Down-modulation of mu-activity through empathic top-down processes.

Simulation theories argue that humans simulate motor processes of others to gain information about intentions and emotional states of others. Mu-suppression is a valid electrophysiological correlate of these processes. Mu-activity can be measured via electroencephalography (EEG) in the alpha-band (8-13 Hz) above the sensorimotor cortex and is suppressed when actions are executed or observed. Based on a within-subject design, including 28 participants, it was tested whether the processes measured by mu-suppression could be modulated by empathic top-down-processes. Participants were asked to take the perspective of two actors, telling a story about a sad or neutral life event (video sequences). Afterwards, EEG was measured at central (C3, Cz, C4) and occipital (O1, Oz, O2) electrodes, while participants observed the actors drinking water (standardized video sequences, 8 s duration). Fast fourier transformation showed stronger suppression of power in the alpha-range (relative to baseline) at central and occipital electrodes while the actor with the sad story was observed relative to the actor with the neutral story. Furthermore, measures of state empathy correlated positively with the difference of mu-suppression between executed and observed movements, an indicator of self-other discrimination. Thus, mirror neuron activity measured by mu-suppression is modulated by empathic processes.