Characterizing biased visuospatial perception in complex regional pain syndrome.

BACKGROUND: Patients suffering from complex regional pain syndrome (CRPS) are increasingly shown to be affected by cognitive difficulties. While these cognitive symptoms were initially described as limited to the perception, representation and use of the body, that is, the somatic space, they were recently shown to also extend to the perception of extra-somatic space. CRPS patients seem indeed to pay less attention to visual stimuli occurring in the same side of space as their affected limb and especially those occurring close to that limb. The aim of the present study was to more precisely characterize these visuospatial biases, by investigating whether they may be dependent on the visually perceived proximity between the visual stimuli and the affected limb. METHODS: Upper-limb CRPS patients and matched control participants performed temporal order judgements on visual stimuli, one presented in either side of space, while they could either see their hands near the visual stimuli or not. RESULTS: Visuospatial biases were not modulated by the availability of visual feedback about the hands. However, secondary analyses revealed that these biases depended on the type of rehabilitation program that the patients followed: whereas patients who did not follow any specific program presented significant biases to the detriment of visual stimuli in the affected side of space, patients who did follow a CRPS-specialized program did not. CONCLUSIONS: Patients' cognitive strategies will be important to consider when studying inter-individual differences in the cognitive symptomatology and associated cognitive-based rehabilitation procedures in CRPS. SIGNIFICANCE: The existence of biases in visuospatial perception in Complex Regional Pain Syndrome has been reported but not always systematically replicated. We show that these biases might depend on the type of general rehabilitation program that the patients follow. Patients' individual cognitive strategies will be important to consider when studying the cognitive symptomatology of CRPS.

No evidence for an effect of selective spatial attention on the development of secondary hyperalgesia: A replication study.

Central sensitization refers to the increased responsiveness of nociceptive neurons in the central nervous system after repeated or sustained peripheral nociceptor activation. It is hypothesized to play a key role in the development of chronic pain. A hallmark of central sensitization is an increased sensitivity to noxious mechanical stimuli extending beyond the injured location, known as secondary hyperalgesia. For its ability to modulate the transmission and the processing of nociceptive inputs, attention could constitute a promising target to prevent central sensitization and the development of chronic pain. It was recently shown that the experimental induction of central sensitization at both forearms of healthy volunteers using bilateral high-frequency electrocutaneous stimulation (HFS), can be modulated by encouraging participants to selectively focus their attention to one arm, to the detriment of the other arm, resulting in a greater secondary hyperalgesia on the attended arm as compared to the unattended one. Given the potential value of the question being addressed, we conducted a preregistered replication study in a well-powered independent sample to assess the robustness of the effect, i.e., the modulatory role of spatial attention on the induction of central sensitization. This hypothesis was tested using a double-blind, within-subject design. Sixty-seven healthy volunteers performed a task that required focusing attention toward one forearm to discriminate innocuous vibrotactile stimuli while HFS was applied on both forearms simultaneously. Our results showed a significant increase in mechanical sensitivity directly and 20 min after HFS. However, in contrast to the previous study, we did not find a significant difference in the development of secondary hyperalgesia between the attended vs. unattended arms. Our results question whether spatial selective attention affects the development of secondary hyperalgesia. Alternatively, the non-replication could be because the bottom-up capture of attention caused by the HFS-mediated sensation was too strong in comparison to the top-down modulation exerted by the attentional task. In other words, the task was not engaging enough and the HFS pulses, including those on the unattended arm, were too salient to allow a selective focus on one arm and modulate nociceptive processing.