The third and final prediction was that, despite shared variance between EEG and EMG activity, EMG (70–90 Hz) asymmetry would not eliminate the overall pattern of EEG asymmetry differences between depressed and never-depressed groups. Comparison of Figure 3 (alpha asymmetry findings) and Figure 5 (EMG-residualized alpha asymmetry findings) indicates that the overall pattern of mean differences between depressed and never-depressed participants persisted when EMG-related activity was taken into account, supporting this hypothesis. However, statistical analyses demonstrated that differences between MDD+ and MDD− groups largely remained for the withdrawal condition but not the approach condition when shared variance between EMG and the alpha band was removed. Overall, these findings show that brain asymmetry associated with muscle movements during happy and angry facial expressions may account for some portion of asymmetry in the alpha band during these expressions, and suggest that differences between lifetime MDD+ and MDD− groups for these faces are partially influenced by facial activity, consistent with assertions that alpha power asymmetries may be vulnerable to contributions from facial muscle activity (e.g., Davidson, 1998; Friedman & Thayer, 1991. Although Coan
