Abstract:

Observing other in pain triggers the empathic responses, which involve two stages of processing temporally: an early, automatic processing that result in emotional contagion and affective sharing, and a later, cognitively controlled process related to emotional regulation. Previous studies suggest that this neural response can be modulated by numerous factors. However, no study has explored how working memory (WM) load can influence empathy for pain. Actually, almost every individual has to deal with other’s emotions with concurrent cognitive task in everyday life. To explore how other’s pain is processed under different cognitive load seems to be meaningful both theoretically and practically. In the present study, we investigated how different levels of working memory load can influence the processing of task-irrelevant stimuli showing other’s pain. Twenty two healthy undergraduates (eleven males) participated in the 2×2 within-subject designed experiment (mean age 20 ± 2.4). We manipulated cognitive load by requiring participants to memorize two (low WM load) or six (high WM load) digits at the beginning of each trial. Then picture depicting a person’s hands/forearms/feet in painful or non-painful situations was presented as a distractor. The participants were informed that these pictures were task-irrelevant and they should focus on memorizing the digits and they were required to judge if a given set of digits was the same as the one they saw at the beginning of the trial after the presentation of the picture. EEG during the observation of pictures under different WM loads was recorded by a 64-channel amplifier using a standard 10-20 system (Brain Products). The ERP results revealed that the WM load can influence the early automatic component P2 and N2. Comparing to low WM load, in the high WM-load condition, the painful pictures elicited significantly larger amplitudes in P2 and more negative amplitudes in N2 than the non-painful pictures. Meanwhile, under the low WM-load conditions, there was no significant difference between the painful and non-painful pictures. The present study found that the cognitive load mainly influence the early automatic stage of processing in empathy for pain. This result indicate that other’s pain attracts greater attention and can be better processed when the cognitive control resources were depleted (i.e., under high, relative to low, concurrent WM load). Under high WM load, enhanced emotional sharing and affective arousal level was reflected in the effect observed on P2 and N2. These findings were explained from the perspective of load theory.

Key words: cognitive load, pain empathy, event-related potential, N2, P2