Fig. 4.

Cortical myoclonus. A: Multiple brief myoclonus electromyographic (EMG) discharges seen in the lower trace during postural activation of the right wrist extensor musculature (RWE1). The contralateral EEG motor area (C3) shows no gross encephalographic (EEG) transient correlate in the upper trace. B: Cortical myoclonus. Using 100 surface myoclonus EMG discharges to perform EEG-EMG back-averaging to increase signal to noise ratio, a sharp EEG transient is elicited at C3. The averaged EEG transient at C4 is smaller, has different configuration, and not significantly different from the C4 EEG waves before and after the trigger (time 0). These findings together demonstrate a cortical myoclonus physiology.