Fig. 4

Time–frequency maps and topographical distribution for each mental task. a Event-related spectral perturbation (ERSP) maps during left-hand motor imagery (LMI) (b) ERSP maps during tongue motor imagery (TMI) (c) ERSP maps during mental subtraction (MS). EEG epochs from − 1 to 5 s were used for the time–frequency analysis. Red vertical dotted lines in the time–frequency maps of the first row represent the onset of each instruction. The values in the topographical distributions are averaged ERSP values from 0 to 5 s for each frequency band. The topographical maps in the posterior areas were not visualized because no electrode was attached in the parietal and occipital areas. Brown circles in the topographical maps of the second row indicate the electrodes used in the time–frequency analysis. All the figures were drawn using functions implemented in the EEGLAB toolbox (https://sccn.ucsd.edu/eeglab/index.php)