Predictability and probability modulate the neural responses to other's pain: An event-related potential investigation

Two ERP experiments were designed to explore the effect of predictability (Exp1) and probability (Exp2) on the perception of others' pain, respectively. In Exp1, we compared the ERP responses to painful and non-painful pictures when they were fully predictable and fully unpredictable. Results revealed that when the valence of the pictures (painful or non-painful) was fully predictable, the amplitudes of N2 and P3 components triggered by the painful pictures were significantly more positive than the amplitudes of N2 and P3 components triggered by the non-painful ones. When the valence of the pictures was fully unpredictable, the amplitudes of N2 and P3 triggered by the painful and the non-painful pictures were comparable. Besides, the P3 amplitude was positively correlated with the scores of empathy trait (i.e., personal distress). In Exp2, the probability of the presentation of a painful picture was manipulated as low (30%), medium (60%) and high (90%). Results showed that with the increase in the probability of a painful picture's presentation, the amplitude of N2 elicited decreased. No significant effect was observed on P3. These findings indicated that the early perceptual processing stage reflected in N2 was more likely to be a threat-detection stage, while the later stage reflected in P3 may actually be the stage in which participant empathized other's pain. Moreover, the more expected pain of others induced stronger empathic responses reflected in the P3. To the best of our knowledge, this study offers the very first psychophysical evidence of the predictability and probability's effect on pain empathy.