Pain modulates early sensory brain responses to task-irrelevant emotional faces

Background: Pain can have a significant impact on an individual's life, as it has both cognitive and affective consequences. However, our understanding of how pain affects social cognition is limited. Previous studies have shown that pain, as an alarm stimulus, can disrupt cognitive processing when focal attention is required, but whether pain also affects task-irrelevant perceptual processing remains unclear. Methods: We examined the effect of laboratory-induced pain on event-related potentials (ERPs) to neutral, sad and happy faces before, during and after a cold pressor pain. ERPs reflecting different stages of visual processing (P1, N170 and P2) were analysed. Results: Pain decreased the P1 amplitude for happy faces and increased the N170 amplitude for happy and sad faces compared to the pre-pain phase. The effect of pain on N170 was also observed in the post-pain phase. The P2 component was not affected by pain. Conclusions: Our results suggest that pain alters both featural (P1) and structural face-sensitive (N170) visual encoding of emotional faces, even when the faces are irrelevant to the task. While the effect of pain on initial feature encoding seemed to be disruptive and specific to happy faces, later processing stages showed long-lasting and increased activity for both sad and happy emotional faces. Significance: The observed alterations in face perception due to pain may have consequences for real-life interactions, as fast and automatic encoding of facial emotions is important for social interactions.