Observational Learning Figure 5. Interaction between Fronto-Parietal Coherence and Imitation Accuracy. (A) Median split between individuals with high accuracy (good imitators) and low accuracy (bad imitators). Values reflect the percentage of correctly imitated movement sequences. Error bars reflect the Standard Errors of Means. (B) Fronto-parietal coherence for good imitators (diamonds) and bad imitators (triangles) over time. Good imitators show stronger fronto-parietal coherence as compared to bad imitators. Squares labelled with ‘‘Imitate’’ represent coherence of bad and good imitators during execution of the observed movement sequence. (C) Pearson correlations between fronto-parietal coherence per sequence repetition (S1, S2, S3, S4) and interval (observation, pause) and imitation accuracy. The difference in performance between good and bad imitators is predicted by fronto-parietal coherence during the first sequence observation and the third pause interval for repetition. Significant correlations (p,.05) labelled with *. doi:10.1371/journal.pone.0014482.g005 the functional contribution of mu and alpha rhythms in observation learning and the possible coupling between mu and alpha generators in this process, both power and coherence analysis were conducted. Results point towards the independency of mu and alpha generators in observation learning as reflected by changes in mu and alpha power over time and the absence of coherence between parieto-occipital and central electrodes. Mu desynchronization was found maximal during pause intervals, consistent with the hypothesized rehearsal of movement sequences via motor imagery. Alpha desynchronization, instead, was stronger during the observation of action sequences, reflecting involvement in perceptual processing of action sequences. These findings argue against the global entrainment hypothesis [15] which proposed functional coupling between alpha and mu generators as the basic psychophysiological mechanism supporting imitation learning. Instead, results provide clear evidence for the alternative, i.e. the direct matching hypothesis of observational learning [1] which proposed that imitation learning relies on motor resonance in the MNS, independent from visual processing. This hypothesis receives support from the discovery of two ipsilateral parieto- frontal networks overlying the two respective hemispheres that were found activated during observation of action sequences for imitation. Importantly, individual differences in the strength of coherence in these two parallel networks were found to predict imitation accuracy, underlining their central role in observational learning. Previous studies on motor resonance during action observation typically focused on the mu rhythm and systematically ignored possible confounding modulations in alpha over posterior regions. In the current study this possible confound was investigated by PLoS ONE | www.plosone.org 6 December 2010 | Volume 5 | Issue 12 | e14482