A computer-assisted method for averaging movement-related cortical potentials with respect to EMG onset

The recording of movement-related cortical potentials (MRCP) relies on the use of EMG activity or some other index of movement as a trigger for averaging. EMG activity can vary considerably from one movement to the next, particularly in patients with movement disorders. This results in an MRCP formed from individual sweeps which are averaged with respect to differing periods during the EMG activity. We describe a computer-assisted method for identifying EMG onset associated with each movement made by the subject. The method allows the experimenter to reject trials associated with artefacts or with spurious trigger pulses produced by resting EMG activity. It is also possible to average the MRCP into categories associated with differing EMG characteristics such as EMG duration, peak EMG amplitude and the duration from EMG onset to peak. Using this method we have been able to record reliable MRCP from patients with movement disorders in whom this would otherwise have been technically impossible.