Comments on “Pain-Related Fear Modulates Attentional Bias for Threat Processing in Chronic Pain: An ERP Study” [Letter]

Dear editor

We read with interest the ERP study by Luo et al¹ examining pain-related fear (PRF) and emotional-face processing in patients with epigastric pain syndrome. The reported P2 finding is noteworthy. However, several conceptual and methodological issues make the conclusion of “threat-specific attentional bias” less certain.

First, it is unclear whether the stimuli established the proposed threat hierarchy. Fearful, sad, and happy faces were treated as high-threat, low-threat, and non-threat stimuli, respectively. However, the reported ratings assessed valence and arousal rather than perceived threat or pain relevance. Fearful and sad faces had almost identical arousal scores (6.57 versus 6.44) and valence scores (3.72 versus 3.78). Thus, the results do not show that patients with epigastric pain syndrome perceived fearful faces as more threatening than sad faces. A fearful expression may convey danger generally, but it is not necessarily related to pain, gastrointestinal symptoms, or fear of disease progression. This distinction is important because attentional bias in chronic pain generally refers to preferential attention to pain-related information.²

The oddball task further complicates this interpretation. Neutral faces were frequent standard stimuli, whereas emotional faces were infrequent deviants requiring a different response. Emotional-minus-neutral ERP differences may therefore reflect stimulus probability, novelty detection, target classification, and response selection in addition to emotion. These factors are particularly relevant to P3 amplitude.³ Comparisons among the three emotional conditions partly control for deviant status and response requirements. Nevertheless, the paradigm provides stronger evidence for differential processing of emotional deviants than for attentional bias itself. “Selective ERP processing of fearful faces” may therefore be a more accurate description unless perceived threat and pain relevance are directly validated.

Second, the definition of the PRF groups warrants clarification. Participants were ranked using a composite of transformed Pain Catastrophizing Scale (PCS) and Tampa Scale for Kinesiophobia (TSK) scores and then divided into upper and lower halves. Algebraically, the ranking is determined by PCS/13 + TSK/17 because subtracting the clinical cutoffs adds the same constant to every participant. The cutoffs therefore do not influence group assignment. Consistent with this, the median PCS score in the high-PRF group was 29.50, below the stated cutoff of 30. These groups represent relatively higher and lower composite scores within this sample rather than clinically established high and low PRF.

Catastrophizing and kinesiophobia are related but distinguishable constructs. Combining them assumes that they form one PRF dimension and that their selected weights are appropriate. The difference in fear-of-progression scores provides supportive evidence, but it does not validate the structure or weighting of the composite. Dichotomization may also obscure whether the ERP association is mainly related to PCS, TSK, or a small number of participants at the extremes.⁴ Reporting continuous associations between ERP amplitudes and PCS, TSK, and fear-of-progression scores separately would clarify what is driving the observed group difference.

Finally, some information needed to assess ERP robustness is unclear. The Methods state that 60 emotional images were selected, but the reported category counts—10 fearful, 10 sad, and 10 happy—sum to 30. It is therefore uncertain whether each category contained 20 unique images or whether 10 images were repeated. Repeated presentation and reliance on a small number of facial identities could influence ERP amplitudes.

The article also does not explain how blinks and eye movements were corrected or report the number of usable trials retained in each group and emotion condition. This is especially relevant because frontal electrodes contributed to the main P2 and P3 analyses. Current EEG recommendations emphasize reporting ocular-artifact procedures and condition-specific trial retention.⁵ If the 60 deviant trials were equally distributed, each emotional category contained only about 20 trials before artifact rejection. ERP estimates based on small or unequal trial numbers can be unstable, particularly in between-group analyses.⁶ Reporting retained trial counts and conducting a trial-count-matched sensitivity analysis would make the P2 finding easier to evaluate. The P3 result should be interpreted more cautiously because the fearful-face group comparison did not survive Bonferroni correction.

This study provides interesting evidence of emotional processing differences in epigastric pain syndrome. At present, however, the findings more directly support an association between a sample-relative PCS–TSK composite and ERP responses to fearful emotional deviants. Further validation is needed before this association can be considered pain-related, threat-specific attentional bias.

Funding Statement

The authors received no specific funding for this work.

Ethics Statement

Ethics approval was not required for this Letter to the Editor.

Disclosure

The authors declare no conflicts of interest in this communication.