Figure 5.

(Color online) Time-dependent cross-correlations between EMG amplitudes and EEG amplitudes during gait (time: –9 to 0 s) followed by a commanded stop or a FOG episode (time: 0 to +5 s). Data for all pairs of EMG amplitude signals (both legs and both muscles) and all EEG amplitude signals (four bands, see caption of Figure 4) have been averaged. The legend in (A) is valid for all panels showing results for stop episodes in all three groups of subjects and for FOG episodes in the PD+FOG group, (A) without detrending, (B) with linear detrending, and (C) with quadratic detrending (see Equation 3). The large drop in the cross-correlation curves for stop episodes after detrending (especially for PD+FOG) indicates that the pronounced maximum at the beginning of the stops is mainly caused by non-stationarities (nearly step-like trends) in the amplitude signals. However, the detrended cross-correlation curves for stop and FOG episodes in the PD+FOG group are not clearly different, since there is an overlap of their error bars at all time points. Error bars indicate standard errors of the means. We note that because we are considering 4-s windows in the cross correlation analysis, Equation (3), two data points appearing to the left (right) of the vertical line (time 0) are influenced by data originating from the right (left) of this line. Cross-correlations between EEG amplitudes and EMG frequencies do not change with transition to FOG as also shown in (A).