Figure 1
(A, B) Interictal EEG during sleep shows sporadic isolated spikes in the vertex region and both right and left centro-parietal regions, often related to single myoclonic jerks of the lower limbs (A) or upper limbs (B), asynchronous on the two sides. (C, D) Back-averaging of 30 different myoclonic events (trigger channel R-flex and L-flex, respectively): note that in both cases, there is evidence of agonist muscle co-contraction, followed by a contralateral myoclonic event (probably due to a propagation of the discharge); the myoclonic event is preceded by a positive transient discharge maximal on the central vertex and central region in the hemisphere contralateral to the earliest myoclonic potential. EMG abbreviations: R-delt: right deltoideus; R-ext: right extensor carpi; R-flex: right flexor carpi; R-quad: right quadriceps femoris; L-delt: left deltoideus; L-ext: left extensor carpi; L-flex: left flexor carpi; L-quad: left quadriceps femoris.