Audio-visual facilitation of the mu rhythm.

Previous studies demonstrate that perception of action presented audio-visually facilitates greater mirror neuron system (MNS) activity in humans (Kaplan and Iacoboni in Cogn Process 8(2):103-113, 2007) and non-human primates (Keysers et al. in Exp Brain Res 153(4):628-636, 2003) than perception of action presented unimodally. In the current study, we examined whether audio-visual facilitation of the MNS can be indexed using electroencephalography (EEG) measurement of the mu rhythm. The mu rhythm is an EEG oscillation with peaks at 10 and 20 Hz that is suppressed during the execution and perception of action and is speculated to reflect activity in the premotor and inferior parietal cortices as a result of MNS activation (Pineda in Behav Brain Funct 4(1):47, 2008). Participants observed experimental stimuli unimodally (visual-alone or audio-alone) or bimodally during randomized presentations of two hands ripping a sheet of paper, and a control video depicting a box moving up and down. Audio-visual perception of action stimuli led to greater event-related desynchrony (ERD) of the 8-13 Hz mu rhythm compared to unimodal perception of the same stimuli over the C3 electrode, as well as in a left central cluster when data were examined in source space. These results are consistent with Kaplan and Iacoboni's (in Cogn Process 8(2):103-113, 2007), findings that indicate audio-visual facilitation of the MNS; our left central cluster was localized approximately 13.89 mm away from the ventral premotor cluster identified in their fMRI study, suggesting that these clusters originate from similar sources. Consistency of results in electrode space and component space support the use of ICA as a valid source localization tool.