Somatosensory mu activity reflects imagined pain intensity of others.

In accordance with simulation theories of empathy, the somatosensory cortex is involved in the perception of pain of others. Cognitive processes, like perspective taking, can alter empathy-related activity within the somatosensory cortex. The current study investigates whether this modulation is caused by the imagined sensation of pain or by the cognitive load of a perspective-taking task. Applying a within-subject design, participants (N = 30) watched pictures of painful and nonpainful actions, while imagining reduced, normal, or increased pain perception of the observed individual. Mu activity (8-13 Hz), which is inversely correlated with sensorimotor-cortex activity, was measured via EEG. To calculate mu activity (central electrodes) and alpha activity (occipital electrodes), which served as a control for effects of cognitive load, a fast Fourier transform was applied. Mu suppression linearly increased from reduced to normal to increased imagined pain (p < .05), while alpha activity was unaffected by the imagined pain (p > .80). Suppression of the 8-13 Hz band at central and occipital electrodes was stronger in response to painful actions compared to nonpainful actions (p < .01). These results indicate that modulation of mu activity through perspective taking reflects the imagined pain intensity and not the cognitive load induced by the task.