Self-Selected Versus Assigned Emotion Regulation in Pain Expectancy: Behavioral and fNIRS Evidence

Background: Expectation is a powerful cognitive modulator of pain, but how different types of emotion regulation approaches interact with expectancy to influence pain processing remains unclear. The present study compared self-selected habitual strategies (cognitive reappraisal or deep breathing) with an assigned non-habitual imagery-based strategy. Methods: Twenty-four right-handed healthy participants (11 in the self-selected group, 13 in the assigned strategy group) completed a pain expectancy task under two conditions: Attend (passive observation without regulation) and Regulate (active application of the assigned or self-selected strategy). Electrical stimuli were delivered to the left or right forearm. Functional near-infrared spectroscopy (fNIRS) was used to record prefrontal and sensorimotor cortical activation, and subjective pain ratings were collected using a 0–10 Visual Analogue Scale (VAS). Behavioral ratings, cortical activation (β-values in four regions of interest, ROIs), and neural–behavioral correlations were examined. Results: In Attend trials, negative expectancy (high cue followed by medium pain, HM) enhanced pain compared with the no-bias condition (medium cue followed by medium pain, MM), while positive expectancy (low cue followed by medium pain, LM) reduced pain. In Regulate trials, the self-selected group showed a significant LM–MM difference under both left- and right-side stimulation, whereas the assigned strategy group showed a significant LM–MM difference only under left-side stimulation. At the neural level, the Stimulating Location × Group interaction in the left primary somatosensory cortex (L-S1) and right premotor cortex/supplementary motor area (R-PMC/SMA) showed moderate effect sizes (ηp2 = 0.177 and 0.165), but none survived false discovery rate (FDR) correction. In neural–behavioral correlation analyses, one significant correlation was observed in the Attend condition (R-PMC/SMA), along with one marginal trend (L-S1); no significant correlations were found in the Regulate condition after FDR correction. Conclusions: Self-selected habitual strategies and assigned non-habitual imagery-based strategies modulate pain expectancy through different behavioral patterns. Habitual self-selected approaches produced more consistent pain reduction under positive expectancy, whereas the assigned imagery-based approach showed weaker and less consistent regulatory effects. However, the neural findings were exploratory and did not survive FDR correction. The advantage of self-selected habitual approaches may lie in self-selection and automaticity rather than in activating specific brain regions. Because stimulation side was not counterbalanced, laterality inferences cannot be drawn.