PMC5736540_01
The ECI conductive electro-gel by  was used in this current study.
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F3
Six Electrodes (small metal disks) were placed on the subject's scalp over central motor areas on two hemispheres (C5, C3, C1, CZ, C2, and C4) and then secured with a plastic cap as shown in Figure 3.
The event-related desynchronization (ERD) plotted in blue color, showing the decrease in electroencephalography rhythmic amplitude as indicated in the circle, revealed in the beta band centered around 20 Hz starting 0.5 s after the sound cue was provided at 0 s. The ERD was associated with the actual toe extension. According to the time-spectral analysis of ERD, the beta band frequency from 16 to 24 Hz were determined for feedback training and subsequently for control of knee lock.
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PMC5736540_01_fneur-08-00696-g004.jpg
F4
The EEG signals were then bandpassed (1-100 Hz) using a custom-made MATLAB tool box (BCI2VR). The ERD of the beta band (16-24 Hz) was calculated in real time against baseline activity when the subject was relaxed. The frequency band was determined by the ERD analysis of cued motor task managed in the first training session as shown in the Figure 4.