Fig. 3

Normalized peak-to-peak MEP amplitudes during motor imagery of right wrist extension at ERD 35% and ERD 70%, calculated by the online FFT or LIA algorithm. The averaged normalized peak-to-peak MEP amplitudes in Condition 3 “FFT, ERD70%” showed a significant increase compared to those in Condition 2 “FFT, ERD35%.” Similarly, the averaged MEP amplitudes in Condition 5 “LIA, ERD70%” showed a significant increase compared to those in Condition 4 “LIA, ERD35%,” suggesting that in both online estimation algorithms (FFT and LIA), SM1 excitability was significantly associated with the different levels of motor imagery-related alpha ERDs. Each line shows the result obtained from each participant. *p < 0.05. ERD, event-related desynchronization; FFT, fast Fourier transformation; LIA, lock-in amplifier; MEP, motor evoked potential