up. We included people with CRPS (N = 114) and pain-free controls (N = 69). People with CRPS obtained higher scores than pain-free controls on all B-CRPS-BPDS items, except the item on attention. Because this item also had an insufficient corrected item-total correlation, we propose a revised B-CRPS-BPDS (r-B-CRPS-BPDS) excluding this item. The internal consistency of the r-B-CRPS-BPDS was good. The r-B-CRPS-BPDS showed a large positive relationship with "motor neglect-like symptoms", indicating good construct validity. The r-B-CRPS-BPDS showed positive relationships with pain intensity, fear of movement, depression, and upper limb disability. There were no independent relationships with handedness, affected side, affected limb, disease duration, CRPS severity score, tension, anger, fatigue, confusion, and vigour. Finally, r-B-CRPS-BPDS scores did not consistently change over time. Our results demonstrate the utility of the r-B-CRPS-BPDS for measuring body perception disturbances in CRPS. PERSPECTIVE: This article evaluates the validity of the Bath Complex Regional Pain Syndrome Body Perception Disturbance Scale ("B-CRPS-BPDS") in CRPS, and assesses relationships with demographic and clinical variables. The proposed revised B-CRPS-BPDS appears to be a valid measure of body perception disturbances in CRPS.