Frequency and phase relationship between the EEG and rhythmic automated movements

During a tapping task 28 right-handed subjects were investigated by correlation analysis of EGG and the mechanogram. After the instruction to tap in a convenient rhythm two types of tapping frequencies were registered depending on the S’s motivation; Type I: 1.5 +/- 0.8 c/s, Type II: 4.5 +/- 1.2 c/s. The cross-correlograms between EEG and mechanogram gave evidence of movement-related potentials in all EEG-derivations, both in Type I and in Type II. In Type II they could be observed at a frequency twice as high as the tapping frequency. Although there were equal frequency relations between the mechanogram and the EEG-derivations, the phase relations between both parameters were interindividually quite different, but intraindividually very constant. In absence of external pacemakers the stabilization of tapping frequency points to the influence or rhythmic processes in the central nervous system which may be of different origin. The coupling between them and the automated motor patterns could be explained assuming that the intrinsic rhythms of certain neural populations will act as a pacemaker on the timing of the motor control.