Analysis of Electroencephalography Event-Related Desynchronisation and Synchronisation Induced by Lower-Limb Stepping Motor Imagery

Bilateral upper-limb motor imagery has been demonstrated to be a useful mental task in electroencephalography (EEG)-based brain-computer interfaces (BCIs). By contrast, few studies have examined bilateral lower-limb motor imagery, and all of them have focused on imaginary foot movements. The left-right classification accuracy reported in these studies based on the EEG mu rhythm (8-13Hz) and beta band (13-30Hz) remains unsatisfactory. The present study investigated the possibility of using lower-limb stepping motor imagery as the mental task and analysed the EEG difference between imaginary left-leg stepping (L-stepping) and right-leg stepping (R-stepping) movements. An experimental paradigm was designed to collect 5-s motor imagery EEG signals at nine recording sites around the vertex of the brain. Results from eight able-bodied participants indicated that the commonly used mu event-related desynchronisation (ERD) feature exhibited no significant difference between the two imaginary movements for all recording sites and all time intervals within the 5-s motor imagery period. Regarding the other commonly used feature, beta event-related synchronisation, no significant difference between the two imagery tasks was observed for most of the recording sites and time intervals. Instead, theta band (4-8Hz) ERD significantly differed between the L- and R-stepping imagery tasks at five sites (FC4, C3, CP3, Cz, CPz) within the first 2s after motor imagery cue onset. The findings from the present study may be a basis for further development of BCI systems for decoding left and right stepping during mental exercise where the two motions are alternately imagined.