Cortical excitability after myoclonus: jerk-locked somatosensory evoked potentials.

Cortical excitability after myoclonus was investigated by electrically stimulating the median nerve just at the time of, or at intervals after, the onset of myoclonus and by averaging the EEG and EMG, using the myoclonus onset pulse as a trigger (jerk-locked somatosensory evoked potential technique). In a patient with "cortical reflex" myoclonus, cortical excitability was relatively enhanced for 20 msec just after the myoclonus, although it was suppressed throughout the postmyoclonus period. In a patient with Creutzfeldt-Jakob disease, cortical excitability was suppressed between periodic myoclonic jerks. In a patient with oculopalatal-somatic myoclonus, there was no change of cortical excitability in relation to myoclonus.