Fig 1.
Trial structure for pain expression and movement imitation tasks.
At the beginning of each trial, a one-second cue screen indicated which task—“pain” or “movement”—to perform on the upcoming clip. Next, the clip was presented (observation phase), immediately followed by a variable length pause of 3, 4, or 5 seconds, during which the screen displayed the cue word for the current task (“pain” or “movement”) below a dash symbol. This pause was followed by the response window of 3 seconds, during which the dash symbol was replaced by a circle, signaling the subject to begin their facial response (execution phase). Each trial ended with an ITI (inter-trial-interval) of variable duraction, during which subjects viewed a screen marked with a fixation cross.
Table 1.
Contrast models used in the analysis of imaging data in this study.
Fig 2.
Results of FACS analysis of facial expressions.
(A) Facial response, by intensity level, during subject responses. Results of FACS analysis of facial expressions shown by participants for different pain intensity levels, during response phase of both movement task and pain task conditions. ANOVA confirmed a main effect of pain levels (p < 0.001) but no significant effect of, or interaction with, task (p > 0.05). (B) Facial response accuracy. Facial responses displayed by the participants were more similar to those in the target expressions in the movement task condition, vs the pain task condition (p = 0.002).
Table 2.
Effects of observation and execution of facial expressions in the pain expression task (including pain and neutral conditions).
Fig 3.
Areas commonly activated during observation and execution phases of the pain task (Obs∩Exec(PT)).
Significant clusters are shown in the mACC, the SMA, IFG/aINS, and IPL (p < 0.001, uncorrected). Inset figure shows rostral-caudal extent of activation in the right IFG. See Table 2 for coordinates and peak t-values.
Table 3.
Effects of observation and execution of pain expressions (pain vs neutral).
Fig 4.
Effects of pain during both observation and execution of pain expressions (Obs∩Exec(Pain;PT)).
A conjunction analysis of pain expressions, minus neutral expressions, during clip and response events, in the pain task condition revealed clusters in the ACC, SMA, the bilateral PrCG, and the left IFG/aINS (p < 0.001, uncorrected). Inset figure shows rostral-caudal extent of activation in the left IFG. See Table 3 for coordinates and t-values of peaks.
Table 4.
Main effects of task during both observation and execution (pain expressions only†):
Fig 5.
Effects of task during both observation and execution of pain expressions.
For the pain task (PT—MT (Obs∩Exec); orange), a cluster of activation was observed in the left IFG, while bilateral clusters were observed in the IPL for the movement task (MT—PT (Obs∩Exec); blue) (p ≤ 0.005, uncorrected). Analysis included pain expressions only, no neutrals. See Table 4 for coordinates and t-values of peaks.