Figure 5
Left panel: EEG-EMG polygraphic recording in a patient with PME manifesting positive myoclonus in the hands at rest. Note that most myoclonic jerks were associated with a spike-and-wave complex on EEG, and the upward negativity recorded from the ipsilateral earlobe electrode. ECR: extensor carpi radialis muscle; 1stDI: first dorsal interosseous muscle; Rt: right. Right panel: Records of jerk-locked back-averaging obtained from the same patient. The onset of the EMG discharge from the right thenar muscle was used as a trigger pulse to back-average multichannel EEGs. EEG was recorded from the ipsilateral earlobe electrode. A positive-negative, biphasic EEG spike is observed maximally near the midline vertex, slightly shifted to the left (C1-Cz), and widespread over the scalp. Note that the myoclonic EMG discharge, which was also averaged with respect to the same fiducial point, spreads rapidly from the proximal muscles to the distal ones (Modified from Shibasaki & Hallett [2005]).