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

Abstract

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.

The impact of the social context on the development of secondary hyperalgesia: an experimental study

“…Although the effect size is small, our findings are in line with studies that have shown that other top-down factors can modulate SH [22,32,45,57,67]. Importantly however, other recent studies that have used similar electrical stimulation protocols, have found either modest or no modulation of SH [4,18,48,65]. This apparent difficulty may be due to the intense nature of the electrical stimulation and the large magnitude of SH that these procedures induce (eg.…”

“…22,32,45,58,68 Importantly however, other recent studies that have used similar electrical stimulation protocols have found either modest or no modulation of SH. 4,18,48,66 This apparent difficulty may be due to the intense nature of the electrical stimulation and the large magnitude of SH that these procedures induce (eg, h p 2 5 0.47 in the current study). In addition, MFS stimulation induces the largest increase in perceived pinprick intensity compared with other frequencies.…”

Top-down Attention Does not Modulate Pain Sensitization: Insights from an Experimental Analysis

“…These stimuli elicit pinprick sensations related to the activation of mechanosensitive nociceptors [23,58]. The stimulus was applied following a standardized procedure ( e.g., [12,16]). In line with previous studies (e.g., [12,45,66]) the perceived mechanical sensitivity was assessed three times throughout the whole procedure: before HFS for a baseline assessment (T0), at 20 (T1) and 40 minutes (T2) after the delivery of HFS.…”

“…During the assessment, participants were asked to look away from their arms. Immediately after each stimulus, participants were asked to rate the intensity felt using a numerical scale from 0 (not felt at all) to 100 (maximal pain), with 50 being the transition from a non-painful stimulation to a painful one [16,22,44,45,64]. The same area on the arm was never stimulated more than once.…”

“…Progress in this field has been made by investigating how psychological factors affect pain sensitization [5,6,16,22,29,42,44,45,55,64,66,72] and the subsequent development of secondary hypersensitivity -characterized by a long-lasting increased mechanical pinprick sensitivity in the area surrounding an injured or inflamed site [30,32,52,63]. For instance, Torta et al [64] found that performing an n-back (working memory updating) task during the application of electrocutaneous stimulation reduced consecutive mechanical hypersensitivity, while performing a Flanker (inhibition) task resulted in its enhancement.…”