Time-frequency analysis of EEG signals evoked by voluntary, stimulated and imaginary motions

In order to investigate the characteristics of sensorimotor cortex during motor execution (ME), voluntary, stimulated and imaginary finger flexions were performed by ten volunteer subjects. Electroencephalogram (EEG) data were recorded according to the modified 10–20 International EEG System. The patterns were compared by the analysis of the motion-evoked EEG signals focusing on the contralateral (C3) and ipsilateral (C4) channels for hemispheric differences. The EEG energy distributions at alpha (8–13 Hz), beta (14–30 Hz) and gamma (30–50 Hz) bands were computed by wavelet transform (WT) and compared by the analysis of variance (ANOVA). The timefrequency (TF) analysis indicated that there existed a contralateral dominance of alpha post-movement event-related synchronization (ERS) pattern during the voluntary task, and that the energy of alpha band increased in the ipsilateral area during the stimulated (median nerve of wrist) task. Besides, the contralateral alpha and beta event-related desynchronization (ERD) patterns were observed in both stimulated and imaginary tasks. Another significant difference was found in the mean power values of gamma band( p <0.01)between the imaginary and other tasks. The results show that significant hemispheric differences such as alpha and beta band EEG energy distributions and TF changing phenomena (ERS/ERD) were found between C3 and C4 areas during all of the three patterns. The largest energy distribution was always at the alpha band for each task.